Glossary of Perception Terms

























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Another useful resource for visual perception terms is Visionary (Lars Liden).


A-beta fibers One of the three types of nerve fibers that transmit pain. The A-beta fibers are relatively large and moderately fast.

A-delta fibers One of the three types of nerve fibers that transmit pain. The A-delta fibers are relatively small and fast. Their speed likely makes them responsible for the initial sharp pain felt in double pain. (See Double pain.)

Absolute pitch People with absolute pitch are extremely accurate in identifying the pitch of an isolated tone or producing a requested tone.

Absolute threshold The smallest intensity required for a stimulus to be reported 50% of the time.

Accommodation Change in the shape of the lens of the eye, necessary to keep an image in proper focus on the retina; it occurs as the observer focuses on objects at different distances.

Achromatic (a-crow-maa-tick) Without color.

Achromatic afterimage Image that appears after the presentation of a stimulus; both the stimulus and the afterimage are uncolored, and one is the opposite of the other.

Achromatic colors Colors found along the middle axis of the color spindle -- white, shades of gray, and black.

Achromatopsia A disorder of the visual cortex leading to an inability to see color.

Action potentials Short bursts of electrical activity such as those generated by the ganglion cells.

Active touch Touch perception in which a person actively explores objects and touches them.

Acuity Degree of precision with which fine details can be seen.

Acupuncture A procedure to relieve pain that involves inserting thin needles into various locations on the body.

Adaptation Change in sensitivity (see also Dark adaptation and Light adaptation).

Adaptation stimulus In dark adaptation studies, the intense light to which observers are exposed prior to the darkness.

Additive mixture In color mixing, the addition of beams of light from different parts of the spectrum.

Afferent fibers Nerve fibers carrying information from the receptors to the brain.

Affordances Actions one could perform with objects -- a concept introduced by James J. Gibson.

Ageusia The inability to perceive taste.

Akinetopsia The inability to perceive motion, due to damage to the cortex.

Albedo Proportion of light reflected by an object; the albedo remains constant despite changes in the amount of light falling on the object.

Albinos Individuals who are born without pigmentation. The lack of pigmentation in the iris leads to visual problems.

Amacrine cells (am-ah-krihn) Cells in the retina that allow the ganglion cells to communicate with each other. They also allow the bipolar cells to communicate with each other.

Ambiguous figure-ground relationships Situations in which the figure and the ground reverse from time to time, with the figure becoming the ground and then becoming the figure again.

Ames room Room specially designed to produce distance and size illusions (see Figure 6.28).

Amplitude In vision, the height of the light wave; amplitude is related to the brightness or lightness of a visual stimulus. In audition, the change in pressure created by sound waves; amplitude is related to the loudness of an auditory stimulus.

Analgesic medication Class of drugs specifically designed to relieve pain.

Analytic sense Sense in which the observer can detect the separate parts. For example, in hearing, an observer can typically separate two notes played together.

Analytical orientation In contrast to a holistic orientation, an analytical orientation emphasizes the importance of the components that combine to form our perceptual experiences.

Anomalous trichromat The most common form of color deficiency. An anomalous trichromat has all three cone systems, but one of the systems has an abnormal absorption spectrum.

Anosmia Inability to perceive smells.

Antagonistic surrounds The surrounding or outer region of a receptive field that responds in an opposite manner to the inner region. For example, if the inner region is excited by a light stimulus, the outer or antagonistic surround will be inhibited by it.

Anterior chamber The area directly behind the cornea and in front of the iris -- contains the aqueous humor.

Aperture The part of a camera analogous to the pupil.

Apparent-distance theory Theory of the moon illusion in which the moon seems to be farther from the viewer when it is on the horizon than when it is at the zenith.

Aqueous humor (a-kwee-us) Watery liquid found between the cornea and the lens.

Area 17 Area of the visual cortex where the neurons from the lateral geniculate nucleus terminate. Also called the striate cortex or the primary visual cortex.

Ascending series Series of trials in the method of limits in which the stimulus is systematically increased.

Astigmatism Visual disorder in which the cornea is not perfectly round. Therefore, if the eye is focused for some parts of the cornea, it is out of focus for others.

Atmospheric perspective Distance cue provided by the fact that distant objects often look blurry and bluish in contrast to nearby objects.

Attack In music perception, the beginning buildup of a tone.

Attention Focusing or concentration of mental activity.

Audiometry Measurement of the sensitivity of audition, typically by measuring thresholds for tones of differing frequency.

Auditory adaptation Decrease in the perceived loudness of a tone after it has been presented continuously.

Auditory fatigue Change in thresholds for other tones that occurs after a loud tone is presented and then turned off.

Auditory localization Ability to identify the location of sound sources in the environment.

Auditory nerve Bundle of nerve fibers that carries information from the inner ear to the auditory cortex.

Autokinesis (ah-toe-kin-nee-siss) Illusion of movement in which a stationary object, with no clear background, appears to move.

Autostereogram Developed by Tyler, an autostereogram is a single image that contains binocular depth information when viewed appropriately.




b (beta) (bay-tuh) Symbol for criterion, which is the measure in signal detection theory that assesses the observer's willingness to say, "I detect the stimulus."

Backward masking Phenomenon in which accuracy is reduced for reporting a stimulus because it was followed rapidly by a second stimulus. Backward masking is found in both vision and audition.

Basilar membrane Membrane on the base of the organ of Corti, in the inner ear.

Beats Changes in loudness produced by combinations of pure tones with similar frequencies.

Behaviorism Approach to psychology that stresses the objective description of an organism's behavior.

Bifocals Special eyeglasses that have two types of lenses, one for viewing distant objects and one for viewing close objects.

Binaural (buy-nohr-ul) Pertaining to both ears.

Binocular disparity Source of distance information provided by the fact that the two eyes have slightly different views of the world.

Binocular rivalry Occurs when the images falling on each eye are too different to be fused into one unified percept.

Biological motion Pattern of movement of living things.

Bipolar cells (buy-pole-ur) Cells in the retina that receive information from the rods and cones and pass it on to ganglion cells.

Blind spot Region of the eye in which there is no vision because the optic disk contains no light receptors.

Blindsight Blindsight occurs when a person has some visual experience in spite of damage to the visual cortex that would typically preclude such experience.

Blobs "Blob"-shaped cells distributed throughout the column structure in the primary cortex; these cells are responsive to color.

Bottom-up processing Approach that emphasizes how the sensory receptors register the stimuli, with information flowing from this low level upward to the higher (more cognitive) levels.

Boundary extension A tendency to report seeing more of a scene than was actually visible.

Braille Representation of letters in the alphabet by a system of raised dots, used in books for the blind.

Brightness Psychological reaction corresponding to the intensity of light waves; the apparent intensity of a light source.





C-fibers One of the three types of nerve fibers that transmit pain. The C-fibers are relatively small and slow. Their speed likely makes them responsible for the terminal dull pain felt in double pain. (See Double pain.)

Cataract Clouding of the lens of the eye, caused by injury or disease.

Categorical perception Grouping perceptions into categories. People have difficulty discriminating between members of the same category, even though discriminations can be readily made between members of different categories.

Categorization Process of treating objects as similar or equivalent, as in categorical perception.

Cerebral cortex (suh-ree-brul) Outer part of the brain.

Chemical senses Smell and taste.

Choroid (kore-oid) Layer on the back of the eye just inside the sclera. The choroid provides nutrients for the retina and absorbs extra light.

Chromatic adaptation Decrease in response to a color after it is viewed continuously for a long time.

Cilia (sill-ee-uh) Tiny hairlike protrusions from the receptor cells in the auditory and olfactory systems.

Ciliary muscle (sill-ee-air-ee) Muscle that controls the shape of the lens.

Cochlea (cock-lee-ah) Bony, fluid-filled structure containing the receptors for auditory stimuli.

Cochlear duct (cock-lee-er) One of the canals in the cochlea.

