Dictionary of Terms


T Lymphocytes Cells that develop in the thymus gland that produce antibodies, which defend the body against fungi, viruses, and multicellular parasites.

Tachistoscope A device that can present visual stimuli for controlled (usually very brief) durations of time.

Tardive dyskinesia A serious movement disorder that can occur when a person has been treated with antipsychotic drugs for an extended period.

Target Cell A cell whose physiological processes are affected by a particular hormone; contains special receptor molecules that respond to the presence of the hormone.

Taste Bud A small organ on the tongue that contains a group of gustatory receptor cells.

Tectorial Membrane A membrane located above the basilar membrane; serves as a shelf against which the cilia of the auditory hair cells move.

Template A hypothetical pattern that resides in the nervous system and is used to perceive objects or shapes by a process of comparison.

Temporal Coding A means of representing information by the nervous system; different features are coded by the pattern of activity of neurons.

Temporal Lobe The portion of the cerebral cortex below the frontal and parietal lobes and containing the auditory cortex.

Teratogens Drugs or other substances that can cause birth defects.

Terminal Button The rounded swelling at the end of the axon of a neuron; releases transmitter substance.

Texture A monocular cue of depth perception; the fineness of detail present in the surface of objects or in the ground or floor of a scene.

Thalamus A region of the brain near the center of the cerebral hemispheres. All sensory information except smell is sent to the thalamus and then relayed to the cerebral cortex.

Thematic Apperception Test (TAT) A projective test in which a person is shown a series of ambiguous pictures that involve people. The person is asked to make up a story about what the people are doing or thinking. The personís responses are believed to reflect aspects of his or her personality.

Theory A set of statements designed to explain a set of phenomena; more encompassing than a hypothesis.

Theta Activity EEG activity of 3.5-7.5 Hz; occurs during the transition between sleep and wakefulness.

Thought Disorder A pattern of disorganized, illogical, and irrational thought that often accompanies schizophrenia.

Threat Gesture A stereotyped gesture that signifies that one animal is likely to attack another member of the species.

Three-Term Contingency The relation among discriminative stimuli, behavior, and the consequences of that behavior. A motivated organism emits a specific response in presence of a discriminative stimulus because in the past, that response has been reinforced only when the discriminative stimulus is present.

Threshold The point at which a stimulus, or a change in the value of a stimulus, can just be detected.

Timbre A perceptual dimension of sound, determined by the complexity of the sound; for example, as shown by a mathematical analysis of the sound wave.

Tip of the Tongue Phenomenon An occasional problem with retrieval of information that we are sure we know but cannot immediately remember.

Token Economy A program often used in institutions in which a personís adaptive behavior is reinforced with tokens that are exchangeable for desirable goods or special privileges.

Tolerance The decreased sensitivity to a drug resulting from its continued use.

Top-Down Processing A perception based on information provided by the context in which a particular stimulus is encountered.

Touretteís Syndrome A neurological disorder characterized by tics and involuntary utterances, some of which may involve obscenities and the repetition of others' utterances.

Transduction The conversion of physical stimuli into changes in the activity of receptor cells of sensory organs.

Transference The process by which a client begins to project powerful attitudes and emotions onto the therapist.

Transmitter Substance A chemical released by the terminal buttons that causes the postsynaptic neuron to be excited or inhibited.

Trephining A surgical procedure in which a hole is made in the skull of a living person

Trichromatic Theory The theory that color vision is accomplished by three types of photodetectors, each of which is maximally sensitive to a different wavelength of light.

Tritanopia A form of hereditary anomalous color vision; caused by a lack of "blue" cones in the retina.

Two-Point Discrimination Threshold The minimum distance between two small points that can be detected as separate stimuli when pressed against a particular region of the skin.

Type A Pattern A behavior pattern characterized by high levels of competitiveness and hostility, impatience, and an intense disposition; supposedly associated with an increased risk of CHD.

Type B Pattern A behavior pattern characterized by lower levels of competitiveness and hostility, patience, and an easygoing disposition; supposedly associated with a decreased risk of CHD.

Type C Personality A behavior pattern characterized by cooperativeness, unassertiveness, patience, suppression of negative emotions, and acceptance of external authority; supposedly associated with an increased likelihood of cancer.

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