Summary and Key Terms

Sensation versus Perception

Sensation occurs when sensory receptors detect sensory stimuli. Perception involves the organization, interpretation, and conscious experience of those sensations. All sensory systems have both absolute and difference thresholds, which refer to the minimum amount of stimulus energy or the minimum amount of difference in stimulus energy required to be detected about 50% of the time, respectively. Sensory adaptation, selective attention, and signal detection theory can help explain what is perceived and what is not. In addition, our perceptions are affected by a number of factors, including beliefs, values, prejudices, culture, and life experiences.

Waves and Wavelengths

Both light and sound can be described in terms of wave forms with physical characteristics like amplitude, wavelength, and timbre. Wavelength and frequency are inversely related so that longer waves have lower frequencies, and shorter waves have higher frequencies. In the visual system, a light wave’s wavelength is generally associated with color, and its amplitude is associated with brightness. In the auditory system, a sound’s frequency is associated with pitch, and its amplitude is associated with loudness.


Light waves cross the cornea and enter the eye at the pupil. The eye’s lens focuses this light so that the image is focused on a region of the retina known as the fovea. The fovea contains cones that possess high levels of visual acuity and operate best in bright light conditions. Rods are located throughout the retina and operate best under dim light conditions. Visual information leaves the eye via the optic nerve. Information from each visual field is sent to the opposite side of the brain at the optic chiasm. Visual information then moves through a number of brain sites before reaching the occipital lobe, where it is processed.

Two theories explain color perception. The trichromatic theory asserts that three distinct cone groups are tuned to slightly different wavelengths of light, and it is the combination of activity across these cone types that results in our perception of all the colors we see. The opponent-process theory of color vision asserts that color is processed in opponent pairs and accounts for the interesting phenomenon of a negative afterimage. We perceive depth through a combination of monocular and binocular depth cues.

Gestalt Principles of Perception

Gestalt theorists have been incredibly influential in the areas of sensation and perception. Gestalt principles such as figure-ground relationship, grouping by proximity or similarity, the law of good continuation, and closure are all used to help explain how we organize sensory information. Our perceptions are not infallible, and they can be influenced by bias, prejudice, and other factors.

Hearing and the Other Senses

Sound waves are funneled into the auditory canal and cause vibrations of the eardrum; these vibrations move the ossicles. As the ossicles move, the stapes presses against the oval window of the cochlea, which causes fluid inside the cochlea to move. As a result, hair cells embedded in the basilar membrane become enlarged, which sends neural impulses to the brain via the auditory nerve.

Pitch perception and sound localization are important aspects of hearing. Our ability to perceive pitch relies on both the firing rate of the hair cells in the basilar membrane as well as their location within the membrane. In terms of sound localization, both monaural and binaural cues are used to locate where sounds originate in our environment.

Individuals can be born deaf, or they can develop deafness as a result of age, genetic predisposition, and/or environmental causes. Hearing loss that results from a failure of the vibration of the eardrum or the resultant movement of the ossicles is called conductive hearing loss. Hearing loss that involves a failure of the transmission of auditory nerve impulses to the brain is called sensorineural hearing loss.

Taste (gustation) and smell (olfaction) are chemical senses that employ receptors on the tongue and in the nose that bind directly with taste and odor molecules in order to transmit information to the brain for processing. Our ability to perceive touch, temperature, and pain is mediated by a number of receptors and free nerve endings that are distributed throughout the skin and various tissues of the body. The vestibular sense helps us maintain a sense of balance through the response of hair cells in the utricle, saccule, and semi-circular canals that respond to changes in head position and gravity. Our proprioceptive and kinesthetic systems provide information about body position and body movement through receptors that detect stretch and tension in the muscles, joints, tendons, and skin of the body.