Cochlear microphonic Phenomenon in which a waveform falling on the ear is replicated by graded potentials from the outer hair cells.

Cochlear nucleus A structure in auditory processing to which the auditory nerve travels after leaving the inner ear.

Cognition Acquisition, storage, retrieval, and use of knowledge.

Cognitive-behavioral approaches In the treatment of pain, methods that help the patient develop more adaptive cognitive and behavioral reactions to a physical problem.

Color constancy Tendency to see the hue of an object as staying the same despite changes in the color of the light falling on it.

Color solid Three-dimensional figure, resembling two cones joined together, that represents the hue, saturation, and lightness of all colors; also called a color spindle.

Color spindle A color solid.

Color stereopsis Depth differences due to viewing color stimuli binocularly through some lenses (such as magnifying glasses).

Color vision deficiencies Disorders or difficulties in discriminating different colors, commonly called "color-blindness."

Color wheel Circle with the different wavelengths arranged around the edge; used to represent the colors of the spectrum.

Column In the visual cortex, a vertical series of cells that have the highest response rate to a line of one particular orientation.

Common region An area determined by edges or shading, within which we tend to group stimuli together (see Figure 5.10).

Comparison stimulus The stimulus in discrimination studies that varies throughout the experiment.

Complementary hues Hues whose additive mixture makes gray, such as blue and yellow.

Complex cells Cells in the primary visual cortex that respond most vigorously to moving stimuli.

Complex tones Tones that cannot be represented by a simple sound wave and are more likely to be encountered in everyday life.

Computational approach Approach to perception suggesting that although the stimuli themselves are rich in information, higher-level processes involving general physical principles are also necessary for perception to occur.

Conceptually driven processing Approach that emphasizes the importance of the observers' concepts and cognitive processes in shaping perception.

Conditioning method In testing infant perception, a method in which the experimenter selects a response that the baby can make and delivers a reward when the baby makes that particular response. Later, the experimenter tests for generalization to new stimuli.

Conduction deafness Type of deafness that involves problems in conducting the sound stimulus, occurring in either the external ear or the middle ear.

Cone of confusion Cone-shaped area around each ear in which the auditory system receives the same set of information about the location of the source of the sound.

Cones Photoreceptors used for color vision under well-lit conditions.

Confounding variable Factor in an experiment -- other than the factor being studied -- that may be responsible for the effects being observed.

Consonance Combination of two or more tones, played at the same time, that is judged pleasant.

Constancy Tendency for qualities of objects to seem to stay the same, despite changes in the way people view the objects.

Constrict Refers to the action of the iris that makes the pupil become smaller.

Constructivist theory Theory that proposes that the perceiver has an internal constructive (or problem-solving) process that transforms the incoming stimulus into the perception.

Contour Location at which lightness, brightness, or color changes suddenly; also called an edge.

Contrast sensitivity function Diagram that shows the relationship between spatial frequency and sensitivity.

Converge When viewing nearby objects, each eye rotates in its socket bringing the pupil toward the nose. (See also Diverge.)

Convergence (of eyes) Type of vergence movement used when looking at nearby objects. (See also Converge.)

Convergence (of photoreceptors) Refers to the number of photoreceptors that synapse onto each ganglion cell. For the rods, a great deal of convergence occurs (perhaps 100 rods per ganglion cell). For the cones, much less convergence occurs (a few cones per ganglion cell).

Cornea (kore-nee-uh) Clear membrane just in front of the iris.

Corollary discharge theory Theory of motion perception in which the visual system compares the movement registered on the retina with signals that the brain sends regarding eye movements.

Correct rejection In signal detection theory, a correct rejection occurs when a signal is not presented and the observer does not report it.

Correspondence problem The correspondence problem is the difficulty our visual system can face in linking the input from the two retinas. The difficulty occurs in both distance and motion perception when input at similar areas of the two retinas differs.

Cortical magnification Overrepresentation of information from the fovea with respect to the cortex.

Counterirritants Methods of pain control that stimulate or irritate one area so that pain is diminished in another.

Criterion The measure in signal detection theory that assesses the observer's willingness to say, "I detect the stimulus."

Critical band The range of frequencies that can be masked by a particular tone is referred to as the critical band of that tone.

Cross-adaptation In odor perception, the change in threshold for one odor that occurs after exposure to another.

Cross-enhancement Lowering a threshold for one substance after adaptation to another.

Cross-modality matching Technique in which observers are asked to judge stimuli in one mode of perception (such as hearing) by providing responses from another mode (such as sight).

Crossed disparity Objects nearer to the viewer than the focal point create crossed disparity, with the image falling outside of the focal point on each retina.

Cue Any factor that lets an observer make a decision automatically, such as a distance cue; cues do not require elaborate thought.

Cycle For sound stimuli, a cycle is the full range of pressure changes from normal, to high, to normal, to low, and back to normal.





d' (dee prime) In signal detection theory, an index of sensitivity; d' depends upon the intensity of the stimulus and the sensitivity of the observer.

Dark adaptation Increase in sensitivity that occurs as the eyes remain in the dark.

Dark adaptation curve Graph showing the relationship between the time in the dark and the threshold for the test stimulus.

Dark focus An intermediate resting state of the lens due to relaxation of the ciliary muscles -- thought to be caused by a balance of input from the sympathetic and parasympathetic systems.

Data-driven processing Approach that emphasizes how sensory receptors register stimuli, with information flowing from this low level upward to the higher, more cognitive levels.

Decay In music perception, the decrease in amplitude at the end of a tone.

Decibel (dB) One measure of the amount of pressure created by a stimulus such as a sound wave.

Depolarization Process in which a neuron changes from its resting potential to a less negative potential.

Depth of field Refers to the range over which we can see objects clearly. When the pupil is at its smallest, we are able to see objects over a wider range more clearly than when the pupil is larger -- we have a greater depth of field.

Depth perception Perception of objects as three-dimensional, having depth in addition to height and width.

Dermis Middle layer of skin, which makes new skin cells.

Descending series Series of trials in the method of limits in which the stimulus is systematically decreased.

Detection In acuity measures, a task that requires the observer to judge whether a target is present or absent.

Deuteranopes (doo-tur-uh-nopes) People who are dichromats and are insensitive to red and green.

Dichromat (die-krow-mat) Person who requires only two primary colors to match his or her perception of all other colors due to a missing cone system.

Difference threshold The smallest change in a stimulus that is required to produce a difference noticeable 50% of the time.

Diffuse bipolar cells Diffuse bipolar cells make several connections with different photoreceptors, typically rods, initiating the convergence process. (See also Midget bipolar cells.)

Dilate Refers to the action of the iris that makes the pupil become larger.

Diopter A measure of the optical power of a lens (reciprocal of focal length measured in meters). Thus, a 2 diopter lens would bring light rays into focus at 1/2 meter.

Direct perception approach Approach to perception proposed by James J. Gibson. It suggests that the stimuli themselves contain all the necessary information for perception to occur -- learning and cognition are not needed.

Discrimination In psychophysics, the smallest amount that a stimulus must be changed to be perceived as just noticeably different.

Disc shedding Process of shedding old discs in the photoreceptors.

Dishabituation Increase in looking time that occurs when a new stimulus is presented following repeated presentation of another stimulus.

Disocclusion (dis-uh-clue-zyun) Process in which a moving object systematically uncovers the background.

Disparity-selective cells Disparity-selective cells are important for depth perception, because they have high rates of electrical discharge when stimuli are registered on different (disparate) areas of the two retinas.

Dissonance Combination of two or more tones, played at the same time, that is judged unpleasant.

Distal stimulus Stimulus or object as it exists in the world, as opposed to the proximal stimulus.

Distance perception Distance perception refers to your ability to perceive the distance relationships within the visual scene. (See also Depth perception.)

Diverge Rotation of the eyes to bring the pupils to the center, for viewing distant objects. (See also Converge.)

Divergence Type of vergence movement of the eyes in which the eyes rotate away from each other. (See also Diverge.)

