Instruction Book of Psychological
Experiment
Liudexiang
Medical School of Shandong University
PREFACE
Nowdays, more and more people realize that psychology is playing an
important role in our society, infecting nearly a variety of fields which
include economy, politics, culture, education, and so on. In that way, it is
necessary for us to learning something about basic knowledge about
psychology. In this Instruction Book of Psychological Experiment, we
sought to respond to the needs of college students who eagerly would like
to expand their coverage of psychological experiment. So they could
master some material and methods relating to psychological experiment.
For this goal, we have been trying our effort to write this book.
Thoughout the book students will encounter recent, also could called
classical, psychological experiments developed in our modern history of
psychology which influenced a lot of psychologists and people who
showed enthusiasm for this field around the world. In this book, we are
mainly discussing major theory and methods about some psychological
experiment as follows:
1. Perception and characteristics of perception
2. Emotion and galvanic skin response
3. Learning and memory
4. Psychological testing such as 16-PF, EPQ and SPM
5. Evoked potential including VEP, BAEP and SEP
The aim of this book is to help students, who at good at English, like
foreign students, get more information about psychological experiment.
Also, they could become increasingly interested in this subject which
would build a solid foundation for them in their future.
Many people provided us with the help, criticism, and encouragement
we needed to create the book. We also owe an enormous debt to the
colleagues in our department. We especially want to thank these
colleagues and students.
Once again, we, hopefully, would like our students to learn
something from this book. And if you have any criticisms and advice,
we are prepared to accept all these things which could improve quality
of the book.
CONTENTS
1. Perception
2. Psychological testing
2.1 Sixteen Personality Factor Questionnaire (16PF)
2.2 Raven Standard Progressive Matrices
2.3 The Eysenck Personality Questionnaire (EPQ)
3. Evoked Potentials
3.1 Visual Evoked Potentials (VEP):
3.2 Brainstem Auditory Evoked Potentials (BAEP)
3.3 Sensory Evoked Potentials (SEP):
4. MEMORY
4.1 Sensory memory
4.2 Short-Term
4.3 Forgetting
5. Biofeedback
6. Galvanic skin response
PERCEPTION
Visual Perception 1
This discussion of visual perception is part of an introduction to perception theory. The prime
concern here is with how mediated our experience of the world is. The study of visual perception
offers considerable evidence that the world or the image is not 'given', as people sometimes say,
but constructed. In visual perception we are not like passive cameras, and even the idea that the
mind takes selective 'snapshots' underplays our active interpretation of the world. These notes
focus on key factors which contribute to shaping what we see.
The distinctiveness of human vision
It is worth reminding ourselves that 'the world' which we often regard as objectively 'out there' is
experienced in very different ways by other creatures.
Sight dominates the way we 'see' the world. It even dominates our descriptive vocabulary. We
don't know how other creatures see the world, though we do know how eyes differ in the animal
kingdom amd we know that different animals vary in their reliance on vision. Of course, some
creatures don't 'see' the world at all. And many creatures rely far less on vision than we do (e.g.
bats, dolphins). Most mammals live in more of a world of scent than of sight. We share our
reliance on sight more than scent with other primates. However, of all vertebrate animals, birds are
the most dependent on sight.
Flies have what are called 'compound eyes', but it's likely to be a myth that they see multiple
images. However, if we had the eyes of a fly we would see television images as separate frames,
since TV images are displayed at 25 frames per second, which for the rapid scanning eye of the fly
is quite slow. Although the image can be misleading, our eyes are typically described in contrast to
'compound eyes' as being 'camera-style' eyes. Animals with such eyes comprise less than 6% of
the species in the animal kingdom; more than 77% are insects and crustaceans with compound
eyes.
Animals differ in visual acuity. Insects are short-sighted whereas a kestrel can spot a mouse from
1.5 km up. Hawks can spot prey 8 times further away than human beings can. The range of
distances that animals can focus on is measured in dioptres. We have a good focal range (or
'accommodation') compared with most mammals. A child's range is about 14 dioptres, though an
old person's is about 1 dioptre. Many creatures have poor accommodation or none. A dog copes
with 1 dioptre. However, diving birds have 50 dioptres - the greatest of all animals.
Most invertebrates don't need to accommodate - sight involves short focal length and great depth
of field - keeping everything in equal focus (though without much fine detail). A bee can see
things from an inch or so away whereas we can't focus on things much under 6 inches away
(without a magnifier). The 'f-number' of human eyes is about 2.55, whilst a standard camera lens
has an f-number of 1.8. The most sensitive is a deep-sea crustacean, Gigantocypris (f-0.25), but its
eyes are small, and so the quality of vision is limited.
The position of the eyes on the head also varies amongst animals. Eye position controls the extent
of the field of view when the head is stationary, and also the possibility and extent of binocular
vision. When the eyes are on either side of the head, the view is almost panoramic, but there is a
loss of stereoscopic depth perception. Hunting animals tend to have a broader field of binocular
vision. Hunted animals tend to have a far broader field of view. Hunters tend to have a much
larger 'blind area' behind the head than hunted animals do. Humans have a total field of view of
somewhere between 160-208 degrees, about 140 degrees or so for each eye and a binocular field
of 120-180 degrees. A dog has a total field of view of about 280 degrees, 180-190 degrees for each
eye and 90 degrees of binocular field. A hare has a total field of view of 360 degrees, 220 degrees
for each eye, with only 30 degrees of binocular field in front and 10 degrees behind the head.
Some humans can distinguish 250 colours. Whilst some mammals are colour-blind, birds probably
see more colours than we do. The desert ant has the most refined colour system amongst insects
and can discriminate between colours we can't see. As we age our lenses grow more yellow and
filter out some of the violet. Many insects are sensitive to ultraviolet light; vertebrates are not. We
know that the colour vision of bees is different from ours, bees being highly sensitive to ultraviolet
light and insensitive to red light. Many insects, fish and birds can see beyond violet into ultraviolet
radiation. Ultraviolet light gives flowers such as the yellow daisy a bright glowing core for
honey-bees. At the other end of the spectrum of electromagnetic energy, some snakes are sensitive
to infra-red which they use to detect the presence of warm-blooded animals. Some freshwater fish
can see far further into the red or longer wavelength part of the spectrum than we can. If our eyes
were as sensitive as those of goldfish we'd see the infra-red beams that control our TVs and videos.
Whilst we are not sensitive to polarized light, many other animals are, and must therefore see the
sky as having a far more intricate pattern than we are aware of. Of course, we can use tools to
temporarily extend the visibility of the spectrum.
No creature sees fine detail in darkness, but some other creatures have far better 'night sight' than
we do (e.g. foxes, cats and owls). Creatures with good night sight typically have the reflective
'eye-shine' that we often notice. It is this which allows them to make the most of whatever light
there is. Owls have a sensitivity to low light intensities 50-100 times greater than that of unaided
human night vision. Cats' eyes catch 50% more light than ours and are eight times more sensitive
than ours at night. But such sight is typically supplemented by other senses. And even within
vision, movement is the key for some creatures: the eyes of such creatures as the bee and the frog
are very sensitive to movement.
Different creatures vary in the amount of the brain which is devoted to vision. Over half of the
brain of the octopus and the squid is devoted to vision. But we still don't know how other creatures
make sense of what their eyes detect. No single creature can see all that others can. We often
forget that the human world of sight is only one such world.
Homo significans
It has been emphasized that the world is 'seen' in different ways by different creatures, and that
human beings in the modern world have come to give primacy to the visual. We do not always
'believe our own eyes' - we know that a pencil in a glass only appears to be bent, that the moon
only appears to be larger when it is near the horizon and that there are such things as optical
illusions.
Now we would like to emphasize that we seem as a species to be driven by a desire to make
meanings: we suggest that we are, above all, Homo significans - meaning-makers. This
fundamental concern underlies the process of human visual perception. Faced even by
'meaningless' patterns the mind restlessly strives to make them meaningful. Look at this image for
a few moments...
It is hard not to start 'seeing things' in this abstract geometrical arrangement. The spacing is even,
but we may start to see rows, or columns, or small groupings - such as of 4 black squares. We
restlessly shift from one way of patterning to another - in this case none is likely to seem much
more meaningful than another so we quickly tire of looking at such a frustrating image. (Yes, and
you can see grey areas at the intersections - a point to which I will refer in a later lecture).
Here is another repetitive arrangement...
This time, you are more likely to impose a particular grouping on what you see. People tend to
refer to five pairs of lines which are close together with fairly broad gaps between them. You are
less likely to group together the lines which are further apart, perhaps partly because this would
leave lonely lines on each side of the image, but also (as we will see in a later lecture) because we
seem to have a predisposition to associate things which are close together.
At this stage, it is useful to note that theories about perception tend to emphasize the role of either
sensory data or knowledge in the process. Some theorists adopt a data-driven or 'bottom-up' stance,
according to which perception is 'direct': visual data is immediately structured in the optical array
prior to any selectivity on the part of the perceiver (James J Gibson is the key proponent of 'direct
perception'). Others (e.g. Richard L Gregory) adopt a 'constructivist' or 'top-down' stance
emphasizing the importance of prior knowledge and hypotheses. Both processes are important: if
we were purely data-driven we would be mindless automatons; if we were purely theory-driven
we would be disembodied dreamers.
We have all heard of the psychoanalyst's 'Rorshach Inkblots'. These were of course intended to be
very much open to interpretation. The idea was that what people reported seeing in these images
involved some projection of their own deep concerns. Here is one such blot...
We all seem to 'see things' in inkblots, flames, stains, clouds and so on. Some of us may, of course,
be more 'suggestible' than others...
Some images are more open to interpretation than others. Most of us would see no 'intended
reading' in such natural phenomena as flames and clouds (though this wouldn't stop us seeing
meaningful patterns in them). We would generally accept that there is typically less openness to
interpretation when it comes to images deliberately designed by human beings. The declaration
that a road sign is 'open to interpretation' is not likely to be much of a defence for ignoring its
intended meaning in the eyes of the law! On the other hand, we would usually feel free to be fairly
free-ranging in our interpretation of an image which we knew to be intended as a work of art.
Here is another black and white image. For some people it will be immediately obvious - others
may not instantly recognize it.
Familiar as this image is, whilst we may recognize it as a map, we may not immediately recognize
it as representing the world (upside down, according to the way we're used to seeing it). However,
once we 'know what to look for', we have no difficulty seeing it as a map of the world which
happens to be upside down.
The illustration below is well-known from psychology textbooks, so most students will already
know what to look for in it.
Those who haven't seen it before shouldn't have too much difficulty if they are told that there is a
dalmation dog nosing around on a path near a tree. The dog is in the centre of the picture, facing
the top-left corner. Often, significant details seem to suddenly lead to the 'click' of recognition, at
which point it is hard to understand why we hadn't seen the 'hidden' image in the first place. On
subsequent occasions we see the image without any of our initial difficulty.
Sometimes images are neither open to almost any interpretation nor constrained to a single
'preferred interpretation'. Some of the images used in the study of visual perception have been
carefully designed to be interpreted in two different but specific ways. Look at the following
example, for instance.
At first sight, this may seem to be either a seal or a donkey (alternatives which we would be
unlikely to confuse in real life). Here, you will initially see either a seal or a donkey, but not both
at once. You bring your own preferred interpretation to the image - a phenomenon known to
psychologists as perceptual set (this will be discussed in a later lecture). In cases where one
alternative interpretation repeatedly elicits far more support than the other, it might be said that the
image itself has a preferred interpretation (though this might be culturally-specific).
Here is another example, though this may be more well-known from psychology textbooks...
Here the intended alternatives are a duck and a hare. What do you see first? Such examples
demonstrate that your own preferred interpretation is part of what you bring to making sense of an
image. In the context of media theory, the relative openness of images to interpretation can serve
as a reminder that the 'meaning' of an image cannot be simply equated with a universal, unitary,
fixed and objective 'content' - meaning is not 'extracted' but is constructed in the process of
interpretation. But such constructed meanings are not unconstrained: if you reported in all
seriousness that your interpretation of the image shown above was an elephant, you would be in
danger of being regarded as either mentally deficient or insane.
Visual Perception 2
The Third Dimension
As part of our imposition of meaning on what we see we seem to seek to turn images into objects
where possible. Look at the following image...
Although it does not strictly follow the rules of linear perspective, we tend to interpret what we
see here in terms of three recurrent black circular shapes (at the bottom of the image) repeated into
depth, as if printed on a cylinder. Strictly speaking, this would necessitate the 'further' shapes
being depicted closer together but that doesn't seem to stop us from reinterpreting the shapes as
the same shapes but at different angles. Such impositions of depth can be seen as trying to make
the shapes more like tangible 3D objects. Where an image seems to lend itself to a possible
interpretation in 3D we seem to prefer this interpretation.
