GLOSSARY OF TERMS IN SENSORY SYSTEMS AND PERCEPTION

a priori knowledge Knowledge that exists regardless of whether an individual becomes aware of it through experience (from the Latin for "from beforehand")

absolute threshold The hypothetical construct of a minimum amount of a particular form of physical energy (e.g., mechanical pressure of sounds, electrochemical scents or tastes) that reaches a sensory receptor, which is sufficient for the individual to detect that energy (stimulus); hypothetically, a person will be able to sense any stimuli that are at or above the absolute threshold, but no stimuli that are below that threshold

accommodation The process by which curvature of the lens changes in order to focus on objects at different distances

achromatic Lacking color; usually refers to stimuli that lack both hue and saturation, but that may differ in terms of brightness (from a-, absence of, not; chroma-, color)

acoustic nerve The bundle of sensory neurons that lead from the hair cells in the inner ear to the portion of the cerebral cortex (primarily the temporal lobe) that processes auditory information (also termed the auditory nerve)

acuity The sharpness of sensation in a given sensory mode

adaptation A temporary physiological response to a sensed change in environment (e.g., see dark adaptation, light adaptation), which is generally not subject to conscious manipulation or control, and which usually does not depend on previous experience with the given type of environmental change

additive mixture The blending of various wavelengths of light (such as spotlights), which add together to produce a summative effect of the combined wavelengths (cf. subtractive mixture)

adequate stimulus A stimulus of sufficient intensity to induce an action potential in a neuron.

afferent Neural pathway in which sensory information is transmitted to the brain and central nervous system.

aftereffects Misperceptions of colour, size, shape, movement, or orientation experienced while viewing a particular test stimulus of a partiuclar colour, shape, intensity, or orientation.

afterimages Misperceptions of colour or brightness and/or size and shape that occur at the retina. Unlike aftereffects, afterimages can be observed in the absence of an external stimulus (e.g., with eyes closed). Afterimages obey Emmert's law of afterimage size, aftereffects do not.

agnosia A severe deficit in the ability to perceive sensory information, usually related to the visual sensory modality; agnosics have normal sensations but lack the ability to interpret and recognize what they sense, usually resulting from lesions in the brain (a-, lack; gnosis, knowledge [Greek])

amacrine cells One of three kinds of interneuron cells in the middle of three layers of cells in the retina; the amacrine cells and the horizontal cells provide lateral connections, which permit lateral communication with adjacent areas of the retina in the middle layer of cells (cf. bipolar cells; see ganglion cells, photoreceptors)

amplitude The objective physical intensity of sound or light; when sound or light energy is displayed on a visual display such as an oscilloscope, higher wave crests correspond to greater intensity; in terms of subjective perception, greater amplitude of light is perceived as increased brightness, and greater amplitude of sound is perceived as increased loudness

association areas Regions of the cerebral lobes that are not part of the sensory (visual, auditory, somatosensory) or motor cortices, believed to connect (associate) the activity of the sensory and motor cortices

association of ideas Related to the school of thought –Associationism – that examines how events or ideas can become associated with one another in the mind, thereby resulting in a form of learning. John Locke was prominent in promoting this point of view.

attention The active cognitive processing of a limited amount of information from the vast amount of information available through the senses, in memory, and through cognitive processes

basilar membrane One of the membranes that separates the fluid-filled canals of cochlea; the physiological structure on which the hair cells (auditory receptors) are arranged; vibrations from the stapes stimulate the hair cells on the membrane in various locations, in association with differing sound frequencies

Bell-Magendie law Based on the discovery that sensory (afferent) fibres enter the spinal chord at a posterior (dorsal) nerve root, and that motor fibres leave the spinal chord by an anterior (ventral) root; led to the separation in the physiology of the nervous system into sensory and motor function

binocular depth cues One of the two chief means of judging the distances of visible objects, based on the two different angles from which eye views a scene, which leads to a disparity of viewing angles that provides information about depth (bi-, "two"; ocular, pertaining to the eye; cf. monocular or pictorial depth cues)

binocular disparity The discrepancy in the viewpoint of each eye due to the slightly different positions of each eye, which leads to slightly different sets of sensory information going to the brain from each of the two optic nerves; in the brain, the information is integrated in order to make determinations regarding depth, as well as height and width

biological Transducer - See receptor

bipolar cells One of three kinds of interneuron cells in the middle of three layers of cells in the retina; provide vertical connections, which permit communication between the ganglion cells in the first, outermost layer of the retina and the photoreceptors in the third, innermost of the three layers of retinal cells (cf. amacrine cells, horizontal cells)

blindsight A condition usually associated with damage to cells in primary visual cortex (V1) or the optic radiations projecting to V1. The defective parts of the visual field corresponding to damage/lesion is known as a scotoma. When asked to locate a stimulus presented in the defective regions of their visual field, blindsight patients do better than chance, even though they report not being consciously aware of the stimulus

blind spot The small area on the retina where the optic nerve leaves the eye, pushing aside photoreceptors to exit the eye; although people cannot see images in the region of the blind spot, it normally does not impair vision because the visual field of the blind spot of one eye falls within the normal visual field of the other eye, and the brain integrates the information from both eyes to compensate for the blind spot in each eye

brightness The psychological perception of light intensity, rather than the actual physical quantity of light intensity, based on light-wave amplitude