Divisionism A painting technique that is based on the interactive effects of larger patches of colors than pointillism. (See also Pointillism.)

Doctrine of specific nerve energies Theory proposed by Müller that each different sensory nerve has its own characteristic type of activity and therefore produces different sensations.

Double pain Experience of sharp pain followed by dull pain, presumably caused by A-delta and C-fibers.

Duplex perception Kind of auditory perception in which the listener perceives both a speech and a nonspeech sound from the same auditory information -- originally thought to provide support for a distinct speech module.

Duplicity theory Approach to vision that proposes two separate kinds of photoreceptors: rods and cones.

Dyne Unit for measuring energy.

Dysgeusia Damage to a taste nerve can lead to the perception of a taste that is not present.





Eardrum Thin piece of membrane that vibrates in response to sound waves.

Ear infection Condition in which the eustachian tube becomes swollen, cutting off the middle ear from the respiratory tract.

Echolocation Sensory technique used by bats, in which the emission of a high-frequency sound is translated into a measure of distance based on the time elapsed before the sound returns.

Edge Place where there is a sudden change in brightness, lightness, or color; an edge is necessary for vision.

Efferent fibers Nerve fibers carrying information from the brain to the receptors.

Egocentric distance Distance between the observer and an object, as used in depth perception.

Electromagnetic radiation All forms of waves produced by electrically charged particles.

Emmert's law Principle that an afterimage appears larger if it is projected on a more distant surface.

Empiricism Approach to perception that states that basic sensory experiences are combined, through learning, to produce perception.

Encapsulated endings Small capsules or bulbs on the end of some kinds of skin receptors.

Endorphins Morphine-like substances that occur naturally within the body.

End-stopped cells Some simple and complex cortical cells are referred to as end-stopped cells because they respond most vigorously if the stimulus ends within the cell's receptive field.

Envelope The shape of a traveling wave determined by connecting the maximum and minimum points of the wave.

Epidermis Outer layer of skin, which has many layers of dead skin cells.

Epistemology Branch of philosophy that concerns how we acquire knowledge.

Equal loudness contour Graph showing the relationship between tone frequency and the number of decibels required to produce a tone of equal loudness.

Errors of anticipation Errors in psychophysics testing in which observers provide a different answer from the one they provided on the last trial; they "jump the gun."

Errors of habituation Errors in psychophysics testing in which observers keep giving the same answer as on the last trial.

Eustachian tube (you-stay-she-un) Structure in the middle ear that connects the ear to the throat.

Evoked acoustic emissions Phenomenon in which a sound presented to the ear is echoed back.

Excitation Stimulation of neurons sufficient to generate an action potential.

External auditory canal Tube that runs inward from the pinna to the eardrum.

Extrastriate cortex (ex-tra-strie-ate) Region of the visual cortex that receives information already processed by the primary visual (or striate) cortex as well as from the superior colliculus.

Eye-movement explanation Explanation of illusions in terms of eye-movement patterns.





False alarm In signal detection theory, a false alarm occurs when the signal is not presented yet the observer reports it nevertheless.

Familiar size An object's customary or standardized size, used as a source of information in distance perception.

Far point The farthest point that the viewer can see clearly.

Farsighted Referring to people who cannot see nearby objects.

Feature-integration approach Approach suggesting that we use different levels of processing for different kinds of shape perception.

Fechner's law (R = k log I) Fechner's law says that the magnitude of the psychological reaction (R) is equal to a constant (k) multiplied by the logarithm of the intensity (I) of the physical stimulus.

Field dependent Reliant on the orientation of the room to determine an upright position.

Field independent Reliant on the orientation of one's own body to determine an upright position.

Figure In shape perception, a distinct shape with clearly defined edges.

Fixation pause The pause between two saccadic eye movements.

Flavor Experience of taste, smell, touch, pressure, and pain associated with substances in the mouth.

Floaters Solid matter suspended in the vitreous humor that will become visible under appropriate conditions.

Focused attention In Treisman's feature-integration theory, the identification of objects in the second stage of processing.

Form An area set off from the surrounding space by its edges.

Formants Horizontal bands of concentrated sound in a speech spectrogram.

Fourier analysis (foo-ryay) Process in which a stimulus is analyzed into its component sine waves.

Fourier synthesis Process of adding together a series of sine waves; the reverse of Fourier analysis.

Fovea (foe-vee-ah) Central region of the retina in which vision is sharpest.

Free nerve endings Skin receptors that do not have bulbs or capsules on the end nearest the epidermis.

Frequency Number of cycles a wave (e.g., of light or sound) completes in 1 second.

Frequency theory Theory of auditory processing that proposes that the entire basilar membrane vibrates at a frequency that matches the frequency of a tone.

Frequency tuning curve Graph showing the relationship between the frequency of an auditory stimulus and an auditory nerve fiber's response rate.

f-stop The setting on a camera that controls the aperture size; analogous to the human iris.

Fundamental frequency The component of a complex sound wave that has the lowest frequency.





G-proteins Short for GTP-binding proteins, this family of about 1,000 proteins is important in vision and the chemical senses.

Ganglion cells (gang-glee-un) Cells that run from the bipolar cells of the retina toward the brain.

Ganzfeld (gahnz-feldt) A visual field that has no contours, based on the German word for "whole field."

Gate-control theory Theory that proposes that pain perception is a complex process in which the neural fibers interact and the brain also has an influence.

General Mechanism account Theory of speech perception positing that speech and other kinds of auditory information are processed by the same mechanisms (no special speech module).

Geons (geometric icons) Basic shapes from which objects may be constructed.

Gestalt (geh-shstahlt) Configuration or pattern.

Gestalt approach Approach to perception that emphasizes that we perceive objects as well-organized, whole structures rather than as separated, isolated parts.

Gibsonian approach (gibb-sone-ee-un) Approach to perception that emphasizes that perceptions are rich and elaborate because the stimuli in the environment are rich with information rather than because thought processes provide that richness; the Gibsonian approach is named after psychologist James J. Gibson. (Also see Direct perception approach.)

Glabrous skin Kind of skin on the soles of the feet and the palms of the hands; does not contain hairs.

Glaucoma (glaw-koe-mah) Visual disorder in which excessive fluid inside the eye causes too much pressure, ultimately producing damage to the ganglion cells in the retina and to the optic nerve.

Golgi tendon organs (goal-jee) Receptors in tendons that respond when the muscle exerts tension on the tendon.

Ground In shape perception, the background that appears to be behind the figure.

Ground theory Theory proposed by J. J. Gibson, in which distance perception depends upon information provided by surfaces in the environment.

Gymnema sylvestre A taste modifier that reduces the intensity of sweet substances.





Habituation method In testing infant perception, a method based on a decrease in attention to repeated stimulation.

Hair cells Receptors for auditory stimuli, located in the organ of Corti.

Hairy skin Type of skin that covers most of the human body and contains hairs.

Haptic perception Perception of objects by touch.

Harmonics Those multiples of the fundamental frequency that are present in a complex sound; also called overtones.

Hedonics (hih-donn-icks) Area of perception that involves judgments of pleasantness and unpleasantness.

Height cues Distance information provided by the fact that objects near the horizon are farther away than those far from the horizon.

Helicotrema (hell-ih-koe-treh-ma) Tiny opening at the end of the vestibular canal in the inner ear.

High-amplitude sucking procedure Technique used to assess infant perception, in which babies suck on a pacifier attached to a recording device; a sufficiently fast sucking rate produces a stimulus such as a speech sound.

Hit In signal detection theory, a hit occurs when the signal is presented and the observer reports it.

Holistic orientation Characterized by the Gestalt approach, a holistic orientation argues that the final percept that we experience is not simply the sum of its parts. (See also Analytical orientation.)

Horizontal cells Cells in the retina that allow the photoreceptors to communicate with each other.

