AP Psychology
Sensation and Perception
absolute threshold
In order to determine how people detect stimuli from the outside
world, psychologists first had to figure out at what point a person
first detects stimuli. A test might include pin pricking the skin or
showing a low beam light against the wall.
Absolute threshold is the weakest point a person can detect the
stimuli half the time or more. The results?
Vision – a candle flickering 30 miles away on a clear night
Hearing – a watch ticking 20 feet a way
Taste – 1 teaspoon of sugar dissolved in 2 gallons of water
Smell – 1 drop of perfume in a 3-room house
Touch – A bee’s wing falling 1 centimeter upon one’s cheek
difference threshold
Difference threshold is the smallest change in physical stimuli that
can be detected by a person. You would be quite unique if you
could tell when the room you are in went from 72 to 71 degrees.
This could be an example of difference threshold.
hearing: audition
Audition is the sense of hearing. Hearing is often measured in one
of three ways – decibel, pitch and timbre.
hearing: auditory nerve
The auditory nerve carries impulses from the ear to the brain.
hearing: cochlea
The inner ear is made up of the cochlea – a fluid-filled, coiled tunnel
that contains the receptors for hearing. In essence, the cochlea is
the ear’s neural tissue, like the eye’s retina.
hearing: conduction deafness
Conduction deafness is that which stems from sound waves not
reaching the ear’s sensory structure. If any part of the ear’s
structure from the ear drum to blockage in the form of earwax (for
example), it would greatly affect a person’s hearing. Typically, this
can be corrected (depending on the cause) and full hearing
restored.
hearing: frequency and frequency theory
Frequency is the way in which sound wavelengths are expressed. It is
typically measured in cycles per second or hertz. The higher
frequencies tend to have a higher pitch and vice versa. The range
heard by the average human is between 20 and 20,000 hz.
Frequency theory holds that perception of pitch corresponds to the
rate, or frequency, at which the entire basilar membrane vibrates.
The whole of hair cells trigger simultaneously but differently
depending on the sound frequency. The major criticism with the
frequency theory is that neurons cannot fire at the speed that
certain frequencies travel.
hearing: nerve deafness
The most common form of deafness, nerve deafness (also might be
seen as sensorineural hearing loss) results in the destruction of
nerve cells that would ordinarily send signals from the eardrum to
the brain.
hearing: pitch
Pitch refers to the rate of vibration of the medium through which a
sound wave is transmitted.
hearing: place theory
Place theory, as first proposed by Hermann von Helmholtz in the
1860s, is a theory that holds that perception of pitch corresponds to
the vibration of different portions, or places, along the basilar
membrane. Particular sounds trigger particular hair cells that the
brain then detects at certain frequencies.
The major criticism with von Helmholtz is that the hair cells are not
independent but work in unison as suggested by the frequency
theory. However, it proved correct in that the waves do peak in
certain parts.
hearing: sound localization
A basic function of your hearing is sound localization – locating the
source of a sound in space, not unlike trying to spot an aircraft based
off the sound. Like depth perception with seeing, this is an
important part of hearing. This is done using two important features
– intensity (loudness) and the timing of sounds arriving at each ear.
We have ears on both sides of our head, helping us to determine
this concept.
If you hear thunder 10 seconds after seeing lightening, the lightning
is 2 miles away (10 divided by 5 = 2 miles). Military folks use the
same type of calculations to determine the distance of a shooter or
artillery by counting off distance between seeing the flash and
hearing the sound.
hearing: timbre
People are also sensitive to purity of sound – the purest sound
coming from a single frequency. How pure or how complex a sound
is refers to its timbre.
A single note of a trumpet and one from a harp will differ in timbre.
optical illusions
Optical Illusions are perceptions that misrepresent physical stimuli.
The most famous example of an optical illusion is the Ames room –
a room that shows two people, one incredibly small and one equally
tall but in reality, they are both of the same height. The usage of
lines distorts the image leading to the illusion.
other senses: gustation
Gustation refers to the process of tasting. Taste buds are the
sensory receptors, found in the grooves of the tongue, which carry
impulses to the brain through the gustatory nerve. Impulses are
routed through the thalamus and into the cortex but taste buds
(or cells) have a short shelf life – only ten days or so.