Here is an image which is familiar in psychology textbooks in one form or another...
We all know that the figures in this kind of image seem to get larger as they near the top
right-hand corner, although we also know from previous encounters with such images that the
three figures are in fact all the same size. We find it hard to avoid interpreting the converging lines
as indicating linear perspective, which requires us to accept that the figure is breaking the rules by
seeming to be larger rather than smaller as it gets further away. The desire to interpret in depth
seems to be very strong in us if we are familiar (however unconsciously) with linear perspective.
For reference, it may be useful to know that the simplest version of such illusions deriving from
linear perspective is called the 'Ponzo illusion'. In this basic version, there are two lines
converging towards the top of the image, together with two horizontal lines. The horizontal line (a)
at the top is seen as larger than the horizontal line (b) at the bottom (even though both are the same
size).
Linear perspective is only one kind of depth cue in a static two-dimensional image such as a
painting, drawing or photograph. Relative size is another depth cue. Where an image features
several objects of similar shape, the tendency is to assume that the smaller objects are further away.
This is especially so with familiar objects (the 'familiar size' of which is known). Texture gradient
(or detail perspective) can be seen as a combination of linear perspective and relative size. Where
an image is full of similar shapes which are fairly evenly-spaced (such as pebbles on a beach), the
shapes that seem more densely packed together are seen as being more distant.
Height in field (or plane) (also called relative height) is another cue to judging depth. The usual
assumption is that where the base of a shape is higher than that of a similar shape, then the one
with the higher base is further away. This cue relates objects to the horizon. Another important
depth cue is interposition (also called occlusion, superimposition or overlay) (see illustration
below). When one object is interpreted as obscuring part of another one, the one which seems to
be obscured is seen as being further away. This cue is stronger with familiar shapes, where a
familiar outline is broken by the other shape which is seen as in front of it.
We have already alluded briefly to familiar size. Familiar size is itself a distance cue. Our previous
experience with objects leads us to assume that where some appear smaller than others those
which appear to be smaller are likely to be further away. In a well-known experiment on 'Size as a
cue to distance' published in the American Journal of Psychology in 1951, W H Ittelson presented
observers with three playing cards in a darkened room with all other depth cues removed.
Unknown to the observes only one of the cards was of the conventional size; the others were
respectively half and twice the normal size. The observers tended to judge the larger cards as
being closer than the others.
Shadow is also an important cue for depth. Look at the illustration below. It consists of several
rows and columns of shadowed circular shapes which appear to be either bumps or hollows. The
only cue to whether each shape is a bump or a hollow is the shadow. Some of the circular shapes
are shadowed towards the lower portion and others are shadowed towards the upper portion.
Those which are shadowed in the lower portion seem to be bumps, whilst those which are
shadowed at the top seem to be hollows.
Turning the whole image upside down (see the following illustration) seems to turn the bumps into
hollows and the hollows into bumps. It seems that the 'default' assumption is that the light comes
from the top.
Photographs in which both near and distant details are in focus can offer dramatic illustrations of
how objects which are very close can sometimes seem unnaturally large. For instance, a
photograph of someone lying down with their feet towards can make their feet appear so large that
the effect is humorous. Where the medium is a drawing or a painting we may even feel that the
effect is 'unrealistic'. What is interesting is that were we to be there in person looking from the
same perspective at the person who is lying down we would be very unlikely to notice anything
odd at all. Someone who is used to doing life-drawing with a pencil held at arm's length as a
measuring-stick may be more conscious of this phenomenon - at least when they are drawing.
Visual Perception 3
Selectivity and Perceptual Constancy
Categorization is a key 'top-down' process which is involved in perception. Categories simplify.
Categorization has a number of functions:
it makes complexity manageable;
it speeds up recognition;
it reduces effort and learning;
it makes the most of past experience;
it enables the inferences about further attributes (going beyond what is 'given');
it makes events predictable;
it supports systematization;
it bonds social behaviour (providing shared frameworks);
it tailors the world to our purposes;
it makes the world seem more meaningful.
The cost of these advantages is a loss of particularity and uniqueness in perception and recall. For
Romantics, it is also regarded as inducing a sense of distance from the world. The way we
categorize phenomena seems to be a 'natural' 'reflection of reality', leading us to forget the role of
categorization in constructing the world.
Probably the most well-known example of the cultural diversity of categories is that Eskimos have
dozens of words for 'snow' - an assertion which is frequently attributed to Benjamin Lee Whorf.
Actually, Whorf seems never to have claimed that Eskimos had more than five words for snow
(Whorf 1956, 216). However, a more recent study - not of the Inuit but of the Koyukon Indians of
the subarctic forest - does list 16 terms for snow, representing these distinctions:
snow
deep snow
falling snow
blowing snow
snow on the ground
granular snow beneath the surface
hard drifted snow
snow thawed previously and then frozen
earliest crusted snow in spring
thinly crusted snow
snow drifted over a steep bank, making it steeper
snow cornice on a mountain
heavy drifting snow
slushy snow on the ground
snow caught on tree branches
fluffy or powder snow (Nelson 1983, 262-3)
I do not intend to discuss the controversial issue of the extent to which the way we perceive the
world may be influenced by the categories which are embedded in the language available to us. I
have discussed the so-called Sapir-Whorf hypothesis elsewhere. Suffice it to say that words can
be found in English, as above, to refer to distinctions which we may not habitually make, but that
this does not rule out the possibility that the categories which we employ may not only reflect our
view of the world but may also sometimes exercise subtle influences upon it.
There is research evidence that verbal labels may influence the recall of visual images. In a
well-known experiment by Carmichael, Hogan and Walter (1932), observers were shown simple
line drawings each of which was associated with either of two verbal captions - e.g. a drawing of
two circles linked by a straight line bore either the caption 'eye-glasses' or the caption 'dumb-bells'.
The observers were then asked to reproduce the drawings. Their reproductions showed a strong
tendency to distort the original image to make it closer to the verbal label which had been attached
to it.
The Stroop Colour-Word Test can be used to illustrate the difficulties which we can experience in
separating labels from what they refer to (see below). Try counting the number of green words, for
instance.
red green blue green red yellow blue
yellow red blue yellow green red blue
blue yellow yellow blue red blue yellow
red green green red green green green
green blue blue yellow yellow yellow
yellow red green yellow blue green red
blue green red red green red green blue
red yellow yellow red blue yellow blue
yellow blue red blue green green yellow
green red yellow blue yellow blue red
blue red blue green red yellow blue
green green red yellow blue yellow blue
A well-known study demonstrating the influence of language on recall is that of Elizabeth Loftus
(1974 & 1979). She showed observers a short film of a traffic accident and asked how fast the cars
had been going. However, the wording of the question differed between the two groups asked.
Those in one group were asked 'About how fast were the cars going when they hit each other?'
whilst those in the second group were asked 'About how fast were the cars going when they
smashed into each other?' Those who had been asked the question with the term smashed gave
higher estimates of the cars' speeds than the others did. A week later, the same observers were
asked whether they had seen any broken glass (there had been none). More than twice as many of
those questioned with the word 'smashed' reported seeing the nonexistent glass as those questioned
with the word 'hit'.
It is not only with respect to categorization thay perception is described as 'selective'. Recovering
his sight after 30 years of blindness, one man reported:
When I could see again, objects literally hurled themselves at me. One of the things a normal
person knows from long habit is what not to look at. Things that don't matter, or that confuse, are
simply shut out of their seeing minds. I had forgotten this, and tried to see everything at once;
consequently I saw almost nothing. (Muenzinger 1942)
Perception is unavoidably selective: we can't see all there is to see. There are of course
physiological limits (both for the human species and for individuals); some argue that there are
limits to cognitive capacity. And then there are the constraints of our locational viewpoint: we
can't see things from every angle at once. But in addition to such physical limits we focus on
salient features and ignore details which are irrelevant to our current purposes or interests.
Selectivity thus involves omission. Some commentators use the 'filter' metaphor - we 'filter out'
data, but this suggests a certain passivity: we may also 'seek out' data of a certain kind.
Selective attention is assisted by redundancy: we don't always need much data in order to
recognize something. Often we can manage with minimal visual data, making use of what is
called 'redundancy'. You may know those 'blocky' pictures of famous people in which you can just
about recognize who it is. Our schemata allow us to 'fill in gaps' because we know what should be
there. So selectivity also involves addition.
Selectivity also involves organization: foregrounding, backgrounding and rearranging features.
Objects, events or situations are 'sized up' in relation to our frames of reference, and these
influence how perception is structured (Newcomb 1952, 88-96).
Gordon Allport and Leo Postman (1945; Newcomb 1952, 88-96) offered a classic account of the
selectivity of perception in their study of rumour. Whenever an event is open to divergent
interpretations, reporting it involves transforming it. The selection, retention, reporting and
retelling of events routinely involves several kinds of transformations. All of these involve
simplifying events to make them more meaningful in terms of personal interests, needs and
experience. The process is exaggerated where memory and retelling are involved, but it is already
at work in the selectivity involved in the initial perception of an event.
Contrary to the popular idea that rumours snowball? becoming more elaborate in the telling,
psychological studies suggest that retelling tends to make accounts shorter, more concise, more
easily grasped and told. There is an increasing tendency to use fewer words. Levelling is the
selective process by which certain details are omitted. However, items of particular interest to the
reporters, which confirm their expectations or help to structure their reports, do tend to persist.
Sharpening is the reciprocal selective process of levelling. Alongside the loss of some details,
there also tends to be a pointing-up of a limited number of details which caught the individual 抯
attention, often including attention-grabbing words. Temporal sharpening involves a tendency to
describe events in the present tense. Movement is often emphasized or introduced. Items
prominent because of their relative size or quantity tend to be retained. Labels tend to persist.
Primacy effects may lead to the retention of items coming first in a series. Familiar symbols are
also likely to be retained. Explanations may be introduced, especially to produce closure?
Underlying the selective processes of levelling and sharpening, and of transpositions, importations
and other transformations involved in retellings, Allport and Postman (1945) argue, is the process
of assimilation. This involves the influence of habits, interests and sentiments on reporters and
listeners. Aspects of a story are sharpened or levelled to make them more consistent with what is
seen as the principal theme of the story, thus making the story more coherent and well-rounded?
Items relevant to the theme may be imported and those irrelevant to the theme may be omitted.
And some details may be changed to make them more consistent.
Assimilation by condensation involves fusing several details into one.
Assimilation to expectation involves transforming details into what one’s habits of thought suggest
they usually are.
Assimilation to linguistic habits involves fitting phenomena into the familiar frameworks of
conventional verbal categories.
Assimilation to interest involves retellings from the perspective of the particular occupational
interests or roles of the teller (especially where these interests are shared with listeners), giving
primary attention to details which reflect such interests.
Assimilation to prejudice may simply involve assimilation to expectation or to linguistic
categories, but it may also involve deep emotional assimilation to hostility based on racial, class or
personal prejudices.
Selective perception is based on what seems to 'stand out'. Much of this 'standing out' is related to
our purposes, interests, expectations, past experiences and the current demands of the situation.
However, some seems more widely-shared - throughout a culture or even across the human
species. For instance, we seem to have a general preference for features which are large and/or
bright and/or moving, for the novel, the surprising and the incongruous, and for what is
meaningfully complex ('looking like things'), and our fixation tends to be on discontinuities,
corners and contours. We will turn to such apparently universal features of human perception in
discussing Gestalt theories.
Some aspects of perception can be usefully discussed in terms of 'selectivity', but to see perception
purely in terms of selectivity would be reductive. It would court the danger of implying that
perception is relatively passive and would downplay the active construction of reality.
This is related to what psychologists refer to as perceptual constancy. Our perception of objects is
far more constant or stable than our retinal images. Retinal images change with the movement of
the eyes, the head and our position, together with changing light. If we relied only on retinal
images for visual perception we would always be conscious of people growing physically bigger
when they came closer, objects changing their shapes whenever we moved, and colours changing
with every shift in lighting conditions. Counteracting the chaos of constant change in retinal
images, the visual properties of objects tend to remain constant in consciousness. We are not
usually conscious of people appearing to get bigger as they approach us or of things appearing to
change shape according to the angles from which we view them. In relation to visual perception,
key 'constancies' are: size, shape, lightness and colour.
The following illustration demonstrates how a door appears to change shape as it is opened. Shape
constancy ensures that we are not typically conscious of this.