Horizontal-vertical illusion An illusion shaped like an inverted T, in which the vertical line looks longer than the horizontal line (see Demonstration 6.8).

Horopter An imaginary curved line that can be drawn to represent all the points that are the same distance from the observer as the focal object.

Hue Psychological reaction of color that corresponds to the length of light waves.

Hypercolumn A sequence of 18 to 20 adjacent columns in the visual cortex. A hypercolumn includes enough columns to complete a full cycle of stimulus-orientation preferences.

Hypermetropic Refers to people who are farsighted and cannot see nearby objects.

Hyperpolarization Process in which a neuron changes from its resting potential to a more negative potential.

Hypnosis Altered state of consciousness in which a person is susceptible to suggestions from the hypnotist. Hypnosis is sometimes used to help people suffering from chronic pain.

Hz (hurtz) Abbreviation for the name of Heinrich Hertz; Hz represents the number of cycles a sound wave completes in 1 second.





Illusion An incorrect perception.

Illusory conjunction In Treisman's feature-integration theory, an inappropriate combination of features from two stimuli.

Illusory contour Phenomenon in which contours are seen even though they are not physically present.

Illusory movement Perception that an object is moving even though it is really stationary.

Impedance Resistance to the passage of sound waves.

Impedance mismatch Condition in which the impedances for two media differ; sound waves cannot be readily transmitted when an impedance mismatch exists.

Incorrect comparison explanation An explanation of illusions that states that observers base their judgments on the incorrect parts of the figure.

Incus A small anvil-shaped bone in the middle ear.

Indirect perception approaches Approaches that assume that the information received by the senses is insufficient by itself to arrive at an accurate description of the world.

Induced movement Illusion of movement that occurs when a visual frame of reference moves in one direction and produces the illusion that a stationary target is moving in the opposite direction.

Inducing areas Regions of an illusory contour figure in which true contours exist.

Inducing lines Lines in an illusory contour figure that encourage the perception of illusory contours.

Inferior colliculus (kole-lick-you-luss) Structure in auditory processing between the superior olivary nucleus and the medial geniculate nucleus.

Inferior temporal cortex (IT) The inferior temporal cortex is located on the lower part of the side of the cortex and is important for object perception.

Information-processing approach The approach that identifies psychological processes and connects them by specific patterns of information flow. (See also Cognition.)

Inhibition Stimulation of a neuron that results in a reduced rate of action potentials.

Inner hair cells Auditory receptors on the inner side of the organ of Corti, most likely sensitive to a tone's frequency.

Interaural intensity difference Cue to auditory localization based on small sound intensity differences between the two ears.

Interaural time difference Cue to auditory localization based on small differences between the time a sound arrives in each ear.

Interblobs Cells between blobs that are sensitive to orientation and not wavelength

Interposition Distance cue in which one object partly covers another.

Intraocular lens Substitute lens inserted into the eye after surgically removing a defective lens.

Invariants In the theory of J. J. Gibson, the aspects of perception that persist over time and space and are left unchanged by certain kinds of transformations.

Involuntary eye movements Unavoidable small eye movements that occur during fixation.

Iris Ring of muscles in the eye surrounding the pupil; the colored part of the visible eye.

Ishihara test (ih-she-hah-rah) Test for color deficiencies, in which the observer tries to detect a number hidden in a pattern of different-colored circles. (See Color Plate 5.)





Just noticeable difference (jnd) Smallest difference in sensation that can be noticed.



Kemp echoes Phenomenon in which a sound presented to the ear is echoed back.

Kinesthesia Sensation of movement or static limb position.

Kinesthetic information Nonvisual information (such as muscular information) that can be used to judge distance.

Kinetic depth effect Phenomenon in which a figure looks flat when it is stable but appears to have depth once it moves.





Lateral geniculate nucleus (LGN) (jen-ick-you-late) Part of the thalamus where most of the ganglion cells transfer their information to new neurons.

Lateral inhibition Inhibition of neural activity for points near the part of the retina that is stimulated by light.

Lateralization The perception that sounds move from side to side inside the listener's head, because the sounds are delivered through headphones. (See also Auditory localization.)

Lateral superior olivary nucleus Part of the superior olivary nucleus that is specialized for processing high-frequency auditory information.

Law of closure Gestalt law that says that a figure is perceived as closed and complete rather than containing a blank portion.

Law of common fate Gestalt law that says that items perceived as moving in the same direction are seen as belonging together.

Law of good continuation Gestalt law that says that a line is perceived as continuing in the same direction it was going prior to intersection.

Law of Prägnanz (Prahg-nahntz) Gestalt law that says that when faced with several alternate perceptions, the one that will actually occur is the one with the best, simplest, and most stable shape.

Law of proximity Objects near each other are grouped as one unit.

Law of similarity Gestalt law that says that items that are similar are grouped together.

Laws of grouping Ideas that explain the way we organize or group information.

Left visual field Portion of the visual world on the left-hand side.

Lemniscal system (lemm-niss-kull) One of the two neuronal systems responsible for the skin senses. It has larger nerve fibers and faster transmission than the spinothalamic system.

Lens Structure inside the eye whose shape changes to bring objects into focus.

Light Portion of the electromagnetic radiation spectrum made up of waves that range in length from about 400 nm to about 700 nm.

Light adaptation Decline in sensitivity that occurs as the eyes remain in the light.

Lightness Psychological reaction corresponding to the amount of light reflected by an object.

Lightness constancy Phenomenon in which an object seems to stay the same lightness despite changes in the amount of light falling on it.

Limbic system A portion of the brain that is involved in regulating behaviors such as fleeing, fighting, feeding, and sexual behavior.

Linear perspective Distance cue provided by the fact that parallel lines appear to meet in the distance.

Logarithm Type of numerical transformation; the logarithm of a number equals the exponent to which 10 must be raised to equal that number.

Long-range process Analysis of the kind of movement that occurs over a long distance or time.

Loudness Psychological reaction that corresponds roughly to a tone's amplitude.





Mach band (mock) Phenomenon in which bright and dark regions are perceived within a single stripe, although there is no corresponding variation in the physical distribution of light.

Magnitude estimation Technique in which the observer is told that one particular stimulus is to be assigned a certain value, and this value is used as a "yardstick" to estimate the magnitude of all future stimuli.

Magno pathway The magno (short for magnocellular) pathway is involved in the perception of illumination differences and moderate or rapid movement. The pathway begins with information passing from the photoreceptors through diffuse bipolar cells and parasol ganglion cells.

Maintained activity In the absence of a visual stimulus, a ganglion cell fires at a relatively low rate, referred to as spontaneous or maintained activity.

Malleus (mal-lee-uss) A small hammer-shaped bone in the middle ear.

Manner of articulation One of the three dimensions in pronouncing consonants; it specifies how completely the air is blocked and where it passes.

Margin illusion We usually perceive the margins of a page as taking up little room, but in fact they can take up over a third of the page.

Masking A phenomenon in which one stimulus makes another stimulus difficult to perceive. The masking stimulus can precede the obscured stimulus (forward masking) or it can follow the obscured stimulus (backward masking).

McGurk effect Occurs when listeners are exposed to one phoneme and simultaneously observe a speaker saying a different one. Listeners report hearing a completely different phoneme that is actually a combination of the two.

Medial geniculate nucleus (jen-ick-you-late) Structure involved in auditory processing that lies between the inferior colliculus and the auditory cortex.

Medial superior olivary nucleus Part of the superior olivary nucleus specialized for processing low-frequency information.

Mel scale In audition, a scale produced by magnitude estimation, in which a 1000-Hz tone with an intensity of 60 dB is assigned a pitch of 1000 mels, and comparison tones are assigned other, relative mel values.

Memory color Phenomenon in which an object's typical color influences the observer's perception of the object's actual color.

Mesopic Mesopic conditions exist when the light is sufficiently bright that cones are still functional, but sufficiently dim that rods can also function.

Metameric matching Process in which a subject can match any hue of a single wavelength by combining various amounts of three different colored lights (usually red, green, and blue).