There are generally agreed upon four primary tastes – sweet, sour,
bitter, salty – and tastes vary to the individual but most prefer a
combination of tastes. There is evidence that some taste
preference is genetic. However, most taste preferences are
learned and part of social processes.
other senses: kinesthesis
Kinesthesis refers to the sense of movement and body position. It
coordinates with the vestibular and visual senses to maintain
posture and balance. This is based on impulses from the joints,
muscles and tendons. Without kinesthesis, one’s movement would
be jerky and uncoordinated.
other senses: olfaction
The olfactory nerve carries impulses from the nose to the brain.
The ability to smell is directly related to the sense of taste. It is one
reason why a congested nose can lead to an inability to taste.
other senses: somatosensation
Somatosensation is based on a system made up of components of
the central and peripheral nervous systems and stems from sensory
information from organs in the joints, ligaments, muscles and skin.
other senses: vestibular system
The vestibular system regulates the body’s sense of balance. It is
located within the inner ear. Movements serve as the stimuli for
the system but overstimulation through excessive spinning, falling
or tilting the head or body can lead to dizziness or motion sickness.
parapsychology
Emerging as a focus of study in the late 1800s in Europe and later
the U.S., parapsychology concerns itself with that which nature
cannot account for and with which our senses cannot detect.
Extrasensory perception or ESP is a common form of cognitive
processes that highlights the experiences at the center of
parapsychology.
perception and perceptual constancy
Perception is how one’s mind organizes sensory information into
meaningful experiences. Psychophysics is a science to explain
the relationship between sensory experiences and the physical
stimuli that engender them.
Perceptual constancy is the tendency to perceive things as the
same though other physical conditions might change.
The white background of these PowerPoint slides are seen as
consistently white to the observer, but the light, angle of vision,
distance and the image on the retina might alter the actual
brightness.
perceptual processes: attention
Attention refers to the stimulus, in the midst of a slew of stimuli,
upon which one decides to focus. The attention allows for further
processing of the selected stimulus.
perceptual processes:
bottom-up and top-down processing
Feature analysis is a process of detecting specific elements in
visual input and assembling them into a more complex form.
There are two ways in which this is done:
Bottom-up processing is a progression of understanding going
from individual elements to the whole. You see those kids at
spelling bees who attempt to devise the language or origin and
parts of speech to understand the spelling of the whole word.
Top-down processing is a progression from the whole to the
elements. Seeing a road sign with missing letters in it might not
mean you can’t understand the sign – your knowledge of the
language might help fill in the missing pieces (top-down).
perceptual processes:
extrasensory perception (ESP)
ESP is the ability to gain information by some means other than the
ordinary senses. There are four main types of ESP:
Clairvoyance – perceiving objects or information without
sensory input
Telepathy – reading another’s mind or transferring one’s
thoughts
Psychokinesis – moving objects through mental efforts
Precognition – the ability to predict events
Such abilities are largely ignored by the scientific community
because experiments that suggest such abilities are considered
unstable, meaning not repeatable.
psychophysics
Psychophysics is the study of how physical stimuli are translated into
psychological experience. It represents the first focus on
psychologists in the late 1800s.
schemas
Schemas are mental frameworks that help people interpret events
or stimuli. They help people make sense of the world around
them.
In one particular study, a group of participants were asked to watch
a film that showed a car accident. Afterwards, they were given a
questionnaire about the accident. One question was asked
differently among the participants. The question, “About how fast
were the cars going when they contacted each other?” was asked
differently, exchanging the word contacted with words such as
slammed, collided, bumped or hit. With each verb, the participants
provided different information on the speed.
sensation
Sensation is the process of a stimuli activating a receptor. Each
sensory perception notices different things and react differently.
signal detection theory
The single-detection theory attempts to study and quantify
people’s ability to perceive the presence or absence of a stimulus.
In testing this, there are four possible outcomes – hit, miss, false
alarm, correct rejection. One’s ability to do well depends on the
criteria and the amount of noise from irrelevant sources.
This theory fine-tuned Gustav Fechner’s work with the idea of
detectability – measured by probability, decision-making processes
as well as sensory processes.
stimulus
A stimulus is any event or thing that engenders a response.
