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daily hassles: The relatively minor yet chronic and persistent life stressors that combine to have a strong, negative influence on personal well-being.

defence mechanisms: In psychoanalytic theory, reality-distorting strategies unconsciously adopted to protect the ego from anxiety.

deinstitutionalization: The increasing tendency for treatment to take place in the community, perhaps on an outpatient basis, rather than having patients reside in a public institution, such as a provincial mental hospital.

delay of reward gradient: The learning theory term for the finding that rewards and punishments lose their effectiveness the further they are removed in time from the response in question.

delayed echolalia: See echolalia.

: A state of great mental confusion in which consciousness is clouded, attention cannot be sustained, and the stream of thought and speech is incoherent. The person is probably disoriented, emotionally erratic, restless or lethargic, and often has illusions, delusions, and hallucinations.

delirium tremens (DTs): One of the withdrawal symptoms that sometimes occurs when a period of heavy alcohol consumption is terminated; marked by fever, sweating, trembling, cognitive impairment, and hallucinations.

delusional (paranoid) disorder: A disorder in which the individual has persistent persecutory delusions or delusional jealousy and is very often contentious but has no thought disorder or hallucinations.

delusional jealousy: The unfounded conviction that one’s mate is unfaithful; the individual may collect small bits of "evidence" to justify the delusion.

delusions: Beliefs contrary to reality, firmly held in spite of evidence to the contrary; common in paranoid disorders; of control, belief that one is being manipulated by some external force such as radar, television, or a creature from outer space; of grandeur, belief that one is an especially important or powerful person; of persecution, belief that one is being plotted against or oppressed by others.

dementia: Deterioration of mental faculties—memory, judgment, abstract thought, control of impulses, intellectual ability—that impairs social and occupational functioning and eventually changes the personality. See Alzheimer’s disease.

dementia praecox: An older term for schizophrenia, chosen to describe what was believed to be an incurable and progressive deterioration of mental functioning beginning in adolescence.

demographic variable: A varying characteristic that is a vital or social statistic of an individual, sample group, or population, for example, age, sex, socioeconomic status, racial origin, education.

demonology: The doctrine that a person’s abnormal behaviour is caused by an autonomous evil spirit.

denial: Defence mechanism in which a thought, feeling, or action is disavowed by the person.

dependent personality disorder: Lacking in self-confidence, such people passively allow others to run their lives and make no demands on them so as not to endanger these protective relationships.

dependent variable: In a psychological experiment, the behaviour that is measured and is expected to change with manipulation of the independent variable.

depersonalization: An alteration in perception of the self in which the individual loses a sense of reality and feels estranged from the self and perhaps separated from the body. It may be a temporary reaction to stress and fatigue or part of panic disorder, depersonalization disorder, or schizophrenia.

depersonalization disorder: A dissociative disorder in which the individual feels unreal and estranged from the self and surroundings enough to disrupt functioning. People with this disorder may feel that their extremities have changed in size or that they are watching themselves from a distance.

depression: A disorder marked by great sadness and apprehension, feelings of worthlessness and guilt, withdrawal from others, loss of sleep, appetite, sexual desire, loss of interest and pleasure in usual activities, and either lethargy or agitation. Called major depression in DSM-IV and unipolar depression by others. It can be an associated symptom of other disorders.

depressive paradox: A cognitive tendency for depressed individuals to accept personal responsibility for negative outcomes despite feeling a lack of personal control.

depressive predictive certainty: This concept, derived from the hopelessness theory of depression, states that people become prone to depression when they perceived that an anticipated state of helplessness is certain to occur.

derealization: Loss of the sense that the surroundings are real; present in several psychological disorders, such as panic disorder, depersonalization disorder, and schizophrenia.

descriptive responsibility: In legal proceedings, the judgment that the accused performed an illegal act. Contrast with ascriptive responsibility.

deterioration effect: In abnormal psychology, a harmful outcome from being in psychotherapy.

detoxification: The initial stage in weaning an addicted person from a drug; involves medical supervision of the sometimes painful withdrawal.

detumescence: The flow of blood out of the genital area.

diagnosis: The determination that the set of symptoms or problems of a patient indicates a particular disorder.

dialectical behaviour therapy: A therapeutic approach to borderline personality disorder that combines client-centred empathy and acceptance with behavioural problem solving, social-skills training, and limit setting.

diathesis: Predisposition toward a disease or abnormality.

diathesis–stress paradigm: As applied in psychopathology, a view that assumes that individuals predisposed toward a particular mental disorder will be particularly affected by stress and will then manifest abnormal behaviour.

dichotic listening: An experimental procedure in which a person hears two different taped messages simultaneously through earphones, one in each ear, usually with the instruction to attend to only one of the messages.