Metamers Pairs of lights that look exactly the same but are composed of physically different stimuli.

Method of adjustment Psychophysical technique in which observers adjust the intensity of the stimulus until it is just barely detectable.

Method of adjustment for measuring discrimination Psychophysical technique in which observers themselves adjust the comparison stimulus until it seems to match the standard stimulus.

Method of constant stimuli Psychophysical technique in which the stimuli are presented in random order.

Method of constant stimuli for measuring discrimination Psychophysical technique in which the experimenter presents the comparison stimuli in random order and asks observers to judge whether each comparison stimulus is greater than or less than the standard stimulus.

Method of limits Psychophysical technique in which the researcher begins with a stimulus that is clearly noticeable and then presents increasingly weaker stimuli until observers are unable to detect the stimulus; these trials alternate with trials in which increasingly stronger stimuli are presented.

Method of limits for measuring discrimination Psychophysical technique in which the standard stimulus remains the same, and the comparison stimulus varies from low to high on some series and from high to low on other series.

Mexican-hat filter A filter with characteristics similar to the receptive fields found in the visual system (see Figures 5.13 and 5.14b). Computational theorists have demonstrated that this filter is capable of extracting edges from visual input.

Microelectrode Very small electrode used in single cell recording.

Microspectrophotometry Procedure in which an extremely small beam of light from one part of the color spectrum is passed through individual receptors in dissected retinal tissue. The amount of light absorbed at each wavelength is then measured.

Microvilli (my-crow-vill-lie) Tips of the taste receptors.

Midget bipolar cells Cells that connect to a single cone or a small number of cones, initiating the parvo pathway. (See also Diffuse bipolar cells.)

Midget ganglion cells Cells that carry information away from the midget bipolar cells, continuing the parvo pathway. (See also Parasol ganglion cells.)

Minimum audible angle (MAA) The smallest difference (measured in degrees) between two sound sources such that a listener can perceive them as coming from two different sources.

Miracle fruit A taste modifier that sweetens the taste of sour substances.

Misapplied constancy explanation According to the misapplied constancy explanation, an illusion occurs because observers interpret portions of the illusion as cues for maintaining size constancy.

Miss In signal detection theory, a miss occurs when a signal is presented and the observer does not report it.

Missing fundamental An auditory illusion in which only the harmonics but not the fundamental frequency of a complex sound are present. Nonetheless, listeners do not perceive its absence.

Module A special-purpose neural mechanism used to process one kind of information.

Monaural (monn-ahr-ul) Pertaining to only one ear.

Monochromat (mah-noe-crow-mat) Person who requires only one color to match his or her perception of all other colors; every hue looks the same to this person.

Monochromatic colors Colors produced by a single wavelength.

Monocular factors Factors seen with one eye that can provide information about distance.

Moon illusion Illusion in which the moon at the horizon looks bigger than the moon at its highest position.

Motility The independent elongation and contraction of the outer hair cells that enhances our ability to make fine frequency discriminations.

Motion parallax Distance cue provided by the fact that as the observer moves the head sideways, objects at different distances appear to move in different directions and at different speeds.

Motion perspective Continuous change in the way objects look as the observer moves about in the world.

Motor theory of speech perception Theory in which humans possess a specialized device that allows them to decode speech stimuli and permits them to connect the stimuli they hear with the way these sounds are produced by the speaker.

Movement aftereffects Illusion of movement that occurs after looking at continuous movement. When looking at another surface, it will seem to move in a direction opposite that of the original movement.

MSG Monosodium glutamate; a substance used in cooking that reduces the thresholds for sour and bitter tastes.

Müller-Lyer illusion (mew-lur lie-ur) Famous illusion in which two lines of the same length appear to be different in length because of wings pointing outward on one line and inward on the other line (see Figure 6.20).

Muscle spindles Muscle spindles are receptors that are located within the muscle itself, which are important for kinesthesia. (See also Kinesthesia.)

Myopic Refers to people who are nearsighted and cannot see faraway objects.





Nanometer (nm) One-billionth of a meter; measure used for wavelength.

Nasal cavity Hollow space behind each nostril.

Near point The nearest point that the viewer can see clearly.

Nearsighted Refers to people who cannot see faraway objects.

Negative afterimage Image that appears after the presentation of a stimulus. The afterimage is the opposite of the original stimulus. (See also Successive color contrast.)

Nerve deafness Type of deafness that involves problems either in the cochlea or in the auditory nerve.

Neuromatrix Proposed by Ronald Melzack, the neuromatrix receives input from three brain systems to generate a unique pattern of impulses that serves to identify the self.

Neurons (new-rons) Nerve cells.

Noise In signal detection theory, the situation in which no signal occurs. In audition, irrelevant, excessive, or unwanted sound.

Nonspectral hues Hues that cannot be described in terms of a single wavelength from a part of the spectrum.

Nontasters In taste perception, people who are insensitive to some particular tastes.

Normal trichromat (try-krow-mat) Person who requires three primary colors to match all other colors.





Occlusion (uh-clue-zyun) Process in which a moving object systematically covers up the background.

Octave A doubling of frequency; used by musicians to represent the distance between two notes that have the same name, such as two successive C notes on the piano.

Octave illusion Musical illusion in which one tone is presented to one ear and another tone an octave away is simultaneously presented to the other ear. The tones shift from ear to ear, yet the listener reports one ear hearing only high notes and the other hearing only low notes.

Ocular dominance Tendency for cells in the visual cortex to have a higher response rate for one of the two eyes.

Odorant Smell stimulus.

Odor constancy Odor constancy means that the perceived strength of an odor remains the same despite variations in sniff vigor.

Olfaction Smell.

Olfactory bulb Structure that receives the signals from the smell receptors.

Olfactory epithelium Region at the top of the nasal cavity that contains the smell receptor cells.

Omnivore Plant-and-animal-eating organism.

Onset difference An important cue in auditory localization, because a sound originating from one side will arrive at the ear on that side prior to arriving at the ear on the other side. (See also Interaural time difference.)

Op art Artistic movement that developed in the 1960s that attempted to produce a strictly optical art.

Ophthalmologists Doctors specializing in eye diseases.

Ophthalmoscope Special tool used to look inside the eye.

Opiate receptors Specific locations on the surface of brain cells that respond to opiate drugs in a lock-and-key fashion.

Opponent-process theory Theory of color vision that states that there are cells in the visual system that respond to stimulation by an increase in activity when one color is present and by a decrease in activity when another color is present.

Optacon II The Optacon II translates written letters and numbers into a vibratory display, to allow people who are blind to read.

Optic chiasm (kie-as-em) Area in which the two optic nerves come together and cross over.

Optic disc Region of the retina in which the optic nerve leaves the eye.

Optic flow field The complex pattern on our retinas where peripheral objects move more rapidly than central objects. The optic flow field is important for motion perception.

Optic nerve Bundle of ends from the ganglion cells that passes out of the eye toward the optic chiasm.

Optic tract Bundle of nerve fibers in the visual system that runs between the optic chiasm and the superior colliculus or the lateral geniculate nucleus.

Organ of Corti (court-eye) Part of the cochlea that contains the auditory receptors.

Orientation tuning curve Graph illustrating the relationship between the angular orientation of a line and a cell's response rate.

Ossicles Three small bones in the middle ear: malleus, incus, and stapes.

Otoacoustic emissions All emissions produced by the ear, whether in response to a stimulus or not.

Otosclerosis A bone disease that causes immobility of the stapes, ultimately making conduction of sound stimuli difficult.

Outer hair cells Auditory receptors on the outer side of the organ of Corti, most likely responsible for tuning the traveling wave on the basilar membrane to allow fine frequency discrimination. (See also Motility.)

Oval window Membrane that covers an opening in the cochlea.

Overtones Harmonics, or the other components of a complex tone, excluding the fundamental frequency, that are multiples of that fundamental frequency.





