Glossary

absolute threshold In psychophysics, the faintest (lowest-intensity) stimulus of a given sensation (such as sound or light) that an individual can detect. For contrast, see difference threshold. (p. 250)

accommodation In Piaget’s theory of cognitive development, the change that occurs in an existing mental scheme or set of schemes as a result of the incorporation of the experience of a new event or object. See also assimilation. (p. 426)

action potentials Neural impulses; the all-or-nothing electrical bursts that begin at one end of the axon of a neuron and move along the axon to the other end. (p. 151)

activating effects of sex hormones Temporary, reversible effects that sex hormones have on sexual drive. Contrast to differentiating effects of sex hormones. (p. 215)

adaptation In evolutionary theory, universal and reliably developing inherited feature that arose as a result of natural selection and helped to solve some problem of survival. (p. 58)

ADHD Common acronym for attention-deficit/hyperactivity disorder, a frequently diagnosed disorder in children, characterized by impulsiveness and difficulties in focusing attention on tasks. (p. 623)

affect (pronounced ă′-fekt) a noun referring to any emotional feeling. (p. 232)

aggression Fighting and threats of fighting among members of the same species. (p. 93)

alleles Different genes that can occupy the same locus on a pair of chromosomes and thus can potentially pair with one another. (p. 62)

altruism In sociobiology, a type of helping behavior in which an individual increases the survival chance or reproductive capacity of another individual while decreasing its own survival chance or reproductive capacity. For contrast, see cooperation. (p. 94)

Alzheimer’s disease A disorder found primarily in older adults, characterized by progressive deterioration in cognitive functioning and the presence of deposits in the brain referred to as amyloid plaques. (p. 626)

amplitude The amount of physical energy or force exerted by a physical stimulus at any given moment. For sound, this physical measure is related to the psychological experience of loudness. (p. 269)

amygdala A brain structure that is part of the limbic system and is particularly important for evaluating the emotional and motivational significance of stimuli and generating emotional responses. (p. 171)

analogy In ethology and comparative psychology, any similarity among species that is not due to common ancestry but has evolved independently because of some similarity in their habitats or lifestyles. For contrast, see homology. (p. 82)

androgen A category of hormones, including testosterone, which are produced by the testes in male animals and are normally thought of as “male hormones.” These hormones are also produced at lower levels by the adrenal glands, in females as well as in males. (p. 215)

anterograde amnesia Loss, due to injury to the brain, in ability to form new long-term memories for events that occur after the injury. Contrast to retrograde amnesia. (p. 355)

antisocial personality disorder A personality disorder in which people consistently violate or disregard the rights of others. People with this disorder are sometimes referred to as sociopaths or psychopaths. (p. 654)

anxiety disorders The class of mental disorders in which fear or anxiety is the most prominent symptom. It includes generalized anxiety disorder, panic disorder, and phobias. (p. 631)

aphasia Any loss in language ability due to brain damage. See also Broca’s aphasia, Wernicke’s aphasia. (p. 184)

apoptosis See selective cell death.

arcuate nucleus A nucleus (cluster of neural cell bodies) in the hypothalamus of the brain that plays a critical role in the control of appetite. (p. 206)

arousability In discussions of sexuality, refers to the capacity to become sexually aroused in response to sexually relevant stimuli. For contrast, see proceptivity. (p. 215)

artificial selection The deliberate selective breeding of animals or plants by humans for the purpose of modifying the genetic makeup of future generations. See selective breeding. For contrast, see natural selection. (p. 70)

assimilation In Piaget’s theory of cognitive development, the process by which experiences are incorporated into the mind or, more specifically, into mental schemes. See also accommodation. (p. 426)

association Concerning the mind, a link between two memories or mental concepts, such that recall of one tends to promote recall of the other. (p. 358)

association areas Areas of the cerebral cortex that receive input from the primary or secondary sensory areas for more than one sensory modality (such as vision and hearing) and are involved in associating this input with stored memories, in the processes of perception, thought, and decision making. (p. 172)

association by contiguity Aristotle’s principle that if two environmental events (stimuli) occur at the same time or one right after the other (contiguously), those events will be linked together in the mind. (p. 358)

association by similarity Aristotle’s principle that objects, events, or ideas that are similar to one another become linked (associated) in the person’s mind (structure of memory), such that the thought of one tends to elicit the thought of the other. (p. 358)

attachment The long-lasting emotional bonds that infants develop toward their principal caregivers. More broadly, the long-lasting emotional bonds that any individual develops toward any other individual or object. (p. 462)

attention The process that controls the flow of information from the sensory store into working memory. More broadly, any focusing of mental activity along a specific track, whether that track consists purely of inner memories and knowledge or is based on external stimuli. (p. 324)

attitude Any belief or opinion that has an evaluative component—a belief that something is good or bad, likable or unlikable, attractive or repulsive. (p. 528)

attribution In social cognition, any inference about the cause of a person’s behavioral action or set of actions. More generally, any inference about the cause of any observed action or event. (p. 504)

auditory masking The phenomenon by which one sound (usually a lower-frequency sound) tends to prevent the hearing of another sound (usually a higher-frequency sound). (p. 275)

autism A congenital (present-at-birth) disorder, typically marked by severe deficits in social interaction, severe deficits in language acquisition, a tendency to perform repetitive actions, and a restricted focus of attention and interest. (pp. 49, 441)

automatic processes Cognitive processes that require no mental effort (or mental space) for their execution and are hypothesized (1) to occur without intention and without conscious awareness, (2) not to interfere with the execution of other processes, (3) not to improve with practice, and (4) not to be influenced by individual differences in intelligence, motivation, or education. Contrast with effortful processes. (p. 325)

autonomic portion of the peripheral motor system The set of motor neurons that act upon visceral muscles and glands. (p. 166)

availability bias Tendency, in reasoning, to rely too much on information that is readily available to us and to ignore information that is less available. (p. 376)

avoidant personality disorder A personality disorder in which people are excessively shy, being uncomfortable and inhibited in social situations. They feel inadequate and are extremely sensitive to being evaluated, experiencing a dread of criticism. (p. 654)

axon A thin, tube-like extension from a neuron that is specialized to carry neural impulses (action potentials) to other cells. (p. 151)

axon terminal A swelling at the end of an axon that is designed to release a chemical substance (neurotransmitter) onto another neuron, muscle cell, or gland cell. (p. 151)

basal ganglia The large masses of gray matter in the brain that lie on each side of the thalamus; they are especially important for the initiation and coordination of deliberate movements. (p. 170)

basilar membrane A flexible membrane in the cochlea of the inner ear; the wavelike movement of this structure in response to sound stimulates the receptor cells for hearing. See also hair cells. (p. 272)

behavior The observable actions of an individual person or animal. (p. 3)

behavior analysis The use of principles of operant conditioning to predict behavior. From this perspective, one has achieved “understanding” to the degree to which one can predict and influence future occurrences of behavior. (p. 124)

behavior therapy Category of treatment methods that use basic principles of learning in order to weaken unwanted behavioral responses or strengthen desired behavioral responses. (p. 685)

behavioral genetics Research specialty that attempts to explain psychological differences among individuals in terms of differences in their genes. (p. 15)

behavioral neuroscience Research specialty that attempts to explain behavior in terms of processes occurring within the nervous system. (p. 13)

behaviorism A school of psychological thought that holds that the proper subject of study is observable behavior, not the mind, and that behavior should be understood in terms of its relationship to observable events in the environment rather than in terms of hypothetical events within the individual. (p. 106)

bias A technical term referring to nonrandom (directed) effects on research results, caused by some factor or factors extraneous to the research hypothesis. For contrast, see error. (p. 45)

biased sample A subset of the population under study that is not representative of the population as a whole. (p. 46)

binocular disparity The cue for depth perception that stems from the separate (disparate) views that the two eyes have of any given visual object or scene. The farther away the object is, the more similar are the two views of it. (p. 307)

bipolar disorders Mood disorders that are characterized by episodes of abnormally high mood (mania) and abnormally low mood (depression). See bipolar I disorder and bipolar II disorder. (p. 638)

bipolar I disorder The most severe type of bipolar disorder, characterized by at least one episode of mania and one episode of major depression. See bipolar disorder. For contrast, see bipolar II disorder. (p. 643)

bipolar II disorder The type of bipolar disorder in which the manic phase is less extreme than it is in bipolar I disorder and is referred to as hypomania rather than mania. See bipolar disorder. For contrast, see bipolar I disorder. (p. 643)

blind In scientific research, the condition in which those who collect the data are deliberately kept uninformed about aspects of the study’s design (such as which subjects have had which treatment) that could lead them either unconsciously or consciously to bias the results. See also bias, observer-expectancy effect. (p. 51)

blind spot The place in the retina of the eye where the axons of visual sensory neurons come together to form the optic nerve. Because the blind spot lacks receptor cells, light that strikes it is not seen. (p. 284)

borderline personality disorder A personality disorder characterized by instability, including in emotions—swinging in and out of extreme moods and self-image—often showing dramatic changes in identity, goals, friends, and even sexual orientation. (p. 654)

bottom-up control In theories of perception, mental processes that bring the individual stimulus features recorded by the senses together to form a perception of the larger object or scene. For contrast, see top-down control. (p. 300)

brainstem The primitive, stalk-like portion of the brain that can be thought of as an extension of the spinal cord into the head; it consists of the medulla, pons, and midbrain. (p. 168)

