Sensation and Perception Unit Review
sensation
perception
bottom-up processing
top-down processing
selective attention
change blindness
psychophysics
absolute threshold
signal detection theory
difference threshold
sensory adaptation
transduction
pupil
iris
lens
retina
accommodation
rods
cones
optic nerve
blind spot
fovea
feature detectors
Young-Helmholtz trichromatic (three-color)
theory
opponent-process theory
audition
frequency
pitch
middle ear
cochlea [KOHK-lee-uh]
inner ear
cochlear implant
kinesthesis [kin-ehs-THEE-sehs]
vestibular sense
gate-control theory
sensory interaction
gestalt
figure-ground
depth perception
visual cliff
binocular cues
monocular cues
perceptual set
What are sensation and perception? What do we mean by bottom-up processing and top-down
processing?
How are we affected by selective attention?
What are the absolute and difference thresholds, and do stimuli below the absolute threshold
have any influence?
What is the function of sensory adaptation?
What is the energy that we see as visible light?
How does the eye transform light energy into neural messages?
How does the brain process visual information?
What theories help us understand color vision?
What are the characteristics of air pressure waves that we hear as sound?
How does the ear transform sound energy into neural messages?
What theories help us understand pitch perception?
How do we locate sounds?
What are the common causes of hearing loss, and why does controversy surround cochlear
implants?
How do we sense touch and sense our body’s position and movement? How do we experience
pain?
How do we experience taste?
How do we experience smell?
How did the Gestalt psychologists understand perceptual organization?
How do figure-ground and grouping principles contribute to our perceptions?
How do we see the world in three dimensions?
How do we perceive motion?
How do perceptual constancies help us organize our sensations into meaningful perceptions?
Perceptual interpretation
How adaptable is our ability to perceive?
How do our expectations, contexts, and emotions influence our perceptions?
What are sensation and perception? What do we mean by bottom-up processing and top-down
processing?
Sensation is the process by which our sensory receptors and nervous system receive and represent
stimulus energies from our environment. Perception is the process of organizing and interpreting
this information. Although we view sensation and perception separately to analyze and discuss
them, they are actually parts of one continuous process. Bottom-up processing is sensory analysis
that begins at the entry level, with information flowing from the sensory receptors to the brain. Topdown processing is analysis that begins with the brain and flows down, filtering information through
our experience and expectations to produce perceptions.
How are we affected by selective attention?
We selectively attend to, and process, a very limited aspect of incoming information, blocking out
most, often shifting the spotlight of our attention from one thing to another. We even display
inattentional blindness to events and changes in our visual world.
What are the absolute and difference thresholds, and do stimuli below the absolute threshold
have any influence?
Our absolute threshold for any stimulus is the minimum stimulation necessary for us to be
consciously aware of it percent of the time. Signal detection theory demonstrates that individual
absolute thresholds vary, depending on the strength of the signal and also on our experience,
expectations, motivation, and alertness. Our difference threshold (also called just noticeable
difference, or JND) is the barely noticeable difference we discern between two stimuli percent of
the time. Priming shows that we can process some information from stimuli below our absolute
threshold for conscious awareness. But the effect is too fleeting to enable people to exploit us with
subliminal messages. Weber’s law states that two stimuli must differ by a constant proportion to be
perceived as different.
What is the function of sensory adaptation?
Sensory adaptation (our diminished sensitivity to constant or routine odors, sounds, and touches)
focuses our attention on informative changes in our environment.
What is the energy that we see as visible light?
Each sense receives stimulation, transforms (transduces) it into neural signals, and sends these
neural messages to the brain. In vision, the signals consist of light-energy particles from a thin slice
of the broad spectrum of electromagnetic energy. The hue we perceive in a light depends on its
wavelength, and its brightness depends on its intensity.
How does the eye transform light energy into neural messages?
After entering the eye and being focused by a lens, light-energy particles strike the eye’s inner
surface, the retina. The retina’s light-sensitive rods and color-sensitive cones convert the light energy
into neural impulses which, after processing by bipolar and ganglion cells, travel through the optic
nerve to the brain.
How does the brain process visual information?
Impulses travel along the optic nerve, to the thalamus, and on to the visual cortex. In the visual
cortex, feature detectors respond to specific features of the visual stimulus. Higher-level supercells
integrate this pool of data for processing in other cortical areas. Parallel processing in the brain
handles many aspects of a problem simultaneously, and separate neural teams work on visual
subtasks (color, movement, depth, and form). Other neural teams integrate the results, comparing
them with stored information, and enabling perceptions.
What theories help us understand color vision?
The Young-Helmholtz trichromatic (three-color) theory proposed that the retina contains three types
of color receptors. Contemporary research has found three types of cones, each most sensitive to
the wavelengths of one of the three primary colors of light (red, green, or blue). Hering’s opponentprocess theory proposed three additional color processes (red-versus-green, blue-versus-yellow,
black-versus-white). Contemporary research has confirmed that, en route to the brain, neurons in
the retina and the thalamus code the color-related information from the cones into pairs of
opponent colors. Thus we know that color processing occurs in these two stages.
What are the characteristics of air pressure waves that we hear as sound?
Sound waves are bands of compressed and expanded air. Our ears detect these changes in air
pressure and transform them into neural impulses, which the brain decodes as sound. Sound waves
vary in frequency, which we experience as differing pitch, and amplitude, which we perceive as
differing loudness.
How does the ear transform sound energy into neural messages?