Pacinian corpuscles One variety of skin receptors with encapsulated endings; they are very sensitive to the indentation of the skin.

Pain Perception of actual or threatened tissue damage and the private experience of unpleasantness.

Pain threshold Intensity of stimulation in which pain is reported on half the trials.

Pain tolerance Maximum pain level at which people voluntarily accept pain.

Panum's area An area on and near the horopter in which the images of the object on the two retinas can be fused. (See also Horopter.)

Papillae (paa-pill-ee) Small bumps on the tongue that contain the taste buds.

Paradoxical cold Phenomenon in which a very hot stimulus produces the sensation of cold by stimulating a cold spot.

Parallel process Process that allows several targets or tasks to be handled simultaneously, typically by different modules. (See also Module.)

Parallel transmission Tendency for some sounds in a syllable to be transmitted at about the same time rather than one at a time.

Parasol ganglion cells Ganglion cells with widely spread dendrites, which are primarily connected to rods. These cells receive input from diffuse bipolar cells, continuing the magno pathway. (See also Diffuse bipolar cells.)

Parvo pathway The parvo (short for parvocellular) pathway is predominantly responsible for carrying information about the color and detail of stimuli, as well as slowly moving stimuli. The pathway begins with input from photoreceptors passing to midget bipolar and midget ganglion cells.

Passive touch Touch perception in which an object is placed on a person's skin.

Pattern theory Theory about the skin senses that proposes that the pattern of nerve impulses determines sensation.

Pattern theory of pain perception States that pain is perceived when the sum of all the individual receptor cells' levels of stimulation surpasses a critical point.

Payoff In signal detection theory, the rewards and punishments associated with a particular response.

Perception Interpretation of sensations, involving meaning and organization.

Permanent threshold shift Permanent increase in a hearing threshold as a result of exposure to noise.

Phantom limb pain Perceived pain in an amputated arm or leg.

Phase angle Phase angle is the position of the wave in degrees over one complete cycle (0 degrees, 90 degrees, etc.). It helps to describe the wave's pressure at each position. For example, at 90 degrees, pressure is at a maximum, and at 270 degrees a minimum.

Phase difference The difference in phase angle of a sound at the two ears, which serves as a cue to the location of the sound source (see Figure 10.6).

Phenomenological observation Approach in which observers look at their immediate experience and attempt to describe it completely.

Pheromones (fear-uh-moans) Substances that act like chemical signals in communicating with other members of the same species.

Phi movement Illusion of movement in which observers report that they see movement, yet they cannot perceive an actual object moving across a gap; phi movement can be produced by two light flashes about 100 milliseconds apart.

Phoneme Basic unit of speech, such as an /h/ or an /r/ sound.

Phonemic restoration Phenomenon that occurs when a speech sound is replaced or masked by an irrelevant sound and the perceptual system restores or fills in the gap appropriately.

Phonetic boundary Refers to auditory perception; the point on a continuum where our perception of phonemes changes -- to the left of the boundary we perceive one phoneme, and to the right we hear a different one.

Photopic vision (foe-top-ick) Vision that uses cones.

Photopigments Chemical substances that accomplish the transduction of light.

Photoreceptors Light receptors; the rods and cones.

Pictorial cues Cues used to convey depth in a picture.

Pinna Flap of external tissue that aids in auditory localization, typically referred to as "the ear."

Pitch Psychological reaction that corresponds to the frequency of a tone.

Placebo (pluh-see-bow) Inactive substance such as a sugar pill that the patient believes is a medication.

Place of articulation One of the three dimensions for consonants; specifies where the airstream is blocked when the consonant is spoken.

Place theory Theory of auditory processing that proposes that frequency information is encoded at different places along the basilar membrane.

Pointillism Artistic technique in which discrete dots of pigment are applied to a canvas; the dots blend into solid colors when viewed from a distance.

Point-light display A display that shows only points of light at the joints of an organism. Such a minimal display is useful in studying biological motion.

Ponzo illusion Illusion in which two parallel lines the same length appear to be different lengths because of the presence of depth cues.

Preattentive processing In Treisman's feature-integration theory, the automatic registration of stimulus features.

Preference method In testing infant perception, a method based on the idea that if the infant spends consistently longer looking at one figure in preference to another figure, the infant must be able to discriminate between the two figures.

Prepared childbirth methods Methods that educate women and men about the anatomy of childbirth, controlled muscular relaxation, and focusing attention on something other than pain (e.g., the Lamaze method).

Presbycusis (prez-bee-koo-siss) Progressive loss of hearing in both ears for high-frequency tones, occurring with aging.

Presbyopia (prez-bee-owe-pee-ah) Type of farsightedness that occurs with aging, due to inelasticity of the lens.

Primal sketch A kind of map for shape perception produced by the visual system, which yields edges and intensity differences.

Primary auditory cortex Located in the temporal lobe, it receives information from the medial geniculate nucleus.

Primary visual cortex Area of the visual cortex where the neurons from the lateral geniculate nucleus terminate.

Probe-tone technique Technique in which the listener hears either a musical chord or a scale in order to establish a key; then a probe tone is presented and the listener is asked to rate how well that tone fits within the octave of the key being examined.

Profile analysis Process in which subjects are able to detect differences in intensities of complex tones by comparing the activity that each produces on the basilar membrane.

PROP Bitter substance, 6-n-propylthiouracil, which some people cannot taste.

Proprioception Sensation of movement or static limb position; synonym for kinesthesia.

Prosopagnosia A disorder in which a person cannot organize facial features to recognize a face.

Protanopes (proe-tuh-nopes) People who are dichromats and insensitive to deep red.

Prototype Ideal figure proposed to serve as a basis of comparison in the prototype-matching approach to pattern recognition.

Prototype-matching approach Approach to shape perception suggesting that we have information regarding various abstract shapes and patterns stored in memory (the prototype) and recognition occurs when we match a newly presented stimulus to a prototype.

Proximal stimulus Representation of objects in contact with a sense organ, such as the representation on the retina, as opposed to the distal stimulus.

Psychophysics Study of the relationship between physical stimuli and psychological reactions to those stimuli.

PTC Bitter substance, phenylthiocarbamide, which some people cannot taste.

Pupil Opening in the center of the iris.

Pure tone Tone that can be represented by a simple sine wave.

Purity In the description of color, the lack of white light. Colors low in purity have large amounts of white light added to the monochromatic light.

Purkinje shift (purr-kin-gee) Phenomenon in which an observer's sensitivity to various wavelengths shifts toward the shorter wavelengths as he or she shifts from cone to rod conditions.

Pursuit movements Slow, smooth eye movements used in tracking an object moving against a stationary background.





Rapidly adapting (RA) fibers Kind of touch receptors that respond to a change in stimulation.

Ratio principle According to the ratio principle, the important factor that determines how light an object appears is the stimulus intensity of that object in comparison to other objects in the scene.

Receiver operating characteristic (ROC) curve In signal detection theory, a curve showing the relationship between the probability of a hit and the probability of a false alarm.

Receptive field For a given cell, the portion of the retina that, when stimulated, produces a change in the activity of that cell.

Recognition-by-components approach The approach suggesting that recognition of complex shapes occurs by analyzing the basic components from which they are constructed.

Recognition threshold In taste perception, the concentration of a solution that can be recognized by quality.

Recruitment Condition in which a deaf person perceives very loud sounds normally but does not hear weak sounds at all.

Reference theory Theory of the moon illusion in which both the sky and the ground are important referents when observers judge the size of the moon.

Refractory period Time immediately following an action potential, during which a nerve cell returns to its resting potential.

Reissner's membrane Membrane separating the cochlear duct from the vestibular canal.

Relative distance Distance between two objects, as used in depth perception.

Relative size Object's size relative to other ob jects, used as a cue in distance perception.

Relative-size explanation Theory of size constancy in which people notice the size of an object compared to other objects, thereby retaining constancy.

