PERCEPTION
Vessels Unit 2 Lecture Notes
I.
THE NATURE AND NURTURE OF PERCEPTION:
A. People think of perception or the ability to make sense of input from sensory organs as inborn or
innate. This is understandable since perception seems so effortless and automatic. But your
past experiences (nurture) play an important determinative role in your perceptions, or how you
interpret and make sense out of what you see, hear, smell, feel, and taste.
B. Perceptual abilities such as color discrimination and discriminating figure from ground or
background seem to be “wired-in” at birth. Additionally, there are receptor cells that react to very
shapes of types of motion in our environment. These are called complex and hypercomplex cells.
The fact that they are wired-in, however, does not mean that environmental influences in our lives
are not also determinative. Sensory experience is necessary (a) in order for our wired-in
perceptual abilities to fully mature or develop, and (b) in order for us to be able to make sense of
things in our world quickly without having to attend to every little tidbit of sensory data. Item (a)
concerns early experience and its relationship to the maturation of “bottom-up” sensory
mechanisms, for lack of a better word, and item (b) concerns the effects of past experience on
present perceptions or “top-down” influences on perception. Let’s look in more detail at item (a)
first in items 1 and 2 below, and then item (b) in numbers 3 and 4.
1. Early visual-sensory deprivation for infants born with cataracts interferes with visualperceptual maturation (physical development) and results in diminished visual-perceptual
abilities thereafter or throughout life. The person’s genetically determined visual-perceptual
potential is never fully realized.
2. Held and Heid (1963) found that kittens who were allowed to be active developed better
depth perception than those kept inactive or sensory deprived. This affect was also
permanent.
3. Richard Gregory (1997a) found that we experience illusions because of our experiences with
three-dimensional objects in our environment. These set us up to automatically formulate
erroneous hypotheses about what we see. With the Muller-Lyer illusion, for example, his
explanation is that the lines seem different in length because figure A resembles a receding
corner and figure B resembles a projecting corner. Such illusions depend on the many years
of experience we have moving around in our environment learning the usual relationships
among objects.
Experiments completed in 1966 by Segal, Campbell, and Herskovitz revealed that this illusion
is not experienced as an illusion by people who have grown up in natural environments. Zulu
people who live in circular huts with curved doorways and no exposure to western-style
angles and rectangles were more inclined to see the horizontal lines as equal in length.
4. Our perceptual systems also adapt to changes in the relationships among visual images as
we encounter and move through them. Our systems constantly make “judgments” based on
our experiences and try to present us with the perceptual interpretations that make the most
sense. Some end up making sense to us in more than one way such as the Necker Cube
and our attention to either figure or ground but not both at the same time.
II. BOTTOM-UP PERCEPTION: A CLOSER LOOK:
A. Marr investigated the mechanisms of vision and visual perception. As described by Bell (2004),
Marr linked the neurophysiology of the visual system with an information processing (from
cognitive psychology) view of the mind. “He treated the patterns on the Retina as information
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from which more detailed visual experience could be extracted by the computations of the brain”
(Bell, 2004, paragraph 3).
He assumed that the visual system makes a number of inferences from the
[sensory input] data from an earlier stage, and that these inferences are
constrained by the physiology of the visual pathways. Because he argued that
high level perceptual experience (such as being able to perceive individual
objects) was derived from computations based on low level perceptions (such as
edges and . . . light/darks contrasts) his approach is . . . a type of ‘bottom-up’
[theory of perception] . . . (Bell, 2004, paragraph 4).
B. Marr proposed that visual perception occurs in four stages:
1. The first “raw primal sketch” stage involved getting information from a stimulus in terms of
edges and intensity changes, which come from the light and dark patterns on the retina. His
computational or mathematical model actually computed this information. “Edges are
assumed to fall where there is a transition between light and dark, and we know there are
specific cells in the visual cortex [of the brain that] . . . activate when lines . . . are seen”
(Bell, 2004, paragraph 6).