With regard to shape constancy, R H Thouless published a paper entitled 'Phenomenal regression
to the "real" object' in the British Journal of Psychology in 1931. He reported an experiment in
which he exposed a circular disc at various angles and asked observers to judge its shape each
time. The observers did so by selecting a matching disc from a series of circular and elliptical ones
which they had been given. When the disc was directly in front of them and in a vertical plane the
judgement was easy, of course. But when Thouless rotated the disc away from the observer so that
it appeared elliptical, the task was more difficult. Judgements of shape reflected a compromise
between the shape as displayed at an angle (an ellipse) and the actual shape of the object (the
circle). Observers did not see the shape as it would be on the retina but instead exhibited a
'phenomenal regression' - the phenomenal or apparent shape was inbetween the tilted shape and
the vertical shape. This has been called a 'perceptual compromise'.
Familiarity of shape is also an explanation of the illusion generated by a special 'room' called 'the
Ames Room' (students in Wales: note that there is an Ames Room at Techniquest in Cardiff).
Observers peer through a single hole in a wall of this structure (thus having only monocular cues
to depth, as in looking at a photograph or painting, rather than a space around which one could
move). Two people of similar size within this special room would look very different in size to
observers as indicated in the following illustration.
The reason for this strange illusion is to do with the extraordinary construction of the room, the
lefthand wall of which actually goes far further back than the righthand wall, for instance. We are
so used to rooms being rectangular that we intepret everything within it on this assumption. The
Ames Room represents the mind making a habitual bet, and only getting it wrong because of a
careful conspiracy.
Visual Perception 4
Cultural and Environmental Factors
Most features of the general process of visual perception appear to be virtually universal rather
than being culturally-specific. However, certain features do seem to be subject to some degree of
cultural variability.
Everyone is thought to be subject to certain optical illusions, such as seeing grey areas at the
intersections of what is known as the Hermann Grid...
Some other optical illusions seem to be culturally variable. One example is the Muler-Lyer
Illusion...
This illusion is well-known - most of us are aware that the vertical lines here are actually the same
size but that the righthand line appears to be substantially longer. One explanation of why the
righthand figure appears to be so much larger involves interpreting the images in depth. The
righthand figure can be easily interpreted as representing the inside corner of a room whilst the
arrowlike lefthand figure can be seen as the outside corner of a building. As an inside corner the
righthand figure may appear to be nearer (and therefore larger) than the outside corner.
Experiments reported in 1966 by Segall, Campbell and Herskovitz suggested that the Muler-Lyer
illusion may be absent or reduced amongst people who grow up in certain environments. They
tested some Zulu people in South Africa who, at the time, lived in circular huts with arched
doorways and had little experience of Western rectangular buildings. The Zulus seemed less
affected by the Muler-Lyer illusion. The argument is that these people lived in a 'circular culture'
whereas those who are more subject to the illusion live in a 'carpentered world' of rectangles and
parallel lines (Segall, Campbell & Herskovits 1966). Europeans and Americans are more likely to
interpret oblique and acute angles as displaced right angles and to perceive two-dimensional
drawings in terms of depth.
So-called 'selective rearing' experiments have been conducted which involve rearing animals in
conditions in which they are exposed only to certain kinds of perceptual experience such as only
to vertical or to horizontal stripes. Whilst these experiments have been conducted with animals,
Coren et al. (1994) argue that this can be seen as related to the way in which many human beings
are selectively reared in rectilinear (or 'carpentered') urban environments (see Segall, Campbell &
Herskovits 1996) in which the inhabitants are frequently exposed to lines in vertical and horizontal
orientations. Coren et al. note that human vision shows a slight bias towards horizontal or vertical
lines rather than oblique lines (Coren et al. 1994, 587). In experiments conducted by Hirsch (1972)
and Blasdel et al. (1977), kittens which were reared only with vertical stripes had measurably
lower visual acuity for stripes in other orientations.
Another well-known illusion of size is called simply the 'horizontal-vertical illusion. It is shown
below...
The lines are of equal length but the vertical one seems longer. This may be because the vertical
line seems to recede in depth. The illusion may be stronger for people who are familiar with
straight lines receding over a considerable distance. It has been argued that people who dwell in
enclosed areas such as forests who are not used to vast open spaces and who have little
opportunity to see the horizon or for great distances would be less susceptible to the
horizontal-vertical illusion than those with long uninterrupted views. Segall, Campbell and
Herskovits (1966) found that people who lived in very open rural environments tended to be more
subject to the horizontal-vertical illusion than others. In very open environments height in the
plane is a key depth cue.
The anthropologist Colin Turnbull described what happened in the former Congo in the 1950s
when a BaMbuti pygmy, used in living in the dense Ituri forest (which had only small clearings),
went with him to the plains:
And then he saw the buffalo, still grazing lazily several miles away, far down below. He turned to
me and said, 'What insects are those?'
At first I hardly understood, then I realized that in the forest vision is so limited that there is no
great need to make an automatic allowance for distance when judging size. Out here in the plains,
Kenge was looking for the first time over apparently unending miles of unfamiliar grasslands,
with not a tree worth the name to give him any basis for comparison...
When I told Kenge that the insects were buffalo, he roared with laughter and told me not to tell
such stupid lies. (Turnbull 1963, 217)
Because Kenge had no experience of seeing distant objects he saw them simply as small.
In a study reported in 1960, W Hudson and others investigated the influence of culture on visual
perception amongst Bantu, European and Indian workers and children in South Africa and Ghana
(Lloyd 1972, 61ff). Hudson used a set of picture cards, each including an elephant, an antelope
and a man with a spear. In each one the spear was aligned with both the elephant and the antelope,
but depth cues such as object size, superimposition and linear perspective clearly supported the
interpretation that the spear was pointing towards the antelope rather than the elephant. Individuals
were asked 'What do you see?', 'What is the man doing?' and 'Which is nearer the man, the
elephant or antelope?'.
Hudson's results showed that at the beginning of primary school all of these children had difficulty
perceiving the pictures as three-dimensional and said that the hunter was pointing his spear at
whatever it was aligned with, regardless of cues as to depth. By the end of the primary school,
virtually all of the European children interpreted the pictures in three dimensions, but some Bantu
and Ghanian children still tended to see them as two-dimensional, as also did non-literate workers,
both Bantu and European. and Indian children in South Africa.
Hudson concluded that 'formal schooling in the normal course is not the primary determinant in
pictorial perception. Informal instruction in the home and habitual exposure to pictures play a
much larger role' (cited in Cole & Scribner 1974, 68). The adequacy of Hudson's findings has been
questioned, since greater success has been achieved when individuals are asked to respond by
making models (ibid., 69-70). But it remains clear that pictorial conventions representing depth
which literate European adults take for granted have to be learned.
Look at the next image...
Asked for a quick description of this image, many people tend to describe a set of stairs going up.
But of course you can go both ways on stairs. This response is likely to be influenced by the
Western style of reading from left to right. Arabs, for instance, would read this (right to left) as a
set of stairs going down.
Here is a famous 'impossible object', sometimes known as the Devil's Pitchfork...
After looking at it for a few moments, turn away and try drawing it. Are there three prongs or only
two? Not suprisingly, this figure is sometimes given the paradoxical name of 'the two-pronged
trident'. It is an impossible object since it could not be constructed in three dimensions - it only
appears to be in three dimensions at first glance. You have to look quite carefully in order to
realize this. This figure confuses many Western observers. The confusion arises from trying to
interpret it as a three-dimensional figure. Deregowski (1969) found that people who habitually
ascribed three-dimensionality to pictures had more difficulty in reproducing this figure than
people who did not seek to impose three-dimensionality on images. The shorter the prongs the less
easily fooled we are, which suggests that in the illusory version we are less able to relate one part
to another.
The following image is an impossible object devised by L S and R Penrose...
It is likely that much the same process is at work here. Whilst each of its intersections makes sense
on its own, the parts could not physically be joined together. We have a powerful illusion of
three-dimensionality because we don't initially notice how the parts relate to each other.
Another impossible object is this one (also devised by L S and R Penrose).
Only a cruel parent would suggest this as a Lego building-brick project for a child! The Dutch
graphic artist Escher produced several variations on this theme. Here is a detail from one of
them...
The perception of depth, and especially the cultural factors touched on briefly here, suggest that
visual perception is in part at least learned. There is other evidence of this which is not dealt with
here at all: in particular, perceptual development in childhood. This is a standard topic in
psychology textbooks.
Another kind of evidence concerns adults learning to perceive differently using artificial devices.
A number of experiments have explored perceptual learning by designing and using various kinds
of goggles to alter the way in which things appear to those wearing them. Sometimes the goggles
rotate the field of view so that, for instance, everything seems to be upside down or shifted to one
side. A prism is often used. The goggles are sometimes worn for several weeks. Wearers typically
report that the world at first seems very unstable. Some people can perform simple skills after only
minutes of practice. After a few days it is often possible to do such things as riding a bicycle, and
after a few weeks even skiing may be possible for those who could ski beforehand. After taking
off such goggles, the world again seems to be unstable, though typically recovery occurs within an
hour or so. You can simulate the early stages of using such spectacles by looking up at a
hand-mirror slanted against your forehead and trying to do such things as pouring water into a
cup.
Visual Perception 5
Individual Differences, Purposes and Needs
Whilst there appear to be some subtle cultural differences in some aspects of visual perception, it
is also worth reminding ourselves that in terms of perception we have far more in common with
the rest of the human species than with the rest of the animal kingdom. However, in addition to
cultural differences, certain individual differences can affect our visual perception - quite apart
from physiological differences such as impairment of sight. People differ, for instance, in spatial
skills (e.g. 'mental rotation' - competence in mentally rotating 3D shapes so as to assess them from
another angle).
In a well-known experiment by Asch (1955), one subject was seated in a room with six other
people. Unknown to the subject the other people were confederates of the experimenter. The
experimenter told the group that accuracy of perception was the focus of the study. The group was
then shown two cards (see illustration below). On one card was a single vertical line and on the
other there were three vertical lines of markedly different lengths, one of which being the same as
the one on the other card. The group was told that each individual should match the line on the
first card with one of the lines on the other card. There were eighteen trials with different lengths
of lines on the second card. In each trial the real subject was second from last in being asked for a
response, thus hearing five other people each time offering their own answers. In the first two
trials the confederates all gave the correct answer but they only did this four times in the following
trials - in the other twelve trials they were all primed to give the same wrong answer. About a
quarter of the subjects stuck to their own judgement and gave the correct response. The rest
accepted the majority verdict at least some of the time. This would suggest that conformity may
sometimes influence perception.
Some factors related to personality may have an influence on perception. One such factor is
'tolerance of ambiguity' (a term employed by Else Frenkel-Brunswik). In 1951, two psychologists
called Block reported an experiment in which subjects were placed in a dark room where only a
point of light was visible. Since they had nothing else to go by, all of them saw the light sway in
various directions. However, some reported the light as moving in a constant direction from trial
to trial and to a constant number of inches. Such people have been described as having a low
'tolerance of ambiguity': they require more stability than most, and quickly tend to manufacture it
in situations of ambiguity. Other people tend to take longer to establish such a norm: they have a
high tolerance of ambiguity.
Another experimenter, Fisher, reported in the same year comparing people classified as having
high or low prejudice. He briefly showed both groups a picture of a truncated pyramid (see below)
and then asked them to draw it from memory. About 40% of people tended to draw it as
symmetrical, equalizing the two margins of the drawing. This is quite usual, since memory
simplifies. But after a four-week interval, 62% of the prejudiced group and only 34% of the
tolerant group equalized the margins. One group seemed to need a clear and simple image much
more than the other group did. Those tolerant of ambiguity seemed to favour uniqueness (for both
Block & Block and Fisher see Allport 1958, 377-8).
Differences in cognitive style have implications for perception. Jerome Kagan outlined a
difference in cognitive style which he referred to as impulsivity vs. reflectivity. When asked to
find a match for a 'familiar figure' (such as a drawing of a telephone) from a choice of 6, some
people seem habitually 'leap in' with a response before checking the alternative fully - these are
the impulsives - whilst others seem unwilling to respond until they are sure that they have made
the correct choice - these are the reflective types.
Another kind of cognitive style was referred to as 'field dependence or independence' by Herman
Witkin. Field independence refers to an aptitude for disembedding figures from their contexts.
Someone who finds words easily in word-search grids has considerable field independence. There
is a current vogue for Where's Wally? books in which one has to find a recurrent character amidst
a crowd of people and a frenzy of depicted activity on a very detailed double-page spread. Those
who are good at this are field independent. Similarly children's puzzles sometimes include the task
of identifying faces, objects or animals 'hidden' in a relatively detailed drawing (an adult
equivalent sometimes uses paintings). These are of course very artificial tasks, but field
independent people would be just as quick at spotting someone in a real crowd.