Retina (reh-tin-nuh) Portion of the eye that absorbs light rays; contains the photoreceptors.

Retinex theory Retinex theory seeks to explain color perception and color constancy based primarily on perception of the pattern of reflectances from the stimuli

Retinotopic Arrangement in which the spatial distribution is similar to that found on the retina. For example, in the lateral geniculate nucleus (LGN), ganglion cells that originated on neighboring parts of the retina also terminate on neighboring parts of the LGN.

Rhodopsin (roe-dopp-sin) Photopigment found in rods.

Right visual field Portion of the visual world on the right-hand side.

Rods Photoreceptors used for black-and-white vision under poorly lit conditions.

Round window Membrane that covers an opening in the tympanic canal.





Saccade (suh-kaad) A single rapid eye movement in which the eye is moved from one location to the next.

Saccadic movement (suh-kaad-dick) Very rapid eye movements in which the eye is moved from one fixation point to the next.

Sander parallelogram Line-length illusion involving the diagonal lines in a parallelogram (see Figure 6.22).

Saturation Psychological reaction to the purity of a light; a highly saturated light appears to have very little white light added to it.

Sclera Shiny white part of the external eye.

Scotoma (skuh-toe-muh) Blind area caused by damage to the visual cortex; plural is scotomata (skuh-toe-muh-tuh).

Scotopic vision (skoe-top-ick) Vision that uses rods.

Secondary visual cortex Region of the visual cortex that receives information that has already been processed by the primary visual cortex as well as from the superior colliculus.

Selective adaptation procedure Technique in which a particular stimulus is continuously exposed in order to produce "fatigue" in neurons sensitive to certain spatial frequencies.

Self-adaptation When a particular odorant leads to a loss of sensitivity to that odorant, the process is called self-adaptation.

Self-motion illusion Perception that you are moving, although you are really stationary.

Sensation Immediate and basic experiences generated by isolated, simple stimuli.

Sensitivity Ability to detect a change in the stimulus; sensitivity is inversely related to threshold level.

Serial process Processing information that requires the targets or tasks to be handled one at a time.

Shading Distance cue provided by the pattern of light and shadows.

Shape Area set off from the rest of a visual stimulus because it has a contour.

Shape constancy Phenomenon in which an object seems to stay the same shape despite changes in its orientation.

Shape from highlights Cue to the three-dimensionality of a shape arising from light reflected from the surface of the object.

Shape from motion Cue to the three-dimensionality of a shape arising from the motion of the object. (See also Kinetic depth effect.)

Shape from shading Cue to the three-dimensionality of a shape from the shadows attached to the object.

Shape-slant invariance hypothesis Theory of shape constancy in which the viewer calculates objective shape by combining information about an object's retinal shape and its slant.

Short-range process Analysis of the kind of movement that occurs over a short distance or time.

Signal Stimulus used in psychophysics studies, most often in signal detection theory.

Signal detection theory (SDT) Psychophysical approach that assesses both the observer's sensitivity and his or her decision-making strategy (or criterion).

Signal + noise In signal detection theory, the situations in which the appropriate signal occurs, in addition to the irrelevant "noise."

Simple cells Cells in layer IVb of the primary visual cortex that respond most vigorously to lines.

Simultaneous color contrast The changing of an object's perceived color, or hue, due to the surrounding color.

Sine wave Smooth wave pattern resembling the pattern of light waves or pure tones.

Single cell recording Research technique in which small electrodes are placed in a precise location to record action potentials, such as those generated by a single ganglion cell.

Sinusoidal grating (sine-you-soid-ul) Set of blurry stripes that alternate between dark and light.

Size constancy Phenomenon in which an object seems to stay the same size despite changes in its distance.

Size cues Distance information conveyed by relative size.

Size-distance invariance hypothesis Theory of constancy in which the viewer calculates an object's perceived size by combining the object's retinal size and its perceived distance.

Slowly adapting (SA) receptors Kind of touch receptor that responds to steady continuous stimulation (pressure on skin).

Soft palate Region in the upper part of the mouth above the back of the tongue.

Somatosensory cortex Region of the cortex that processes information about touch and taste.

Sone scale Scale of loudness obtained by the magnitude-estimation technique, in which a 40-dB tone at 1000 Hz is assigned a loudness of 1 sone.

Sound pressure level (SPL) A logarithmic scale of sound pressure relative to threshold pressure. It is used to measure amplitude in decibels.

Sounds Successive changes in atmospheric pressure.

Sound spectrogram Diagram that shows the frequency components of speech.

Spacing illusion An illusion in which lines whose ends are separated by a constant amount will seem to be closer together when the lines are tilted (see Figure 6.25).

Spatial frequency analysis approach Approach to shape perception suggesting that to process visual information, the visual system breaks the stimulus down into a series of light and dark stripes. (See also Fourier analysis.)

Spatial frequency channels Channels in the visual system that are sensitive to a narrow range of spatial frequencies.

Special Mechanism account Theory of speech perception positing that speech is processed by a distinct unit separate from that used for other auditory information. (See also Module.)

Specificity theory Theory based on the doctrine of specific nerve energies stating that each kind of skin receptor responds exclusively to only one kind of physical stimulus, and each kind of receptor is responsible for only one kind of sensation.

Specificity theory of pain perception Theory stating that pain is produced by the stimulation of specific pain receptors.

Spectral sensitivity Region of the spectrum in which light is absorbed, such as the region in which a particular kind of cone absorbs light.

Speech spectrogram Diagram that shows the frequency components of speech.

Spinothalamic system (spy-know-thuh-laa-mick) One of the two neuronal systems responsible for the skin senses. It has smaller nerve fibers and slower transmission than the lemniscal system.

Spontaneous acoustic emissions Emissions produced by the ear when no stimulus has been presented.

Stabilized retinal image An image that is kept on the same part of the retina through various means. A stabilized retinal image will ultimately disappear, showing the importance of change for perception.

Standard stimulus The stimulus in discrimination studies that remains constant throughout the experiment.

Stapes (stay-peas) Small stirrup-shaped bone in the middle ear.

Steady state In music perception, the middle portion of a tone.

Stereochemical theory Theory proposed by Amoore that odorous molecules have definite shapes that determine the kind of odor we smell.

Stereocilia Tiny hairs attached to the ends of the inner and outer hair cells. Displacement of the stereocilia causes action potentials to be produced, the first step in auditory perception.

Stereopsis Ability to judge depth with two eyes, as provided by binocular disparity.

Stereoscope Piece of equipment that presents two photographs of a scene taken from slightly different viewpoints; one picture is presented to each eye, creating the impression of depth.

Stereoscopic picture Two pictures, one presented to the right eye and one presented to the left eye, creating the impression of depth.

Stevens's power law (R =kIn) Stevens's power law says that the magnitude of the psychological reaction (R) is equal to a constant (k) multiplied by the intensity (I) of the stimulus, which has been raised to the nth power.

Stimulation deafness experiment An experiment in which an animal is exposed to an extremely high-amplitude tone, which causes damage to the stereocilia. The location of the damage depends on the frequency used.

Stimulation-produced analgesia Procedure in which certain regions of the brain are electrically stimulated, leading to a loss of sensitivity to pain.

Stress-induced analgesia A reduction in pain perception caused by stress.

Striate cortex (strie-ate) Area of the visual cortex where the neurons from the lateral geniculate nucleus terminate, called striate because of its microscopically visible stripes. This area is also called the primary visual cortex and Area 17.

Stroboscopic movement (stroe-buh-skope-ick) Illusion of movement produced by a rapid pattern of stimulation on different parts of the retina.

Subcutaneous tissue Inner layer of skin, which contains connective tissue and fat globules.

Subjective colors Impressions of color that are produced by a black-and-white stimulus (like Benham's top).

Subjective contour Phenomenon in which contours are seen even though they are not physically present; also known as illusory contour.

Substantia gelatinosa Proposed part of the gate-control theory, which produces stimulation with input from the large fibers and inhibition with input from the small fibers.