Broca’s aphasia A specific syndrome of loss in language ability that occurs due to damage in a particular part of the brain called Broca’s area; it is characterized by telegraphic speech in which the meaning is usually clear but the small words and word endings that serve grammatical purposes are missing; also called nonfluent aphasia. For contrast, see Wernicke’s aphasia. (p. 184)

cell body The widest part of a neuron, which contains the cell nucleus and the other basic machinery common to all cells. (p. 150)

cell membrane The thin, porous outer covering of a neuron or other cell that separates the cell’s intracellular fluid from extracellular fluid. (p. 151)

central drive system According to the central-state theory of drives, a set of neurons in the brain that, when active, most directly promotes a specific motivational state, or drive. (p. 199)

central executive In Baddeley’s theory, a component of the mind responsible for coordinating all the activities of working memory and for bringing new information into working memory. (p. 334)

central nervous system The brain and spinal cord. (p. 148)

central-state theory of drives The theory that the most direct physiological bases for motivational states, or drives, lie in neural activity in the brain. According to most versions of this theory, different drives correspond to activity in different, localizable sets of neurons. See also central drive system. (p. 199)

cerebellum The relatively large, conspicuous, convoluted portion of the brain attached to the rear side of the brainstem; it is especially important for the coordination of rapid movements. (p. 170)

cerebral cortex The outermost, evolutionarily newest, and (in humans) by far the largest portion of the brain; it is divisible into two hemispheres (right and left), and each hemisphere is divisible into four lobes—the occipital, temporal, parietal, and frontal. (p. 171)

chromosomes The structures within the cell nucleus that contain the genetic material (DNA). (p. 61)

chunking A strategy for improving the ability to remember a set of items by grouping them mentally to form fewer items. (p. 352)

circadian rhythm Any cyclic physiological or behavioral change in a person or other living thing that has a period of about 1 day even in the absence of external cues signaling the time of day. (p. 230)

classical conditioning A training procedure or learning experience in which a neutral stimulus (the conditioned stimulus) comes to elicit a reflexive response through its being paired with another stimulus (usually an unconditioned stimulus) that already elicits that reflexive response; originally studied by Pavlov. See also conditioned response, conditioned stimulus, unconditioned response, unconditioned stimulus. (p. 103)

clinical psychology The field of practice and research that is directed toward helping people who suffer from psychological problems and disorders. (p. 663)

closure principle See Gestalt principles of grouping. (p. 297)

cochlea A coiled structure in the inner ear in which the receptor cells for hearing are located. (p. 272)

cognitive dissonance theory Festinger’s theory that people seek to relieve the discomfort associated with the awareness of inconsistency between two or more of one’s own cognitions (beliefs or bits of knowledge). (p. 533)

cognitive psychology Research specialty that attempts to explain behavior or mental experiences in terms of the cognitions (items of mental information or knowledge) that underlie the behavior or experience. (p. 17)

cognitive therapy An approach to psychotherapy that begins with the assumption that people disturb themselves through their own thoughts and that they can overcome their problems through changing the way they think about their experiences. (p. 680)

cognitive-behavior therapy The psychotherapy approach that stems from a union of cognitive and behavioral theory; it usually characterizes psychological problems as learned habits of thought and action, and its approach to treatment is to help people change those habits. See also behavior therapy, cognitive therapy. (p. 680)

common movement principle See Gestalt principles of grouping. (p. 297)

concept A rule or other form of mental information for categorizing stimuli into groups. (p. 123)

concordance In behavioral genetics research, an index of heritability that is found by identifying a set of individuals who have a particular trait or disorder and then determining the percentage of some specific class of their relatives (such as identical twins) who have the same trait or disorder. (p. 649)

concrete-operational scheme In Piaget’s theory, the type of mental structure that allows a child to think logically about reversible actions (operations) but only when applied to objects with which the child has had direct (concrete) experience. See also operation. (p. 429)

conditioned response In classical conditioning, a reflexive response that is elicited by a stimulus (the conditioned stimulus) because of the previous pairing of that stimulus with another stimulus (the unconditioned stimulus) that already elicits a reflexive response. For contrast, see unconditioned response. (p. 103)

conditioned stimulus In classical conditioning, a stimulus that comes to elicit a reflexive response (the conditioned response) because of its previous pairing with another stimulus (the unconditioned stimulus) that already elicits a reflexive response. For contrast, see unconditioned stimulus. (p. 103)

cone vision The high-acuity color vision that occurs in moderate to bright light and is mediated by cones in the retina; also called photopic or bright-light vision. See cones. For contrast, see rod vision. (p. 284)

cones The class of receptor cells for vision that are located in and near the fovea of the retina, operate in moderate to bright light, and are most important for the perception of color and fine detail. For contrast, see rods. (p. 283)

confirmation bias Tendency of people to seek evidence that confirms, rather than disconfirms, their current hypotheses. (p. 377)

consolidation The process by which a new memory becomes solidified in the brain, such that it is not easily forgotten. (p. 355)

contingency management In behavior therapy, any systematic alteration in the relationship (contingency) between actions and rewards that is designed to alter the client’s behavior in a desired direction. See behavior therapy. (p. 685)

continuous reinforcement In operant conditioning, any condition in which the response is always reinforced. Contrast with partial reinforcement. See reinforcer. (p. 119)

control processes The mental processes that operate on information in the memory stores and move information from one store to another. See attention, encoding, retrieval. (p. 322)

cooperation In sociobiology, a type of helping behavior in which interaction among two or more individuals increases the survival chance or reproductive capacity of each individual involved in the interaction. For contrast, see altruism. (p. 94)

cornea The curved, transparent tissue at the front of the eyeball that helps to focus light rays as they first enter the eye. (p. 282)

corpus callosum A massive bundle of axons connecting the right and left hemispheres of the higher parts of the brain, including the cerebral cortex. (p. 180)

correlation coefficient A numerical measure of the strength and direction of the relationship between two variables. (p. 42)

correlational study Any scientific study in which the researcher observes or measures (without directly manipulating) two or more variables to find relationships between them. Such studies can identify lawful relationships but cannot determine whether change in one variable is the cause of change in another. (p. 35)

cranial nerve A nerve that extends directly from the brain. See nerves. For contrast, see spinal nerve. (p. 165)

creole language A new language, with grammatical rules, that develops from a pidgin language in colonies established by people who had different native languages. See pidgin language. (p. 450)

critical period A relatively restricted time period in an individual’s development during which a particular form of learning can best occur. See imprinting. (p. 141)

crystallized intelligence In Cattell’s theory, the variety of intelligence that derives directly from previous experience. It includes one’s accumulated knowledge and verbal skills. For contrast, see fluid intelligence. (p. 396)

cultural psychology Research specialty that attempts to explain mental experiences and behavior in terms of the culture in which the person developed. (p. 18)

dark adaptation The increased visual sensitivity that occurs when the eyes are exposed for a period of time to dimmer light than was present before the adaptation period. For contrast, see light adaptation. (p. 284)

deductive reasoning Logical reasoning from the general to the specific; the reasoner begins by accepting the truth of one or more general premises or axioms and uses them to assert whether a specific conclusion is true, false, or indeterminate. For contrast, see inductive reasoning. (p. 380)

deep brain stimulation A procedure used for treating obsessive-compulsive disorder and depression, in which a hair-thin wire electrode is implanted permanently into the brain and activated to stimulate neurons near the targeted area. (p. 672)

defense mechanisms In psychoanalytic theory, self-deceptive means by which the mind defends itself against anxiety. See displacement, projection, rationalization, reaction formation, repression, sublimation. (p. 598)

dendrites The thin, tube-like extensions of a neuron that typically branch repeatedly near the neuron’s cell body and are specialized for receiving signals from other neurons. (p. 150)

dependent personality disorder A personality disorder in which people show an extreme need to be cared for. They are clingy and fear separation from significant people in their lives, believing they cannot care for themselves. (p. 654)

dependent variable In an experiment, the variable that is believed to be dependent upon (affected by) another variable (the independent variable). In psychological experiments, it is usually some measure of behavior. (p. 34)

depressive disorders The class of mood disorders characterized by prolonged or frequent bouts of depression. See dysthymia, major depression. (p. 638)

descriptive statistics Mathematical methods for summarizing sets of data. (p. 41)

descriptive study Any study in which the researcher describes the behavior of an individual or set of individuals without systematically investigating relationships between specific variables. (p. 37)

deterministic fallacy The mistaken belief that genes control, or determine, behavior in a manner that is independent of environmental influences. (p. 97)

developmental psychology The branch of psychology that charts changes in people’s abilities and styles of behaving as they get older and tries to understand the factors that produce or influence those changes. (pp. 18, 413)

difference threshold In psychophysics, the minimal difference that must exist between two otherwise similar stimuli for an individual to detect them as different; also called the just-noticeable difference (jnd). (p. 250)

differential lighting of surfaces A pictorial cue for perceiving depth in which the amount of light reflecting on different surfaces indicates the position of objects relative to the light source. (p. 310)

differential susceptibility to environmental influences The idea that people are differentially susceptible to being influenced by their environment. Highly susceptible children (sometimes referred to as orchid children) will flourish in good environments and do especially poorly in adverse environments. Less-susceptible children (sometimes referred to as dandelion children) are less affected by their rearing conditions so that extreme environments (both good and bad) will have less of an impact on their psychological outcomes. (p. 588)

differentiating effects of sex hormones Effects of sex hormones that create the long-lasting structural differences between males and females of a species. Contrast to activating effects of sex hormones. (p. 215)

discrete emotion theory The belief that basic emotions are innate and associated with distinctive bodily and facial reactions. (p. 233)

discrimination training The procedure, in both classical and operant conditioning, by which generalization between two stimuli is diminished or abolished by reinforcing the response to one stimulus and extinguishing the response to the other. See extinction, generalization, reinforcement. (p. 105)

discriminative stimulus In operant conditioning, a stimulus that serves as a signal that a particular response will produce a particular reinforcer. (p. 122)

displacement The defense mechanism by which a drive is diverted from one goal to another that is more realistic or acceptable. Also called sublimation in cases where the goal toward which the drive is diverted is highly valued by society. (p. 598)

distal explanations Functional explanations of behavior that state the role that the behavior plays or once played in survival and reproduction, that is, explanations of why the potential for the behavior was favored by natural selection. For contrast, see proximate explanations. (p. 75)

dominant gene A gene that produces its observable effects even if the person is heterozygous for that gene (that is, has that gene allele on only one of the two paired chromosomes). Contrast to recessive gene. (p. 62)

dopamine One of many neurotransmitter substances in the brain. It is, among other things, crucial for the “wanting” component of reward. (p. 202)

double-blind experiment An experiment in which both the observer and the subjects are blind with respect to the subjects’ treatment conditions. See also blind. (p. 51)

Down syndrome A disorder that results from having an extra chromosome 21, characterized by a specific set of physical symptoms and moderate to severe intellectual disability. (p. 626)

drive See motivational state.

drug tolerance The phenomenon by which a drug produces successively smaller physiological and behavioral effects, at any given dose, if it is taken repeatedly. (p. 113)