Gender plays a part in perception too. One gender-related influence concerns how our attention
may be drawn to different aspects of a scene or image. In a study by Hess (1965) the
eye-movements of a man and a woman were compared when they looked at a figurative painting
by Leon Kroll called 'Morning on the Cape', featuring a bare-backed man ploughing with a horse,
and two women - one in the foreground and another leaning against a tree. Both subjects began
scanning the painting from almost the same point, but the location, duration and sequence of their
gaze were different. Unsurprisingly, the female observer paid much more attention to the male
figure in the picture than the man did, and the male observer paid more attention to the female
figure in the foreground than the female observer did. The woman observer focused only on the
head of the foreground woman whilst the man focused on both the head and the upper body of this
female figure. The female observer did not focus on the house and field at all, whilst the man did.
This direction of attention reflects conventional gender stereotypes of course.
Using ambiguous doodle-like black-and-white figures (see illustration below), Coren, Porac and
Ward (1978, 413) found gender differences in interpretation. A figure which was more likely to be
viewed as a brush or a centipede by males was more likely to be viewed as a comb or teeth by
females. Another figure viewed as a target mostly by males was more likely to be viewed by
females as a dinner plate. And a third figure which was viewed mostly by men as a head was
viewed mostly by females as a cup.
Other roles can also influence perception. An aerial photograph of a river delta may appear
obvious to a geographer or a pilot, but if the image lacked an explicit label, others might have
quite different interpretations. What is Corvus corax to a professional ornithologist is simply a pest
to some farmers, an ill omen to the superstitious, 'Old Grandfather' to the Koyukon Indians of the
subarctic forest of North America, a crow to most of us, and a raven to the amateur naturalist.
Prejudice can affect perception as Gordon Allport and Leo Postman showed in a famous study
(1945). After briefly looking at a drawing of figures inside an underground train - five men, two
women and a baby, with two of the men standing - a black man and a white man face-to-face in
the centre of the picture. Observers were asked to describe what they had seen. Over half of the
observers reported having seen a cut-throat razor in the hands of the black man. Some even
claimed that he had been 'brandishing it widely' or 'threatening' the white man whereas it was
actually in the left hand of the white man standing with him. This experiment was part of a study
of rumour so memory as well as perception was involved.
Many factors which play a part in influencing how things are perceived are relatively 'stable' or
long-term individual factors. These include personality, cognitive styles, gender, occupation, age,
values, attitudes, long-term motivations, religious beliefs, socio-economic status, cultural
background, education, habits and past experience. But there are other factors which may
contribute to individual differences in perception which are more transitory. These include current
mental 'set', mood (affective/emotional state), goals, intentions, situational motivation and
contextual expectancies (Warr & Knapper 1968).
It is worth reminding ourselves that even photographs reflect not only the scene they depict but the
purposes of the photographer. As Susan Sontag noted: 'photographs are as much an interpretation
of the world as paintings and drawings are' (Sontag 1979, 7). A photograph is a particular
photographer's selection from the world of something which they regarded as significant for some
reason and is framed in a way which reflects certain considerations. Such purposes include:
making a record of something
aesthetic reasons - the subject and/or the framing seemed aesthetically interesting (e.g. 'beautiful')
'self-expression' - to express how they felt about something
persuasion (social/political) e.g. to shock
'Nobody takes the same picture of the same thing', so 'photographs are evidence not only of what's
there but of what an individual sees, not just a record but an evaluation of the world' (Sontag 1979,
88). Furthermore, each photograph alludes to photographic conventions:
of a particular historical period
for photographs of particular types (e.g. news photos, snapshots, portraits, passport photos)
composition/framing, lighting, point of view
of other photographs by the same photographer
Returning to the perception of images, a well-known study by Yarbus (1967) showed how the
eye-movements of observers of pictures varied according to the questions they were asked to
consider. In relation to a figurative painting showing people in a sitting room and a figure at the
open door, people were asked to estimate the material circumstances of the family in the picture,
to give the ages of the people in the picture, to suggest what the family had been doing before the
arrival of the 'unexpected visitor', to remember the clothes worn by the people, to remember the
position of the people and objects in the room, and to estimate how long the visitor had been away
from the family. The pattern of eye movement and the areas on which the gaze rested in each case
were markedly different.
Here is a rough idea of the painting which Yarbus's subjects were asked to look at...
And here one recorded pattern of eye movements of an observer looking at the painting. We
clearly do not scan pictures in either a random or robotic manner.
Levine, Chein and Murphy (1942) presented people with a set of ambiguous line-drawings and
asked them to describe what they saw. One group was hungry whilst the other group had just eaten.
The ones who were hungry more often perceived food items in the ambiguous drawings than those
who had just had a meal. Current needs can thus affect perception.
In a well-known experiment conducted by Jerome Bruner and Cecile Goodman (1947), two
groups of children were asked to judge the size of coins. One was a poor group from a slum area
in Boston and the other was an affluent group from the same city. The poor group over-estimated
the size of the coins far more than did the affluent group. Thus social values and individual needs
can influence perception.
Dannenmaier and Thumin (1964) asked 46 nursing students to estimate the heights of the
Assistant Director, their instructor and two fellow-students. The researchers found a relationship
between perceived status and estimated height. Those in authority were judged to be taller than
they actually were, whilst those in lower status were judged to be shorter. Memory as well as
perception may have played a part here. Perceived size was clearly related to the importance
ascribed to the people perceived in this experiment.
Thematic Apperception Test (TAT) cards are sometimes used in psychoanalysis as a way of
exploring the thoughts and feelings of the person interpreting the ambiguous but figurative
situational images depicted on the card. The scenes depicted are emotionally charged but open to
interpretation in a variety of ways. The use of such images acknowledges the role of personal
concerns in perception.
Mood may also influence perception. Leuba and Lucas (1945) conducted an experiment involving
the description of 6 pictures by 3 people when in each of 3 different moods. Each mood was
induced by hypnosis and then the pictures were shown. Here are the descriptions that one person
gave for a picture of 'four college men on a sunny lawn, listening to radio':
Happy mood: 'Complete relaxation. Not much to do - just sit, listen and relax. Not much at all to
think about.'
Critical mood: 'Someone ruining a good pair of pressed pants by lying down like that. They're
unsuccessfully trying to study.'
Anxious mood: 'They're listening to a football game or world series. Probably a tight game. One
guy looks as if his side wasn't winning.'
We need to remind ourselves that it was the same picture each time. Mood can clearly play an
important part in perception.
Albert Hastorf and Hadley Cantril (1954) conducted what became a famous study of the reactions
of opposing fans to an American football game between two university teams - the Princeton
Tigers and the Dartmouth Indians (Princeton won). It was a rough and tense game. One Dartmouth
player was taken off with a broken leg and a star Princeton player suffered a broken nose. Both
sides were penalized. Undergraduate students from each of the universities were asked for their
reactions to the game a week later.
69% of the Princeton students who had seen the game saw it as 'rough and dirty' compared to only
24% of the Dartmouth supporters, whilst 25% of the Dartmouth students invented their own
category of 'rough and fair'. When shown a film of the game later, the Princeton students 'saw' the
Dartmouth team make over twice as many rule infractions as were seen by Dartmouth students.
Hastorf and Cantril comment that:
The data here indicate that there is no such 'thing' as a 'game' existing 'out there' in its own right
which people merely 'observe'. The game 'exists' for a person and is experienced by him only
insofar as certain happenings have significances in terms of his purpose.
For these students, the perception and recall of what might seem to be 'the same event' involved a
very active construction of differing realities. Hastorf and Cantril's classic case-study emphasizes
the crucial role of values in shaping perception.
Visual Perception 6
Context and Expectations
Someone once said that there is no meaning without context. Various kinds of context are
important in shaping our interpretation of what we see. As a reminder of the importance of making
clear what is meant by the importance of 'context' in perception I briefly list here several very
different uses of the term. However, I would not suggest that in practice tidy distinctions can
always be usefully made.
The largest frame is that of the historical context of perception. Some theorists, such as Marshall
McLuhan (1962), Walter Ong (1967) and Donald Lowe (1982), have argued that there have been
shifts over time in the human 'sensorium' - that is, in the 'balance' of our senses or the priority
which we give to some compared with others. Such argue that in western urban cultures we have
come to rely more on sight than on any other sense.
Another major framework is that of the socio-cultural context of perception. Just as there may be
subtle differences in human perception over time there may also be differences attributable to
culture. Some of these were alluded to in Visual Perception 3. Constance Classen (1993) in her
book Worlds of Sense shows that different cultures accord priority to different senses - the Ongee
of the Andaman Islands, for instance, live in a world ordered by smell.
A native American Indian writer called Jamake Highwater, who is of Blackfeet/Cherokee heritage,
draws attention in the following extract to radically different ways of seeing the world:
Evidence that Indians have a different manner of looking at the world can be found in the contrast
between the ways in which Indian and non-Indian artists depict the same events. That difference is
not necessarily a matter of 'error' or simply a variation in imagery. It represents an entirely
individual way of seeing the world. For instance, in a sixteenth-century anonymous engraving of a
famous scene from the white man's history an artist depicted a sailing vessel anchored offshore
with a landing party of elegantly dressed gentlemen disembarking while regal, Europeanized
Indians look on - one carrying a 'peace pipe' expressly for this festive occasion.
The drawing by an Indian, on the other hand, records a totally different scene: Indians gasping in
amazement as a floating island, covered with tall defoliated trees and odd creatures with hairy
faces, approaches.
When I showed the two pictures to white people they said in effect: 'Well, of course you realize
that what those Indians thought they saw was not really there. They were unfamiliar with what
was happening to them and so they misunderstood their experience.' In other words, there were no
defoliated trees, no floating island, but a ship with a party of explorers.
Indians, looking at the same pictures, pause with perplexity, and then say, 'Well, after all, a ship is
a floating island, and what really are the masts of a ship but the trunks of tall trees?' In other words,
what the Indians saw was real in terms of their own experience.
The Indians saw a floating island while white people saw a ship. Isn't it also possible - if we use
the bounds of twentieth-century imagination - that another, more alien people with an entirely
different way of seeing and thinking might see neither an island or a ship? They might for example
see the complex networks of molecules that physics tells us produce the outward shapes, colours
and textures that we simply see as objects. Albert Einstein showed us that objects, as well as
scientific observation of them, are not experienced directly, and that common- sense thinking is a
kind of shorthand that attempts to convert the fluid, sensuous animation and immediacy of the
world into illusory constructs such as stones, trees, ships and stars.
We see the world in terms of our cultural heritage and the capacity of our perceptual organs to
deliver culturally predetermined messages to us. (Highwater 1981, 6-8)
Both the historical and socio-cultural context of perception are vast themes which will not be
explored further here, but such studies do help to emphasize that 'the world' is not simply
indisputably 'out there' but is to some extent constructed in the process of perception. Within a
given socio-cultural context, there are widely-shared interpretive conventions and practices.
Whilst the basic processes of human perception are largely universal there is scope for subtle but
significant variations over space and time.
Several other kinds of context are commonly referred to. I have referred already, in Visual
Perception 3, to the importance of individual factors which can have an influence on perception.
An emphasis on the individual as a context emphasizes the role of the various long-term
characteristics of individual perceivers such as values, attitudes, habits and so on. An emphasis on
the situational context considers such transitory situational factors as goals, intentions, situational
constraints and contextual expectancies. Finally, an emphasis on the structural context stresses
structural features and relationships (such as the relationship between one line and another) 'in'
what is perceived - though the extent to which there is agreement about even such low-level
formal features may vary.
Five main definitions of the scope of the term 'context' have been listed here in relation to their
potential influence on perception:
historical
socio-cultural
individual
situational
structural
Whilst it may be useful to be alert to the very different meanings that the word 'context' can have,
disentangling them is problematic.
A very well-known study by Bugelski and Alampay (1961) can be seen as showing the importance
of situational context. Their experiment is often used as an example of the influence of what
psychologists call 'perceptual set': a predisposition to perceive something in relation to prior
perceptual experiences. Perceptual set is broader than situational context, since it may involve
either long-term (for instance, cultural) prior experience or, as in this case, short-term or
situational factors (Murch 1973, 300-301). Groups of observers in the experiment were shown an
ambiguous line drawing which was designed to be open to interpretation either as a rat or as a bald
man wearing spectacles. Prior to seeing this image, two groups were shown from one to four
drawings in a similar style. One group was shown drawings of various animals and the second
group was shown drawings of human faces (see illustration below). A control group was shown no
pictures beforehand. 81% of the control group reported seeing the ambiguous image as a man
rather than a rat. The more pictures of animals that the 'animal' group had seen, the more likely
they were to see a rat rather than a man (with 4 prior images of animals 100% then saw a rat).
From 73-80% of the 'faces' group subsequently saw a man rather than a rat.
