Dictionary of Terms


Dark Adaptation The process by which the eye becomes capable of distinguishing dimly illuminated objects after going from a bright region to a dark one.

Debriefing Full disclosure to research participants of the true nature and purpose of a research project after its completion.

Deductive Reasoning Inferring specific instances from general principles or rules.

Deep Processing The analysis of the complex characteristics of a stimulus, such as its meaning or its relationship to other stimuli.

Deep Structure The essential meaning of a sentence, without regard to the grammatical features (surface structure) of the sentence that are needed to express it in words. See also surface structure.

Defense Mechanisms Mental systems that become active whenever unconscious instinctual drives of the id come into conflict with internalized prohibitions of the superego.

Deferred Imitation A childís ability to imitate the actions he or she has observed others perform. Piaget believed deferred imitation to result from the childís increasing ability to form mental representations of behavior performed by others.

Deindividuation The replacement of oneís personal identity by identification with the groupís values and goals.

Deinstitutionalization The process of returning previously hospitalized patients to their communities for treatment of psychological problems and mental disorders.

Delta Activity The rhythmical activity of the electroencephalogram, having a frequency of less than 3.5 Hz, indicating deep (slow-wave) sleep.

Delusions of Control The false belief that oneís thoughts and actions are being controlled by other people or forces.

Delusions of Grandeur The false belief that one is famous, powerful, or important.

Delusions of Persecution The false belief that other people are plotting against one; symptom of schizophrenia.

Dendrite A treelike part of a neuron on which the terminal buttons of other neurons form synapses.

Dependent Variable The event whose value is measured in an experiment. Manipulation of independent variables demonstrates whether they affect the value of dependent variables.

Descriptive Statistics Mathematical procedures for organizing collections of data, such as determining the mean, the median, the range, the variance, and the correlation coefficient.

Detector In a regulatory process, a mechanism that signals when the system variable deviates from its set point.

Deuteranopia A form of hereditary anomalous color vision; caused by defective "green" cones in the retina.

Developmental Approach An approach to the study of intelligence that studies the way infants and children learn to perceive, manipulate, and think about the world.

Developmental Psychology The branch of psychology that studies the changes in behavioral, perceptual, and cognitive capacities of organisms as a function of age and experience.

Deviation IQ A procedure for computing the intelligence quotient; compares a childís score with those received by other children of the same chronological age.

Diagnostic and Statistical Manual IV (DSM-IV) A widely used manual for classifying psychological disorders.

Diathesis-Stress Model A causal account of mental disorders based on the idea that mental disorders develop when a person possesses a predisposition for a disorder, acquired through genetics and early learning experiences, and faces stressors that exceed his or her abilities to cope with them.

Dichotic Listening A task that requires a person to attend to one of two different messages being presented simultaneously, one to each ear, through headphones.

Diffusion of Responsibility An explanation of the failure of bystander intervention stating that when several bystanders are present, no one person assumes responsibility for helping.

Direct Dyslexia A language disorder caused by brain damage in which people can read words aloud without understanding them.

Discrimination In classical conditioning, the appearance of a CR when one stimulus is presented (the CS+) but not another (the CS-). In operant conditioning, responding only when a specific discriminative stimulus is present but not when similar stimuli are present. In social psychology, the differential treatment of people based on their membership in a particular group.

Discriminative Stimulus In operant conditioning, the stimulus that sets the occasion for responding because, in the past, a behavior has produced certain consequences in the presence of that stimulus.

Disorganized Schizophrenia A type of schizophrenia characterized primarily by disturbances of thought and a flattened or silly affect.

Display Rule A culturally determined rule that prescribes the expression of emotions in particular situations.

Dispositional Factors Individual personality characteristics that affect a personís behavior.

Dissociative Disorders A class of disorders in which anxiety is reduced by a sudden disruption in consciousness, which in turn produces changes in oneís sense of identity.

Distinctive Feature A physical characteristic of an object that helps distinguish it from other objects.

Distinctiveness The extent to which a person engages in a particular behavior in one situation but not in others.

DNA Deoxyribonucleic acid, the structure of chromosomes. DNA structure resembles that of a twisted ladder. Strands of sugar and phosphates are connected by rungs made from adenine and thymine and guanine and cytosine.

Doctrine of Specific Nerve Energies Johannes Müllerís observation that different nerve fibers convey specific information from one part of the body to the brain or from the brain to one part of the body.

Dominant Allele The form of the gene that controls the expression of a trait. When a gene pair contains two dominant alleles or when it contains both a dominant and recessive allele, the trait regulated by the dominant gene will be expressed.

Dopamine Hypothesis The hypothesis that the positive symptoms of schizophrenia are caused by overactivity of synapses in the brain that use dopamine.

Double-Bind The conflict caused for a child when he or she is given inconsistent messages or cues from a parent.

Double-Blind Study An experiment in which neither the subjects nor the experimenter knows the value of the independent variable.

Down Syndrome A genetic disorder caused by a chromosomal aberration resulting in an extra 21st chromosome. People with Down syndrome are generally short with broad skulls and round faces, and suffer impairments in physical, psychomotor, and cognitive development.

Drive A condition, often caused by physiological changes or homeostatic disequilibrium, that energizes an organismís behavior.

Drive Reduction Hypothesis The hypothesis that a drive (resulting from physiological need or deprivation) produces an unpleasant state that causes an organism to engage in motivated behaviors. Reduction of drive is assumed to be reinforcing.

Dualism The philosophical belief that humans consist of physical bodies and nonmaterial minds or souls.

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