2. His second stage was called a “complete primal sketch.” He proposed that from
this low-level raw sketch surfaces and common areas are grouped. He incorporated here
much of the grouping or organizational principles of perception discovered by the Gestalt
psychologists in the 1920s included proximity (things close together are seen as a group),
similarity (things that look alike are grouped), common fate (grouping of things that move
together), closure (incomplete familiar patterns seen as closed), and continuation (crossing
lines see as two straight or curved lines rather than v-shapes touching at the points of each).
These gestalt principles can also be viewed as top-down when examined in isolation because
each principle relies on the perceiver’s past experience, but in Marr’s sequence of stages,
they play a part in a bottom-up visual-perceptual process where the whole is constructed
from the parts, or simple to complex process.
3. Stage three is Marr’s 2½ dimension sketch (shy of 3D). This has to do with location in space
relative to the perceiver. Here he brought in some other perceptual phenomena you are
reading about in your text such as perceptual constancy in terms of size, color, and shape.
An object look very different from different angles, but we know it is the same object. Figureground discrimination is also a part of this 2½ D sketch along with the processes that enable
us to determine depth including relative size, binocular disparity (a slightly different view by
each eye), texture clarity, and occlusion (overlap). Like gestalt principles, these too are not
purely bottom-up when viewed in isolation — they depend on experience (Bell, 2004).
4. Stage four is of course the 3D perception. This mental representation of what is in your
visual field is supposedly independent of your perspective.
III. CAUSES OF INDIVIDUAL DIFFERENCES IN TOP-DOWN PERCEPTION:
A. Differences in how we perceive the same stimuli are also a product our experiences. These
differences from sociocultural and gender-specific to those that are unusual and even unique to
an individual. Some are relatively long-term or permanent and those that are more temporary or
transitory. Let’s look at this more closely.
1. Asch (1955) found that when people were told that others perceived something differently,
many conformed and came to share others’ interpretation even when these interpretations
were experimentally contrived to be false.
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2. Personality differences also cause differences in how things in our environment are
perceived. Jerome Kagan found that some have less tolerance for ambiguity than others and
will manufacture order, clarity, or stability when it is not actually there. He also found that
impulsive personality types perceived things differently than people with reflective
personalities.
3. Prejudice and related fear has been found to distort perceptions. Gordon Allport found that
when people were shown a picture of a multicultural group in an underground train, many
recalled that the young black male was holding a knife when in fact it was the young white
male.
4. People described as field independent and who are capable of disembedding figures from
their contexts, as in a word search puzzle perceive things differently than people who are
field dependent.
5. Yarbus (1967) found that even the questions people are asked to consider affects what they
attend to and see in pictures shown to them thereafter.
6. Levine et al. (1989) found that hunger caused people to see food items in ambiguous
drawings where nothing was clearly any specific thing.
7. Jerome Bruner (1949) found that poor children over-estimated the size of coins they were
shown and did so far more often than affluent children.
8. Clinical and school psychologists use the Thematic Apperception Test and Rorschach picture
and inkblot cards as a way of getting people to reveal their needs, concerns, attitudes,
problems, in the stories they create. They reveal these things unknowingly.
9. Hastorf and Contril (1954) studied how sports fans from opposing sides perceive events
differently.
B. Daniel Chandler examined the all encompassing concept of “context” as this applies to
experiences and their influence on perception. He offered five definitions for the term: historical,
sociocultural, individual, situational, structural. The Ebbinghaus or Tichener illusion illustrates
structural. It has two daisey-like designs with a white circle in the center of each. These white
circles are the same size, but the black petal-like circles around each are not: one has small black
circles and the other has large black circles. The context of each makes the white circle
surrounded by small black circles look bigger than the one surrounded by large black circles.
