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.