DSM-5 Commonly used abbreviation for the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, published by the American Psychiatric Association, which defines a wide variety of mental disorders and establishes criteria for diagnosing them. (p. 618)

dualism The philosophical theory that two distinct systems—the material body and the immaterial soul—are involved in the control of behavior. For contrast, see materialism. (p. 5)

dysthymia A mental disorder characterized by feelings of depression that are less severe than those in major depression but which last for at least a 2-year period. See also major depression. (p. 638)

echoic memory Sensory memory for the sense of hearing. (p. 328)

ECT See electroconvulsive therapy.

effortful processes Cognitive processes that consume some of the information-processing system’s limited capacity and are hypothesized to (1) be available to conscious awareness, (2) interfere with the execution of other processes, (3) improve with practice, and (4) be influenced by individual differences in intelligence, motivation, or education. Contrast with automatic processes. (p. 325)

ego depletion The idea that self-control draws upon a limited pool of mental resources, and that performing one demanding task results in poorer self-control on a subsequent task. (p. 519)

elaboration The process of thinking about an item of information in such a way as to tie the item mentally to other information in memory, which helps to encode the item into long-term memory; also called elaborative rehearsal. (p. 350)

elaboration likelihood model A theory of persuasion postulating that people are more likely to think logically about a message (that is, elaborate upon the message) if it is personally relevant than if it is not. (p. 532)

electroconvulsive therapy (ECT) A procedure for treating severe depression, in which a patient is anesthetized and given a muscle relaxant, and then an electric current is passed through the patient’s skull in such a way as to set up a seizure either in one hemisphere of the brain or in both hemispheres. (p. 671)

electroencephalogram (EEG) A record of the electrical activity of the brain that can be obtained by amplifying the weak electrical signals picked up by recording electrodes pasted to the person’s scalp. It is usually described in terms of wave patterns. (p. 161)

embryonic phase Developmental period that extends from the third to about the eighth week after conception, during which all major organ systems develop. (p. 414)

emotion A subjective feeling that is experienced as directed toward some particular object or event. Contrast to mood. (p. 231)

empiricism The idea that all human knowledge and thought ultimately come from sensory experience; the philosophical approach to understanding the mind that is based on that idea. For contrast, see nativism. (p. 8)

encephalization quotient (EQ) Formula for evaluating the expected ratio between brain weight and body weight for animals. (p. 191)

encoding The mental process by which long-term memories are formed. See also long-term memory. (p. 325)

encoding rehearsal Any active mental process by which a person strives to encode information into long-term memory. For contrast, see maintenance rehearsal. (p. 350)

endorphins Chemicals produced in the body that act like morphine in inhibiting pain. (p. 203)

epigenetics Field that examines gene-regulating activity, with no changes to actual DNA, that can have lasting effects for one or more generations. (p. 68)

episodic memory Explicit memory of past events (episodes) in one’s own life. For contrast, see semantic memory, implicit memory. (p. 342)

error A technical term referring to random variability in research results. For contrast, see bias. (p. 46)

evaluative conditioning The changing in the strength of liking or disliking of a stimulus as a result of being paired with another positive or negative stimulus. (p. 111)

evolutionary psychology Research specialty that attempts to explain how or why specific behavioral characteristics would have come about, by natural selection, in the course of evolution. (p. 15)

excitatory synapse A synapse at which the neurotransmitter increases the likelihood that an action potential will occur, or increases the rate at which they are already occurring, in the neuron on which it acts. For contrast, see inhibitory synapse. (p. 154)

executive functions The processes involved in regulating attention and in determining what to do with information just gathered or retrieved from long-term memory. (p. 337)

experience-expectant processes (or experience-expectant synaptogenesis) Processes whereby synapses are formed and maintained when an organism has species-typical experiences; as a result, functions (such as vision) will develop for all members of a species, given a species-typical environment. (p. 292)

experiment A research design for testing hypotheses about cause-effect relationships, in which the researcher manipulates one variable (the independent variable) in order to assess its effect on another variable (the dependent variable). (p. 34)

explicit attitudes Conscious attitudes; that is, attitudes that people are aware of holding and can state verbally. For contrast, see implicit attitudes. (p. 528)

explicit memory The class of memory that can be consciously recalled and used to answer explicit questions about what one knows or remembers. See episodic memory, semantic memory. For contrast, see implicit memory. (p. 341)

explicit stereotypes Stereotypes that people hold consciously. See stereotypes. For contrast, see implicit stereotypes. (p. 524)

exposure treatment Any method of treating fears—including flooding and systematic desensitization—that involves exposing the client to the feared object or situation (either in reality or imagination) so that the process of extinction or habituation of the fear response can occur. (p. 686)

extinction In classical conditioning, the gradual disappearance of a conditioned reflex that results when a conditioned stimulus occurs repeatedly without the unconditioned stimulus. (p. 104) In operant conditioning, the decline in response rate that results when an operant response is no longer followed by a reinforcer. (p. 119) See classical conditioning, operant conditioning.

fact An objective statement, usually based on direct observation, that reasonable observers agree is true. In psychology, facts are usually particular behaviors, or reliable patterns of behaviors, of persons or animals. (p. 31)

factor analysis A statistical procedure for analyzing the correlations among various measurements (such as test scores) taken from a given set of individuals; it identifies hypothetical, underlying variables called factors that could account for the observed pattern of correlations and assesses the degree to which each factor is adequately measured by each of the measurements that was used in the analysis. (p. 575)

feature detector In vision, any neuron in the brain that responds to a specific property of a visual stimulus, such as its color, orientation, movement, or shape of its contour. More generally, any neuron in the brain that responds to a particular property (feature) of any sensory stimulus. (p. 294)

Fechner’s law The idea that the magnitude of the sensory experience of a stimulus is directly proportional to the logarithm of the physical magnitude of the stimulus. (p. 252)

fetal phase Developmental period that extends from about 9 weeks until birth, which usually takes place about 38 weeks after conception. (p. 414)

field study Any scientific research study in which data are collected in a setting other than the laboratory. (p. 38)

figure In perception, the portion of a visual scene that draws the perceiver’s attention and is interpreted as an object rather than as the background. For contrast, see ground. (p. 298)

five-factor model of personality Model holding that a person’s personality is most efficiently described in terms of his or her score on each of five relatively independent global trait dimensions: neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness. (p. 577)

fixed-interval (FI) schedule In operant conditioning, a schedule of reinforcement in which a fixed period of time must elapse after each reinforced response before it produces a reinforcer. (p. 120)

fixed-ratio (FR) schedule In operant conditioning, a schedule of reinforcement in which a response must be produced a certain fixed number of times (more than once) before it produces a reinforcer. (p. 120)

fluid intelligence In Cattell’s theory, the variety of intelligence that enables one to perceive relationships independent of previous specific practice or instruction concerning those relationships. For contrast, see crystallized intelligence. (p. 395)

fMRI See functional magnetic resonance imaging.

foot-in-the-door technique A technique for gaining compliance in which one first asks for some relatively small contribution or favor before asking for a larger one. Complying with the first request predisposes the person to comply with the second. (p. 554)

formal-operational scheme In Piaget’s theory, the type of mental structure that allows a person to reason about abstract concepts and hypothetical ideas. See also operation, schemes. (p. 429)

fovea The pinhead-size area of the retina of the eye in which the cones are concentrated and that is specialized for high visual acuity. (p. 283)

fraternal twins Two individuals who developed simultaneously in the same womb, but who originated from separate zygotes (fertilized eggs) and are therefore no more genetically similar to one another than are nontwin siblings; also called dizygotic twins. For contrast, see identical twins. (p. 62)

free association In psychoanalysis, the procedure in which a patient relaxes, frees his or her mind from the constraints of conscious logic, and reports every image and idea that enters his or her awareness. (p. 676)

frequency For any form of energy that changes in a cyclic or wavelike way, the number of cycles or waves that occur during a standard unit of time. For sound, this physical measure is related to the psychological experience of pitch. (p. 269)

frequency distribution A table or graph depicting the number of individual scores, in a set of scores, that fall within each of a set of equal intervals. (p. A-2)

frontal lobe The frontmost lobe of the cerebral cortex, bounded in the rear by the parietal and temporal lobes; it contains the motor area and parts of the association areas involved in planning and making judgments. (p. 172)

functional fixedness The failure to see an object as having a function other than its usual one. (p. 384)

functional magnetic resonance imagining (fMRI) A method for visually displaying brain activity that is based on the fact that protons in certain molecules can be made to resonate and give off radio waves indicating relative amounts of neural activity in each portion of the brain. (p. 162)

functionalism A school of psychological thought, founded by William James and others, that focuses on understanding the functions, or adaptive purposes, of mental processes. (p. 74)

gate-control theory Melzack and Wall’s theory that pain will be experienced only if the input from peripheral pain neurons passes through a “gate” located at the point that the pain-carrying neurons enter the spinal cord or lower brainstem. (p. 266)

gaze following The automatic, reflexive action by which one individual’s eyes move when another individual’s eyes move so that both end up looking at the same object. (p. 134)

gender identity A person’s subjective sense of being male or female. (p. 480)

gene Component of long molecules of a substance called DNA (deoxyribonucleic acid) that codes for a particular protein; the basic unit of heredity. (p. 58)

general intelligence (g) In Spearman’s theory of intelligence (and in other theories based on Spearman’s), the underlying mental ability that affects performance on a wide variety of mental tests and accounts for the statistical correlation among scores on such tests. (p. 395)

generalization In classical conditioning, the phenomenon by which a stimulus that resembles a conditioned stimulus will elicit the conditioned response even though it has never been paired with the unconditioned stimulus. (p. 105) In operant conditioning, the phenomenon by which a stimulus that resembles a discriminative stimulus will increase the rate at which the animal produces the operant response, even though the response has never been reinforced in the presence of that stimulus. (p. 122)

generalized anxiety disorder A mental disorder characterized by prolonged, severe anxiety that is not consistently associated in the person’s mind with any particular object or event in the environment or any specific life experience. (p. 631)

genotype The set of genes inherited by the individual. See also phenotype. (p. 60)