C. Summary for section II:
Experience in a world full of stimuli is needed in infancy and our early years in order to fully
develop sensory receptor cells and perceptual potential we are each born with (bottom-up
sensory-perceptual equipment or neurophysiological capacity). It is also needed in order to
acquire the concepts, categories, expectations, predispositions, mind sets, etc. that enables us to
perceive stimuli more quickly and inferentially without having to engage in a time-consuming
process of attending to many or all features of objects in our environment (top-down short-cut
perception that enables us to make sense of what would otherwise be a continual and relentless
bombardment of disconnected input from each of our senses. So experience fosters maturation
early in life (bottom-up perceptual equipment) and familiarization throughout life (top-down
perceptual predispositions) so that we can interpret our world quickly and efficiently. Top-down
experiential influences can be divided into short-term and long-term.
1. Long-Term Top-Down: personality characteristics, cognitive style, gender, occupation, age,
values, attitudes, beliefs, prejudices, motivations, culture, social class, knowledge, etc. Some
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of these influences are more likely to cause misperception than perception that is factually
accurate.
2. Short-Term Top-Down: mental set created by what you have been doing immediately before
exposure to a stimulus, salient deficiency needs or physical drives, your state of mental and
physical health at any given time, those you are with, the presence or absence of an authority
figure, etc.
IV. PERCEPTION AS CONSTRUCTION:
A. As perceivers, we are not like cameras; rather, we actively interpret our world and construct our
perceptions of it. As Daniels Chandler has put it, we are “homosignificans” or “meaning makers”
who try to make even meaningless visual patters meaningful. This view of our selves as active
agent perceivers corresponds to Richard Gregory’s “constructivist” or “top-down” theory of
perception, which emphasizes the importance of acquired knowledge and forming hypotheses.
1. Schemata Theory states that we use mental templates of clusters of knowledge called
schemas to make sense of our world. The term schema was first introduced by Jean Piaget.
Chandler explains this as follows:
“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 ‘go 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
favor of our expectations” (Chandler, 2004, Module 5, paragraph 24).
2. Closely related to schema is the concept of categorization. Categorization is also an
important simplifying top-down mechanism involved in perception, and it can be viewed as a
building block for concepts. Categories and concepts when activated or brought to
consciousness by sensory input (a) make complexity manageable, (b) speed up recognition,
(c) reduce required effort and new learning, (c) make the best use of past experience, (d)
enable inferences about other attributes that have not been attended to, (e) make sensoryperceptual events predictable, (f) connect us with others through shared perceptions, (g)
tailor and even distort the world to fit our purposes, (h) give the world meaning that it would
not otherwise have. The cost of these advantages is what Chandler calls “a loss of
particularity and uniqueness in perception.” He goes on to state that “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.”
B. But James Gibson (1979) and others have proposed a more bottom-up, data-driven explanation
of perception that yields constructions that are far less unique to the individual and more aligned
with the objective facts with respect to incoming stimuli. Chandler wrote that we would be
“mindless automatons” if bottom-up perception was the only type of perceiving we engaged in
and “disembodied dreamer” if we engaged only in top-down perception only.
V. SOME ILLUSTRATIONS:
Can you read the following? Do you know why? A form of Top-Down Processing that depends on
your visual memory capacity and the words you have stored there. You are born with a certain
potential for visual-spatial and visual-sequential memory. Then experience determines if these
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potentials, which vary greatly among people, are fully developed. Recognizing these words depends
partly on visual memory and perhaps to a lesser degree on your auditory-verbal and tactilekinesthetic memory for the letters that comprise each of these words. So what you are concluding is
that each set of letters can only be a particular word. This may require a mental re-sequencing that
uses imagery or perhaps checking by spelling the word you think it is aloud. Some of you will be
better at this than others based on who among you have processing strengths that are relevant.
Those who have these may not be the smartest among you overall. The passage states that all that
matters is that the first letter be in the right place, which implies that your visual-sequencing memory
is essential. I’m not so sure that would be true if at least a couple of the other letters in each word are
in the right order thus serving as a clue just like the first letter does here.