bottom-up processes An approach to perceptual processing that begins with the analysis of simple, basic sensory features, such as luminance differences and spatial frequencies, which are then integrated to form identifiable patterns and shapes

inference A conclusion regarding one or more antecedents that are believed to have led to a given consequence. One view of perception is that it involves a process analogous to the drawing of inferences in everyday reasoning. Whereas in the latterinferences are open to conscious awareness, however, perceptual inferences are presumed to be unconscious (after the sensory physiologist Helmholtz)

chromatic aberration Distortion of chromatic retinal images by the lens due to greater refraction of short wavelengths than of long ones

ciliary muscle Muscle that changes the shape or curvature of the lens of the eye and promotes accommodation

clairvoyance One of several forms of extrasensory perception (ESP), in which an individual allegedly perceives objects or events for there is no apparent stimulation of the known senses (clair-, "clear"; -voyance, related to seeing)

closure A Gestalt principle of form perception (see Gestalt approach): the tendency to complete (perceptually to close up) objects that are not actually complete

cochlea The coiled and channeled main structure of the inner ear, which contains three fluid-filled canals that run along its entire convoluted length; the fluid-filled canals are separated by membranes, one of which is the basilar membrane, on which thousands of hair cells (auditory receptors) are arranged and are stimulated by the vibration of the stapes

cocktail party phenomenon The process of tracking one conversation in the face of the of other conversations, a phenomenon often experienced at cocktail parties

color constancy A form of perceptual constancy in which an individual continues to perceive a color as being constant, even though the sensation of the hue changes, due to changes in the light shining on the object

complementary colours The hues of two wave-lengths that, when mixed in the correct proportions, yield achromatic gray or white. complementary colours lie opposite each other on teh colour circle

complex cells Cells in primary visual cortex described by David Hubel and Torsten Wiesel in the 1960s. Any given simple cell, or groups of such cells, may prompt the complex cell to fire in response to lines of orientations anywhere in the receptive field for the given complex cell; the particular type of light/dark contrasts of a line segment appear not to affect the firing of the complex cell, as long as the line segment demonstrates the appropriate orientation; however, for some complex cells, the length of the line segments may also play a role in whether the cells fire

computerized axial tomogram/tomography (CAT) A highly sophisticated X-ray-based technique that produces pictures (-gram, "drawing" or "recording") of cross-sectional slices (tomo-, Greek for "slice" or "cut") of the living brain, derived from computer analysis of X rays that pass through the brain at various angles around a central axis in the brain (often termed CAT scan); usually used clinically to detect blood clots, tumors, or brain diseases, but also used experimentally to study how particular types and locations of brain damage (lesions) affect people's behavior

conductive hearing loss Deficiency in hearing due to a defect in the conduction mechanism of the auditory system. Hearing loss is distributed aobut equally over all frequencies. Also known as transmission hearing loss.

cones One of the two kinds of photoreceptors in the eye; less numerous, shorter, thicker, and more highly concentrated in the foveal region of the retina than in the periphery of the retina than are rods (the other type of photoreceptor); virtually nonfunctional in dim light, but highly effective in bright light, and essential to color vision (see fovea)

consciousness The complex phenomenon of evaluating the environment and then filtering that information through the mind, with awareness of doing so; may be viewed as the mental reality created in order to adapt to the world

contingent aftereffects The class of aftereffects that results from continued stimulation and selective adaptation or fatigue of combinations of specific stimulus features. Accordingly, the resultant aftereffect is linked to and contingent on the presence of one of the adapted stimulus features. The McCollough effect is the classic example of contingent aftereffects.

convergence (ocular) The tendency of the eyes to turn toward each other in a coordinated action to fixate on targets located nearby

continuity Characterized by a lack of interruption; sometimes used to describe one of the Gestalt principles of form perception (see Gestalt approach): the tendency to perceive smoothly flowing or continuous forms rather than disrupted or discontinuous ones

contour The features of a surface that permit differentiation of one surface from another (e.g., convexity or concavity)

contralateral Occurring or appearing on the opposite side (contra-, oppo-site; lateral, side); often used for describing the crossed pattern of sensory and motor connections between the physiological structures of the body and those of the brain (cf. ipsilateral)

cornea The clear dome-shaped window that forms a specialized region of the sclera (the external layer that holds in the gelatinous substance of the eye), through which light passes and which serves primarily as a curved exterior surface that gathers and focuses the entering light, making gross adjustments of the curvature in order to focus the image relatively well

correct rejection One of the four possible combinations of stimulus and response, according to signal-detection theory (SDT) (cf. false alarm, hit, miss): the accurate recognition that a signal stimulus was not detected

dark adaptation The physiological response to a reduction of light intensity in the environment, characterized by an increase in pupil size a , and an increase in visual sensitivity to light by a factor of as much as 100,000; usually takes about 30 - 40 minutes for full dark adaptation to occur (cf. light adaptation)

decibel (dB) The customary unit of measurement for the intensity of sound; 0 (zero) decibels is the absolute threshold for normal human hearing

depth As applied to perception: the perceived distance of something from the body of the perceiver (see monocular depth cues, binocular depth cues)

differentiation A progressive developmental change from the general to the particular and from the simpler to the more complex which characterises embryological development. According to some theorists, the same pattern holds for the development of behaviour after birth

direct perception One of the two key views of perception (cf. constructive perception): asserts that the array of information in the sensory receptors, including the sensory context, is all that is for an individual to perceive anything; according to this view, prior knowledge or thought processes are not necessary for perception (see feature matching)

