Unit 4: Sensation
Sensation: The process by which sensory receptors (in
eye, ear, etc.) receive and are stimulated by stimulus
energies from the environment.
Perception: The process of organizing and interpreting
sensory information, enabling us to recognize
meaningful objects and events.
Bottom-up-processing: Analysis that begins with the
sense receptors and works up to the brain's processing of
the information.
Top-down-processing: Information processing guided
by higher-level processes, such as our expectations.
Absolute Threshold: The minimum stimulation needed
to detect a particular stimulus 50% of the time.
Signal Detection Theory: Predicts how and when we
detect faint stimuli (dependent on experience,
expectations, motivation & fatigue.
Subliminal Stimulation: Stimulation below one's
threshold of conscious awareness. Research reveals a
subtle, fleeting effect on thinking, but no effect on
behavior.
Difference Threshold: The minimum difference
between two stimuli required for detection 50% of the
time. It is also called the just noticeable difference or
JND. It is based on Weber's Law: The difference
threshold is in proportion to the strength of the original
stimulus.
Sensory Adaptation: Our diminishing sensitivity to
unchanging stimuli.
Selective Attention: The focusing of attention on
specific stimuli, while ignoring other stimuli (e.g., the
cocktail party effect).
Transduction: The transforming of stimulus energies
(i.e., light waves, sound waves) into neural impulses.
VISION & LIGHT ENERGY
Wavelength: Distance from the peak of one light or
sound wave to the next. Wavelength determines HUE
or color in vision and Pitch in audition.
Shorter wavelengths are bluish in color, while longer
wavelengths are reddish.
Amplitude: The height of a light or sound wave. It
determines brightness in vision and loudness in
hearing.
THE EYE
Pupil: Adjustable opening in the center of the eye
through which light passes.
Iris: A ring of muscle tissue that forms the colored
part of the eye. It controls the size of the pupil
Lens: The transparent structure behind the pupil that
changes shape (called accommodation) to help focus
images on the retina.
Visual Acuity: The sharpness of vision.
Nearsightedness: Can see nearby objects more
clearly because distant object focus in front of the
retina (eyeball may be too long).
Farsightedness: Can see distant objects more
clearly because nearby objects focus behind the retina
(eyeball may be too short).
Rods & Cones: The receptor cells for
vision. Receptor cells are specialized neurons
designed, in this case, to transduce light energy into
neural impulses.
Rods: detect black, white, & grey. Found mainly in
the periphery of the retina. More than one rod
connects to each bipolar cell. Thus, less light energy
is necessary for them to cause the bipolar cells to
fire. Necessary for NIGHT VISION & PERIPHERAL
VISION.
Cones: Found mainly in the center (fovea) of the
retina. Necessary for COLOR VISION and VISUAL
ACUITY.
Unit 4: Sensation (cont.)
VISION (cont.)
Light waves stimulate rods & cones which synapse to
bipolar cells, which synapse to ganglion cells. The
axons of the ganglion cells come together to form the
Optic nerves which transmit visual information to the
brain.
Blindspot: The area in the retina where the optic nerve
leaves the back of eye. No rods or cones are located
there, so no vision is possible at that location.
Feature Detectors: Nerve cells in the brain that
respond to specific features of a visual stimulus, such
as shape, angle, or movement.
Parallel Processing: The ability of the brain to process
several aspect of a situation simultaneously.
COLOR VISION
Young-Helmholtz Trichromatic Theory: The theory
that the retina contains three different types of cones-one most sensitive to red, one to blue, and one to
green--which when stimulated in combination can
produce any color. RED, GREEN, & BLUE are the
PRIMARY COLORS OF LIGHT WAVES.
Opponent Process Theory: Theory that opposing
retinal processes (red-green, yellow-blue, & blackwhite) enable color vision. For example some cells are
stimulated by red while inhibited by green; others are
stimulated by yellow, while inhibited by blue. This
helps explain afterimages.
Color constancy: Perceiving familiar objects as
having consistent color, even if changing illumination
alters the wavelength reflected by the object.
Middle Ear: Chamber between the eardrum and the
oval window which contains the ossicles (three tiny
bones--hammer, anvil, & stirrup) which concentrate the
vibrations of the eardrum.
