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the process by which stimulation of a sensory receptor produces neural impulses that the brain interprets as a sound, a visual image, an odor, a taste, a pain, or other sensory image. Sensation represents the first series of steps in processing of incoming information


a process that makes sensory patterns meaningful. It is perception that makes these words meaningful, rather than just a string of visual patterns. To make this happen, perception draws heavily on memory, motivation, emotion, and other psychological processes


transformation of one form of energy into another-especially the transformation of stimulus information into nerve signals by the sense organs. Without transduction, ripe tomatoes would not appear red (or pinking-gray, in the case of tomatoes purchased in many grocery stores)

sensory adaptation

loss of responsiveness in receptor cells that after stimulation has remained unchanged for a while, as when a swimmer becomes adapted to the temperature of the water

absolute threshold

the amount of stimulation necessary for a stimulus to be detected. In practice, this means that the presence or absence of a stimulus is detected correctly half the time over many trials

difference threshold

The smallest amount by which a stimulus can be changed and the difference be detected half the time

just noticeable difference

(JND) same as the difference threshold

Weber's law

this concept says that the size of a JND is proportional to the intensity of the stimulus; the JND is large when the stimulus intensity is high and is small when the stimulus intensity is low

Fechner's law

the magnitude of a stimulus can be estimated by the formula S=k log R, where S= sensation, R = stimulus, and k= a constant that differs for each sensory modality (sight, touch, temperature, etc.)

Steven's power law

a law of magnitude estimation that is more accurate than Fechner's law and covers a wider variety of stimuli. It is represented by the formula S=kla, where S= sensation, k= a constant, I= stimulus intensity, and a= a power exponent that depends on the sense being measured

signal detection theory

explains how we detect "signals," consisting of stimulation affecting our eyes, ears, nose, skin, and other sense organs. Signal detection theory says that sensation is judgment the sensory system makes about incoming stimulation. Often, it occurs outside of consciousness. In contrast to older theories from psychophysics, signal detection theory takes observer characteristics into account


the thin, light-sensitive layer at the back of the eyeball. The retina contains millions of photoreceptors and other nerve cells


light-sensitive cells (neurons) in the retina that convert light energy to neural impulses. The photoreceptors are as far as light gets into the visual system


photoreceptors in the retina that are especially sensitive to dim light but not to colors


photoreceptors in the retina that are especially to colors but not to dim light


the tiny area of sharpest vision in the retina

optic nerve

the bundle of neurons that carries visual information from the retina to the brain

blind spot

the point where the optic nerve exits the eye and where there are no photoreceptors. Any stimulus that falls on this area cannot be seen


a psychological sensation caused by the intensity of light waves


also called hue. Color is not a property of things in the external world. Rather, it is a psychological sensation created in the brain from information obtained by the eyes from the wavelengths of visible light

electromagnetic spectrum

the entire range of electromagnetic energy, including radio waves, X rays, microwaves, and visible light

visible spectrum

the tiny part of the electromagnetic spectrum to which our eyes are sensitive. The visible spectrum of other creatures may be slightly different from our own

trichromatic theory

the idea that colors are sensed by three different types of cones sensitive to light in the red, blue, and green wavelengths. The trichromatic theory explains the earliest stage of color sensation

opponent-process theory

the idea that cells in the visual system process colors in complementary pairs, such as red or green or as yellow or blue. The opponent-process theory explains color sensation from the bipolar cells onward in the visual system


sensations that linger after the stimulus is removed. Most visual images are negative afterimages, which appear in reversed color

color blindness

Typically a genetic disorder (although sometimes the result of trauma, as in the case of Jonathan) that prevents an individual from discriminating certain colors. The most common form is rd-green color blindness


The number of cycles completed by a wave in a given amount of time, usually a second


the physical strength of a wave. This is usually measured from peak (top) to valley (bottom) on a graph of the wave

tympanic membrane

the eardrum


the primary organ of hearing; a coiled tube in the inner ear, where sound waves are transduced into nerve messages

basilar membrane

a thin strip of tissue sensitive to vibrations in the cochlea. The basilar membrane contains hair cells connected to neurons. When a sound wave causes the hair cells to vibrate, the associated neurons become exited. As a result, the sound waves are converted (transduced) into nerve activity


the sensory characteristic of sound produced by the frequency of the sound wave


a sensory characteristic of sound produced by the amplitude (intensity) of the sound wave