Gestalt principles of grouping The rules, proposed by Gestalt psychologists, concerning the manner by which the perceptual system groups sensory elements together to produce organized perceptions of whole objects and scenes. They include the principles of (a) proximity (nearby elements are grouped together), (b) similarity (elements that resemble one another are grouped together), (c) closure (gaps in what would otherwise be a continuous border are ignored), (d) good continuation (when lines intersect, those segments that would form a continuous line with minimal change in direction are grouped together), (e) common movement (elements moving in the same direction and velocity are grouped together), and (f) good form (elements are grouped in such a way as to form percepts that are simple and symmetrical). (p. 297)

Gestalt psychology A school of psychological thought, founded in Germany, which emphasizes the idea that the mind must be understood in terms of organized wholes, not elementary parts. (p. 296)

good continuation principle See Gestalt principles of grouping. (p. 297)

good form principle See Gestalt principles of grouping. (p. 297)

grammar The entire set of rules that specify the permissible ways that smaller units can be arranged to form morphemes, words, phrases, and sentences in a language. (p. 444)

ground In perception, the portion of a visual scene that is interpreted as the background rather than as the object of attention. For contrast, see figure. (p. 298)

group polarization The tendency for a group of people who already share a particular opinion to hold that opinion more strongly—or in a more extreme form—after discussing the issue among themselves. (p. 550)

groupthink A model of thinking in which members of a group are more concerned with group cohesiveness and unanimity than with realistic appraisal of the actions being considered. (p. 552)

habituation The decline in the magnitude or likelihood of a reflexive response that occurs when the stimulus is repeated several or many times in succession. (p. 102)

hair cells The receptor cells for hearing, which are arranged in rows along the basilar membrane of the cochlea in the inner ear. (p. 272)

Hawthorne effect Changes in subjects’ behavior as a result of knowing they are being watched, attributed to the special attention they receive. (p. 40)

helping In sociobiology, any behavior that increases the survival chance or reproductive capacity of another individual. See also altruism, cooperation. (p. 94)

heritability The proportion of the variability in a particular characteristic, in a particular group of individuals, that is due to genetic rather than environmental differences among the individuals. (p. 400)

heritability coefficient A measure of heritability, which can vary from 0 (no heritability) to 1 (complete heritability); specifically, variance due to genes divided by total variance. See heritability. (p. 400)

heterozygous The condition in which a pair of genes occupying the same locus on a pair of chromosomes are different from one another. For contrast, see homozygous. (p. 62)

hippocampus A structure in the limbic system of the brain that is essential for encoding explicit memories for long-term storage. (p. 171)

histrionic personality disorder A personality disorder in which people continually seek to be the center of attention, behaving as if they are always “on stage,” using theatrical gestures and mannerisms; they are often described as “emotionally charged,” displaying exaggerated moods and emotions. (p. 654)

homeostasis The constancy in the body’s internal environment that must be maintained through the expenditure of energy. (p. 197)

homology In ethology and comparative psychology, any similarity among species that exists because of the species’ common ancestry. For contrast, see analogy. (p. 82)

homozygous The condition in which a pair of genes occupying the same locus on a pair of chromosomes are identical to one another. For contrast, see heterozygous. (p. 62)

hormone Any chemical substance that is secreted naturally by the body into the blood and can influence physiological processes at specific target tissues (such as the brain) and thereby influence behavior. (p. 177)

humanistic theories Personality theories that attempt to focus attention on the whole, unique person, especially on the person’s conscious understanding of his or her self and the world. (p. 602)

humanistic therapy Any of several types of psychotherapy that emerged from humanistic personality theories, usually emphasizing the client’s own constructions of his or her reality. See humanistic theories and person-centered therapy. (p. 678)

hypothalamus A small brain structure lying just below the thalamus, connected directly to the pituitary gland and to the limbic system, that is especially important for the regulation of motivation, emotion, and the internal physiological conditions of the body. (p. 171)

hypothesis A specific prediction about what will be observed in a research study, usually derived from a more general conception or theory. See also theory. (p. 31)

iconic memory Sensory memory for the sense of vision. (p. 329)

identical twins Two individuals who are genetically identical to one another because they originated from a single zygote (fertilized egg); also called monozygotic twins. For contrast, see fraternal twins. (p. 62)

implicit association tests Tests of a person’s automatic, unconscious mental associations, designed to assess implicit stereotypes or other implicit attitudes. See implicit stereotypes. (p. 525)

implicit attitudes Attitudes that are manifested in a person’s behavior or automatic mental associations, even though the person may not be conscious of holding those attitudes. For contrast, see explicit attitudes. (p. 529)

implicit memory Memory that influences one’s behavior or thought but does not itself enter consciousness. See priming, procedural memory. (p. 341)

implicit stereotypes Stereotypes that automatically, unconsciously influence people’s judgments and actions toward others. See stereotypes. For contrast, see explicit stereotypes. (p. 525)

impression management The entire set of ways by which people either consciously or unconsciously attempt to influence other people’s impressions (perceptions and judgments) of them. (p. 542)

imprinting Ethologists’ term for a relatively sudden and irreversible form of learning that can occur only during some critical period of the individual’s development. See critical period. (p. 141)

independent variable In an experiment, the condition that the researcher varies in order to assess its effect upon some other variable (the dependent variable). In psychology, it is usually some condition of the environment or of the organism’s physiology that is hypothesized to affect the individual’s behavior. (p. 34)

inductive reasoning Logical reasoning from the specific to the general; the reasoner begins with a set of specific observations or facts and uses them to infer a more general rule to account for those observations or facts; also called hypothesis construction. For contrast, see deductive reasoning. (p. 375)

infantile amnesia The inability to remember events from infancy and early childhood. (p. 347)

inferential statistics Mathematical methods for helping researchers determine how confident they can be in drawing general conclusions (inferences) from specific sets of data. (p. 41)

informational influence The class of social influence that derives from the use of others’ behavior or opinions as information in forming one’s own judgment about the objective nature of an event or situation. For contrast, see normative influence. (p. 544)

inhibitory synapse A synapse at which the neurotransmitter decreases the likelihood that an action potential will occur, or decreases the rate at which they are already occurring, in the neuron upon which it acts. For contrast, see excitatory synapse. (p. 154)

inner ear The portion of the ear lying farthest inward in the head; it contains the cochlea (for hearing) and the vestibular apparatus (for the sense of balance). (p. 272)

insight problem A problem that is difficult to solve until it is viewed in a new way, involving a different mental set from that originally taken. See mental set. (p. 382)

insufficient-justification effect A change in attitude that serves to justify an action that seems unjustified in the light of the previously held attitude. (p. 535)

intelligence The variable mental capacity that underlies individual differences in reasoning, solving problems, and acquiring new knowledge. (p. 391)

interneuron A neuron that exists entirely within the brain or spinal cord and carries messages from one set of neurons to another. (p. 150)

introspection The personal observations of one’s thoughts, perceptions, and feelings. Introspection was used in experimental studies by Wundt and other early psychologists, but the subjective nature of such observations made it an inappropriate source of scientific data. (p. 39)

IQ Abbreviation for intelligence quotient, defined as a score on a test of intelligence that is standardized in such a way that the average score for the population is 100 and the distribution of scores around that average matches a normal distribution. See standardized score and normal distribution. (p. 393)

iris The colored (usually brown or blue), doughnut-shaped, muscular structure in the eye, located behind the cornea and in front of the lens, that controls the size of the pupil and in that way controls the amount of light that can enter the eye’s interior. (p. 282)

just-noticeable difference (jnd) See difference threshold. (p. 250)

kin selection theory of altruism The sociobiological theory that apparent acts of altruism have come about through natural selection because such actions are disproportionately directed toward close genetic relatives and thus promote the survival of others who have the same genes. See also altruism. (p. 95)

laboratory study Any research study in which the subjects are brought to a specially designated area (laboratory) that has been set up to facilitate the researcher’s ability to control the environment or collect data. (p. 38)

language-acquisition device (LAD) Chomsky’s term for the special, innate characteristics of the human mind that allow children to learn their native language; it includes innate knowledge of basic aspects of grammar that are common to all languages and an innate predisposition to attend to and remember the critical, unique aspects of the language. (p. 450)

language-acquisition support system (LASS) The term used by social-learning theorists to refer to the simplification of language and the use of gestures that occur when parents or other language users speak to young children, which helps children learn language; developed as a complement to Chomsky’s concept of the LAD (language-acquisition device). (p. 452)

latent learning Learning that is not demonstrated in the subject’s behavior at the time that the learning occurs but can be inferred from its effect on the subject’s behavior at some later time. (p. 131)

law of complementarity The observation that certain pairs of limited-wavelength lights that produce different colors (such as red and green) alone will produce the perception of white (no color) when mixed. (p. 286)

law of effect Thorndike’s principle that responses that produce a satisfying effect in a particular situation become more likely to recur in that situation, and responses that produce a discomforting effect become less likely to recur in that situation. (p. 116)

learning The process or set of processes through which sensory experience at one time can affect an individual’s behavior at a future time. (p. 101)

learning psychology Research specialty, in psychology, that attempts to understand how the behavior of individuals is shaped through basic learning processes. (p. 16)

lens In the eye, the transparent structure behind the iris that helps focus light that passes through the pupil. (p. 282)

leptin A hormone produced by fat cells that acts in the brain to inhibit hunger and regulate body weight. (p. 207)

level of analysis The type (“level”) of causal process that is referred to in explaining some phenomenon. In psychology, a given type of behavior might be explained at the neural, genetic, evolutionary, learning, cognitive, social, cultural, or developmental level of analysis. (p. 12)

light adaptation The decreased visual sensitivity that occurs when the eyes are exposed for a period of time to brighter light than was present before the adaptation period. For contrast, see dark adaptation. (p. 284)

limbic system An interconnected set of brain structures (including the amygdala and hippocampus) that form a circuit wrapped around the thalamus and basal ganglia, underneath the cerebral cortex. These structures are especially important for the regulation of emotion and motivation and are involved in the formation of long-term memories. (p. 171)

linear perspective A pictorial cue for perceiving depth in which the convergence of parallel lines indicates the distance of objects. Parallel lines appear to converge as they become more distant. (p. 310)

locus In genetics, a position on a chromosome that contains the DNA of a single gene. (p. 62)

locus of control According to Rotter, a person’s perception of the typical source of control over rewards. Internal locus of control refers to the perception that people control their own rewards through their own behavior, and external locus of control refers to the perception that rewards are controlled by external circumstances or fate. (p. 605)

long-term memory Information that is retained in the mind for long periods (often throughout life). For contrasts, see sensory memory, working memory. (p. 324)

long-term potentiation (LTP) A process by which repeated activation of synapses results in strengthening of those synapses. (p. 189)

loudness The quality of the psychological experience (sensation) of a sound that is most directly related to the amplitude of the physical sound stimulus. (p. 269)

low-ball technique A sales trick in which the salesperson suggests a low price for the item being sold, and then, when the potential customer has agreed to buy it at that price, pretends to discover that the item cannot be sold for that price. (p. 554)