diencephalon: The lower area of the forebrain, containing the thalamus and hypothalamus.

dimensional classification: An approach to assessment according to which a person is placed on a continuum. Contrast with categorical classification.

directionality problem: A difficulty that arises in the correlational method of research when it is known that two variables are related but it is unclear which is causing the other.

discriminative stimulus: An event that informs an organism that if a particular response is made, reinforcement will follow.

disease: The medical concept that distinguishes an impairment of the normal state of the organism by its particular group of symptoms and its specific cause.

disease model: See medical model.

disorder of written expression: Difficulties writing without errors in spelling, grammar, or punctuation.

disorganized attachment style: An attachment orientation in which the infant demonstrates a confused attachment style that emerges after being raised in a chaotic and abusive environment.

disorganized schizophrenia: In this subtype of schizophrenia the person has diffuse and regressive symptoms; the individual is given to silliness, facial grimaces, and inconsequential rituals and has constantly changeable moods and poor hygiene. There are few significant remissions and eventually considerable deterioration. This form of schizophrenia was formerly called hebephrenia.

disorganized speech (thought disorder): Speech found in schizophrenics that is marked by problems in the organization of ideas and in speaking so that others can understand.

disorientation: A state of mental confusion with respect to time, place, identity of self, other persons, and objects.

displacement: A defence mechanism whereby an emotional response is unconsciously redirected from an object or concept perceived as dangerous to a substitute less threatening to the ego.

dissociation: A process whereby a group of mental processes is split off from the mainstream of consciousness, or behaviour loses its relationship with the rest of the personality.

dissociative amnesia: A dissociative disorder in which the person suddenly becomes unable to recall important personal information to an extent that cannot be explained by ordinary forgetfulness.

dissociative disorders: Disorders in which the normal integration of consciousness, memory, or identity is suddenly and temporarily altered; dissociative amnesia, dissociative fugue, dissociative identity disorder (multiple personality), and depersonalization disorder are examples.

dissociative fugue: Disorder in which the person experiences total amnesia, moves, and establishes a new identity.

dissociative identity disorder (DID): A rare dissociative disorder in which two or more fairly distinct and separate personalities are present within the same individual, each with his or her own memories, relationships, and behaviour patterns, with only one of them dominant at any given time. Formerly called multiple personality disorder.

divorce mediation: A form of couples (marital) therapy in which a distressed couple is helped to collaborate on issues such as child custody outside the adversarial framework of a formal legal process.

dizygotic (DZ) twins: Birth partners who have developed from separate fertilized eggs and who are only 50 percent alike genetically, no more so than siblings born from different pregnancies; sometimes called fraternal twins.

dominant gene: One of a pair of genes that predominates over the other and determines that the trait it fosters will prevail in the phenotype.

dopamine: A catecholamine that is both a precursor of norepinephrine and itself a neurotransmitter of the central nervous system. Disturbances in certain of its tracts apparently figure in schizophrenia and Parkinson’s disease.

dopamine activity theory: The view that schizophrenia arises from an increase in the number of dopamine receptors.

double-bind theory: An interpersonal situation in which an individual is confronted over long periods of time by mutually inconsistent messages to which she or he must respond, formerly believed by some theorists to cause schizophrenia.

double-blind procedure: A method for reducing the biasing effects of the expectations of research participant and experimenter; neither is allowed to know whether the independent variable of the experiment is being applied to the participant.

double depression: A comorbid condition that applies to someone characterized by both dysthymia and major depression.

Down syndrome (trisomy 21): A form of mental retardation generally caused by an extra chromosome. The child’s IQ is usually less than 50, and the child has distinctive physical characteristics, most notably slanted eyes.

dream analysis: A key psychoanalytic technique in which the unconscious meanings of dream material are uncovered.

drive: A construct explaining the motivation of behaviour, or an internal physiological tension impelling an organism to activity.

drug abuse: See substance abuse.

drug addiction: See substance dependence.

DSM-IV: The current Diagnostic and Statistical Manual of the American Psychiatric Association.

dualism: Philosophical doctrine, advanced most definitively by Descartes, that a human being is both mental and physical and that these two aspects are separate but interacting. Contrast with monism.

Durham decision: A 1954 U.S. court ruling that an accused person is not ascriptively responsible if his or her crime is judged attributable to mental disease or defect.

dysfunction: An impairment or disturbance in the functioning of an organ, organ system, behaviour, or cognition.

dyslexia: A disturbance in the ability to read; it is one of the learning disorders.

dyspareunia: Painful or difficult sexual intercourse; the pain or difficulty is usually caused by infection or a physical injury, such as torn ligaments in the pelvic region.

dysthymic disorder: State of depression that is long lasting but not severe enough for the diagnosis of major depression.