If you are sitting at home and hungry as a commercial comes on the
television showcasing a large pepperoni pizza. If you like pizza, your
mouth will begin to water, the stomach will begin to grumble and you
will not be able to get pizza off the brain until you order one. In fact,
if you are hungry right now as you read this, your mouth might be
watering at this very instant. The stimulus in this case is the pizza
commercial (or this well-written PowerPoint slide) and the response
in the mouth watering and desire to eat pizza.
subliminal (messages) stimulation
Subliminal messages are brief auditory or visual messages that are
presented below the absolute threshold.
Various forms of media have been charged with producing
subliminal messages. Everything from commercials to political
magazines to rock music have been castigated for subliminal
messaging.
There have been studies on the impact of subliminal messages or
even people’s ability to recognize them and as a result, it is much
debated whether such messages are impactful.
transduction
Transduction is the process of converting physical energy into
neural impulses that travel to the brain, relaying information from
the sensory receptors.
Some cars, like the Maserati, have drive-by-wire systems where
pedals are connected to wiring that transfers physical action
(stepping on the gas, clutch or brake) into electrical impulses to
the engine.
Psychologically speaking, if you walk out of your darken house and
are hit with bright sunshine, that physical energy (light waves) are
converted into neural impulses, traveling along the optic nerve to
send to the brain the squint and adjust to the change in light wave
reception.
vision: accommodation
Visual accommodation is the eye’s ability to adjust and focus on the
different things, from various distances – shifting back and forth.
However, the older one becomes, the harder and inflexible the lens is
and therefore, less capable of such adjusting. A person who has
never needed glasses finds it takes an increasing amount of time for
the eyes to adjust to words on a page, suggesting either the
requirement of reading or prescription glasses.
vision: acuity
Visual acuity refers to the clarity of a person’s vision. How sharply
you can read the instructions on a medicine bottle is a measure of
your visual acuity. Acuity can also refer to one’s ability to
understand three-dimensional images.
Your sight might be fine now but as you get older, like most things,
it begins to wear down and the usage of reading or prescription
glasses might be needed.
vision:
binocular fusion and retinal disparity
The binocular fusion (referred to as a binocular cue) is the
bringing together the two images picked up by the two eyes into a
single image.
Though we pick up an image twice, the two eyes pick up a
different image. This binocular cue is called retinal disparity. The
difference is accounted for by the different eye’s perception and
viewpoint. Retinal disparity is key to depth perception. A large
retinal disparity means an object is near while a small retinal
disparity means the object is far away.
vision: bipolar cells
Bipolar cells are nerve cells that bring together all visual receptor
cell information and then transmit it to the cortex by way of the
ganglion cells.
vision: blind spot
On the retina, there is a hole (called the optic disk) where the optic
nerve fibers leave the eyes. The hole in the retina creates a blind
spot in both eyes.
vision: cones
Within the retina are millions of receptor cells that are sensitive and
receptive to light though only 10% of the light that hits the cornea
makes it to the receptors and the two main receptor cells are rods
and cones.
Cones are specialized visual receptors that play a key role in daylight
vision and color vision. Providing sharpness and detail in daylight,
cones are concentrated in the center of the retina and then taper
off in density toward the sides.
vision: cornea
The cornea is the transparent outer covering of the front of the
eye that covers the iris and pupil.
vision: dark adaptation
Dark adaptation is the process in which the eyes become more
sensitive to light in low illumination. This is done, for example,
when you walk out of a bright day into a darken theater that can
cause, temporarily, a blinding effect. Within 10 minutes, you are
doing fine and by 30 minutes, adaptation is complete.
vision: depth perception
One’s depth perception refers to the ability to judge the distance of
objects.
One’s depth perception is a combination of two sets of cues –
monocular and binocular. (See perceptual processes)
vision: human eye
(pupil, lens, retina, optic nerve)
The human eye is made up of many parts, including:
Pupil – the opening within the iris that regulates how much
light enters the eye
Lens – a flexible, transparent structure in the eye that
changes its shape to focus light upon the retina
Retina – the innermost coating at the back of the eye that
contains light-sensitive receptor cells
Optic nerve – the nerve that carries impulses from the retina
to the brain
vision: farsighted and nearsighted
The many problems with focusing stems from issues with the lens:
Farsighted occurs when distant objects are seen clearly but close
objects appear blurry. The focus of light falls behind the retina
because the eyeball is too short.