LTP See long-term potentiation.

maintenance rehearsal Any active mental process by which a person strives to hold information in short-term memory for a period of time. For contrast, see encoding rehearsal. (p. 349)

major depression A mental disorder characterized by severe depression that lasts essentially without remission for at least 2 weeks. (p. 638)

materialism Hobbes’s theory that nothing exists but matter and energy. For contrast, see dualism. (p. 6)

mean The arithmetic average of a set of scores, determined by adding the scores and dividing the sum by the number of scores. (pp. 41, A-3)

medial forebrain bundle A bundle of neurons that runs from the midbrain to the basal ganglia and other forebrain areas. (p. 201)

median The center score in a set of scores that have been rank-ordered. (pp. 41, A-3)

medulla The lowest portion of the brainstem, bounded at one end by the spinal cord and at the other by the pons. It is responsible, with the pons, for organizing reflexes more complex than spinal reflexes. (p. 168)

meiosis The form of cell division involved in producing egg or sperm cells, which results in cells that are genetically dissimilar and that each have half the number of chromosomes of the original cell. (p. 61)

memory 1. The mind’s ability to retain information over time. 2. Information retained in the mind over time. (p. 340)

memory stores In cognitive psychology, hypothetical constructs that are conceived of as places where information is held in the mind. (p. 322)

mental disorder A disturbance in a person’s emotions, drives, thought processes, or behavior that (a) involves serious and relatively prolonged distress and/or impairment in ability to function, (b) is not simply a normal response to some event or set of events in the person’s environment, and (c) is not explainable as an effect of poverty, prejudice, or other social forces that prevent the person from behaving adaptively, nor as a deliberate decision to act in a way that is contrary to the norms of society. (p. 618)

mental set A habit of perception or thought, stemming from previous experience, that can either help or hinder a person in solving a new problem. (p. 383)

midbrain The upper portion of the brainstem, bounded at its lower end by the pons and at its upper end by the thalamus, that contains neural centers that organize basic movement patterns. (p. 168)

middle ear The air-filled cavity separated from the outer ear by the eardrum; its main structures are three ossicles (tiny bones) that vibrate in response to sound waves and stimulate the inner ear. (p. 271)

mind 1. The entire set of an individual’s sensations, perceptions, memories, thoughts, dreams, motives, emotional feelings, and other subjective experiences. (p. 3) 2. In cognitive psychology, the set of hypothesized information-processing steps that analyze stimulus information and organize behavioral responses. (p. 3)

mirror neurons Neurons in the brain that become active both when the individual makes a particular motion and when the individual sees another individual making that same motion. These neurons are believed to facilitate observational learning. (p. 133)

mitosis The form of cell division involved in normal body growth, which produces cells that are genetically identical to each other. (p. 61)

mode The most frequently occurring score in a set of scores; in a frequency distribution, the interval that contains the highest frequency of scores. (p. A-3)

monogamy A mating system in which one female and one male bond only with each other. For contrast, see polyandry, polygyny, promiscuity. (p. 86)

mood A free-floating emotional feeling, not directed at a specific object. Contrast to emotion. (p. 232)

moon illusion The illusion by which the moon appears larger when seen near the horizon and smaller when seen near the zenith, even though it is objectively the same size and distance from the viewer in either location. (p. 312)

morphemes The smallest meaningful units of a verbal language; words, prefixes, or suffixes that have discrete meanings. (p. 443)

motion parallax The cue for depth perception that stems from the changed view one has of a scene or object when one’s head moves sideways to the scene or object; the farther away an object is, the smaller is the change in view. (p. 308)

motivation The entire constellation of factors, some inside the organism and some outside, that cause an individual to behave in a particular way at a particular time. See also motivational state. (p. 195)

motivational state An internal, reversible condition in an individual that orients the individual toward one or another type of goal (such as food or water). This condition is not observed directly but is inferred from the individual’s behavior; also called a drive. (p. 196)

motor neuron A neuron that carries messages from the brain or spinal cord, through a nerve, to a muscle or gland. (p. 150)

Müller-Lyer illusion A visual size illusion in which a horizontal line looks longer if attached at each end to an outward-extending, V-shaped object, and looks shorter if attached at each end to an inward-extending, V-shaped object. (p. 311)

multisensory integration The integration of information from different senses by the nervous system. (p. 314)

mutations Errors that occasionally and unpredictably occur during DNA replication, producing a “replica” that is different from the original. Mutations are believed to be the original source of all genetic variability. (p. 71)

myelin sheath A casing of fatty cells wrapped tightly around the axon of some neurons. (p. 151)

narcissistic personality disorder A personality disorder in which people are self-centered, seek admiration from others, tend to lack empathy, and are grandiose and confident in their own exceptional talents or characteristics. (p. 654)

nativism The idea that certain elementary ideas are innate to the human mind and do not need to be gained through experience; the philosophical approach to understanding the mind that is based on that idea. For contrast, see empiricism. (p. 10)

natural selection The selective breeding that results from the obstacles to reproduction that are imposed by the natural environment; it is the driving force of evolution. See selective breeding. (p. 70)

naturalistic fallacy The mistaken belief that whatever is natural (and particularly whatever is a product of natural selection) is right, good, or moral. (p. 97)

naturalistic observation Any data-collection procedure in which the researcher records subjects’ ongoing behavior in a natural setting, without interfering with that behavior. (p. 39)

nature-nurture debate The long-standing controversy as to whether the differences among people are principally due to their genetic differences (nature) or differences in their past and present environment (nurture). (p. 399)

negative punishment In operant conditioning, the type of punishment in which the removal of a stimulus (such as taking food or money) when a response occurs decreases the likelihood that the response will recur. For contrast, see positive punishment. (p. 121)

negative reinforcement In operant conditioning, the condition in which a response results in removal of a negative reinforcer. See negative reinforcer. (p. 120)

negative reinforcer In operant conditioning, a stimulus (such as electric shock or loud noise) that is removed after a response and whose removal increases the likelihood that the response will recur. (p. 121)

nerve A large bundle containing the axons of many neurons. Located in the peripheral nervous system, nerves connect the central nervous system with muscles, glands, and sensory organs. (p. 149)

neurogenesis The creation of new neurons in which neuronal stem cells divide and replicate themselves by mitosis. (p. 156)

neurons Single cells in the nervous system that are specialized for carrying information rapidly from one place to another and/or integrating information from various sources; also called nerve cells. (p. 148)

neurotransmitter A chemical substance released from the axon terminal of a neuron, at a synapse, that influences the activity of another neuron, a muscle cell, or a glandular cell; also called a transmitter. (p. 154)

nonregulatory drive Any motivational state (such as the sex drive) that serves some function other than that of preserving some constancy of the body’s internal environment. For contrast, see regulatory drive. (p. 197)

non-REM sleep Stages 2, 3, and 4 of sleep, characterized by the occurrence of slow (delta) waves in the EEG and the lack of rapid eye movements. Contrast to REM sleep. (p. 223)

normal distribution A bell-shaped frequency distribution in which the mean, median, and mode are identical and the frequency of scores tapers off symmetrically on both sides, as defined by a specific mathematical equation. See frequency distribution. (pp. 66, A-2)

normative influence The class of social influence that derives from people’s concern about what others will think of them if they behave in a certain way or express a certain belief. For contrast, see informational influence. (p. 545)

nucleus In neuroanatomy, a cluster of cell bodies of neurons within the central nervous system (not to be confused with the cell nucleus within each cell). (p. 159)

nucleus accumbens A nucleus (center of neural cell bodies) in the basal ganglia that is a crucial part of the brain’s reward mechanism. (p. 201)

object permanence Piaget’s term for the understanding that an object still exists even when it is out of view. (p. 424)

observational learning Learning by watching others. (p. 131)

observational method Any data-collection procedure in which the researcher directly observes the behavior of interest rather than relying on subjects’ self-descriptions. (p. 39)

observer-expectancy effect Any bias in research results that derives from the researcher’s desire or expectation that a subject or set of subjects will behave in a certain way. See bias, subject-expectancy effect. (p. 49)

obsessive-compulsive disorder A mental disorder characterized by a repeated, disturbing, irrational thought (the obsession) that can only be terminated (temporarily) by performing some action (the compulsion). (p. 636)

obsessive-compulsive personality disorder A personality disorder in which people are preoccupied with order and control, and as a result are inflexible and resist change. (p. 636)

occipital lobe The rearmost lobe of the cerebral cortex, bounded in front by the temporal and parietal lobes; it contains the visual area of the brain. (p. 172)

occlusion A pictorial cue for perceiving depth in which the closer object occludes (cuts off) part of the view of the more distant object. (p. 309)

operant conditioning A training or learning process by which the consequence of a behavioral response affects the likelihood that the individual will produce that response again; also called instrumental conditioning. (p. 115)

operant response Any behavioral response that produces some reliable effect on the environment that influences the likelihood that the individual will produce that response again; also called instrumental response. (p. 115)

operation Piaget’s term for a reversible action that can be performed either in reality or mentally upon some object or set of objects. For example, rolling a clay ball into a clay sausage is an operation because the sausage can be rolled back again to form the ball. (p. 427)

operational definition Defining something in terms of the operations by which it could be observed and measured. (p. 47)

opponent-process theory of color vision A theory designed by Hering to explain the law of complementarity, it holds that units (neurons) that mediate the perception of color are excited by one range of wavelengths and inhibited by another (complementary) range of wavelengths. According to the theory, such units cancel out the perception of color when two complementary wavelength ranges are superimposed. See also law of complementarity. (p. 289)

optic nerve The cranial nerve that contains the sensory neurons for vision, which run from the eye’s retina into the brain. (p. 283)