discrimination The ability to report the difference between one stimulus and another

distal stimulus An external source of stimulation as it exists in the world, which may differ somewhat from the internal sensation of the source of stimulation that is detected in the sensory receptors (cf. proximal stimulus; see also perceptual constancy)

divided attention The ability to allocate attentional resources simultaneously to several ongoing sets of events

duplex retina A psychophysical principle recognizing the existence of two separate visual systems, one of which is for vision in dim light (which depends on the rods), and the other of which is responsible for vision in brighter light (which depends on the cones)

duplicity theory of audition The view of human pitch perception that gives credence to both place theory and frequency theory

eardrum A physiological structure of the outer ear, which vibrates in response to sound waves that have moved through the canal from the pinna; its vibrations are passed to the middle ear, where it transfers its vibrations to a series of ossicles (see incus, malleus, stapes), such that higher frequencies of sound cause more rapid vibrations (also termed tympanum)

ecological approach See direct perception, evolution, natural selection

effectors The neurons and nerves that transmit motor information (e.g., movements of the large and small muscles) either from the brain through the spinal cord to the muscles (for voluntary muscle movements) or directly from the spinal cord to the muscles (in the case of reflexes), thus controlling bodily responses (cf. receptors; see motor neuron)

efferent signals Neural excitations that carry signals from the brain to muscle and organ tissue

Emmert's law The size of afterimages varies directly as a function of distance of viewing surface (as distance decreases, so too does the apparent size of the afterimage

encephalisation The process in the evolution of species referring to increasing specialization of function at the anterior, or head end of animals (from 'encephalon' meaning "in the head," "brain")

empiricism and classical empiricism A philosophical school of thought that the only basis for knowledge is sensory perception, and all else is idle conjecture. Related to logical positivism.

epistemology That area of philosophy dealing with questions concerning the nature and origins of knowledge (see empiricism, rationalism)

eustachian tube Tube that connects the middle ear chamber with the back of the mouth. The tube permits pressure from the outside to be equalised with air pressure in the middle ear. This is accomplished when the mouth is opened.

evolution See natural seclection, direct perception

false alarm A response in which an individual inaccurately asserts that a signal stimulus has been observed; in signal-detection theory (SDT), the inaccurate belief that a signal stimulus was detected when it was actually absent (cf. correct rejection, hit, miss)

feature detectors See single cell revolution

Fechner's law The principle that relates the psychological magnitude of a to the physical magnitude of the stimulus that prompts the sensation, by noting the following relation: S = K log I, where S is the magnitude of sensation elicited by a stimulus, I is the physical magnitude of the stimulus (as in Weber's law), and K is a constant (based on the value of the Weber fraction)

figure-ground segregation A Gestalt principle of form perception (see Gestalt approach): the tendency to perceive that an object in or an aspect of a perceptual field seems prominent (termed the figure), other aspects or objects recede into the background (termed the ground)

fovea The central region of the retina. It is a small indentation about 0.3 mm across, subtending a visual angle of 1 degree to 2 degrees. The fovea contains primarily cone photorecptors

free nerve endings Sensory receptors in the skin, which lack the globular swellings that characterize some other somatosensory receptors

frequency In psychophysical, sensory contexts, applies to the number of waves of sound or light that occur within a specified interval, usually a second; in sound waves, higher frequencies are associated with higher pitches of sounds; in light waves (which are usually measured in terms of wavelengths, which are inversely related to frequencies), various frequencies are associated with various colors in the visible electromagnetic as well as with various other forms of radiance (e.g., microwaves or gamma waves)

frequency theory in audition One of two views of the way in which humans sense pitch (cf. place theory): The basilar membrane reproduces the vibrations that enter the ear, triggering neural impulses at the same frequency as the original sound wave, so that the of the impulses that enter the auditory nerve determines the number of electrical responses per second in the auditory nerve; these responses are then sensed as a given pitch by the brain (see also duplicity theory)

functionalism A school of thought in the history of the psychological sciences that focuses on active psychological processes (cf. passive psychological structures or elements of mind as in 'structuralism"); for example, functionalists were more interested in how people think than in what they think, in how people perceive rather than in what they perceive. The same ideas in the broader biological context emphasise how and why organisms evolve as they do rather than in what particular outcomes are produced by the evolutionary process (biological structuralism)

functional equivalence The idea that some functional aspects of perception (the outcomes of what people do when they perceive) have corresponding counterparts in mental imagery (cf. structural equivalaence)

fundamental frequency The lowest tone of the series of tones produced by a sound-emitting instrument. Also called the first harmonic.

ganglion cells Cells that form the first of three layers of cells in the retina; the axons of these cells form the optic nerve and communicate with the photoreceptors (in the third layer) via the middle layer of cells in the retina (cf. amacrine cells, bipolar cells, horizontal cells)

gestalt The distinctive totality of an integrated whole, as opposed to merely a sum of various parts (from the German word Gestalt)

