Glossary of Psychological Terms
Definitions of terms used in psychology, psychometric testing and occupational assessment, organised alphabetically.
Dark adaptation
The gradual process by which the eye adjusts to lowered levels of illumination, chiefly through changes in the pupil and increased sensitivity of the retina's rod photoreceptors.
Darwin, Charles (1809-1882)
The English naturalist who presented the systematic evidence for evolution and proposed natural selection as its mechanism, in On the Origin of Species (1859). His work reshaped psychology's understanding of instinct, emotion and the continuity between human and animal behaviour. See also: social Darwinism, a later and largely discredited application of his ideas to human societies.
Darwinian reflex
A grasping reflex found in very young infants and some young animals — the tendency to grip a bar or finger firmly enough to be briefly suspended by it — thought to be a vestige of an ancestral clinging reflex.
David's Dictum
An informal, humorous observation that in any given place, at any given time, people are never quite where they are supposed to be — a light-hearted combination of Sod's Law and the physicist's Heisenberg Uncertainty Principle.
Death instinct
In Freud's later theory, an unconscious drive toward self-destruction, aggression and the eventual dissolution of the personality — always contrasted with the life instinct (Eros). The concept, sometimes called Thanatos, was taken up most seriously by later analysts such as Melanie Klein.
Decentring
The tendency to keep perceiving or responding to a situation in a way that changed circumstances have made ineffective or outdated — a psychological, individual-level parallel to the social phenomenon of cultural lag.
Decision rule
In consumer psychology, the conscious or unconscious rule of thumb, or heuristic, that a person applies when making a purchasing decision, allowing a choice without weighing every possible factor.
Declarative knowledge
Factual knowledge — conscious knowledge that something is the case, such as knowing a date or a definition. Compare with procedural knowledge, which is knowledge of how to do something.
Decoding
In information processing, the process by which a recipient attempts to interpret and make sense of a communication. Compare with encoding, the sender's process of putting a message into a transmittable form.
Decortication
The surgical removal of the cerebral cortex, used historically in animal research to study the functions the cortex supports by observing their loss.
Deductive reasoning
A form of reasoning that draws specific conclusions that necessarily follow from a given set of general premises or assumptions. Compare with inductive reasoning, which builds general conclusions from specific observations.
Deep processing
In information-processing accounts of memory, the encoding of information in a way that is personally meaningful to the individual, involving genuine understanding or interpretation of the material rather than surface features. Proposed by Fergus Craik and Robert Lockhart as part of their levels-of-processing framework, deep processing generally produces stronger, more durable memories than shallow processing, which involves only superficial sensory analysis such as rote repetition.
Defence mechanism
Freud's term for the range of strategies by which the ego protects itself from threatening unconscious material arising from the id or superego, or from external dangers. Key examples include denial, projection, rationalisation, reaction formation, regression, repression, sublimation and undoing.
Defensive attribution
A concept important in both clinical and social psychology describing the tendency to blame the victim of a frightening misfortune, as a way of avoiding the anxiety-provoking thought that one could just as easily be a victim oneself — for example, the belief that victims of crime somehow provoked it.
Definition of the situation
The way a person perceives and interprets the nature of a social interaction they are part of. Associated with sociologist W. I. Thomas's dictum that if people define a situation as real, it becomes real in its practical consequences, regardless of its objective truth.
Dehumanisation
The process of perceiving or treating other people as less than fully human, often driven by fear and serving to reduce the guilt associated with aggression toward them. See also: diabolism.
Deindividuation
A state of feeling anonymous and submerged within a crowd, marked by a blurring of individual identity and a loosening of ordinary inhibitions on behaviour. See also: collective mind, contagion theory of crowds.
Deja vu
Literally “already seen”: the illusion of recognising something as familiar even though it is, in fact, a new experience — thought to arise from a brief disturbance in the brain's memory-processing functions.
Delayed gratification
The act of forgoing an immediate reward in favour of a greater reward later — saving rather than spending, for instance. Long studied in developmental and social psychology (notably in Walter Mischel's “marshmallow test”) as a marker of self-control associated with later life outcomes.
Delinquency
Behaviour, particularly among teenagers (“juvenile delinquency”), that breaches the law — theft or vandalism, for example. Explanations proposed over the years have ranged from deprived environment and unhappy home life to innate character and the self-fulfilling prophecy created by being formally labelled “delinquent.”
Delirium
An altered, fluctuating state of consciousness marked by confusion, disorientation, delusions, hallucinations and illusions, typically arising acutely from an underlying medical cause such as infection, medication or withdrawal.
Delirium tremens
A severe delirium suffered by people with chronic alcohol dependence during withdrawal from alcohol — a classic and potentially life-threatening withdrawal symptom, marked by tremor, confusion and vivid hallucinations.
Delta waves
Large, slow brain waves, occurring at roughly three cycles per second, characteristic of deep, dreamless sleep.
Delusion
A firmly held false belief that persists despite clear evidence or reasoning against it; often a symptom of psychosis. See also: delusions of grandeur, delusions of persecution.
Delusions of grandeur
A delusion in which a person believes themselves to be an unusually important, celebrated or exalted individual, disproportionate to reality.
Delusions of persecution
A delusion in which a person believes their problems are caused by other people deliberately conspiring against them.