I cdnuolt blveiee taht I cluod aulaclty uesdnatnrd waht I was rdanieg. Tish swohs teh phaonmneal
pweor of the hmuan mnid. Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht
oredr the ltteers in a wrod are. The olny iprmoatnt tihng is taht the frist and lsat ltteer be in the rghit
pclae. The rset can be a taotl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the
huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.
We can construct a different version of this passage that will force you to use a different set of mental
processing skills: visual-spatial memory and visual closure, which is the ability to quickly recognize a
familiar visual pattern with part of it missing or without having to look at each and every part. Some
can recognize a whole word based on its overall shape, as revealed by drawing a line around it. Or
they may recall it easily as a total pattern or design without paying much attention to individual letters.
This would be visual-spatial memory. People vary greatly in these processing skills, and they do not
necessarily correlate with overall intelligence. Many mentally handicapped people have high levels of
these reading-related processing skills.
I cou_ _n’t be_ _eve th_t I c_ _ld ac_ _ally un_ _ _st_ _d wh_t I w_s r_ _d_ _ng. Th_ _ sh_
_s t_e ph_n_m_nal p_we_ o_ th_ _um_n _ _nd. _cco_d_ng _o r_s_arch a_ C_m_rigde _
_ _ _ersity, i_ d_ _ _n't m_tt_r in w_ _t or_ _r t_e _ _tt_rs _n a _ord _re. T_e o_ly _mp_
_tant th_ _g _s t_ _t t_e f_ _st _nd l_st _et_er b_ _n th_ _gh_t pl_c_. T_e r_st c_n _e a
_ot_l m_ss, a_d yo_ c_n s_i_l re_d it w_th_ _t a pr_ _ _em. Th_ _ _s be_ _ _ _ _ the h_
_an mi_d d_ _s n_t r_ad _ver_ l_ _ _er by it_ _ _ _, bu_ the _ord as a wh_ _ _.
What type of top-down processing do you think a person uses to fill in the missing words below?
Would it be your general knowledge of the subject matter? How about the fact that some words tend
to show up together in a particular order irrespective of the meaning of the sentence? Do you
sometimes have to consider the number of letters in the word missing and scan your memory for
possibilities, or can you figure them out based on meaning or context alone?
I couldn’t believe that I _ _ _ _ _ actually under_ _ _ _ _ what I _ _ _ reading. This shows the
phenomenal _ _ _ _ _ of the human _ _ _ _. According to research at Cambridge _ _ _ _ _ _ _ _ _ _
_, it doesn’t matter in _ _ _ _ order the _ _ _ _ _ _ _ in words are. The only _ _ _ _ _ _ _ _ _ thing is
that the first and _ _ _ _ letter be in the _ _ _ _ _ place. The rest can be a total mess and _ _ _ can
still _ _ _ _ it _ _ _ _ _ _ _ a problem. This is _ _ _ _ _ _ _ the human _ _ _ _ does _ _ _ read every _
_ _ _ by itself _ _ _ the _ _ _ _ as a whole.
VI. TOP-DOWN VERSUS BOTTOM-UP PROCESSING:
For each of the first two illustrations, you must do more “bottom-up” processing than usual, that is,
you have to look at more of the letters of each word than you would ordinarily. Whether you realize it
or not, you rarely if ever attend to all of the letters in words you know how to read. For a child who
has not learned to read the words, they must pay attention to every letter and may have to think about
the sounds of letters and letter combinations. They often get confused with words that look similar,
have trouble lending the sounds, or may even begin sounding a word without looking at it and
realizing they can already recognize it by sight. The process of learning how to read words requires
many mental processing abilities, both auditory and visual, and the ability to associate the two, that is,
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sound and symbol. It is a rough bottom-up perceptual road to what eventually becomes a rather
automatic effortless ability to read and understand words quickly in a more top-down manner.