Gestalt psychology A school of psychological thought, which holds that psychological phenomena are best understood when viewed as organized, structured wholes, not analyzed into myriad component elements (Gestalt, form). The school was derived from studies of visual form perception – based on the notion that the whole of the form is greater than the sum of its individual parts (Gestalt, form ; see also closure, continuity, figure-ground, proximity, similarity, symmetry)

hair cells The thousands of specialized hairlike appendages on the basilar membrane, which function as auditory receptors, transducing mechanical energy from the vibration of the stapes into electrochemical energy that goes to the sensory which carry the auditory information to the brain (see transduce; see also cochlea)

haptic Term coined by Geza Revez to refer to the active perception of objects through touch, pressure, temperature, and kinesthesis

harmonics Distinctive tones that musical instruments generate, along with the fundamental frequency of the note being played, which are higher multiples of the fundamental frequency (cf. noise); different musical instruments yield distinctive multiples of the fundamental frequencies, resulting in the distinctive tonal qualities of the instruments

hertz (Hz) A frequency of one cycle per second, often applied to sound waves

hit One of the four possible combinations of stimulus and response described in signal-detection theory (SDT) (cf. correct rejection, false alarm, miss): the accurate recognition that a signal stimulus was detected, which was truly present

horizontal cells One of three kinds of interneuron cells in the middle of three layers of cells in the retina: The amacrine cells and the horizontal cells provide lateral connections, which permit communication with adjacent areas of the retina in the middle layer of cells (cf. bipolar cells; see ganglion cells, photoreceptors)

hue Physical properties of light waves that correspond closely to the psychological properties of color, which is the subjective interpretation of the physiological processing of various wavelengths of the narrow band of visible light within the electromagnetic spectrum human

hyperopia Refractive error of the lens of the eye in which the image formed of a nearby target falls on a focal plane behind the retina. Also known as farsightedness

impedance mismatch The difference in the resistance of sound pressure transmitted from the middle ear to the inner ear, due to the change from the airborne vibrations of the middle ear cavity to the fluid-filled inner chambers of the cochlea

incus One of the three bones of the middle ear (cf. malleus, which normally receive and amplify the vibrations transmitted by the tympanum (eardrum) and then transmit those vibrations to the cochlea. Also known as the anvil.

indirect perception One of the two key views of perception (cf. direct perception); assertion that the perceiver constructs the stimulus that is perceived, using sensory information as the foundation for the structure, but also considering the existing knowledge and thought processes of the individual; in this view, cognitive processes are considered as the prototype for perception

interposition See monocular and/or pictorial depth cues.

introspection Self-examination of inner ideas and experiences, used by early psychologists as a method of studying psychological phenomena (intro-, "inward, within"; -spect, "look"). In the history of experimental psychology, analytical introspection was a highly disciplined technique of self-observation and mental analysis used by the nineteenth-century structuralists to uncover the fundamental units of sensation.

iris Circular diaphragm-like structure forming the coloured portion of the eye that controls the size of the pupil opening

just noticeable difference (jnd) The minimum amount of difference between two sensory stimuli that a given individual can detect at a particular time and place. Variations in observations between and within indvividuals, measurement error in psychophysics, can be interpreted by averaging data from multiple trials; operationally defined as the difference between two stimuli that can be detected 50% of the time (sometimes termed the difference threshold) (cf. absolute threshold)

kinaesthesis The perception of body-part position and movement in space of the limbs and other mobile parts of the jointed skeleton

lateral geniculate nucleus (LGN) Relay centre for vision located in teh thalamus. Neural fibres from the LGN project to the visual area in the occipital lobe of the cortex

law/doctrine of Specific Nerve Energies (Johannes Müller) There are three main assertions: (i) We are aware not of objects, but only the activity of the nerves; (ii) there are five kinds of nerves, and each imposes its specific quality on the mind (or sensorium); and (iii) the same stimulus affecting different nerves gives rise to the different qualities appropriate to the particular nerves, and, conversely, different stimuli affecting the same nerve always give rise to the specific quality for that nerve

lens A curved interior structure in the eye, which bends (refracts) light and complements the cornea's gross adjustments in curvature, by making fine adjustments in the amount of curvature in order to focus the image as clearly as (cf. cornea)

lobes Each of the four major regions of the cortex – frontal lobe, occipital lobe, parietal lobe, temporal lobe

loudness The attribute of an auditory sensation in which tones are ordered from soft to loud. Loudness is primarily determined by the amplitude of a sound wave.

mental telepathy Communication from one mind to another at a distance other than through known senses

metaphysics A branch of enquiry that deals with fundamental questions about BEING, and about what kinds of things there are in the world.

mind-body problem Concerns the question of how the mind and the body are related. Are they two different things (Dualism); or two 'aspects' of one thing (see Monism)?

magnetic resonance imaging (MRI) An imaging technique for revealing high-resolution pictures of the structure and function (functional MRI, or fMRI) of the living brain by computing and analyzing magnetic changes in the energy of the orbits of nuclear particles in the molecules of the body (also sometimes termed NMR, for nuclear magnetic resonance); produces clearer and more detailed images than computerized tomography (CAT) scans and uses no X radiation maintenance

malleus One of the three bones of the middle ear, which normally receive and amplify the vibrations transmitted by the tympanum (eardrum) and then transmit those vibrations to cochlea (cf. incus, stapes). Also known as the hammer.

medulla oblongata An elongated interior structure of the brain, located at the point where the spinal cord enters the skull and joins with the brain; forms part of the reticular activating system. In sensory processing it is the site where nerves from the right side of the body cross over to the left side of the brain, and nerves from the left side of the body cross over to the right side of the brain (see contralateral)

mental imagery and visualization Ability either to imagine oneself in spatial surroundings, or to spatially manipulate mental images of objects in the 'mind's eye' (e.g., mental rotation)

monism A philosophical belief that the body and mind are unified, based on the belief that reality is a unified whole, rather than separated in terms of physical substance versus nonphysical mind (mon[o]-, one; -ism, set of beliefs, school of thought, or dogma [Greek]) (cf. mind-body dualism). In the history of perception of the more well known proponents of monism was Gustav Fechner (i.e., panpsyhcism).