The influence of perceptual set has also been explored in relation to the famous image shown
below:
This image was designed to be interpreted as either a young woman or an old woman. It was
introduced into the psychological literature by Edwin G Boring (1930) (though it was published
by the British cartoonist W E Hill in 1915, and is thought to be based on a French version of 15
years earlier). It is sometimes given the chauvinistic label of 'The Wife and the Mother-in-Law'. In
order to study the role of perceptual set Robert Leeper (1935) had the image redrawn in two
'biased' forms: one which emphasized the old woman and the other which emphasized the young
woman (see image below).
Leeper varied the conditions of viewing for five groups. A control group was shown only the
ambiguous drawing, and 65% of this group spontaneously described the image as that of a young
woman. The second and third groups were first given a verbal description of the old woman and
the young woman respectively. The fourth and fifth groups were first shown the 'old' version and
the 'young' version respectively. Groups 2 to 5 were then shown the original ambiguous image.
Leeper found that each of the primed groups was 'locked-in' to their previous interpretation. 100%
of group 5, which had seen the young version first, interpreted the ambiguous image as a young
woman. 94% of group 4, which had seen the old version first, reported seeing the old woman in
the ambiguous image. The percentages opting for each interpretation amongst those given verbal
descriptions were much the same as for the control group. Gerald Murch (1973, 305) was unable
to replicate these findings (94% of his control group first saw the young woman) and suggested
that the image was by then so well-known that this may have influenced the results.
Particular situational contexts set up expectations in the observer. Bruner and Postman (1949)
conducted an experiment in which playing-cards were used, some of which had the colour
changed from red to black or vice versa. The cards were exposed in succession for a very short
time. Subjects identified them as follows:
some normalized the colours of the anomalous cards;
some normalized the suits to make them compatible with the anomalous colours;
some compromised and saw the anomalous cards as brown or purple.
Interpretation here was dominated by what the situational context suggested that people ought to
be seeing. A shorter time of exposure was necessary for people to name the normal cards than the
anomalous ones.
In one experiment, Steven Palmer (1975) first presented a situational context such as a kitchen
scene and then briefly flashed on a target image. When asked to identify a loaf-like image, people
who had first seen the kitchen correctly identified it as a loaf 80% of the time. Obviously, a loaf of
bread is the kind of thing you 抎 expect to find in a kitchen. They were asked to identify an image
like an open US mailbox and an image resembling a drum - two objects not usually associated
with the kitchen. The images were a little ambiguous: the mailbox was a little like the shape of a
loaf with a slice of bread lying next to it, and the drum could have been interpreted as the lid of a
jar. People who had first seen the kitchen only identified these as a mailbox and a drum 40% of the
time. The ability to identify objects was affected by people 抯 expectations concerning what is
likely to be found in a kitchen.
I have mentioned that situational contexts generate certain (short-term) expectations but it is worth
noting in passing that expectations may also be set up by longer-term influences - such as by
stereotypes, prejudices and past experience.
To return to contexts, here is an example of structural context. This pattern of circles is known as
the Ebbinghaus (or Titchener) illusion. It is an illusion of relative size (or more strictly, area). Here
the formal relationship between the parts of the image leads the small white circle (which is the
same size in both images) to seem larger in the structural context of the tiny black circles than
amongst the large black circles. There is no shortage of examples of the role of structural context
amongst the geometrical illusions which can be found in psychology textbooks so no further
examples of the role of structural context will be discussed here.
At this point it is useful to introduce schema theory briefly. A schema (plural 'schemata' or
'schemas') is a kind of mental template or framework which we use to make sense of things.
Particular circumstances seem to activate appropriate schemata, which set up various standard
expectations about such contexts. Such schemata develop from experience. They help us to 慻 o
beyond the information given? (as Jerome Bruner famously put it) by making assumptions about
what is usual in similar contexts. They allow us, for instance, to make inferences about things
which are not currently directly visible. The application of schemata and the expectations which
they set up represents 'top-down' processes in perception (whilst the activation of schemata by
sensory data is a 'bottom-up' process). A good example of the role of top-down processes is where
you think that you recognize someone in the street and then realize (from sensory data) that you
are wrong. We are often misled in this way by situational contexts, by wishful thinking and so on,
ignoring contradictory sensory data in favour of our expectations.
In an experiment by Brewer and Treyens (1981), individual participants were asked to wait in an
office. The experimenter said that this was his office and that they should wait there whilst he
checked the laboratory to see if the previous participant had finished. After 35 seconds, he
returned and took the participant to another room where they were asked to recall everything in
the room in which they had been waiting. People showed a strong tendency to recall objects
consistent with the typical office schema? Nearly everyone remembered the desk and the chair
next to it. Only eight out of the 30 recalled the skull (!), few recalled the wine bottle or the coffee
pot, and only one recalled the picnic basket. Some recalled items that had not been there at all: 9
remembered books. This shows how people may introduce new items consistent with the schema.
In an experiment by Baggett (1975) participants were shown a series of simple line drawings
telling a story. One story showed a long-haired man entering a barbershop, then sitting in the
barber 抯 chair, and finally leaving the shop with shorter hair. In a later test they also saw a
picture showing the actual haircut, which had not been present originally. People were fairly good
at remembering that this picture had not been present if the test followed immediately after the
initial showing. However, if the test occurred a week after the initial presentation most people
claimed that they had seen the haircutting picture in the original sequence. This shows the way in
which we incorporate in our memories inferences derived from our schemata. This experiment
was concerned with memory rather than perception, but it is difficult to separate these processes if
you take the stance that no perception is 'immediate'.
Visual Perception 7
Gestalt Principles of Visual Organization
In discussing the 'selectivity' of perception I have alluded to foregrounding and backgrounding.
We owe the concept of 'figure' and 'ground' in perception to the Gestalt psychologists: notably
Max Wertheimer (1880-1943), Wolfgang Keler (1887-1967) and Kurt Koffka (1886-1941).
Confronted by a visual image, we seem to need to separate a dominant shape (a 'figure' with a
definite contour) from what our current concerns relegate to 'background' (or 'ground'). An
illustration of this is the famous ambiguous figure devised by the Danish psychologist Edgar
Rubin.
Images such as this are ambiguous concerning figure and ground. Is the figure a white vase (or
goblet, or bird-bath) on a black background or silhouetted profiles on a white background?
Perceptual set operates in such cases and we tend to favour one interpretation over the other
(though altering the amount of black or white which is visible can create a bias towards one or the
other). When we have identified a figure, the contours seem to belong to it, and it appears to be in
front of the ground.
In addition to introducing the terms 'figure' and 'ground', the Gestalt psychologists outlined what
seemed to be several fundamental and universal principles (sometimes even called 'laws') of
perceptual organization. The main ones are as follows (some of the terms vary a little): proximity,
similarity, good continuation, closure, smallness, surroundedness, symmetry and pr 鋑 nanz.
The principle of proximity can be demonstrated thus:
What you are likely to notice fairly quickly is that this is not just a square pattern of dots but rather
is a series of columns of dots. The principle of proximity is that features which are close together
are associated. Below is another example. Here we are likely to group the dots together in rows.
The principle also applies in the illustration below. We are more likely to associate the lines which
are close together than those which are further apart. In this example we tend to see three pairs of
lines which are fairly close together (and a lonely line on the far right) rather than three pairs of
lines which are further apart (and a lonely line on the far left).
The significance of this principle on its own is likely to seem unclear initially; it is in their
interaction that the principles become more apparent. So we will turn to a second major principle
of perceptual organization - that of similarity. Look at the example below.
Here the little circles and squares are evenly spaced both horizontally and vertically so proximity
does not come into play. However, we do tend to see alternating columns of circles and squares.
This, the Gestalt psychologists would argue, is because of the principle of similarity - features
which look similar are associated. Without the two different recurrent features we would see either
rows or columns or both...
A third principle of perceptual organization is that of good continuity. This principle is that
contours based on smooth continuity are preferred to abrupt changes of direction. Here, for
instance, we are more likely to identify lines a-b and c-d crossing than to identify a-d and c-b or
a-c and d-b as lines.
Closure is a fourth principle of perceptual organization: interpretations which produce 'closed'
rather than 'open' figures are favoured.
Here we tend to see three broken rectangles (and a lonely shape on the far left) rather than three
'girder' profiles (and a lonely shape on the right). In this case the principle of closure cuts across
the principle of proximity, since if we remove the bracket shapes, we return to an image used
earlier to illustrate proximity...
A fifth principle of perceptual organization is that of smallness. Smaller areas tend to be seen as
figures against a larger background. In the figure below we are more likely to see a black cross
rather than a white cross within the circle because of this principle.
As an illustration of this Gestalt principle, Coren, Ward and Enns (1994, 377) argue that it is easier
to see Rubin's vase when the area it occupies is smaller. The lower portion of the illustration below
offers negative image versions in case this may play a part. To avoid implicating the
surroundedness principle I have removed the conventional broad borders from the four versions.
The Gestalt principle of smallness would suggest that it should be easier to see the vase rather than
the faces in the two versions on the left below.
The principle of symmetry is that symmetrical areas tend to be seen as figures against
asymmetrical backgrounds.
Then there is the principle of surroundedness, according to which areas which can be seen as
surrounded by others tend to be perceived as figures.
Now we're in this frame of mind, interpreting the image shown above should not be too difficult.
What tends to confuse observers initially is that they assume that the white area is the ground
rather than the figure. If you couldn't before, you should now be able to discern the word 'TIE'.
All of these principles of perceptual organization serve the overarching principle of practise,
which is that the simplest and most stable interpretations are favoured.
What the Gestalt principles of perceptual organization suggest is that we may be predisposed
towards interpreting ambiguous images in one way rather than another by universal principles. We
may accept such a proposition at the same time as accepting that such predispositions may also be
generated by other factors. Similarly, we may accept the Gestalt principles whilst at the same time
regarding other aspects of perception as being learned and culturally variable rather than innate.
The Gestalt principles can be seen as reinforcing the notion that the world is not simply and
objectively 'out there' but is constructed in the process of perception.
PSYCHOLOGICAL TESTING
Sixteen Personality Factor Questionnaire (16PF)
Description
The Sixteen Personality Factor Questionnaire (16PF) is an objective test of 16 multidimensional
personality attributes arranged in omnibus form. In general, it provides normed references to each
of these attributes (the primary scales). Conceptualized and initially developed by Raymond B.
Cattell in 1949 as a broad, multipurpose measure of the "source traits" of individual personality,
the 16PF is appropriate for a wide range of multifaceted populations. It provides a global
representation of an individual’s coping style, the person’s reactive stance to an ever-fluid and
transactional environment and that individual’s ability to perceive accurately certain specific
environmental requisites for personal behavior.
Scoring
A subject’s raw score for each of the 16 primary factors is obtained through a weighted procedure
where particular responses count as "1" or "2" summatively toward the final raw score. These
weighted or unweighted sums are then compared to the desired normative score tables in the
tabular supplement where a particular sten score is identified based on the magnitudinal range of
the response and the individual normative demographics of the respondent. This sten score is
entered on the profile form and subsequently depicted graphically for ease of interpretation.
Reliability
Reliability coefficients calculated by test-retest with short intervals (single or
multiple day) demonstrate relatively acceptable coefficients, with only sporadic instances of a
scale falling below a .70 magnitude. For stability coefficients, test-retest administrations
conducted over long intervals (several weeks), magnitudes are expectedly reduced.
Intercorrelations between primary factor scales generated from different test forms are seldom
greater than .50 when Forms A and B are compared. Fewer coefficients of .50 or more magnitude
exist for Forms C and D.
Validity
Forms A and B are reported to have the greatest total direct validity where each form has seven
scales with validity coefficients of at least .70 magnitude. Indirect construct validities for Forms A,
B, C, and D are also reported in the form of multiple correlation coefficients, representing the
degree of relationship between each primary scale magnitude and the total remaining primary
scale magnitudes in the 16PF. As might be anticipated, correlational coefficients fall below a .80
magnitude in only two instances: .63 for Shrewdness and .74 for Imagination.
Norms
The norms were constructed for high-school juniors and seniors, college students, and a general
nation-wide population of age and income levels commensurate with the then current U.S. Bureau
of Census figures.
Suggested Uses
The 16PF is recommended for use in personality assessment as part of a battery in clinical and
research settings.
Purpose
Designed as an objective personality test.
Population
Ages 16 and above.
Time
30-60 minutes.