Various approaches to reading place greater or lesser emphasis on each of these bottom-up
perceptual processing skills, so highly killed learning disability teachers and school psychologists can
match method to each child’s profile of mental processing strengths and weaknesses. If they have a
weak visual memory and strong auditory memory, for example, the obvious choice is a heavily
phonetic approach. For our purposes, you need to be aware that there is always some combination
of bottom-up or stimulus-driven perception and top-down or experience-driven perception.
Perceptual errors occur from too much reliance on top-down and the numerous prior experiences that
allow for it.
VII. SELECTIVITY OF ATTENTION:
A. Perception is unavoidably selective because we can't see all there is to see and can’t fully attend
to more than one thing at a time. There are limits to what we can perceive, and they are both
cognitive and local or situational, that is, we can't see things from every angle at once.
Additionally we focus on salient features and ignore details that are irrelevant to our purposes.
“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”
(Chandler, 2004). “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.' Our schemata allow us to 'fill in gaps' because we know what
should be there. So selectivity also involves addition” (Chandler, 2004).
VIII. REFERENCES
Asch, S E (1955). Opinions and social pressures, Scientific American 193: 31-55.
Bell, Vaughan (2004). Perception and perceptual distortions. An article retrieved from the author’s
website at http://cardiff.ac.uk/psych/home/bellv1/conf/VaughanPerceptionLectureNotes2004.doc All
quotes of his paper are included in this lecture with his permission.
Bruner, Jerome & Cecile C. Goodman (1947). Value and need as organizing factors in perception.
Journal of Abnormal and Social Psychology, 47: 33-44
Chandler, Daniel (1997-2004). Modules 1-6 on Perception: Searching for Patterns;
The Third Dimension; Cultural and Environmental Factors; Individual Differences, Purposes, and
Needs; Context and Expectations: Categorization and Selectivity; Gestalt Principles of Visual
Organization. He is at the University of Wales. Retrieved from
http://www.aber.ac.uk/media/Modules/MC10220/visindex.html
Gibson, James J. (1979). The Ecological Approach to Visual Perception. Boston: Houghton Mifflin.
Gregory, Richard (1997). Mirrors in Mind. Oxford: W.H.Freeman/Spektrum
Gregory, Richard (1997). Knowledge in perception and illusion. Paper in pdf retrieved from
http://www.richardgregory.org/papers/knowl_illusion/knowledge-in-perception.pdf. Professor of
Neuropsychology at the University of Bristol.
Gregory, Richard L & E H Gombrich (Eds.) (1973). Illusion in Nature and Art. London: Duckworth
Hastorf, A.H. & Cantril, H. (1954). They saw a game: A case study. Journal of
Abnormal and Social Psychology, 49, 129-134.
Held, R. and Hein, A. (1963). Movement produced stimulation in the development of visually guided
behaviour. Journal of Comparative and Physiological Psychology, 56, 872-76.
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Kagan, Jerome (1984). The Nature of the Child. New York: Basic Books.
Levine, Robert, Isidor Chein & Gardner Murphy (1942). The relation of the intensity of a need to the
amount of perceptual distortion. Journal of Psychology 13: 283-93
Levine, A.S., Tallman, J.R., Grace, M.K., Parker, S.A., Billington, C.J., and Levitt, M.D. (1989). Effect
of breakfast cereals on short-term food intake. American Journal of Clinical Nutrition, Vol. 50, 13031307.
Marr, David (1982). Vision: A computational investigation into the human representation and
processing of visual information. San Francisco, CA: W.H. Freeman and Company.
Segall, H.H., Campbell, D.T., and Herskovits, M.J. (1966). The Influence of Culture on Visual
Perception. Indianapolis, IN: Bobbs-Merrill.
Yarbus, A.F. (1967). Eye Movements and Vision. New York: Plenum Press.
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