Inner Ear: Contains the cochlea, semicircular canals,
and vestibular sacs.
Cochlea: a coiled, bony, fluid-filled tube through
which sound waves trigger nerve impulses.
Basilar Membrane: Membrane along the center of
the cochlea that contains hair cells (the receptor cells
for sound). Axons from the hair cells for the Auditory
Nerves, which transmit neural impulses to the brain.
PITCH PERCEPTION
Place Theory: Theory that the pitch we hear is
associated with the place where the basilar membrane
is stimulated. Best for explaining high-pitched tones.
Frequency Theory: Theory that the rate of nerve
impulses traveling up the auditory nerve matches the
frequency of the tone we are hearing. Best for
explaining low-pitched tones.
AUDITION
Volley Principle: Helps explain in frequency theory
Audition: The sense of hearing.
how we can hear sounds with a frequency greater than
Frequency: The number of complete wavelengths in a 1000 cycles per second. While some neurons are
given period of time. Frequency determines pitch.
"recharging" during the refractory period, others are
Amplitude: Height of each wavelength--determines
firing.
loudness.
Conduction Deafness: Caused by damage to the
structures that conduct sound waves through the ear
Sound Localization: Sound waves strike one ear
(eardrum, ossicles).
sooner and with more intensity than the other
Nerve Deafness: Caused by damage to the cochlea's
ear. With this information, the brain can determine the hair cells or the auditory nerve.
location of the sound.
Unit 4: Sensation (cont.)
TOUCH
Touch or tactile sense involves a mixture of at least 4
distinct skin senses--pressure, warmth, cold, and
pain. Only pressure has identifiable sense receptors.
COLD + PRESSURE = WETNESS
COLD + WARMTH = HOT
PAIN
Gate-Control-Theory: Theory that the spinal cord
contains a neurological "gate" that blocks pain signals
or allows them to pass. The gate is opened by
stimulation of small nerve fibers and closed by
stimulation of larger fiber or by information coming
from the brain.
TASTE
Taste is the Gustatory Sense.
Taste is a CHEMICAL SENSE and consists of the
four basic tastes of sweet, sour, bitter, & salty. There
may also be a 5th sense called "umami" or a meaty
taste.
Each bump on the tongue contains over 200 taste
buds. Each bud contains a pore that captures food
molecules. The molecules cause hair-like neurons
within the pores to fire.
Taste Buds reproduce themselves every 2-3 weeks.
Sensory Interaction: The principle that one sense may
be influenced by another, as when the smell of food
influences its taste.
SMELL
Smell is the Olfactory Sense.
Smell is also a CHEMICAL SENSE.
Very little is known about the olfactory
sense. However, we are able to detect about 10,000
different odors.
Smells are processed in the temporal lobes of the brain
and in the LIMBIC SYSTEM, which may explain
why certain smells seem to have an emotional
component and can trigger memories.
Molecules in the air reach millions of receptor cells in
each nasal cavity. These cells send messages to the
olfactory bulb and the olfactory nerve which
transmits the messages to the brain.
BODY POSITION & MOVEMENT
Kinesthesis: The system for sensing the position and
movement of individual body parts. The receptor cells
for kinesthesis are found in our muscles, tendons, &
joints.
Vestibular Sense: The system that monitors the head's
(and thus the body's) position and movement. It is our
sense of equilibrium.
The semicircular canals and vestibular sacs in the
inner ear contain receptors that tell us about our head's
position.
Unit 4: Perception
Perception: The process of organizing and interpreting Monocular Cues: Distance cues that require the use of
sensory information, enabling us to recognize
one eye only.
meaningful objects and events.
1. Relative Size: If we assume two objects are
about the same size, the one that casts the smaller
retinal image is perceived as being farther away.
Perceptual Organization
2. Interposition (Overlap): If one object partially
Figure-ground Relationship: Our ability to perceive
any object (the figure) as distinct from its surroundings blocks another, the one that is partially blocked is
perceived to be farther away.
(the ground).
3. Relative Clarity: Because light from distant
Visual Capture: The tendency for vision to dominate
the other senses when conflicting information is being objects must pass through more atmosphere, we
perceive hazy object as being farther away than clear,
received.
distinct objects.