The outer ear is the visible portion of the ear. The middle ear is the chamber between the eardrum
and cochlea. The inner ear consists of the cochlea, semicircular canals, and vestibular sacs. Through a
mechanical chain of events, sound waves traveling through the auditory canal cause tiny vibrations
in the eardrum. The bones of the middle ear amplify the vibrations and relay them to the fluid-filled
cochlea. Rippling of the basilar membrane, caused by pressure changes in the cochlear fluid, causes
movement of the tiny hair cells, triggering neural messages to be sent (via the thalamus) to the
auditory cortex in the brain.
What theories help us understand pitch perception?
Place theory proposes that our brain interprets a particular pitch by decoding the place where a
sound wave stimulates the cochlea’s basilar membrane. Frequency theory proposes that the brain
deciphers the frequency of the pulses traveling to the brain. Place theory explains how we hear highpitched sounds; frequency theory explains how we hear low-pitched sounds; and some combination
of the two helps explain how we hear sounds in the middle range.
How do we locate sounds?
Sound waves strike one ear sooner and more intensely than the other. The brain analyzes the
minute differences in the sounds received by the two ears and computes the sound’s source.
What are the common causes of hearing loss, and why does controversy surround cochlear
implants?
Conduction hearing loss results from damage to the mechanical system that transmits sound waves
to the cochlea. Sensorineural hearing loss (or nerve deafness) results from damage to the cochlea’s
hair cells or their associated nerves. Diseases and accidents can cause hearing loss, but age-related
disorders and prolonged exposure to loud noises are more common causes. Cochlear implants
restore hearing for some people, but many in the Deaf community believe cochlear implants are
unnecessary for people who have been Deaf from birth and who can speak their own language, sign.
How do we sense touch and sense our body’s position and movement? How do we experience
pain?
Our sense of touch is actually several senses—pressure, warmth, cold, and pain—that combine to
produce other sensations, such as “hot.” Through kinesthesis, we sense the position and movement
of body parts. We monitor the body’s position and maintain our balance with our vestibular sense.
Pain is an alarm system that draws our attention to some physical problem. One theory of pain is
that a “gate” in the spinal cord either opens to permit pain signals traveling up small nerve fibers to
reach the brain, or closes to prevent their passage. The biopsychosocial approach views pain as the
sum of three sets of forces biological influences, such as nerve fibers sending messages to the brain;
psychological influences, such as our expectations; and social-cultural influences, such as the
presence of others.
How do we experience taste?
Taste, a chemical sense, is a composite of five basic sensations—sweet, sour, salty, bitter, and
umami—and of the aromas that interact with information from the taste receptor cells of the taste
buds. The influence of smell on our sense of taste is an example of sensory interaction, the ability of
one sense to influence another.
How do we experience smell?
Smell is a chemical sense. Some million olfactory receptor cells, with their approximately
different receptor proteins, recognize individual odor molecules. The receptor cells send messages
to the brain’s olfactory bulb, then to the temporal lobe and to parts of the limbic system. Odors can
spontaneously evoke memories and feelings, due in part to the close connections between brain
areas that process smell and memory.
How did the Gestalt psychologists understand perceptual organization?
Gestalt psychologists searched for rules by which the brain organizes fragments of sensory data into
gestalts (from the German word for “shape, form, or whole”), or meaningful forms. In pointing out
that the whole is more than the sum of its parts, they noted that we filter sensory information and
infer perceptions in ways that make sense to us.
How do figure-ground and grouping principles contribute to our perceptions?
To recognize an object, we must first perceive it (see it as a figure) as distinct from its surroundings
(the ground). We bring order and form to stimuli by organizing them into meaningful groups,
following the rules of proximity, similarity, continuity, connectedness, and closure.
How do we see the world in three dimensions?
Depth perception is our ability to see objects in three dimensions and judge distance. The visual cliff,
and other research, demonstrates that many species perceive the world in three dimensions at, or
very soon after, birth. Binocular cues, such as retinal disparity, are depth cues that rely on
information from both eyes. Monocular cues (such as relative size, interposition, relative height,
relative motion, linear perspective, and light and shadow) let us judge depth using information
transmitted by only one eye.
How do we perceive motion?
As objects move, we assume that shrinking objects are retreating and enlarging objects are
approaching. But sometimes we miscalculate. A quick succession of images on the retina can create
an illusion of movement, as in stroboscopic movement or the phi phenomenon.
How do perceptual constancies help us organize our sensations into meaningful perceptions?
Perceptual constancy enables us to perceive objects as stable despite the changing image they cast
on our retinas. Shape constancy is our ability to perceive familiar objects (such as an opening door)
as unchanging in shape. Size constancy is the perception of objects as unchanging in size despite
their changing retinal images. Sometimes we misread distance cues and reach the wrong
conclusions, as in the Moon illusion. With lightness constancy, we perceive an object as having a
constant lightness even when illumination changes. With color constancy, we perceive consistent
color in objects, even though the lighting and wavelengths shift.
Perceptual interpretation
People born blind who later regain sight lack the experience to recognize shapes, forms, and
complete faces. Animals who have had restricted visual input suffer enduring visual handicaps. There
is a critical period for some aspects of sensory and perceptual development. Without early
stimulation, the brain’s neural organization does not develop normally.
How adaptable is our ability to perceive?
Perceptual adaptation is evident when people are given glasses that shift the world to the left, right,
or upside-down. People are initially disoriented, but they manage to adapt to the new context.
How do our expectations, contexts, and emotions influence our perceptions?
Perceptual set is a mental predisposition that functions as a lens through which we perceive the
world. Our learned concepts (schemas) prime us to organize and interpret ambiguous stimuli in
certain ways. The surrounding context helps create expectations that guide our perceptions.
Emotional context colors our interpretations as well.