Author
Raymond B. Cattell
The 16 Primary Factors
Primary Factor
Ref
Low
A
Reserved,
impersonal, Warm, outgoing, attentive
distant, cool, reserved, to
others,
kindly,
impersonal,
detached, easygoing, participating,
formal, aloof
likes people
B
Concrete-thinking, lower
general mental capacity,
less intelligent, unable to
handle abstract problems
C
Reactive,
emotionally
Emotionally
stable,
changeable, affected by
adaptive, mature, faces
feelings, emotionally less
reality, calm
stable, easily upset
E
Deferential,
cooperative,
avoids conflict, submissive,
humble, obedient, easily
led, docile, accommodating
Liveliness
F
Lively,
animated,
Serious, estrained, prudent,
spontaneous, enthusiastic,
taciturn,
introspective,
happy-go-lucky, cheerful,
silent
expressive, impulsive
Rule-Consciousness
G
Expedient, nonconforming, Rule-conscious,
dutiful,
disregards
rules, conscientious, conforming,
Warmth
Reasoning
Emotional Stability
Dominance
High
Abstract-thinking, more
intelligent, bright, higher
general mental capacity,
fast learner
Dominant,
assertive,
competitive,
bossy
forceful,
aggressive,
stubborn,
self-indulgent
Social Boldness
Sensitivity
Vigilance
Abstractedness
Privateness
Apprehension
Openness to Change
Self-Reliance
Perfectionism
moralistic,
rule-bound
staid,
H
Socially
bold,
Shy, threat-sensitive, timid, venturesome,
hesitant, intimidated
thick-skinned, uninhibited,
can take stress
I
Utilitarian,
objective,
unsentimental,
tough-minded, self-reliant,
no-nonsense, rough
L
Trusting,
accepting,
easy
M
Abstracted, imaginative,
Grounded,
practical,
absent-minded,
prosaic, solution-oriented,
impractical, absorbed in
steady, conventional
ideas
N
Private,
discreet,
Forthright, genuine, artless,
non-disclosing,
shrewd,
open, guileless, naive,
polished, worldly, astute,
unpretentious, involved
astute, diplomatic
O
Self-assured,
unworried,
complacent, secure, free of
guilt,
confident,
self-satisfied
Q1
Open
to
change,
Traditional, attached to
experimenting,
liberal,
familiar,
conservative,
analytical,
critical,
respecting traditional ideas
free-thinking, flexibility
Q2
Self-reliant,
Group-oriented, affiliative,
resourceful,
a joiner and follower,
individualistic,
dependent
self-sufficient
Q3
Tolerates
disorder,
unexacting,
flexible,
undisciplined,
lax,
self-conflict,
impulsive,
careless of social rules,
uncontrolled
Sensitive,
sentimental,
tender-minded,
refined
aesthetic,
intuitive,
unsuspecting, Vigilant,
suspicious,
unconditional, skeptical, wary, distrustful,
oppositional
Apprehensive,
self-doubting,
worried,
guilt-prone,
insecure,
worrying, self-blaming
solitary,
Perfectionist, organized,
compulsive,
self-disciplined, socially
precise, exacting will
power,
control,
self-sentimental
Tension
Q4
Tense,
high
energy,
Relaxed, placid, tranquil,
impatient,
driven,
torpid, patient, composed,
frustrated, over-wrought,
low drive
has high drive, time-driven
Raven Standard Progressive Matrices
Description
The Standard Progressive Matrices (SPM) was designed to measure a person’s ability to form
perceptual relations and to reason by analogy independent of language and formal schooling, and
may be used with persons ranging in age from 6 years to adult. It is the first and most widely used
of three instruments known as the Raven's Progressive Matrices, the other two being the Coloured
Progressive Matrices (CPM) and the Advanced Progressive Matrices (APM). All three tests are
measures of Spearman's g.
Scoring
The SPM consists of 60 items arranged in five sets (A, B, C, D, & E) of 12 items each. Each item
contains a figure with a missing piece. Below the figure are either six (sets A & B) or eight (sets C
through E) alternative pieces to complete the figure, only one of which is correct. Each set
involves a different principle or "theme" for obtaining the missing piece, and within a set the items
are roughly arranged in increasing order of difficulty. The raw score is typically converted to a
percentile rank by using the appropriate norms.
Reliability
Internal consistency studies using either the split-half method corrected for length or KR20
estimates result in values ranging from .60 to .98, with a median of .90. Test-retest correlations
range from a low of .46 for an eleven-year interval to a high of .97 for a two-day interval. The
median test-retest value is approximately .82. Coefficients close to this median value have been
obtained with time intervals of a week to several weeks, with longer intervals associated with
smaller values. Raven provided test-retest coefficients for several age groups: .88 (13 yrs.
plus), .93 (under 30 yrs.), .88 (30-39 yrs.), .87 (40-49 yrs.), .83 (50 yrs. and over).
Validity
Spearman considered the SPM to be the best measure of g. When evaluated by factor analytic
methods which were used to define g initially, the SPM comes as close to measuring it as one
might expect. The majority of studies which have factor analyzed the SPM along with other
cognitive measures in Western cultures report loadings higher than .75 on a general factor.
Concurrent validity coefficients between the SPM and the Stanford-Binet and Weschler scales
range between .54 and .88, with the majority in the .70s and .80s.
Norms
Norm groups included in the manual are: British children between the ages of 6 and 16; Irish
children between the ages of 6 and 12; military and civilian subjects between the ages of 20 and
65. A supplement includes norms from Canada, the United States, and Germany.
Suggested Uses
Recommended uses include measurement of a person’s ability to form perceptual relations and
reason by analogy in research settings.
Purpose
Designed to measure a person’s ability to form perceptual relations.
Population
Ages 6 to adult.
Score
Percentile ranks.
Time
45 minutes.
Author
J.C. Raven.
The Eysenck Personality Questionnaire (EPQ)
Description
Eysenck's theory is based primarily on physiology and genetics. Although he was a behaviorist
who considered learned habits of great importance, he considers personality differences as
growing out of our genetic inheritance. He is, therefore, primarily interested in what is usually
called temperament.
Temperament is that aspect of our personalities that is genetically based, inborn, there from birth
or even before. That does not mean that a temperament theory says we don't also have aspects of
our personality that are learned, it's just that Eysenck focused on "nature," and left "nurture" to
other theorists.
Construction
Eysenck initially conceptualized personality as two, biologically-based categories of temperament:
1. Extraversion/Introversion
Extraversion is characterized by being outgoing, talkative, high on positive affect (feeling good),
and in need of external stimulation. According to Eysenck's arousal theory of extraversion, there is
an optimal level of cortical arousal, and performance deteriorates as one becomes more or less
aroused than this optimal level. Arousal can be measured by skin conductance, brain waves or
sweating. At very low and very high levels of arousal, performance is low, but at a more optimal
mid-level of arousal, performance is maximized. Extraverts, according to Eysenck's theory, are
chronically under-aroused and bored and are therefore in need of external stimulation to bring
them up to an optimal level of performance. Introverts, on the other hand, are chronically
over-aroused and jittery and are therefore in need of peace and quiet to bring them up to an
optimal level of performance.
2. Neuroticism/Stability
Neuroticism or emotionality is characterized by high levels of negative affect such as depression
and anxiety. Neuroticism, according to Eysenck's theory, is based on activation thresholds in the
sympathetic nervous system or visceral brain. This is the part of the brain that is responsible for
the fight-or-flight response in the face of danger. Activation can be measured by heart rate, blood
pressure, cold hands, sweating and muscular tension (especially in the forehead). Neurotic people,
who have low activation thresholds, and unable to inhibit or control their emotional reactions,
experience negative affect (fight-or-flight) in the face of very minor stressors - they are easily
nervous or upset. Emotionally stable people, who have high activation thresholds and good
emotional control, experience negative affect only in the face of very major stressors - they are
calm and collected under pressure.
This temperament corresponds with Category B (Emotional Stability) in the online test.
The two dimensions or axes, extraversion-introversion and emotional stability-instability, define
four quadrants. These are made up of:
stable extraverts (sanguine qualities such as - outgoing, talkative, responsive, easygoing, lively,
carefree, leadership)
unstable extraverts (choleric qualities such as - touchy, restless, excitable, changeable, impulsive,
irresponsible)
stable introverts (phlegmatic qualities such as - calm, even-tempered, reliable, controlled, peaceful,
thoughtful, careful, passive)
unstable introverts (melancholic qualities such as - quiet, reserved, pessimistic, sober, rigid,
anxious, moody).
Further research demonstrated the need for a third category of temperament:
3. Psychoticism/Socialisation
Psychoticism is associated not only with the liability to have a psychotic episode (or break with
reality), but also with aggression. Psychotic behavior is rooted in the characteristics of
toughmindedness, non-conformity, inconsideration, recklessness, hostility, anger and
impulsiveness. The physiological basis suggested by Eysenck for psychoticism is testosterone,
with higher levels of psychoticism associated with higher levels of testosterone.
This temperament corresponds with Category C (Mastery/Sympathy) in the online test.
Suggested Uses
The EPQ is recommended for use in personality assessment as part of a battery in clinical and
research settings.
Purpose
Designed as an objective personality test.
Population
Ages 16 and above.
Time
30-60 minutes.
Author
Hans Eysenck
Three traits
The following table describes the traits that are associated with the three temperaments in
Eysenck's model of personality:
Psychoticism
Extraversion
Neuroticism
Aggressive
Sociable
Anxious
Assertive
Irresponsible
Depressed
Egocentric
Dominant
Guilt Feelings
Unsympathetic
Lack of reflection
Low self-esteem
Manipulative
Sensation-seeking
Tense
Achievement-oriented
Impulsive
Moody
Dogmatic
Risk-taking
Hypochondriac
Masculine
Expressive
Lack of autonomy
Tough-minded
Active
Obsessive
Evoked Potentials
Procedure Overview
Evoked potentials studies measure electrical activity in the brain in response to stimulation of
sight, sound, or touch. Stimuli delivered to the brain through each of these senses evoke minute
electrical signals. These signals travel along the nerves and through the spinal cord to specific
regions of the brain and are picked up by electrodes, amplified, and displayed for a physician to
interpret.
Different types of evoked potentials studies
Evoked potentials studies involve three major tests that measure response to visual, auditory, and
electrical stimuli.
1. visual evoked response (VER) test - can diagnose problems with the optic nerves that affect
sight. Electrodes are placed along the scalp. The patient is asked to watch a checkerboard pattern
flash for several minutes on a screen, and the electrical responses in the brain are recorded.
2. brainstem auditory evoked response (BAER) test - can diagnose hearing ability and can indicate
the presence of brain stem tumors and multiple sclerosis. Electrodes are placed on the scalp and
earlobes. Auditory stimuli, such as clicking noises and tones, are delivered to one ear.
3. somatosensory evoked response (SSER) test - can detect problems with the spinal cord as well
as numbness and weakness of the extremities. For this test, electrodes are attached to the wrist, the
back of the knee, or other locations. A mild electrical stimulus is applied through the electrodes.
Electrodes on the scalp then determine the amount of time it takes for the current to travel along
the nerve to the brain.
A related procedure that may be performed is an electroencephalogram (EEG). An EEG measures
spontaneous electrical activity of the brain. Please see this procedure for additional information.
Reasons for the Procedure
Evoked potential studies may be used to assess hearing or sight, especially in infants and children,
to diagnose disorders of the optic nerve, and to detect tumors or other problems affecting the brain
and spinal cord. The tests may also be performed to assess brain function during a coma.
A disadvantage of these tests is that they detect abnormalities in sensory function, but usually do
not produce a specific diagnosis about what is causing the abnormality. However, the evoked
potentials test can confirm a diagnosis of multiple sclerosis.
There may be other reasons for your physician to recommend an evoked potentials test.
Risks of the Procedure
The evoked potential studies are considered safe procedures. The tests cause little discomfort. The
electrodes only record activity and do not produce any sensation.
There may be risks depending upon your specific medical condition. Be sure to discuss any
concerns with your physician prior to the procedure.
Certain factors or conditions may interfere with the results of the test. These include, but are not
limited to, the following:
1. severe nearsightedness
2. presence of earwax or inflammation of the middle ear
3. severe hearing impairment
4. muscle spasms in the head or neck
Before the Procedure
Your physician will explain the procedure to you and offer you the opportunity to ask any
questions that you might have about the procedure.
You will be asked to sign a consent form that gives your permission to do the procedure. Read the
form carefully and ask questions if something is not clear.
Generally, no prior preparation, such as fasting or sedation, is required.
Wash your hair the night before the test, but do not use conditioner or apply any hairspray or other
hair products.
Based upon your medical condition, your physician may request other specific preparation.
During the Procedure
An evoked potentials test may be performed on an outpatient basis or as part of your stay in a
hospital. Procedures may vary depending on your condition and your physician's practices.
Generally, the evoked potentials test follows this process:
1. You will be asked to remove any clothing, jewelry, hairpins, eyeglasses, hearing aids, or other
metal objects that may interfere with the procedure.
2. If you are asked to remove clothing, you will be given a gown to wear.
3. You will be asked to relax in a reclining chair or lie on a bed.
4. A paste will be used to attach the electrodes. The electrodes will be positioned depending on
which type of evoked potentials test is being performed.
