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Dark adaptation - The gradual improvement of the eyes' sensitivity after a shift in illumination from light to near darkness.

Date Rape - Unwanted sexual violation by a social acquaintance in the context of a consensual dating situation.

Daytime Sleepiness - The experience of excessive sleepiness during daytime activities; the major complaint of patients evaluated at sleep disorder centers.

Debriefing - A procedure conducted at the end of an experiment in which the researcher provides the participant with as much information about the study as possible and makes sure that no participant leaves feeling confused, upset, or embarrassed.

Decision Aversion - The tendency to avoid decision making; the tougher the decision, the greater the likelihood of decision aversion.

Decision Making - The process of choosing between alternatives; selecting or rejecting available options.

Declarative Memory - Memory for information such as facts and events.

Deductive Reasoning - A form of thinking in which one draws a conclusion that is intended to follow logically from two or more statements or premises.

Delusions - False or irrational beliefs maintained despite clear evidence to the contrary.

Demand Characteristics - Cues in an experimental setting that influence the participants' perception of what is expected of them and that systematically influence their behavior within that setting.

Dendrites - The branched fibers of neurons that receive incoming signals.

Dependent Variable - In an experimental setting, any variable whose values are the results of changes in one or more independent variables.

Descriptive Statistics - Statistical procedures that are used to summarize sets of scores with respect to central tendencies, variability, and correlations.

Determinism The doctrine that all events-physical, behavioral, and mental-are determined by specific causal factors that are potentially knowable.

Developmental age The chronological age at which most children show a particular level of physical or mental development.

Developmental psychology The branch of psychology concerned with interaction between physical and psychological processes and with stages of growth from conception throughout the entire life span.

Diathesis-stress hypothesis A hypothesis about the cause of certain disorders, such as schizophrenia, that suggests that genetic factors predispose an individual to a certain disorder, but that environmental stress factors must impinge in order for the potential risk to manifest itself.

Dichotic listening An experimental technique in which a different auditory stimulus is simultaneously presented to each ear.

Difference threshold The smallest physical difference between two stimuli that can still be recognized as a difference; operationally defined as the point at which the stimuli are recognized as different half of the time.

Diffusion of responsibility In emergency situations, the larger the number of bystanders, the less responsibility any one bystander feels to help.

Discriminative stimuli Stimuli that act as predictors of reinforcement, signaling when particular behaviors will result in positive reinforcement.

Dispositional variables The organismic variables, or inner determinants of behavior, that occur within human and nonhuman animals.

Dissociative amnesia The inability to remember important personal experiences, caused by psychological factors in the absence of any organic dysfunction.

Dissociative disorder A personality disorder marked by a disturbance in the integration of identity, memory, or consciousness.

Dissociative identity disorder (DID) A dissociative mental disorder in which two or more distinct personalities exist within the same individual; formerly known as multiple personality disorder.

Distal stimulus In the processes of perception, the physical object in the world, as contrasted with the proximal stimulus, the optical image on the retina.

Divergent thinking An aspect of creativity characterized by an ability to produce unusual but appropriate responses to problems.

DNA (deoxyribonucleic acid) The physical basis for the transmission of genetic information.

Double-blind control An experimental technique in which biased expectations of experimenters are eliminated by keeping both participants and experimental assistants unaware of which participants have received which treatment.

Dream analysis The psychoanalytic interpretation of dreams used to gain insight into a person's unconscious motives or conflicts.

Dream work In Freudian dream analysis The process by which the internal censor transforms the latent content of a dream into manifest content.

Drives Internal states that arise in response to a disequilibrium in an animal's physiological needs.

DSM-IV-TR The current diagnostic and statistical manual of the American Psychiatric Association that classifies, defines, and describes mental disorders.