outer ear The pinna (the visible, external portion of the ear) and the auditory canal (the air-filled opening that extends inward from the pinna to the middle ear). (p. 271)

overjustification effect The phenomenon in which a person who initially performs a task for no reward (except the enjoyment of the task) becomes less likely to perform that task for no reward after a period during which he or she has been rewarded for performing it. (p. 124)

panic disorder A mental disorder characterized by the repeated occurrence of panic attacks at unpredictable times and with no clear relationship to environmental events. Each attack involves an intense feeling of terror, which usually lasts several minutes and is accompanied by signs of high physiological arousal. (p. 634)

parallel processing In perception, the early (unconscious) steps in the analysis of sensory information that act simultaneously on all (or at least many) of the stimulus elements that are available at any given moment. For contrast, see serial processing. (p. 295)

paranoid personality disorder A personality disorder in which people are deeply distrustful of other people and are suspicious of their motives. (p. 654)

parasympathetic division of the autonomic motor system The set of motor neurons that act upon visceral muscles and glands and mediate many of the body’s regenerative, growth-promoting, and energy-conserving functions. For contrast, see sympathetic division of the autonomic motor system. (p. 167)

parental investment The time, energy, and risk to survival involved in producing, feeding, and otherwise caring for each offspring. (p. 86)

parenting styles The general ways in which parents interact with their children. (p. 474)

parietal lobe The lobe of the cerebral cortex that lies in front of the occipital lobe, above the temporal lobe, and behind the frontal lobe; it contains the somatosensory area of the brain. (p. 172)

partial reinforcement In operant conditioning, any condition in which the response sometimes produces a reinforcer and sometimes does not. See reinforcer. (p. 119)

pattern generators Networks of neurons that stimulate one another in a cyclic manner and thereby produce bursts of action potentials that wax and wane in a regular, repeating rhythm. They help to control rhythmic sequences of muscle movements, such as those involved in walking, running, flying (in birds), or swimming (in fish). (p. 168)

percentile rank For any single score in a set of scores, the percentage of scores in the set that are equal to or lower than that score. (p. A-6)

perception The recognition, organization, and meaningful interpretation of sensory stimuli. For contrast, see sensation. (p. 246)

peripheral nervous system The entire set of cranial and spinal nerves that connect the central nervous system (brain and spinal cord) to the body’s sensory organs, muscles, and glands. (p. 148)

perpetuating causes of a mental disorder Those consequences of a mental disorder—such as the way other people treat the person who has it—that help keep the disorder going once it begins. See precipitating and predisposing causes of a mental disorder. (p. 628)

person bias The tendency to attribute a person’s behavior too much to the person’s inner characteristics (personality) and not enough to the environmental situation. (p. 505)

person-centered therapy The humanistic approach to psychotherapy (also called client-centered therapy) developed by Carl Rogers, in which the therapist generally refrains from offering advice or leading the course of therapy, but rather listens to the client with empathy and respect and reflects the client’s thoughts and feelings back to him or her. See humanistic therapy and humanistic theories. (p. 678)

personal identity The portion of the self-concept that pertains to the self as a distinct, separate individual. For contrast, see social identity. (p. 522)

personality The relatively consistent patterns of thought, feeling, and behavior that characterize each person as a unique individual. (p. 573)

personality disorders Stable patterns of behavior that impair a person’s sense of self, goals, and capacity for empathy and/or intimacy. (p. 654)

PET See positron emission tomography.

phenomenological reality Humanistic theorists’ term for each person’s conscious understanding of his or her world. (p. 602)

phenotype The observable properties of an individual’s body and behavior. See also genotype. (p. 60)

pheromone A chemical that is released by an animal and that acts on other members of the species to promote some specific behavioral or physiological response. (p. 258)

phobia Any mental disorder characterized by a strong, irrational fear of some particular category of object or event. (p. 632)

phonemes The various vowel and consonant sounds that provide the basis for a spoken language. (pp. 277, 444)

phonological loop In Baddeley’s theory, a component of working memory responsible for holding verbal information. (p. 334)

photoreceptors Specialized light-detecting cells connected to the nervous system in many multicellular animals. (p. xxx) In humans and other vertebrates, the photoreceptors are rods and cones. (p. 281)

pictorial cues for depth perception The depth cues that operate not only when viewing real scenes but also when viewing pictures. They include occlusion, relative image size for familiar objects, linear perspective, texture gradient, differential lighting of surfaces, and (for outdoor scenes) position relative to the horizon. (p. 309)

pidgin language A primitive system of communication that emerges when people with different native languages colonize the same region; it uses words from the various native languages and has either no or minimal grammatical structure. See also creole language. (p. 450)

pitch The quality of the psychological experience (sensation) of a sound that is most related to the frequency of the physical sound stimulus. (p. 269)

placebo In drug studies, an inactive substance given to subjects assigned to the nondrug group. More generally, any treatment that alters a person’s behavior or feelings through the power of suggestion. (p. 51)

polyandry A mating system in which one female bonds with more than one male. For contrast, see monogamy, polygyny, promiscuity. (p. 86)

polygenic characteristic Any trait or characteristic for which the observed variation is affected by many genes. (p. 66)

polygyny A mating system in which one male bonds with more than one female. For contrast, see monogamy, polyandry, promiscuity. (p. 86)

pons The portion of the brainstem that is bounded at its lower end by the medulla and its upper end by the midbrain and is responsible, with the medulla, for organizing reflexes more complex than spinal reflexes. (p. 168)

Ponzo illusion A visual size illusion in which two converging lines cause objects between the two lines to look larger near the converging ends of the lines and smaller near the diverging ends. (p. 311)

position relative to the horizon A pictorial cue for perceiving depth in which objects nearer the horizon seem farther away than objects displaced from the horizon. (p. 36)

positive punishment In operant conditioning, the type of punishment in which the presentation of a stimulus (such as an electric shock or scolding) when a response occurs decreases the likelihood that the response will recur. For contrast, see negative punishment. (p. 121)

positive reinforcement In operant conditioning, the condition in which a response results in a positive reinforcer. (p. 120)

positive reinforcer In operant conditioning, a stimulus (such as food or money) that is presented after a response and that increases the likelihood that the response will recur. (p. 120)

positron emission tomography (PET) A method for visually displaying brain activity that is based upon the uptake of a radioactive form of oxygen into active areas of the brain. (p. 162)

posttraumatic stress disorder A mental disorder that is directly and explicitly tied to a particular traumatic incident or set of incidents (such as torture) that the affected person has experienced. (p. 635)

preattentive processing The analysis, at an unconscious level, in which the mind determines which stimuli are worth passing into working memory. (p. 327)

precipitating causes of a mental disorder The events that most immediately bring on a mental disorder in a person who is sufficiently predisposed for the disorder. See also perpetuating and predisposing causes of a mental disorder. (p. 627)

predictable-world bias Tendency to believe that events are more predictable than they actually are. (p. 378)

predisposing causes of a mental disorder Those conditions that are in place well before the onset of a mental disorder and that make the person susceptible to the disorder. They may include genetic predisposition, early childhood experiences, and the sociocultural environment in which one develops. See also perpetuating and precipitating causes of a mental disorder. (p. 627)

prefrontal cortex The frontmost portion of the frontal lobe of the brain’s cerebral cortex. (p. 175)

premotor areas Portions of the brain’s cerebral cortex that lie directly anterior to (in front of) the motor area. They provide neural programs for producing organized movements. (p. 174)

preoperational scheme In Piaget’s theory, mental structures that permit the child to symbolize objects and events that are absent, but do not permit the child to think about the operations that can be performed on objects. See also operation, schemes. (p. 428)

primary motor area An area in the rear part of the frontal lobe of the cerebral cortex that is directly involved in the control of movements, especially finely coordinated movements of small muscles, as in the fingers and vocal apparatus. (p. 172)

primary sensory areas Specialized areas of the cerebral cortex that receive input from sensory nerves and tracts by way of the relay nuclei in the thalamus. They include the visual area (in the occipital lobe), auditory area (in the temporal lobe), and somatosensory area (in the parietal lobe). (p. 172)

primary visual area The area in the rearmost part of the occipital lobe that receives input from the optic nerves (by way of the thalamus) and sends output to other visual-processing areas of the brain. (p. 294)

priming The implicit memory process by which a stimulus (the priming stimulus) activates (makes more retrievable) one or more memories that already exist in a person’s mind. See implicit memory. (p. 330)

prisoner’s dilemma games A class of laboratory games in which the tendency to compete can be pitted against the tendency to cooperate. In such games, the highest combined payoff to the two players occurs if both choose the cooperative response, but the highest individual payoff goes to a player who chooses the competitive response on a play in which the other chooses the cooperative response. (p. 563)

procedural memory The class of implicit memory that enables a person to perform specific learned skills or habitual responses. See implicit memory. (p. 343)

proceptivity In discussions of sexuality, refers to one’s motivation to seek out and initiate sexual activity, even when sexually arousing stimuli are not already present. For contrast, see arousability. (p. 215)

projection The defense mechanism by which a person consciously experiences his or her own unconscious emotion or wish as though it belongs to someone else or to some part of the environment. (p. 598)

promiscuity A mating system in which members of a group consisting of more than one male and more than one female mate with one another. For contrast, see monogamy, polygyny, polyandry. (p. 86)

prosocial behavior Voluntary behavior intended to benefit other people. (p. 469)

prospective memory Remembering to do something in the future. (p. 364)

proximate explanations Explanations of behavior that state the immediate environmental conditions or the mechanisms within the individual that cause the behavior to occur. For contrast, see ultimate explanations. (p. 75)

proximity principle See Gestalt principles of grouping.