5. The test will generally proceed as follows:
Visual evoked response
You will be seated about three feet away from a screen.
Electrodes will be placed on your scalp over the areas of the brain responsible for interpreting
visual stimuli.
You will be asked to focus your gaze on the center of the screen.
You will then be asked to close one eye at a time while the screen displays a checkerboard pattern.
The squares of the checkerboard reverse color once or twice a second.
Brain stem auditory evoked response:
You will sit in a soundproof room and be asked to wear earphones.
Electrodes will be placed on top of your head and on one earlobe and then the other.
A clicking sound or another auditory stimulus will be delivered through the earphones to the ear
being tested while a “masking” noise will be delivered to the other ear to shield it from the
stimulus.
Somatosensory evoked response
Electrodes will be placed on the scalp and at one or more locations on your body, such as the wrist,
back of the knee, or the lower back.
Minute, painless electrical shocks will be delivered through the electrodes placed on the body.
6. For each of the tests, the electrical activity detected by the electrodes on the scalp will be fed
into a recorder, which amplifies the signal and charts it so that your physician can interpret the
results.
After the Procedure
Once the test is complete, the electrodes will be removed and the electrode paste washed off. In
some cases, you may need to wash your hair again at home.
Your physician will inform you as to when to resume any medications you may have stopped
taking before the test.
Your physician may give you additional or alternate instructions after the procedure, depending on
your particular situation.
Figure above shows aspects of auditory evoked response recorded in the Dm. A, Depth profile of
simultaneous single sweeps of AEP recorded with a multichannel, in-line silicon probe (see
Methods). Vertical lines mark the onset of the 100 ms tone pip. Arrows indicate 35-45 Hz waves
that are separated by higher frequency waves and spikes. B, Averaged AEPs to 10 ms and 300 ms
tone pips (thick and thin traces) recorded 100-200 µm below the surface. Traces plotted on log-log
scales to emphasize early, small, far-field potentials. The baseline is arbitrarily set at 7-8 µV
negative instead of the zero of the AC amplifier. The early positive wave at 4 ms (i.e. P4) has a
base-to-peak amplitude of ~ 5 µV, whereas the N40 represents a negative excursion of ~ 85 µV.
Plot is clipped at the beginning of a slow positive potential which lasts for hundreds of
milliseconds. Note that the averaging has greatly reduced the high frequency induced waves and
spikes.
MEMORY
Introduction
Memory (psychology), processes by which people and other organisms encode, store, and retrieve
information. Encoding refers to the initial perception and registration of information. Storage is
the retention of encoded information over time. Retrieval refers to the processes involved in using
stored information. Whenever people successfully recall a prior experience, they must have
encoded, stored, and retrieved information about the experience. Conversely, memory failure—for
example, forgetting an important fact—reflects a breakdown in one of these stages of memory.
Memory is critical to humans and all other living organisms. Practically all of our daily
activities—talking, understanding, reading, socializing—depend on our having learned and stored
information about our environments. Memory allows us to retrieve events from the distant past or
from moments ago. It enables us to learn new skills and to form habits. Without the ability to
access past experiences or information, we would be unable to comprehend language, recognize
our friends and family members, find our way home, or even tie a shoe. Life would be a series of
disconnected experiences, each one new and unfamiliar. Without any sort of memory, humans
would quickly perish.
Philosophers, psychologists, writers, and other thinkers have long been fascinated by memory.
Among their questions: How does the brain store memories? Why do people remember some bits
of information but not others? Can people improve their memories? What is the capacity of
memory? Memory also is frequently a subject of controversy because of questions about its
accuracy. An eyewitness’s memory of a crime can play a crucial role in determining a suspect’s
guilt or innocence. However, psychologists agree that people do not always recall events as they
actually happened, and sometimes people mistakenly recall events that never happened.
Memory and learning are closely related, and the terms often describe roughly the same processes.
The term learning is often used to refer to processes involved in the initial acquisition or encoding
of information, whereas the term memory more often refers to later storage and retrieval of
information. However, this distinction is not hard and fast. After all, information is learned only
when it can be retrieved later, and retrieval cannot occur unless information was learned. Thus,
psychologists often refer to the learning/memory process as a means of incorporating all facets of
encoding, storage, and retrieval.
Types of Memory
Although the English language uses a single word for memory, there are actually many different
kinds. Most theoretical models of memory distinguish three main systems or types: sensory
memory, short-term or working memory, and long-term memory. Within each of these categories
are further divisions.
A Sensory Memory
Sensory memory refers to the initial, momentary recording of information in our sensory systems.
When sensations strike our eyes, they linger briefly in the visual system. This kind of sensory
memory is called iconic memory and refers to the usually brief visual persistence of information
as it is being interpreted by the visual system. Echoic memory is the name applied to the same
phenomenon in the auditory domain: the brief mental echo that persists after information has been
heard. Similar systems are assumed to exist for other sensory systems (touch, taste, and smell),
although researchers have studied these senses less thoroughly.
American psychologist George Sperling demonstrated the existence of sensory memory in an
experiment in 1960. Sperling asked subjects in the experiment to look at a blank screen. Then he
flashed an array of 12 letters on the screen for one-twentieth of a second, arranged in the following
pattern:
Subjects were then asked to recall as many letters from the image as they could. Most could only
recall four or five letters accurately. Subjects knew they had seen more letters, but they were
unable to name them. Sperling hypothesized that the entire letter-array image registered briefly in
sensory memory, but the image faded too quickly for subjects to “see” all the letters. To test this
idea, he conducted another experiment in which he sounded a tone immediately after flashing the
image on the screen. A high tone directed subjects to report the letters in the top row, a medium
tone cued subjects to report the middle row, and a low tone directed subjects to report letters in the
bottom row. Sperling found that subjects could accurately recall the letters in each row most of the
time, no matter which row the tone specified. Thus, all of the letters were momentarily available in
sensory memory.
Sensory memory systems typically function outside of awareness and store information for only a
very short time. Iconic memory seems to last less than a second. Echoic memory probably lasts a
bit longer; estimates range up to three or four seconds. Usually sensory information coming in
next replaces the old information. For example, when we move our eyes, new visual input masks
or erases the first image. The information in sensory memory vanishes unless it captures our
attention and enters working memory.
B Short-Term or Working Memory
Psychologists originally used the term short-term memory to refer to the ability to hold
information in mind over a brief period of time. As conceptions of short-term memory expanded
to include more than just the brief storage of information, psychologists created new terminology.
The term working memory is now commonly used to refer to a broader system that both stores
information briefly and allows manipulation and use of the stored information.
We can keep information circulating in working memory by rehearsing it. For example, suppose
you look up a telephone number in a directory. You can hold the number in memory almost
indefinitely by saying it over and over to yourself. But if something distracts you for a moment,
you may quickly lose it and have to look it up again. Forgetting can occur rapidly from working
memory. For more information on the duration of working memory, see the Rate of Forgetting
section of this article.
Psychologists often study working memory storage by examining how well people remember a
list of items. In a typical experiment, people are presented with a series of words, one every few
seconds. Then they are instructed to recall as many of the words as they can, in any order. Most
people remember the words at the beginning and end of the series better than those in the middle.
This phenomenon is called the serial position effect because the chance of recalling an item is
related to its position in the series. The results from one such experiment are shown in the
accompanying chart entitled “Serial Position Effect.” In this experiment, recall was tested either
immediately after presentation of the list items or after 30 seconds. Subjects in both conditions
demonstrated what is known as the primacy effect, which is better recall of the first few list items.
Psychologists believe this effect occurs because people tend to process the first few items more
than later items. Subjects in the immediate-recall condition also showed the recency effect, or
better recall of the last items on the list. The recency effect occurs because people can store
recently presented information temporarily in working memory. When the recall test is delayed for
30 seconds, however, the information in working memory fades, and the recency effect
disappears.
Working memory has a basic limitation: It can hold only a limited amount of information at one
time. Early research on short-term storage of information focused on memory span—how many
items people can correctly recall in order. Researchers would show people increasingly long
sequences of digits or letters and then ask them to recall as many of the items as they could. In
1956 American psychologist George Miller reviewed many experiments on memory span and
concluded that people could hold an average of seven items in short-term memory. He referred to
this limit as “the magical number seven, plus or minus two” because the results of the studies were
so consistent. More recent studies have attempted to separate true storage capacity from
processing capacity by using tests more complex than memory span. These studies have estimated
a somewhat lower short-term storage capacity than did the earlier experiments. People can
overcome such storage limitations by grouping information into chunks, or meaningful units. This
topic is discussed in the Encoding and Recoding section of this article.
Working memory is critical for mental work, or thinking. Suppose you are trying to solve the
arithmetic problem 64 × 9 in your head. You probably would need to perform some intermediate
calculations in your head before arriving at the final answer. The ability to carry out these kinds of
calculations depends on working memory capacity, which varies individually. Studies have also
shown that working memory changes with age. As children grow older, their working memory
capacity increases. Working memory declines in old age and in some types of brain diseases, such
as Alzheimer’s disease.
Working memory capacity is correlated with intelligence (as measured by intelligence tests). This
correlation has led some psychologists to argue that working memory abilities are essentially
those that underlie general intelligence. The more capacity people have to hold information in
mind while they think, the more intelligent they are. In addition, research suggests that there are
different types of working memory. For example, the ability to hold visual images in mind seems
independent from the ability to retain verbal information.
Memory (psychology), processes by which people and other organisms encode, store, and retrieve
information. Encoding refers to the initial perception and registration of information. Storage is
the retention of encoded information over time. Retrieval refers to the processes involved in using
stored information. Whenever people successfully recall a prior experience, they must have
encoded, stored, and retrieved information about the experience. Conversely, memory failure—for
example, forgetting an important fact—reflects a breakdown in one of these stages of memory.
Forgetting
Forgetting is defined as the loss of information over time. Under most conditions, people recall
information better soon after learning it than after a long delay; as time passes, they forget some of
the information. We have all failed to remember some bit of information when we need it, so we
often see forgetting as a bother. However, forgetting can also be useful because we need to
continually update our memories. When we move and receive a new telephone number, we need
to forget the old one and learn the new one. If you park your car every day on a large lot, you need
to remember where you parked it today and not yesterday or the day before. Thus, forgetting can
have an adaptive function.
Rate of forgetting
The subject of forgetting is one of the oldest topics in experimental psychology. German
philosopher Hermann Ebbinghaus initiated the scientific study of human memory in experiments
that he began in 1879 and published in 1885 in his book, On Memory. Ebbinghaus developed an
ingenious way to measure forgetting. In order to avoid the influence of familiar material, he
created dozens of lists of nonsense syllables, which consisted of pronounceable but meaningless
three-letter combinations such as XAK or CUV. He would learn a list by repeating the items in it
over and over, until he could recite the list once without error. He would note how many trials or
how long it took him to learn the list. He then tested his memory of the list after an interval
ranging from 20 minutes to 31 days. He measured how much he had forgotten by the amount of
time or the number of trials it took him to relearn the list. By conducting this experiment with
many lists, Ebbinghaus found that the rate of forgetting was relatively consistent. Forgetting
occurred relatively rapidly at first and then seemed to level off over time (see the accompanying
chart entitled “Forgetting Curve”). Other psychologists have since confirmed that the general
shape of the forgetting curve holds true for many different types of material. Some researchers
have argued that with very well learned material, the curve eventually flattens out, showing no
additional forgetting over time.
Ebbinghaus’s forgetting curve illustrated the loss of information from long-term memory.
Researchers have also studied rate of forgetting for short-term or working memory. In one
experiment, subjects heard an experimenter speak a three-letter combination (such as CYG or
FTQ). The subjects’ task was to repeat back the three letters after a delay of 3, 6, 9, 12, 15, or 18
seconds. To prevent subjects from mentally rehearsing the letters during the delay, they were
instructed to count backward by threes from a random three-digit number, such as 361, until
signaled to recall the letters. As shown in the accompanying chart entitled “Duration of Working
Memory,” forgetting occurs very rapidly in this situation. Nevertheless, it follows the same
general pattern as in long-term memory, with sharp forgetting at first and then a declining rate of
forgetting. Psychologists have debated for many years whether short-term and long-term
forgetting have similar or different explanations.
Decay theory of forgetting
The oldest idea about forgetting is that it is simply caused by decay. That is, memory traces are
formed in the brain when we learn information, and they gradually disintegrate over time.
Although decay theory was accepted as a general explanation of forgetting for many years, most
psychologists do not lend it credence today for several reasons. First, decay theory does not really
provide an explanation of forgetting, but merely a description. That is, time by itself is not a
causative agent; rather, processes operating over time cause effects. Consider a bicycle left out in
the rain that has rusted. If someone asked why it rusted, he or she would not be satisfied with the
answer of “time out in the rain.” A more accurate explanation would refer to oxidation processes
operating over time as the cause of the rusty bicycle. Likewise, memory decay merely describes
the fact of forgetting, not the processes that cause it.