the quality of a sound wave that derives from the wave's complexity (combination of pure tones). Timbre comes from the Greek word for "drum", as does the term tympanic membrane, or eardrum

conduction deafness

an inability to hear resulting from damage to structures of the middle or inner ear

nerve deafness (sensorineural deafness)

an inability to hear, linked to a deficit in the body's ability to transmit impulses from the cochlea to the brain, usually involving the auditory nerve or higher auditory processing centers

vestibular sense

the sense of body orientation with respect to gravity. The vestibular sense is closely associated with the inner ear and, in fact, is carried to the brain on a branch of the auditory nerve

kinesthetic sense

the sense of body position and movement of body parts relative to each other (also called kinesthesis)


the sense of smell


chemical signals released by organisms to communicate with other members of their species. Pheromones are often used by animals as sexual attractants. It is unclear whether or not humans employ pheromones.


the sense of taste- from the same word as "gusto" - also called the gustatory sense

skin senses

sensory systems for processing touch, warmth, cold, texture, and pain

gate-control theory

an explanation for pain control that proposes we have a neural "gate" that can, under some circumstances, block incoming pain signals

placebo effect

a response to a placebo (fake drug), caused by subjects' belief that they are taking real drugs


the meaningful product of perception- often an image that has been associated with concepts, memories of events, emotions, and motives

feature detectors

cells in the cortex that specialize in extracting certain features of a stimulus

binding problem

refers to the process used by the brain to combine (or "bind") the results of many sensory operations into a single percept. This occurs, for example, when sensations of color, shape, boundary, and texture are combined to produce the percept of a person's face. No one knows exactly how the brain does this. Thus the binding problem is one of the major unsolved mysteries in psychology

bottom-up processing

perceptual analysis that emphasizes characteristic of the stimulus, rather than our concepts and expectations. "Bottom" refers to the stimulus, which occurs at step one of perceptual processing

top-down processing

perceptual analysis that emphasizes the perceiver's expectations, concept memories, and other cognitive factors, rather than being driven by the characteristics of the stimulus. "Top" refers to a mental set in the brain- which stands at the "top" of the perceptual processing system

perceptual consistency

the ability to recognize the same object as remaining "constant" under different conditions, such as changes in illumination, distance, or location


you have experienced an illusion when you have demonstrably incorrect perception of a stimulus patter, especially one that also fools others who are observing the same stimulus. (If no one else sees it the way you do, you could be having a delusion or a hallucination.)

ambiguous figure

images that are capable of more than one interpretation. There is no "right" way to see an ambiguous figure

Gestalt psychology

from a German word (pronounced gush-TAWLT) that means "whole" or "form" or "configuration." (A Gestalt is also a percept.) The Gestalt psychologists believed that much of perception is shaped by innate factors built into the brain


the part of a pattern that commands attention. The figure stands out against the ground


the part of a pattern that does not command attention; the background


the Gestalt principle that identifies the tendency to fill in gaps in figures and to see incomplete figures as complete

law of perceptual grouping

the Gestalt principles of similarity, proximity, continuity, and common fate. These "laws" suggest how our brains prefer to group stimulus elements together from a percept (Gestalt)

law of similarity

the Gestalt principle that we tend to group similar objects together in our perceptions

law of proximity

the Gestalt principle that we tend to group objects together when they are near each other. Proximity means "nearness."

law of continuity

the Gestalt principle that we prefer perceptions of connected and continuous figures to disconnected and disjointed ones

law of common fate

the Gestalt principle that we tend to group similar objects together that share a common motion or destination

law of Pragnanz

the most general Gestalt principle, which states that the simplest organization, requiring the least cognitive effort, will emerge as the figure. Pragnanz shares a common root with pregnant, and so it carries the idea of a "fully developed figure." That is, our perceptual system prefers to see a fully developed Gestalt, such as a complete circle- as opposed to a broken circle

binocular cues

information taken in by both eyes that aids in depth perception, including binocular convergence and retinal disparity

monocular cues

information about depth that relies on the input of just one eye- includes relative size, light, and shadow, interposition, relative motion, and atmospheric perspective

learning-based inference

the view that perception is primarily shaped by learning (or experience), rather than by innate factors

perceptual set

readiness to detect a particular stimulus in a given context- as when a person who is afraid interprets an unfamiliar sound in the night as a threat

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