Subtractive mixture In color mixing, combining dyes or pigments, or placing two or more colored filters together.

Successive color contrast Situation in which the appearance of a color is changed because of another color presented beforehand. (See also Negative afterimage.)

Superior colliculus (kole-lick-you-luss) Portion of the brain important for locating objects and their movement.

Superior olivary nucleus A structure in auditory processing between the cochlear nucleus and the inferior colliculus.

Synapse The gap between neurons across which chemical messages are sent.

Synthetic sense One of the senses in which an observer cannot detect the separate parts; for example, in vision an observer cannot detect the components of a color mixture.





Tadoma method Method of communication in which a deaf person places his or her hands on the lips and jaw of the speaker to pick up tactile information about speech.

Tapetum The equivalent of the human choroid in nocturnal animals. Unlike the choroid, though, the tapetum reflects light rather than absorbing it.

Taste Perceptions that result from the contact of substances with special receptors in the mouth.

Taste bud Receptor for taste stimuli.

Taste modifiers Special substances that change the flavor of other food by modifying the receptors on the tongue.

Taste pore The opening in the taste bud.

Taste tetrahedron Four-sided figure representing one of the four basic tastes (sweet, salty, bitter, and sour) at each of the four corners.

Tectorial membrane Membrane that rests at the top of the organ of Corti in the inner ear.

Template-matching approach Approach to shape perception suggesting that we store specific patterns of information in memory and recognition occurs when we match a newly presented stimulus to a template.

Temporary threshold shift Temporary increase in a hearing threshold as a result of exposure to noise.

Test stimulus In dark adaptation studies, the small spot of light for which the threshold is measured after the lights have been turned off.

Texture gradient Distance cue provided by the fact that the texture of surfaces becomes denser as the distance increases.

The nature-nurture question Are abilities-- such as perceptual abilities -- due to inborn factors (nature), or are they the result of learning and experience (nurture)?

Thermal adaptation Decrease in the perceived intensity of a hot or cold temperature as time passes.

3-D sketch Relating to Marr's theory of space perception, the third step in achieving a 3-D percept. Here the percept changes from viewer- to object-centered, providing a more accurate representation of depth than the 2.5-D sketch.

Timbre (tam-burr) A tone's sound quality.

Tinnitus High-pitched ringing in the ears, caused by a high fever, ear infection, or large doses of aspirin.

Tonality Organization of pitches around one particular tone.

Tone chroma (crow-mah) Similarity shared by all musical tones that have the same name.

Tone height Increase in pitch of a tone that accompanies an increase in frequency.

Tonic One of the 12 pitches within an octave; serves as the tone around which all others in the octave are organized.

Tonometry Technique in which a special instrument is used to measure the pressure inside the eye.

Tonotopic Arrangement in which neurons sensitive to similar frequencies are near one another in the inferior colliculus.

Top-down processing Approach that emphasizes the importance of the observers' concepts and cognitive processes in shaping perception.

Touch adaptation Decrease in the perceived intensity of a repeated tactile stimulus.

Transcutaneous electrical nerve stimulation (TENS) An effective technique for reducing pain produced by a stimulating the surface of the skin

Transduction Process of converting a physical stimulus into a form that can be transmitted through the perceptual system.

Transmission cells Cells proposed by the gate-control theory that are in the spinal cord and receive input from two kinds of neural fibers.

Transposition In a piece of music, changing the pitch of each note while retaining the same spatial relationships.

Traveling wave Pressure wave in auditory processing that travels from the base to the apex of the cochlea.

Trichromatic theory Theory of color vision stating that there are three kinds of color receptors, each sensitive to light from a different part of the spectrum.

Trigeminal nerve A nerve important in olfaction and taste; it has free nerve endings extending into the olfactory epithelium and also registers the spiciness of food such as chili peppers.

Tritanopes (try-tuh-nopes) People who are dichromats and have difficulty with blue shades.

Tritone paradox The tritone paradox involves a misperception of tone heights.

Trompe l'oeil (tromp ley-yeh) Technique in painting that "fools the eye" by creating an impression of depth when the surface is really just two-dimensional.

Turbinate bones Three bones located in the nasal cavity.

Two-alternative forced choice procedure (2AFC) Psychophysical procedure with several variants. In one variant, a person is presented with a stimulus and then must decide which of two subsequent stimuli is identical to the original stimulus. This procedure eliminates consideration of a criterion, because the stimulus is always one of the two subsequently presented stimuli.

Two-point discrimination threshold Point at which the perceiver can determine that two distinct stimuli -- rather than one -- are being presented. For touch perception, this is done by pricking the skin with two pinpoints.

2.5-D sketch Relating to Marr's theory of space perception, the next step in achieving a 3-D percept after the primal sketch is achieved. It is viewer-centered and contains information about motion and the primal sketch.

Tympanic canal Canal in the cochlea.

Tympanic membrane Thin piece of membrane that vibrates in response to sound waves.





Unconscious inference Proposed explanation for constancy in which the observer arrives at a perception via a reasoning-like process without conscious awareness.

Uncrossed disparity Objects behind the horopter create uncrossed disparity, which is a cue that objects are far from us. (See also Horopter.)

Uniform connectedness According to the principle of uniform connectedness, we organize input as a single unit when we perceive a connected region of uniform visual properties, such as lightness, color, and so on.



Velocity detection threshold The minimum velocity that can be detected in motion perception.

Vergence movement Eye movements in which the angle between the lines of sight changes and the eyes move toward or away from each other.

Version movement Eye movement in which the angle between the lines of sight remains constant and the eyes move in the same direction.

Vestibular canal (ves-tih-bue-lur) Canal in the cochlea on which the stapes rests.

Vestibular sense System that provides information about orientation, movement, and acceleration.

Vestibuloocular reflex (VOR) The vestibuloocular reflex (VOR), coordinates vestibular information with eye muscle function, which serves to stabilize our view of the world

Virtual lines Lines that are not actually present in a display, but are "created" by our perceptual system to organize the display into "objects." (See also Illusory contours.)

Visual acuity Ability to see fine details in a scene.

Visual agnosia Due to temporal lobe damage, a person with visual agnosia has intact basic visual abilities but cannot identify a picture of an object.

Visual angle Size of the angle formed by extending two lines from the observer's eye to the outside edges of the target.

Visual cliff Kind of apparatus in which infants must choose between a side that looks shallow and a side that looks deep.

Visual cortex Portion of the cerebral cortex that is concerned with vision.

Vitreous humor (vit-ree-us) Thick, jellylike substance found within the eye, behind the lens.

Vocal tract Anatomical structures involved in speaking, located above the vocal cords.

Voiced consonant Consonant that is spoken with vibration of the vocal cords.

Voiceless consonant Consonant that is spoken without vibration of the vocal cords.

Voice onset time (VOT) In speaking, the VOT is the time before the voiced part of the vowel begins.

Voicing One of the three dimensions for consonants; voicing specifies whether the vocal cords vibrate.

Volley principle Proposal that was added to the frequency theory of auditory processing, which stated that clusters of neurons could "share" in producing a required firing rate.

Vomeronasal organs Olfactory sense organs located on either side of the septum, which separates the two nostrils.





Water taste Distinct taste for water following adaptation to another taste; for example, water tastes sweet after adaptation to a sour substance.

Wavelength The distance a wave (e.g., of light or sound) travels during one cycle.

Weber's fraction (k) Number obtained in discrimination studies that represents the change in stimulus intensity divided by the original intensity.

Weber's law (DI/I = k) Weber's law says that if we take the change in intensity (DI) and divide it by the original intensity (I), we obtain a constant number (k).

Word-apprehension effect Word-superiority effect.

Word-superiority effect Phenomenon in which letters are perceived better when they appear in words than in strings of unrelated letters.



Zero-crossing Related to edge perception; the point of a change in intensity within the visual field.

Zonules Tiny fibers that connect the lens and the ciliary muscle.