The second problem for decay theory is the phenomenon of reminiscence, the fact that sometimes
memories actually recover over time. Experiments confirm an observation experienced by most
people: One can forget some information at one point in time and yet be able to retrieve it
perfectly well at a later point. This feat would be impossible if memories inevitably decayed
further over time. A final reason that decay theory is no longer accepted is that researchers
accumulated support for a different theory—that interference processes cause forgetting.
Interference theory of forgetting
According to many psychologists, forgetting occurs because of interference from other
information or activities over time. A now-classic experiment conducted in 1924 by two American
psychologists, John Jenkins and Karl Dallenbach, provided the first evidence for the role of
interference in forgetting. The experimenters enlisted two students to learn lists of nonsense
syllables either late at night (just before going to bed) or the first thing in the morning (just after
getting up). The researchers then tested the students’ memories of the syllables after one, two, four,
or eight hours. If the students learned the material just before bed, they slept during the time
between the study session and the test. If they learned the material just after waking, they were
awake during the interval before testing. The researchers’ results are shown in the accompanying
chart entitled, “Forgetting in Sleep and Waking.” The students forgot significantly more while they
were awake than while they were asleep. Even when wakened from a sound sleep, they
remembered the syllables better than when they returned to the lab for testing during the day. If
decay of memories occurred automatically with the passage of time, the rate of forgetting should
have been the same during sleep and waking. What seemed to cause forgetting was not time itself,
but interference from activities and events occurring over time.
There are two types of interference. Proactive interference occurs when prior learning or
experience interferes with our ability to recall newer information. For example, suppose you
studied Spanish in tenth grade and French in eleventh grade. If you then took a French vocabulary
test much later, your earlier study of Spanish vocabulary might interfere with your ability to
remember the correct French translations. Retroactive interference occurs when new information
interferes with our ability to recall earlier information or experiences. For example, try to
remember what you had for lunch five days ago. The lunches you have had for the intervening
four days probably interfere with your ability to remember this event. Both proactive and
retroactive interference can have devastating effects on remembering.
Proactive Interference (top) and Retroactive Interference (bottom).
Stroop Effect
Description
The Stroop Effect is a robust phenomenon with a long history of study in cognitive psychology. As
described in chapter 2, the Stroop effect refers to an attentional finding that reveals how difficult it
can be to focus on one thing (or alternatively, ignore something else). In the classic demonstration
of the Stroop effect, words that are names of colours are presented to the participant in coloured
ink, and the participant is required to ignore the word and name the ink colour. When the ink and
word are consistent, (i.e. the word 'red' written in red ink), responses are generally quick. However,
when the ink and word are inconsistent (the word 'red' written in green ink), responses are
relatively slower.
In this experiment, you will be required to indicate the colour of a computer-presented letter string
by pressing a corresponding computer key as quickly as possible. There will be three conditions.
In condition 1 (Neutral) the coloured letter strings will be composed of X's. In condition 2
(Inconsistent) the letter strings will consist of colour words (e.g. red, green, blue) displayed in a
colour different than the colour specified by the word. In condition 3 (Consistent) the letter string
will consist of colour words displayed in the same colour specified by the word. You will test
whether your reaction time in identifying the colour (i.e. the dependent variable) is affected in the
consistent and inconsistent conditions when compared to the neutral condition (i.e. the
independent variable).
The following references are recommended as review materials for completing your paper.
Students are strongly encouraged to seek out additional references.
Logan, G. D. (1980). Attention and automaticity in Stroop and priming tasks: Theory and data.
Cognitive Psychology, 12, 523-553.
MacLeod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review.
Psychological Bulletin, 109, 163-203.
Morton, J. & Chambers, S. M. (1973). Selective attention to words and colours. Quarterly Journal
of Experimental Psychology, 25, 387-397.
Participant Instructions
On each trial in this experiment, a plus sign will appear briefly in the center of the screen for 500
milliseconds and will be immediately followed by a string of letters printed in one of four colours.
Your task is to respond to the COLOUR of the letter string by pressing the correct key as quickly
as possible. The appropriate key to press for each color is as follows:
red = z
green = x
blue = .
yellow = /
The computer key-colour assignments will be displayed at the top of the screen but you may also
want to tape colour terms (or colour patches) to your computer keys to help you keep track of the
colour-key assignments.
If the response is correct, the next trial will begin in 1500 milliseconds. If the response is not made
within the 1500 milliseconds, or if the response is incorrect, or if an invalid key is pressed, a short
tone will be presented and the next trial will begin in 1500 milliseconds.
Each of the three conditions will be presented twice in blocks of 36 trials (i.e. six blocks of 36
trials) and the order of conditions across blocks and the order of trials within a block will be
determined randomly. You will have an opportunity to take a short break between blocks. In
addition, there will be a set of 18 practice trials (6 trials for each condition) at the beginning of the
experiment.
The raw data from the experiment (216 responses) will be placed in a file called DSTROOP.DAT
on your computer and can be examined by using the View Raw Data button.
To summarize this data, click on the Analyze Raw Data button to compute the mean and standard
deviation of the reaction times for correct responses in each of the three conditions. This button
will also calculate the number of valid trials for each condition or the number of trials where a
correct response was provided.
The summarized data will be placed in a file called ASTROOP.ANL on your computer. To view
the results, click on the View Summarized Data button. This summary data is important and will
be necessary to prepare an APA style table to include with your paper. The file ASTROOP.ANL is
a simple text file and can also be read and printed with any word processor. Please note that
although the summary data appear in tabular form, the format is not in APA style.
To view the results of previous participants, click on the Display Group Data button. This button
will display the average reaction time for the three conditions. You can use this information to
compare with your own performance.
Interference: The Stroop Effect
Don't read the words on the right--just say the colors they're printed in, and do this aloud as fast as
you can.
You're in for a surprise!
If you're like most people, your first inclination was to read the words, 'red, yellow, green...,' rather
than the colors they're printed in, 'blue, green, red...'
You've just experienced interference.
When you look at one of the words, you see both its color and its meaning. If those two pieces of
evidence are in conflict, you have to make a choice. Because experience has taught you that word
meaning is more important than ink color, interference occurs when you try to pay attention only
to the ink color.
The interference effect suggests you're not always in complete control of what you pay attention
to.
What do you think would happen:
If you tried this experiment with a very small child who had not yet learned to read?
If you tried this experiment with someone who was just learning to speak English?
If you used the same order of ink colors but wrote non-color words?
If you made up an experiment of your own.
Biofeedback
Introduction
Biofeedback operates on the notion that we have the innate ability and potential to influence the
automatic functions of our bodies through the exertion of will and mind. Biofeedback has recently
been shown to give us what had previously seemed an impossible degree of control over a variety
of physiologic events.
For example, a person can be trained in a matter of days to cause the temperature of one hand to
rise five to ten degrees higher than that of the other hand, while not contracting the hand muscles.
What is amazing is that even animals can be trained. In one experiment, researchers trained a
laboratory rat to produce a differential in the temperature of its two ears in order to receive a food
reward.
This experiment, although it appears to satisfy science fiction enthusiasts at first, nevertheless has
practical applications. When people trained in biofeedback cause their hands to quickly become
warmer than normal, this can effectively short-circuit a migraine attack. The blood which
ordinarily engorges the blood vessels of the head in migraine is diverted to the hands and arms.
This effectively removes the headache. In cases of "pure" migraine, a person can be successfully
taught this technique and stop headaches in a week or less. However in 90 percent of migraine
cases, there is chronic tension that must also be treated over a longer period of time by
biofeedback relaxation techniques. Biofeedback can also be used to train persons to block the pain
of colitis, neuritis, and other conditions. Many of these techniques have been scientifically proven.
Using a special machine and sensors to record muscle contractions and skin temperature, you can
learn to control normally involuntary processes such as heart rate and blood pressure that increase
under stress. The machine "feeds back" the efforts and eventually you can recognize and control
facets of the stress response by yourself. Once viewed with skepticism, the control of
"involuntary" responses is now seen to be effective in the treatment of migraine headaches, asthma
and other disorders in certain individuals.
Biofeedback in Action
In case of biofeedback, there are a number of techniques that can be used, but the most basic one
is-to attach a GSR device to the person's fingertips. This measures the galvanic skin response, or
minute amounts of perspiration on the skin. The more tense you are, the more perspiration there is
on your skin. As you become calm, there is less and less.
The electrodes are attached to a machine which converts the electrical information into an easily
observable form, such as a light or a buzzing noise. The machine can be adjusted, so that the
buzzing sound is moderately audible at the beginning of the session. As the device picks up more
perspiration, meaning more tension, the noise gets louder. If the person becomes calmer and there
is less perspiration, the noise becomes lower and is finally extinguished.
Usually, the person hooked up to the biofeedback machine and told extinguish the buzz or the
light. Since the person has no idea what to do, he or she will start experimenting to stop the
annoying sound. If he tenses his muscles, for example, he will find that the noise is getting louder.
Then, maybe he figures that if he relaxes, the buzz will go softer. So. he relaxes and the buzz does
get softer. But it is not extinguished.
The person now will start putting himself/herself in various frames of mind that he believes will
do the trick. There is a delay of several seconds between the feeling and the buzz, because it takes
that long for the perspiration to appear on the skin, but he will soon enough find out if the machine
is doing what he wants it to do. He tries other frames of mind. He imagines different scenes,
different people, maybe different colors. Then, quite suddenly, he discovers that the sound is no
longer there. He will start mentally examine what he did to get to that condition. In practice, he
will recall it and keeps it up.
The therapist will now readjust the machine so that it has greater sensitivity. In other words, the
buzz is going to sound when smaller amounts of perspiration are detected. In another session or
two the person would probably learn how to counter this, and the process is continued until a
satisfactory degree of relaxation is obtained. Once the person figures out how to do it with the help
of machine, he can accomplish relaxation without the help of the machine by doing what he had to
do as learned from the biofeedback techniques.
The same technique would be used to teach someone how to warm his hands, such as when we
want him to control his migraine headaches. Here, instead of measuring perspiration, skin
temperature would be measured. The person would imagine whatever he found necessary to do the
trick. Incredibly, some people can not only boost the temperature of one hand over the other, but
also to make one part of their palm warmer than the adjacent part!
galvanic skin response
Descrption
A change in the ability of the skin to conduct electricity, caused by an emotional stimulus, such as
fright.
A measure of electrical resistance as a reflection of changes in emotional arousal, taken by
attaching electrodes to any part of the skin and recording changes in moment-to-moment
perspiration and related activity of the autonomic nervous system.
Galvanic skin response (or GSR), also known as electrodermal response (EDR) or psychogalvanic
reflex (PGR), is a method of measuring the electrical resistance of the skin. There has been a long
history of electrodermal activity research, most of it dealing with spontaneous fluctuations. Most
investigators accept the phenomenon without understanding exactly what it means. There is a
relationship between sympathetic activity and emotional arousal, although one cannot identify the
specific emotion being elicited. The GSR is highly sensitive to emotions in some people. Fear,
anger, startle response, orienting response and sexual feelings are all among the emotions which
may produce similar GSR responces.
One branch of GSR explanantion interprets GSR as an image of activity in certain parts of the
body. The mapping of skin areas to internal organs is usually based on acupuncture point.
Practice
GSR is conducted by attaching two leads to the skin, and acquiring a base measure. Then, as the
activity being studied is performed, recordings are made from the leads. There are two ways to
perform a GSR - in active GSR, current is passed through the body, with the resistance measured.
In passive GSR, current generated by the body itself is measured.
History
GSR originated in the early 1900s. It was used for a variety of types of research in the 1960s
through the late 1970s, with a decline in use as more sophisticated techniques (such as EEG and
MRI) replaced it in many areas of psychological research. GSR still sees limited use today, as it is
possible to use with low-cost hardware (galvanometer).
Uses
Because the GSR is relatively simple and well documented it can be used to detect subconscious
semantic knowledge. For example suppose that two subjects are suffering from prosopagnosia,
however one of these subjects gets a GSR while the other does not; from this we could infer that
the two subjects suffered from different (although similar) neural disfunction.
Non-research uses
GSR has seen, outside of the research community, usage as a lie detector, under the theory that
telling of lies increases perspiration, changing the conductance of skin. However, the variety and
rapidity of some responses disproves this theory, as skin would have to 'un-sweat' or dry out in
remarkable ways. Its accuracy, because of its limited scope, is believed to be even less significant
than that of a regular polygraph.
GSR is also used by Scientologists, who call their devices E-meters, in their spiritual counseling.
They claim to have developed a variety of techniques to improve the reliability and accuracy of
the device.