monocular depth cues See pictorial depth cues.

motion parallax See pictorial depth cues

motor Characterized by the movement of muscles (e.g., psychomotor -- motor skills associated with psychological processes)

Muller-Lyer Illusion An optical illusion in which two equally long line segments are perceived to differ in length because one of the line segments is braced by inward-facing arrowhead-shaped diagonal lines, but the other line segment is braced by outward-facing arrowhead-shaped diagonal lines; an optical illusion, which causes the observer to perceive that two equally long line segments differ in length; may be an artifact of some of the monocular depth cues with which perceivers are familiar (cf. Ponzo illusion)

Myopia Refractive error of the lens of the eye in which the image of a distant target is brought ot a focus in front of the retina. Also known as nearsightedness

Nanometer (nm) A billionth of a meter.

nativism In the context of perception, the notion that meaning and organization is inherent in the biological structure of the organism; therefore, experience and learning play a comparatively small role (see rationalism).

natural selection Evolutionary principle describing a mechanism by which species have developed and changed, based on what is commonly called the "survival of the fittest," in that those species that are best suited for adapting to a given environment are the ones most likely to reach sexual maturity and to produce offspring, thereby increasing their of surviving as a species; that is, the species that are best suited for adapting to a given environment are then selected by nature for survival

neonate Newborn (neo-, "new"; -nate, "born")

nerve Bundle of neurons; many neurons can be observed as fibers from the brain down through the center of the back (in the central nervous system) and then out to various parts of the body (in the peripheral nervous system)

nervous system Physiological network of nerves that form the basis of the ability to perceive, adapt to, and interact with the world; the means by which humans and other vertebrates receive, process, and then respond to messages from the environment and from inside our bodies

neurotransmitter Chemical messenger that is released by the terminal buttons on the axon of a presynaptic neuron and then carries the chemical messages across the synapse to receptor sites on the receiving dendrites or soma of the postsynaptic neuron (cf. neuromodulator; see also acetylcholine, dopamine, serotonin)

noise In sound, a confusing, nonsensical, and often unpleasant stimulus that results when the note of a fundamental frequency is accompanied by irregular and unrelated sound waves, rather than by multiples of the fundamental frequency (cf. harmonics). The concept is used by analogy in Signal Detection Theory (SDT) to refer to random background events that have the potential to impair the detection/discrimination of a signal.

occipital lobe One of the four major regions of the cerebral cortex (cf. frontal lobe, parietal lobe, temporal lobe); chiefly responsible for visual processing

olfaction Sense of smell, which is chemically activated by airborne molecules that can dissolve in either water or fat. The olfactory epithelium (skin) in the nasal membranes is analagous to the retina vision, and the basilar mebrane in audition. Scent molecules contact the olfactory receptor cells and then initiate the transduction of the chemical energy of the odors into the electrochemical energy of neural transmission. At the olfactory bulb each olfactory nerve directly synapses with sensory neurons, bypassing the thalamus and instead going directly either to the olfactory cortex in the temporal lobe or to the limbic system (e.g., the hypothalamus)

opponent-process theory of color vision One of the two major theories of color vision (cf. trichromatic theory of color vision): based on the notion of three opposing processes in human vision, two of which contrast each of two colors with another (yielding four fundamental colors -- red/green and yellow/blue), and one of which contrasts black and white as a third opposing set of achromatic primaries that are perceived in much the same way as are the other opposing pairs

organ of Corti Cochlear structure containing the auditory receptors. It lies between the basilar and tectorial membranes.

optic chiasma The place in the occipital lobe of the brain where neural fibers carrying visual information cross over from one side of the body to the contralateral hemisphere of the brain (chiasma, "X-shaped or crossed configuration")

optic disk Region of the retina where the optic nerve fibres leave the eye. There are no photoreceptors in this area and thus no visual response when light strikes this region. The corresponding visual field is termed the blindspot

ossicles Three small bones of the middle ear that conribute to the conduction of sound to the inner ear: the malleus, incus, and stapes.

outer hair cells Specialised hair cells that lie on the organ of Corti and are the transducers for sound; register the presence of weak auditory signals and may be loudness detectors.

oval window A membrane over the inner ear cavity that is connected to the footplate of the stapes; the motion of the stapes causes it to vibrate which, in turn causes mechanical activity in the inner ear.

parallel processing Multiple operations processed simultaneously; as applied to attention, the properties of objects are processed in different channels at the same time (cf. serial processing)

parapsychology A branch of psychology concerned with phenomena that are not presently explained by the application of known psychological principles

perception The set of psychological processes by which people recognize, organize, synthesize, and give meaning (in the brain) to the sensations received from environmental stimuli (in the sense organs) (cf. sensation) perceptual constancy The perception that a given object remains the same even when the immediate sensation of the object changes (see color constancy, lightness constancy, shape constancy, size constancy)

period 1) The time for one complete cycle, vibration, or oscillation. 2) The time required for a single wave to pass a given point.

permanent threshold shift (PTS) The permanent effect on hearing due to chronic or extended exposure to intense noise.