Gestalt Organizational Principles: Gestalt
4. Texture Gradient: A gradual change from a
psychologists emphasize our tendency to integrate
coarse, distinct texture to a fine, indistinct texture
individual pieces of information into a meaningful
signals increasing distance.
whole. To bring order and form to basic visual
5. Relative Height: We perceive objects higher in
sensations, our brains follow certain rules for grouping
our visual field as being further away.
stimuli together.
6. Linear Perspective: Parallel lines (such as
1. Proximity: We group nearby objects and
railroad tracks) appear further away as they converge
belonging together.
2. Similarity: Figures similar to each other (i.e., as in the distance.
7. Light & Shadow (relative brightness): Nearby
in shape or color) are groups together.
objects reflect more light. Thus, given two identical
3. Continuity: We perceive smooth, continuous
objects, the dimmer one seems further away.
patterns rather than discontinuous ones.
8. Relative Motion (motion parallax): If while
4. Connectedness: When the are uniform and
linked, we perceive spots, lines, or areas as single units. riding in a train you fix your gaze on some object (the
fixation point), objects closer than the fixation point
5. Closure: We fill in gaps to create complete,
appear to be moving backward. The nearer an object is
whole objects.
the faster it seems to move. Objects behind the fixation
point appear to be moving with you: The farther away
Depth Perception
the object is from the fixation point, the more slowly it
Visual Cliff: A laboratory device for testing depth
perception in infants. Even when coaxed, infants are appears to move.
Motion Perception
reluctant to venture onto the glass over the cliff.
Binocular Cues: Depth cues that depend on the use of One way we perceive motion is by knowing that if an
object keeps getting bigger, it is probably moving
both of our eyes.
towards us. If an object is shrinking, it is moving away
1. Retinal Disparity: By comparing the two
from us.
slightly different images received on each retina, the
Phi Phenomenon: When two or more adjacent
brain computes the distance of what we are looking
at. The greater the disparity (difference) between the stationary lights blink on and off in quick succession,
we perceive a single light moving. (Lighted signs use
two images, the closer the object.
this phenomenon).
2. Convergence: The extent to which the eyes
Stroboscopic Movement: The brain will interpret a
converge inward when looking at an object. The
rapid series of slightly varying images as continuous
greater the convergence, the closer the object.
movement. By flashing 24 still pictures each second, a
motion picture creates perceived movement.
Unit 4: Perception (cont.)
Perceptual Constancies
Perceiving objects as unchanging (having constant
lightness, color, shape, and size) even when our retinal
images of them change. For example:
Shape Constancy: We perceive the form of familiar
objects as constant even when our retinal images of them
change.
Size Constancy: We perceive familiar objects to
maintain a constant size even when their distance from
us changes.
Lightness Constancy: We perceive an object as having
a constant lightness even when its illumination varies.
Some Visual Illusions
Similarly, Blakemore & Cooper found that kittens
whose vision was restricted to only seeing vertical
lines during a critical period of development, later
could not see horizontal lines.
Perceptual Adaptation: In vision, the ability to
adjust to an artificially displaced or even inverted
visual field.
Perceptual Set: A mental predisposition to perceive
one thing and not another (e.g., seeing the Lock Ness
Monster instead of a piece of driftwood because of
your beliefs).
Context Effects: Any given stimulus may trigger
radically different perceptions depending on the
surrounding environment or circumstances. Culture
may have a great impact on context and perception.
The Ponzo Illusion (in two forms)
Human Factors Psychology: A branch of
psychology that explores how people and machines
interact and how machines and physical environments
can be adapted to human behaviors.
The Ames Room
Muller-Lyer Illusion
**Please see your textbook for explanations of these
illusions.
Sensory Deprivation
People blind from birth, who later have their vision
restored, can distinguish figure-ground relationships, can
sense colors, but have great difficulty recognizing
objects that they were familiar with by touch.
Extrasensory Perception (ESP)
The controversial claim that perception can occur
apart from sensory input.
Telepathy: Mind to mind communication
Clairvoyance: The sensing of remote events that are
presently occuring.
Precognition: The sensing of future events.
Telekinesis (psychokinesis): Ability to affect objects
with the power of the mind.
Parapsychologists: Psychologists who study
paranormal occurrences, including claims of ESP.