psychoanalysis 1. The theory of the mind developed by Freud, which emphasizes the roles of unconscious mental processes, early childhood experiences, and the drives of sex and aggression in personality formation; also called psychoanalytic theory. (p. 595) 2. Freud’s therapy technique in which such methods as free association, dream analysis, and analysis of transference are used to learn about the person’s unconscious mind; the goal is to make the unconscious conscious. (p. 674)

psychodynamic theories of personality Any theory that describes personality and its development in terms of inner mental forces that are often in conflict with one another and are shaped by experiences in early childhood. (p. 595)

psychodynamic therapy Any approach to psychotherapy that is based on the premise that psychological problems are manifestations of inner mental conflicts and that conscious awareness of those conflicts is a key to recovery. See also psychoanalysis. (p. 674)

psychology The science of behavior and the mind. (p. 3)

psychophysics The scientific study of the relationship between physical characteristics of stimuli and the psychological (sensory) experiences that the stimuli produce. (p. 249)

psychosurgery The surgical cutting or production of lesions in a portion of the brain to relieve a mental disorder. (p. 671)

psychotherapy Any formal, theory-based, systematic treatment for mental problems or disorders that uses psychological means (such as dialogue or training) rather than physiological means (such as drugs) and is conducted by a trained therapist. (p. 673)

puberty Period in life in which children attain adult size and physical characteristics, including sexual maturity. (p. 418)

punishment In operant conditioning, the process through which the consequence of a response decreases the likelihood that the response will recur. For contrast, see reinforcement. (p. 121)

pupil The hole in the center of the iris of the eye through which light passes. See iris. (p. 282)

rationalization The defense mechanism by which a person uses conscious reasoning to justify or explain away his or her harmful or irrational behaviors or thoughts. (p. 599)

reaction formation The defense mechanism by which the mind turns a frightening wish into its safer opposite. (p. 598)

recessive gene A gene that produces its observable effects only if the individual is homozygous for that gene (that is, has that gene allele on both of the two paired chromosomes). Contrast to dominant gene. (p. 62)

reciprocity norm The widespread sense of obligation that people have to return favors. (p. 555)

reciprocity theory of altruism The socio-biological theory that apparent acts of altruism have come about through natural selection because they are actually forms of long-term cooperation rather than true altruism. See also altruism, cooperation. (p. 96)

reference group A group of people with whom an individual compares him- or herself for the purpose of self-evaluation. See also social comparison. (p. 515)

reflex A simple, relatively automatic, stimulus-response sequence mediated by the nervous system. (p. 192)

regulatory drive Any motivational state (such as hunger or thirst) that helps maintain some constancy of the body’s internal environment that is necessary for survival. For contrast, see nonregulatory drive. (p. 197)

reinforcement In operant conditioning, the presentation of a positive reinforcer or removal of a negative reinforcer when a response occurs, which increases the likelihood that the subject will repeat the response. See negative reinforcer, positive reinforcer. For contrast, see punishment. (p. 120)

reinforcer In operant conditioning, any stimulus change that occurs after a response and tends to increase the likelihood that the response will be repeated. See negative reinforcer, positive reinforcer. (p. 117)

relative image size for familiar objects A pictorial cue for perceiving depth in which one infers the distance of familiar objects on the basis of their known actual sizes and the size of their retinal images. (p. 310)

reliability Degree to which a measurement system produces similar results each time it is used with a particular subject or set of subjects under a particular set of conditions (p. xxx). Regarding diagnoses of disorders, the degree to which different diagnosticians, all trained in the use of the diagnostic system, reach the same conclusions when they independently diagnose the same individuals. (p. 619)

REM (rapid-eye-movement) sleep The recurring stage of sleep during which the EEG resembles that of an alert person, rapid eye movements occur, the large muscles of the body are most relaxed, and true dreams are most likely to occur. It is sometimes called emergent stage 1. (p. 222)

repression The defense mechanism by which the mind prevents anxiety-provoking ideas from becoming conscious. (p. 598)

resistance Attempts by a patient to avoid bringing unconscious memories or wishes into consciousness. (p. 677)

response Any well-defined behavioral action, especially one that is elicited by some form of environmental stimulation or provocation. (p. 102)

resting potential The constant electrical charge that exists across the membrane of an inactive neuron. (p. 152)

retina A thin membrane of cells that lines the rear interior of the eyeball; it contains the receptor cells for vision (rods and cones). (p. 282)

retrieval The mental process by which long-term memories are brought into working memory, where they become part of the flow of thought. See also long-term memory, working memory. (p. 325)

retrieval cue A word, phrase, or other stimulus that helps one retrieve a specific item of information from long-term memory. (p. 358)

retrograde amnesia Loss, due to injury to the brain, of long-term memories that had been formed before the injury. Contrast to anterograde amnesia. (p. 355)

reversible figure A visual stimulus (usually a picture) in which any given part is seen sometimes as the figure and other times as the ground. (p. 298)

rhodopsin The photochemical in rods that undergoes structural changes in response to light and thereby initiates the transduction process for rod vision. (p. 283)

rod vision The low-acuity, high-sensitivity, noncolor vision that occurs in dim light and is mediated by rods in the retina of the eye. For contrast, see cone vision. (p. 284)

rods The class of receptor cells for vision that are located in the peripheral portions of the retina (away from the fovea) and are most important for seeing in very dim light. For contrast, see cones. (p. 283)

schema The mental representation of a concept; the information stored in long-term memory that allows a person to identify a group of different events or items as members of the same category. (p. 360)

schemes Piaget’s term for the mental entities that provide the basis for thought and that change in a stage-like way through development. They contain information about the actions that one can perform on objects, either in reality or symbolically in the mind. (p. 426)

schizoid personality disorder A personality disorder in which people display little in the way of emotion, either positive or negative, and tend to avoid social relationships. (p. 654)

schizophrenia A serious class of mental disorders that is characterized by disrupted perceptual and thought processes, often including hallucinations and delusions. (p. 645)

schizotypal personality disorder A personality disorder in which people show extreme discomfort in social situations, often bizarre patterns of thinking and perceiving, and behavioral eccentricities. (p. 654)

science An approach to answering questions that is based on the systematic collection and logical analysis of objectively observable data. (p. 3)

script A variety of schema that represents in memory the temporal organization of a category of event (such as the sequence of occurrences at a typical birthday party). (p. 360)

selective breeding The mating of those members of a strain of animals or plants that manifest a particular characteristic, which may or may not be done deliberately, to affect the genetic makeup of future generations of that strain; can be used to assess heritability. (p. 66)

selective cell death (apoptosis) Early developmental process in which neurons die. (p. 157)

self-actualization In humanistic psychology, the fulfillment of drives that go beyond one’s survival needs and pertain to psychological growth, creativity, and self-expression. (p. 603)

self-efficacy A person’s subjective sense of his or her own ability to perform a particular task or set of tasks. (p. 606)

self-esteem A person’s feeling of approval and acceptance of him- or herself. (p. 514)

self-report method A data-collection method in which the people being studied are asked to rate or describe their own behaviors or mental states. (p. 38)

self-serving attributional bias The tendency of people to attribute their successes to their own qualities and their failures to the situation. (p. 517)

semantic memory One’s storehouse of explicit general knowledge, that is, of knowledge that can be expressed in words and is not mentally tied to specific experiences in one’s own life. Semantic memory includes, but is not limited to, one’s knowledge of word meanings. For contrasts, see episodic memory, implicit memory. (p. 342)

sensation The psychological experience associated with a sound, light, or other simple stimulus and the initial information-processing steps by which sense organs and neural pathways take in stimulus information from the environment. For contrast, see perception. (p. 246)

sensorimotor scheme In Piaget’s theory, the type of mental structure that enables an infant to act on objects that are immediately present but does not permit thought about objects that are absent. See also schemes. (p. 428)

sensory adaptation The temporary decrease in sensitivity to sensory stimulation that occurs when a sensory system is stimulated for a period of time, and the temporary increase in sensitivity that occurs when a sensory system is not stimulated for a period of time. See also dark adaptation, light adaptation. (p. 249)

sensory areas of the cerebral cortex Areas of the brain’s cerebral cortex that receive and analyze input from the body’s senses. Separate sensory areas exist for each distinct sense. See primary sensory areas. (p. 247)

sensory coding The process by which information about the quality and quantity of a stimulus is preserved in the pattern of action potentials sent through sensory neurons to the central nervous system. (p. 248)

sensory memory The memory trace that preserves the original information in a sensory stimulus for a brief period (less than 1 second for sights and up to 3 seconds for sounds) following the termination of the stimulus; it is experienced as if one is still sensing the original stimulus. For contrasts, see long-term memory, working memory. (p. 323)

sensory neuron A neuron that carries messages from a sensory organ, through a nerve, into the brain or spinal cord. (p. 149)

sensory receptors Specialized biological structures—which in some cases are separate cells and in other cases are the sensitive tips of sensory neurons—that respond to physical stimuli by producing electrical changes that can initiate neural impulses (action potentials) in sensory neurons. (p. 247)

sensory-specific satiety The phenomenon by which a person or animal who is satiated on one food still has an appetite for another food that has a different taste. (p. 208)

serial processing The steps in the processing of sensory information that operate sequentially, an item at a time, on the available sensory information. For contrast, see parallel processing. (p. 295)

shaping An operant-conditioning procedure in which successively closer approximations to the desired response are reinforced until the response finally occurs. See reinforcement. (p. 119)

shared attention (joint attention) Two individuals both attending to the same thing or event and sharing that experience. (p. 422)

short-term memory (short-term store) See working memory. (p. 323)

short-term memory span The number of pronounceable items of information (such as single, randomly chosen digits) that a person can retain in short-term (working) memory at any given time. (p. 334)

sibling contrast Tendency to emphasize and exaggerate the differences between siblings. (p. 590)

similarity principle See Gestalt principles of grouping.