phase The arrival of a sound wave specified with respect to the phase of its cycle. Two sound waves that are at different phases within a cycle when they arrive at the two ears - for example, compressions occurring at different times relative to each other - change the quality of the sound and may serve as a cue for sound localization.

phase angle The difference between periodic waveforms expressed as an angle between 0 and 360 degrees (one cycle)

phase-locked (time-locked) The neural phenomenon that the firing pattern of auditory nerve fibers is synchronized with the frequency of the stimulating sound wave; hence, the neural activity to a sound wave is time-locked to its frequency.

phenomenology The approach which stresses the fundamental importance of conscious experience – and the method of qualitative analysis – in understanding psychological fact. Historically, proponents of phenomenological method were Goethe, Mach, Purkinje, and Hering. The term was imported into psychology by Husserl in the early part of the 20th century, and popularised by the Gestalt movement.

photon The quantum unit of light energy

photopic vision Vision accomplished with cones

philosophy A system of ideas or a set of fundamental beliefs; a means of seeking to explore and understand the general nature of many aspects of the world (see also materialistic philosophy)

photopigments Chemical substances that absorb light, thereby starting the complex transduction process that transforms physical electromagnetic energy into an electrochemical neural the rods and the cones contain different types of photopigments; different types of photopigments absorb differing amounts of light, and some detect different hues (see photoreceptors) photoreceptors The physiological structures in the retina of the eye that transduce light energy into electrochemical energy, thus enabling the eye to see; located in the innermost layer of the retina, farthest from the light source; the two kinds of photoreceptors are the rods and the cones (see also photopigments)

physiology Scientific study of living organisms and of life-sustaining functions and processes (in contrast to anatomy, which the structures of living organisms)

pictorial depth cues One of the two chief means of judging the distances of visible objects (cf. binocular depth cues), based on sensed information that can be represented in just two dimensions and observed with just one (mono-) eye (ocular): aerial perspective -- the observation that nearer objects appear to be more highly resolved and more clearly distinct than farther objects, which appear to be hazier (occurs because farther objects are observed through greater numbers of moisture and dust particles, whereas closer objects are observed through fewer such particles); interposition -- the observation that an object that appears to block or partially obstruct the of another object is perceived as being nearer, whereas the blocked object is perceived to be farther away, such that the blocking object is perceived to be closer to the observer and in front of the blocked object; linear perspective -- the observation that parallel lines seem to converge as they move farther into the distance; motion parallax -- the perception of stationary objects from a moving viewpoint, such that if an observer visually fixates on a single point in the scene, the objects that are closer to the observer than is the fixation point appear to be moving in the direction opposite to the direction in which the observer is moving, whereas objects farther from the observer than is the fixation point will appear to be moving in the same direction as the observer (also, objects closer to the observer appear to be moving more quickly than objects farther from the observer); relative size -- the observation that things that are farther away appear to be smaller in the retina, and the farther away the object, the smaller is its image on the retina; texture gradient -- the that the relative sizes of objects decrease and the densities of distribution of objects increase as objects appear farther from the observer

pinna Outer part of the ear, which collects sound waves

pitch Perceived height of a tone sounds (high note; low note), based on the frequency of the sound wave that reaches the auditory receptors

place theory One of the two alternative views of the way in which humans sense pitch (cf. frequency theory; see also duplicity theory); suggests that the sensation of pitch is determined by the location on the basilar membrane where the sound wave vibrates the hair cells; thus, hair cells located at various places on the basilar membrane vibrate in response to sounds of different frequencies and then stimulate different sensory neurons, which then determine the pitch that is perceived

posterior From behind

precognition Awareness of an event before (pre-, "before") the event takes place (see extrasensory perception)

primary colors The three colors (red, green, and blue) that can be combined additively to form all other colors (see also additive mixture, trichromatic theory of color vision)

primary (striate) cortex The regions of the brain's lobes that serve as gateways for subsequent sensory function and motor function. The primary visual cortex is in the occipital lobes, and pathways project to areas of speciaised function in extrastriate and association areas of cortex. In the case of motor function, the frontal lobes specialise in the planning, control, and execution of movements, particularly those involving any kind of delayed response; this portion of the cerebral cortex can be mapped to show the places in the brain control specific groups of muscles in the body. Primary somatosensory cortex is found in the parietal lobes (located directly behind the primary motor cortex in the frontal lobe) that receives information from the senses about pressure, texture, temperature, and pain; this portion of the cerebral cortex can also be mapped to show the places in the brain that receive sensory information from precise locations on the surface of the body.

projections The areas in the cortical lobes where sensory and motor processing occurs; sensory projection areas are the locations in the cerebral cortex to which sensory neurons are projected via the thalamus from elsewhere in the body; motor projection areas are the regions that project motor neurons downward through the spinal cord, via the peripheral nervous system, to control desired movement of the appropriate muscles

proximal stimulus The internal locus of stimulation at the sensory receptors (biological transducers), regardless of whether the internal sensation exactly matches the external source of stimulation as it exists in the world (cf. distal stimulus)

proximity (as a Gestalt principle of perception) A Gestalt principle of form perception (see Gestalt approach): the tendency, when viewing an assortment of objects, to perceive objects that are close to each other as forming a group within the assortment

psychokinesis Hypothetical ability to move objects by thought alone, as in trying to bend metal objects via mental concentration (psycho-, "mind"; -kinesis, "movement"; see extrasensory perception)

