Glossary of Perception Terms


























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. Responsible for most of the bending of light to bring it into focus on the retina.

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 read 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.

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-shun) 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-ree-ay) 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 sound wave 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. There are two types of glaucoma (open-angle glaucoma and closed-angle glaucoma) determined by the way in which the aqueous humor is blocked.

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  Studies in which sound stimuli are presented to the listener by headphones rather than speakers, giving the impression that the sound is inside the listener's head rather than outside it (these would be localization studies).

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.

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.