Key Terms

absolute threshold
minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time
continuation of a visual sensation after removal of the stimulus
height of a wave
basilar membrane
thin strip of tissue within the cochlea that contains the hair cells which serve as the sensory receptors for the auditory system
binaural cue
two-eared cue to localize sound
binocular cue
cue that relies on the use of both eyes
binocular disparity
slightly different view of the world that each eye receives
blind spot
point where we cannot respond to visual information in that portion of the visual field
bottom-up processing
system in which perceptions are built from sensory input
organizing our perceptions into complete objects rather than as a series of parts
fluid-filled, snail-shaped structure that contains the sensory receptor cells of the auditory system
cochlear implant
electronic device that consists of a microphone, a speech processor, and an electrode array to directly stimulate the auditory nerve to transmit information to the brain
conductive hearing loss
failure in the vibration of the eardrum and/or movement of the ossicles
specialized photoreceptor that works best in bright light conditions and detects color
congenital deafness
deafness from birth
congenital insensitivity to pain (congenital analgesia)
genetic disorder that results in the inability to experience pain
transparent covering over the eye
partial or complete inability to hear
decibel (dB)
logarithmic unit of sound intensity
depth perception
ability to perceive depth
electromagnetic spectrum
all the electromagnetic radiation that occurs in our environment
figure-ground relationship
segmenting our visual world into figure and ground
small indentation in the retina that contains cones
number of waves that pass a given point in a given time period
Gestalt psychology
field of psychology based on the idea that the whole is different from the sum of its parts
good continuation
(also, continuity) we are more likely to perceive continuous, smooth flowing lines rather than jagged, broken lines
hair cell
auditory receptor cell of the inner ear
hertz (Hz)
cycles per second; measure of frequency
inattentional blindness
failure to notice something that is completely visible because of a lack of attention
middle ear ossicle; also known as the anvil
inflammatory pain
signal that some type of tissue damage has occurred
interaural level difference
sound coming from one side of the body is more intense at the closest ear because of the attenuation of the sound wave as it passes through the head
interaural timing difference
small difference in the time at which a given sound wave arrives at each ear
colored portion of the eye
just noticeable difference
difference in stimuli required to detect a difference between the stimuli
perception of the body’s movement through space
curved, transparent structure that provides additional focus for light entering the eye
linear perspective
perceive depth in an image when two parallel lines seem to converge
middle ear ossicle; also known as the hammer
Meissner’s corpuscle
touch receptor that responds to pressure and lower frequency vibrations
Ménière’s disease
results in a degeneration of inner ear structures that can lead to hearing loss, tinnitus, vertigo, and an increase in pressure within the inner ear
Merkel’s disk
touch receptor that responds to light touch
monaural cue
one-eared cue to localize sound
monocular cue
cue that requires only one eye
neuropathic pain
pain from damage to neurons of either the peripheral or central nervous system
sensory signal indicating potential harm and maybe pain
olfactory bulb
bulb-like structure at the tip of the frontal lobe, where the olfactory nerves begin
olfactory receptor
sensory cell for the olfactory system
opponent-process theory of color perception
color is coded in opponent pairs: black-white, yellow-blue, and red-green
optic chiasm
X-shaped structure that sits just below the brain’s ventral surface; represents the merging of the optic nerves from the two eyes and the separation of information from the two sides of the visual field to the opposite side of the brain
optic nerve
carries visual information from the retina to the brain
Pacinian corpuscle
touch receptor that detects transient pressure and higher frequency vibrations
pattern perception
ability to discriminate among different figures and shapes
(also, crest) highest point of a wave
way that sensory information is interpreted and consciously experienced
perceptual hypothesis
educated guess used to interpret sensory information
chemical message sent by another individual
light-detecting cell
visible part of the ear that protrudes from the head
perception of a sound’s frequency
place theory of pitch perception
different portions of the basilar membrane are sensitive to sounds of different frequencies
principle of closure
organize perceptions into complete objects rather than as a series of parts
perception of body position
things that are close to one another tend to be grouped together
small opening in the eye through which light passes
light-sensitive lining of the eye
specialized photoreceptor that works well in low light conditions
Ruffini corpuscle
touch receptor that detects stretch
what happens when sensory information is detected by a sensory receptor
sensorineural hearing loss
failure to transmit neural signals from the cochlea to the brain
sensory adaptation
not perceiving stimuli that remain relatively constant over prolonged periods of time
signal detection theory
change in stimulus detection as a function of current mental state
things that are alike tend to be grouped together
middle ear ossicle; also known as the stirrup
subliminal message
message presented below the threshold of conscious awareness
taste bud
grouping of taste receptor cells with hair-like extensions that protrude into the central pore of the taste bud
temporal theory of pitch perception
sound’s frequency is coded by the activity level of a sensory neuron
temperature perception
sound’s purity
top-down processing
interpretation of sensations is influenced by available knowledge, experiences, and thoughts
conversion from sensory stimulus energy to action potential
trichromatic theory of color perception
color vision is mediated by the activity across the three groups of cones
lowest point of a wave
tympanic membrane
taste for monosodium glutamate
spinning sensation
vestibular sense
contributes to our ability to maintain balance and body posture
visible spectrum
portion of the electromagnetic spectrum that we can see
length of a wave from one peak to the next peak


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Introduction to Psychology Copyright © 2021 by Southern Alberta Institution of Technology (SAIT) is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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