psychology The study of the mind and of the behavior of people and other organisms

psychometric Characterized by psychological measurement (psycho-, "pertaining to the mind or mental processes," -metric, "measurement")

psychophysics The study and measurement of the functioning of the senses, which involves the attempt to measure the relationship between a form of physical stimulation and the psychological sensations produced as a consequence

pupil The hole in the iris (roughly in its center) through which light gains access to the interior of the eye, particularly the retina; in dim light, the pupil reflexively expands, more light to enter, but in bright light, it reflexively contracts, limiting the amount of light that can enter the eye

purkinje shift The shift in relative brightness of lights from the two ends of the spectrum as illumination decreases owing to the shift from photopic (cone) to scotopic (rod) vision

purity The extent to which a hue cannot be analyzed in terms of a combination of other hues (see also additive mixture, subtractive mixture)

quality The nature of a stimulus that reaches a sensory receptor and is then sensed in the brain (cf. intensity)

rationalism A school of thought (philosophy/epistemology) whereby the means of obtaining information by using philosophical analysis and reasoning in order to understand the world and people's relations to it (from the Latin ratio, meaning "reason" or "thought"; cf. empirical method). A rationalist is a person who believes that knowledge is most effectively acquired through rational methods (cf. empiricism). In practice, rationalism seems to go hand in hand with nativism – the idea if some inborn natural order (see a priori knowledge)

receptive field The region of the external world from which a receptor cell receives sensory information

receptors Physiological structures designed to receive something (e.g., a given substance or a particular kind of information), which may refer either to (a) the structures that receive external stimulation and transduce it into electrochemical sensory information; or to (b) the structures that receive electrochemical sensory information; sensory receptors are physiological structures that provide a mechanism for receiving external stimulation (from outside the body), which can then be transduced into sensation as electrochemical sensory information within the body; receptor nerves and neurons receive electrochemical sensory information (e.g., sensations in the eyes, ears, and skin) from sensory receptors (biological transducers), or from other sensory neurons and transmit that information back up through the spinal cord to the brain (cf. effector, interneuron, motor neuron)

refraction The degree to which light waves are bent, usually by curvature of the surface of the medium (e.g., a lens) through which the light waves are passing

relative size See pictorial depth cues

retina A network of neurons extending over most of the posterior surface of the interior of the eye, containing the photoreceptors responsible for transducing electromagnetic light energy into neural electrochemical impulses (see amacrine cells, bipolar cells, ganglion cells, horizontal cells; see also cones, photopigments, rods)

reversible figures Pictures in which each of a given pair of adjacent or even interconnecting figures can be seen as either figure or ground, although both cannot be the focus of perception simultaneously (see figure-ground); Figure ground relationships are ambiguous (hence ambiguous figures; or multistable figures)

rods One of the two kinds of photoreceptors in the eye; more numerous, longer, thinner, and more highly concentrated in the periphery of the retina than in the foveal region of the retina than are cones, the other type of photoreceptor; function more effectively in dim light than in bright light, but incapable of color vision

scotopic vision Vision accomplished with rods

selective attention the ability to allocate attentional resources to a particular subset of ongoing events

sensation The neural information that the brain receives from the sensory receptors (cf. perception)

sensory coding The way in which sensory receptors transform a range of about various stimuli, which arrives in a variety of forms of energy, changing that information into electrochemical representations that signify the various kinds of information sensory

neurons Nerve cells that receive information from the environment through sensory receptors and then carry that information away from the sensory receptors and toward the central nervous system

serial processing Successive operations in which each operation is executed one at a time, in a series (cf. parallel processing)

shape constancy A form of per-ceptual constancy, in which an individual continues to perceive that an observed object retains its shape, even though the actual retinal events corresponding to the shape of the object change

signal-detection theory (SDT) A psychophysical theory that posits four possible stimulus-response pairs: a hit, a miss, a false alarm, or a correct rejection

similarity A Gestalt principle of form perception (see Gestalt approach): tendency to group various objects in the visual field, based on the similarity of the objects

simple cells One of the key physiological structures described by the feature-detector approach to form perception, according to which primitive cortical cells provide information to adjacent simple cells regarding the features of objects in the receptive field for each simple cell; the simple cells then fire in response to lines with specific features, such as particular angular orientations, particular light/ dark boundaries and contrasts, direction of contrast (dark on the left, light on the right etc) and particular locations in the receptive field of the cell, with the stimulus specificity differing from one simple cell to another (cf. complex cells)

single-cell recording Technique for detecting the firing patterns of individual neurons in response to stimuli

single-cell revolution A reawakening in the 1950s and 60s of sensory physiology as a way of studying form perception; which attempts to link the psychological perception of form to the functioning of neurons in the brain, based on single-cell (neuronal) recording techniques for tracing the route of the neurons from the receptors within the retina, through the cells, then the thalamic nucleus cells, to the visual cortex; these psychophysiological studies indicated that specific neurons of the visual cortex respond to various stimuli that are presented to the specific retinal regions connected to these neurons; apparently, each individual cortical neuron can be mapped to a specific receptive field on the retina (see complex cells, simple cells)

stapes The last in the series of three bones in the middle ear (cf. incus, malleus), which normally receive and amplify the vibrations transmitted by the tympanum (eardrum) and then transmit those vibrations to the cochlea

stereopsis Three-dimensional perception of the world through the fusion of the visual fields seen by each of the two eyes (see binocular depth cues, binocular disparity)