Nearsighted occurs when close objects are seen clearly but distant
objects appear blurry. Light from far off objects is falling short
because cornea or lens bends light too much or the eyeball is too
long.
vision: feature detectors
Feature detectors are neurons that respond selectively to very
specific features of more complex stimuli.
vision: fovea
The fovea is a tiny spot in the center of the retina that contains
only cones; visual acuity is greatest at this spot.
vision: Ganglion cells
Ganglion cells are neurons that send visual information from the
retina to the brain by way of the optic nerve.
vision: iris
The iris controls how much light the pupil takes in and also provides
the color that people notice.
vision: opponent process theory
There has been much speculation on the reason for our ability to
see in color but one of the more intriguing ones was suggested by
Ewald Hering and his opponent process theory of color. It holds
that color perception depends on receptors that make antagonistic
response to three pairs of colors. The three pairs are: red and
green; yellow and blue; black and white
vision: parallel processing
Parallel processing is the brain’s ability to process many forms of
information at one time.
When a person attends a hockey game with seats twenty rows up
from ice level (I hear those seats are nice), there are many different
stimuli that the brain is figuring out at one time. The speed of the
players, the depth of determining where one player is compared to
another, the colors of the uniforms and the ice that helps determine
one team or another, the composition of the hockey sticks and
pucks as solid objects that cause distinct sounds that reverberate
throughout the arena, etc. In short, your brain is capable of
processing so much information near instantaneously and
simultaneously with other processes.
vision: photoreceptors
Photoreceptors are the cells in the retina, such as the rods and cones,
that transfer light and color stimuli to the brain in understandable
(perhaps) images that were picked up by the eyes.
vision: rods
Within the retina are millions of receptor cells that are sensitive and
receptive to light though only 10% of the light that hits the cornea
makes it to the receptors and the two main receptor cells are rods
and cones.
Rods are specialized visual receptors that play a key role in night
vision and peripheral vision. The concentration of rods is more
along the sides of the retina which allow for peripheral vision.
If you are trying to see something slightly illuminated at night, look
below or above the object – away from the fovea in the center of
the retina.
vision: sensory adaptation
Sensory adaptation is our inability to pick up sensory stimuli after
repeated and long-term exposure to the same.
For example, when American soldiers in World War II were
preparing to rescue American POWs in the Philippines, they used
planes flying overhead the camp for weeks prior to allow Japanese
soldiers to grow accustomed to the daily flyovers. When they know
longer noticed it, planes were used to drop the rescuers nearby to
carry out the operation. Over time, the Japanese soldiers’ sensory
adaptation led to the planes no longer being registered and
therefore, no longer seen as a threat.
vision: trichromatic theory
Trichromatic theory of color vision was first stated by Thomas
Young and later perfected by Hermann von Helmholtz. The human
eye has three types of receptors with differing sensitivities to
different light wavelengths. In short, we have three types of visual
color receptors for red, green and blue and the eye performs its
own color mixing.
Color blindness – a variety of deficiencies in the ability to
distinguish among colors – fits well into the notion of the
trichromatic theory. People with this disorder – mostly men – are
dichromats, meaning they only have two colors channels with
difficulties distinguishing the other.
visual capture
Visual capture refers to the likelihood of us using the visual to
dictate how we perceive all other senses.
A magician on a stage will grab our attention and various things will
occur but our tendency is to assume that all things happening are
being done by what we see and not what may be in the
background or done by another person hidden from view.
Weber’s Law
Weber’s Law states that the larger or stronger a stimulus, the longer
it takes for a person to notice a change within the stimulus.
For example, Weber determined the fraction of detecting change in
weight is roughly 1/30 of the original weight. If you held a 30oz
weight, you could feel an additional ounce but starting with 90
ounces, you need another 3 ounces to feel the difference.
Some people are more sensitive to changes in stimuli than others so
individual differences vary greatly.