size constancy The perceptual ability to see an object as the same size despite change in image size as it moves farther away or closer. (p. 310)

skeletal portion of the peripheral motor system The set of peripheral motor neurons that act upon skeletal muscles. (p. 166)

social-cognitive theories of personality Theories of personality that emphasize the roles of beliefs and habits of thought that are acquired through one’s unique experiences in the social environment. Also called social-learning or social-cognitive-learning theories. (p. 604)

social comparison Any process in which an individual evaluates his or her own abilities, characteristics, ideas, or achievements by comparing them with those of other people. See also reference group. (p. 515)

social dilemma A situation in which a particular action will (a) benefit the individual who takes it, (b) harm the individuals who don’t, and (c) cause more harm than benefit to everyone if everyone takes it. See prisoner’s dilemma games. (p. 562)

social facilitation The tendency to perform a task better in front of others than when alone. For contrast, see social interference. (p. 540)

social identity The portion of the self-concept that pertains to the social categories or groups of which the person is a part. For contrast, see personal identity. (p. 522)

social interference The tendency to perform a task worse in front of others than when alone. For contrast, see social facilitation. (p. 540)

social learning Learning occurring in a situation in which one individual comes to behave similarly to another. (p. 131)

social pressure The entire set of psychological forces that are exerted on an individual by other people or by the individual’s beliefs about other people. (p. 539)

social psychology The branch of psychology that attempts to understand how the behavior and subjective experiences of individuals are influenced by the actual or imagined presence of other people. (pp. 17, 503)

social referencing The process by which infants use the nonverbal emotional expressions of a caregiver as cues to guide their behavior. (p. 422)

somatosensation The set of senses that derive from the whole body—such as from the skin, muscles, and tendons—as opposed to those senses that come from the special sensory organs of the head. (p. 165)

species-typical behavior Any behavior pattern that is so characteristic of a given species of animal that it can be used to help identify that species. (p. 78)

spinal nerve A nerve that extends directly from the spinal cord. See nerve. For contrast, see cranial nerve. (p. 165)

split-parent identification Tendency for each of two siblings to identify with a different one of their two parents. (p. 590)

spontaneous recovery In both classical and operant conditioning, the return—due to passage of time with no further testing or training—of a conditioned response that had previously undergone extinction. (p. 104)

standard deviation A measure of the variability in a set of scores, determined by taking the square root of the variance. (pp. 42, A-5)

standardized score A score that is expressed in terms of the number of standard deviations the original score is from the mean of the original scores. (p. A-6)

statistical significance A statistical statement of how small the likelihood is that an obtained result occurred by chance. By convention, research findings are said to be statistically significant if the probability is less than 5 percent that the data could have come out as they did if the research hypothesis were wrong. (p. 44)

stereotype threat The threatened feeling that occurs, during the taking of a test, when a person is reminded of the fact that he or she belongs to a group that, according to a culturally prominent stereotype, is expected to perform poorly on the test. See stereotypes. (p. 541)

stereotypes Mental concepts by which people characterize specific groups or categories of people. (p. 524)

stimulus A well-defined element of the environment that can potentially act on an individual’s nervous system and thereby influence the individual’s behavior. (p. 102)

strange-situation test A test of an infant’s attachment to a particular familiar person, in which the infant’s behavior is observed in an unfamiliar room while the familiar person and a stranger move in and out of the room in a preplanned way. (p. 464)

stress-induced analgesia The reduced sensitivity to pain that occurs when one is subjected to highly arousing (stressful) conditions. (p. 268)

Stroop interference effect Named after J. Ridley Stroop, the effect by which a printed color word (such as the word red) interferes with a person’s ability to name the color of ink in which the word is printed if the ink color is not the same as the color named by the word. (p. 331)

subject-expectancy effect Any bias in research results that derives from subjects’ expectations or beliefs about how they should feel or behave in response to the variables imposed in the study. See also bias, observer-expectancy effect. (p. 51)

sublimation See displacement.

superordinate goals The goals shared by two or more groups, which tend to foster cooperation among the groups. (p. 570)

suprachiasmatic nucleus Nucleus (cluster of neurons) in the brain’s hypothalamus that controls circadian rhythms of sleep and arousal. (p. 230)

sympathetic division of the autonomic motor system The set of motor neurons that act upon visceral muscles and glands and mediate many of the body’s responses to stressful stimulation, preparing the body for possible “fight or flight.” For contrast, see parasympathetic division of the autonomic motor system. (p. 166)

synapse The functional connection through which neural activity in the axon of one neuron influences the action of another neuron, a muscle cell, or a glandular cell. (p. 154)

synesthesia A condition in which sensory stimulation in one modality induces a sensation in a different modality. (p. 316)

syntax The set of grammatical rules for a given language that specifies how words can be arranged to produce phrases and sentences. (p. 444)

temporal lobe The lobe of the cerebral cortex that lies in front of the occipital lobe and below the parietal and frontal lobes and that contains the auditory area of the brain. (p. 172)

temporal-lobe amnesia The loss in memory abilities that occurs as a result of damage to structures in the limbic system that lie under the temporal lobe of the cerebral cortex. (p. 345)

teratogens External agents, such as drugs and radiation, that can have harmful effects on a developing embryo or fetus. (p. 416)

test In psychology, a data collection method in which stimuli or problems are deliberately presented by the researcher for the subject to respond to. (p. 39)

texture gradient A pictorial cue for perceiving depth in which the gradual change in size and density of textured elements (such as pebbles or blades of grass) indicates depth. (p. 310)

thalamus The brain structure that sits directly atop the brainstem; it functions as a sensory relay station, connecting incoming sensory tracts to special sensory areas of the cerebral cortex. (p. 169)

theory A belief or set of interrelated beliefs that one has about some aspect of the universe, which is used to explain observed facts and to predict new ones. See also hypothesis. (p. 31)

theory of mind A person’s concepts of mental activity; used to refer to how people conceptualize mental activity and how they attribute intention to and predict the behavior of others. (p. 438)

three-primaries law The observation that one can choose three limited-wavelength lights (called primaries) and, by mixing them in differing proportions, match any color that the human eye can see. (p. 286)

TMS See transcranial magnetic stimulation.

tolerance See drug tolerance.

tonotopic organization Refers to the manner by which neural cells in the primary auditory area of the cerebral cortex are organized. Each neuron is maximally responsive to sounds of a particular frequency, and the neurons are systematically arranged such that high-frequency tones activate neurons at one end of this cortical area and low-frequency tones activate neurons at the other end. (p. 276)

tools of intellectual adaptation Vygotsky’s term for tools a culture provides for thinking and problem solving. (p. 431)

top-down control In theories of perception, mental processes that bring pre-existing knowledge or expectations about an object or scene to bear upon the perception of that object or scene. For contrast, see bottom-up processes. (p. 300)

tract A bundle of neural axons coursing together within the central nervous system; analogous to a nerve in the peripheral nervous system. (p. 159)

trait A hypothetical, relatively stable, inner characteristic that influences the way a person responds to various environmental situations. (p. 574)

trait theories of personality Theories of personality that are based on the idea that people can be described and differentiated in terms of hypothetical underlying personality dimensions, called traits, which can be measured by questionnaires or other quantitative means. (p. 575)

transcranial magnetic stimulation (TMS) A procedure for temporarily altering the responsiveness of a localized area of the cerebral cortex by creating a magnetic field over that brain area. (p. 160) It is also used as a treatment for depression. (p. 671)

transference The phenomenon by which a patient’s unconscious feelings about a significant person in his or her life are experienced consciously as feelings about the therapist. (p. 677)

trichromatic theory of color vision Theory proposed independently by Young and Helmholtz to explain the three-primaries law of color vision; it holds that the human ability to perceive color is mediated by three different types of receptors, each of which is most sensitive to a different range of wavelengths. See also three-primaries law. (p. 286)

unconditioned response A reflexive response that does not depend upon previous conditioning or learning. For contrast, see conditioned response. (p. 103)

unconditioned stimulus A stimulus that elicits a reflexive response without any previous training or conditioning. For contrast, see conditioned stimulus. (p. 103)

validity Degree to which a measurement system actually measures the characteristic that it is supposed to measure (p. 578). Regarding diagnoses of mental disorders, the degree to which the disorders identified are clinically meaningful; that is, the degree to which the diagnostic labels predict real-world behaviors and treatment outcomes. (p. 621)

variability The degree to which the individual numbers in a set of numbers differ from one another or from their mean. See variance and standard deviation, which are common measures of variability. (p. 42)

variable-interval (VI) schedule In operant conditioning, a schedule of reinforcement in which an unpredictable period of time, varying around some average, must elapse between the receipt of one reinforcer and the availability of another. (p. 120)

variable-ratio (VR) schedule In operant conditioning, a schedule of reinforcement in which the response must be produced a certain average number of times before a reinforcer will appear, but the number needed on any given instance varies randomly around that average. (p. 120)

variance A measure of the variability of a set of scores, determined by obtaining the difference (deviation) between each score and the mean, squaring each deviation, and calculating the mean of the squared deviations. (p. A-4)

vestigial characteristics Inherited characteristics of anatomy or behavior that are no longer useful to the species but were presumably useful at an earlier time in evolution. (p. 76)

vicarious reinforcement In Bandura’s social cognitive theory, learning from observing others’ behaviors and their consequences, without the need to receive specific reinforcement for one’s behavior. (p. 132)

visual agnosia A condition caused by damage to specific portions of the occipital and temporal lobes of the cortex, in which people cannot make sense of what they see. (p. 302)

visual dominance effect The phenomenon in which visual stimuli, when presented simultaneously with stimuli from other senses, tend to dominate awareness. (p. 314)

visual form agnosia A variety of agnosia in which people can identify some elements of what they see but cannot perceive an object’s shape. (p. 303)

visual object agnosia A variety of agnosia in which people can identify and draw the shapes of objects but cannot identify the objects. (p. 303)

visuospatial sketchpad In Baddeley’s theory, a component of working memory responsible for holding visual and spatial information. (p. 334)

Weber’s law The idea that, within a given sensory modality (such as vision), the difference threshold (amount that the stimulus must be changed in magnitude to be perceived as different) is a constant proportion of the magnitude of the original stimulus. (p. 251)

Wernicke’s aphasia A specific syndrome of loss of language ability that occurs due to damage in a particular part of the brain called Wernicke’s area. Speech in a person with this disorder typically retains its grammatical structure but loses its meaning due to the speaker’s failure to provide meaningful content words (nouns, verbs, adjectives, and adverbs); also called fluent aphasia. For contrast, see Broca’s aphasia. (p. 185)

working memory The memory store that is considered to be the main workplace of the mind. Among other things, it is the seat of conscious thought and reasoning. For contrast, see sensory memory, long-term memory. (p. 323)

z score The simplest form of a standardized score; it is the score minus the mean divided by the standard deviation. (p. A-6)

zone of proximal development In Vygotsky’s theory, The range or set of activities that a child can do in collaboration with more competent others but cannot yet do alone. (p. 433)

zygote The single cell that is formed when an egg and sperm cell unite; the first, single-cell form of a newly developing individual. (p. 62)

zygotic phase Developmental phase lasting approximately 2 weeks, which starts when an egg is fertilized and ends when the zygote implants in the uterine wall. (p. 414)