structuralism The first major school of thought in psychology, which focused on analyzing the distinctive configuration of component elements of the mind, such as particular sensations or thoughts; for example, structuralists would be more interested in what people think than in how they think, in what people perceive, rather than how they perceive (cf. functionalism)

subtractive light mixture The remaining combined wavelengths of light that are reflected from an object after other wavelengths of light have been absorbed (subtracted from the reflected light) by the object; darker objects absorb more wavelengths of light and reflect fewer wavelengths than do brighter objects (cf. additive mixture)

symmetry A Gestalt principle of form perception (see Gestalt approach): the tendency to perceive forms that comprise mirror images on either side of a central axis based on limited sensory information

texture gradient See pictorial depth cues

thalamus A two-lobed structure, located in about the center of the at about the level of the eyes, which amongst many other non-sensory functions, serves as a relay for sensory information; contains various nuclei (groups of neurons with a similar function) that receive assorted types of sensory input entering the brain and then transmit that input via projection fibers to the appropriate sensory regions of the cerebral cortex

thesis A statement of an opinion or of a perspective that reflects, or opposes, a particular point of view – thesis, antithesis. Dialectics is the form of argument that relies on reaching a conclusion (a synthesis) by looking for the contradictions between thesis and antithesis

timbre A psychological quality of sound that permits detection of the difference between a note (e.g., E flat) played on a piano and the same note played, say, on a saxaphone; based on the distinctive harmonics produced by each instrument – rather than the fundamental frequency of the note

trichromatic theory of color vision One of two proposed mechanisms in the history of explanations of how color vision occurs (also termed Young-Helmholtz theory; cf. Hering's opponent-process theory); draws on the notion of primary colors, which can combine additively to form all other colors; according to this view, various photoreceptive cones are somehow attuned to each of the primary colors, such that some cones are sensitive to red (and are therefore activated in response to the sight of red), others to green, and others to blue, and the full range of colors may be seen when various combinations of these three primary colors are present

two-point cutaneous threshold The precise distance between two points on the skin at which two touch stimuli can be distinguished, but at which closer points cannot be distinguished and are felt as a single touch; the distances for determining the threshold vary on differing locations on the body (after the work of Weber)

tympanum See eardrum

Type I error An error in interpreting research, which refers to the belief that a finding has appeared due to systematic manipulations of the variables under investigation, when in fact the finding is a chance result

Type II error An error in interpreting research, which refers to the belief that a finding has appeared due to chance, when in fact the finding is a result of systematic manipulations of the relevant variables under investigation

unconscious inference Proposed by Helmholtz as the key to understanding how meaningful perception resulted from the raw sensory data provided by the receptors (the proximal stimulus). perception is indirect (i.e., mediated by inference like operations; cf. direct theories of perception). In general 'unconscious' refers to a level of consciousness at which thoughts, wishes, and feelings are removed from accessibility to conscious awareness – thus guaranteeing that our perceptions of the world are not contaminated by our beliefs about it (cf. delusions).

vestibule central cavity of labyrinth of inner ear Vestibular Canal Upper canal of the inner ear of the cochlea.

vestibular organs The set of organs adjacent to the inner ear that mediate posture, balance, and the general sense of orientation. In mammals the vestibular organs are the ssaccule, utricle, and semicircular canals.

vestibular senses A set of receptors that provide information about the orientation and movements of the head, located in teh semicircular canals and teh vestibular sacs of teh inner ear.

vigilance The ongoing attention for the appearance of an unpredictable stimulus, which may be sensed through any of the sensory modalities (cf. search)

visible light spectrum The range of wavelengths to which our visual system can respnd, extending from about 400 nanometres (the wavelength of the colour violet) to 750 nanometres (the wavelength of the colour reddish orange).

visual illusion Visual stimulus that leads to distortion in visual perception (see Muller-Lyer illusion, Ponzo illusion)

wavelength The distance from the crest of one wave to the crest of the next wave (e.g., sound waves or light waves), often used as a means of measuring a quality of sound or light; for light waves, the objective wavelength of a light wave is associated with hue, and for sound waves, the objective wavelength is associated with the perception of pitch (for sound, frequency is the more common measure)

Weber fraction The value that in-dicates the relation between the intensity of a standard stimulus and the intensity of a stimulus required to produce a just noticeable difference (jnd); this value varies for different types of sensory experiences, and smaller fractions are required for sensory modalities to which humans experience greater sensitivity (e.g., the painful sensation of electric shock), whereas larger fractions are required for less sensitive modalities (e.g., the sensation of taste)

Weber's law A principle relating the intensity of a standard stimulus to the intensity of a stimulus required to produce a just difference (jnd), often expressed as an equation: DI 5 KI, where K is a constant (a numerical value that does not vary, such as pi), I is the intensity of the standard stimulus, and DI is the increase in intensity needed to produce a jnd; broadly interpreted, the law suggests that the greater the magnitude of the stimulus, the larger the difference must be in order to be detectable as a difference

X cells Ganglion cells linked to the fovea that have a slow conduction speed; react in a steady, sustained fashion; have a small cenre-surround receptive field; and respond to precise, fine details and the colour of stationary stimuli.

Y cells Ganglion cells linked to the periphery of the retina that have a fast conduction speed, respond abruptly with transient reactions, have large centre-surround receptive fields, and respond mainly to stimulus movement.