Demand characteristics
In experimental psychology, the conscious or unconscious cues within an experimental situation that reveal to participants what the experimenter expects of their behaviour. Participants may then act to confirm those expectations, to deliberately defy them, or to present themselves favourably, all of which can distort results. See also: experimenter bias.
Dementia
A progressive, disabling disorder affecting both cognition and emotion, impairing higher mental processes such as learning, thinking, decision-making and, especially, memory, and typically accompanied by changes in personality and social behaviour.
Denial
A defence mechanism in which a person refuses to acknowledge either a painful reality or the existence of an anxiety-provoking impulse or feeling within themselves.
Dependence
Used in at least three distinct senses: (1) generally in science, where one thing caused by another is said to be dependent on it; (2) in clinical psychology, where a person needs someone or something in order to function in their regular activities; and (3) in social psychology, where members of a group rely on each other to define and validate a shared sense of reality.
Dependent variable
In an experiment, the variable whose value depends on, and is measured in response to changes in, the independent variable. The independent variable is the manipulated stimulus; the dependent variable is the measured response, and any change in it is attributed to the effect of the stimulus.
Depression
One of the most common forms of emotional disturbance, ranging in severity from everyday low mood to a disabling, sometimes psychotic, state of hopelessness. Characterised by anxiety, dejection and a general reduction in activity and motivation. Clinicians distinguish several forms, including major depression, psychotic depression, dysthymia (persistent low-grade depression), mixed anxiety-depression, and the depressive episodes of bipolar disorder; there remains ongoing debate over the relative roles of unconscious psychological conflict and biochemical processes in its causes.
Deprivation
The absence of something considered essential to psychological wellbeing — commonly discussed in relation to sensory deprivation, maternal deprivation, or social deprivation.
Depth interview
An interviewing approach in which the interviewer attempts to move beyond the interviewee's conscious, surface-level responses to probe underlying unconscious feelings and motivations.
Depth of processing
The American term for levels of processing, the theory that deeper, more meaningful encoding of information produces stronger memory than shallow, surface-level encoding.
Depth perception
The awareness of how far away objects are from the observer, and the related ability to perceive the world as three-dimensional — having depth as well as height and width — drawing on cues including binocular disparity.
Depth psychology
The study of the role the unconscious plays in shaping human behaviour, most closely associated with psychoanalysis. See also: dynamic psychology.
Descriptive statistics
Statistics that summarise or describe a set of measurements — for instance, measures of central tendency such as the mean, median and mode. Compare with inferential statistics, which draw conclusions about a wider population from a sample.
Desensitisation
A reduction in emotional sensitivity to something previously found distressing or undesirable; often achieved deliberately through a form of behaviour therapy that pairs a feared stimulus with a relaxed state, gradually replacing the fear response.
Determinism
The philosophical position that every event, including human behaviour, has a cause, and follows necessarily from prior conditions — implying that complete knowledge of those conditions would allow full understanding, even prediction, of any given behaviour.
Developmental psychology
The branch of psychology concerned with the interacting physical, psychological and social changes that occur across a person's lifespan. Historically focused mainly on child and adolescent development, the field has increasingly expanded to cover middle adulthood and old age (senescence) as well.
Developmental tasks
Skills and achievements generally considered necessary for children to attain at particular ages for healthy psychological development — for example, walking, talking and reading at expected developmental stages.
Deviant
A person whose behaviour violates the prevailing moral or social norms of their society; the label carries strong social and evaluative weight beyond mere statistical rarity.
Deviation
A departure from the norm; in statistics, specifically the difference between a given score and the mean of a distribution, used in calculating measures such as standard deviation.
Diabolism
The attribution of devil-like or evil qualities to a person or group, a particular form of dehumanisation frequently seen in wartime, where casting an enemy as wholly bad helps relieve anxiety and guilt about aggression toward them.
Diagnostic test
An instrument used by psychologists to investigate and clarify the nature of a mental or emotional difficulty, potentially including projective techniques as well as structured clinical measures.
Difference limen
See just noticeable difference — the technical term for the smallest detectable difference between two stimuli.
Differential threshold
See just noticeable difference.
Differentiation
In conditioning, a training procedure by which an animal or person learns to distinguish between two similar stimuli, or between two similar responses, responding differently to each.
Diffusion of responsibility
In social psychology, the phenomenon whereby the perceived responsibility to act — for instance, to help in an emergency — becomes spread across everyone present, sometimes so thinly that no individual takes action. The same underlying process is also invoked to explain social loafing, in which people exert less individual effort on a task the more people are contributing to it.
Digit-span test
A test of memory span in which a person hears a series of random digits and must immediately recall them in order; most people can reliably recall around seven digits, a figure closely tied to estimates of short-term memory capacity.
Diminishing returns
A concept borrowed from economics describing an improvement that becomes progressively smaller with each additional increment of effort. In psychology, applied particularly to learning and memory, where an initial large gain from practice is followed by steadily smaller gains from further repetition.
Dionysian
An anthropological concept borrowed from ancient Greece, where Dionysus, god of wine and physical pleasure, represented the primitive, impulsive and emotional aspects of human nature. Always contrasted with the Apollonian, representing restraint, order and rationality.
Dipsomania
A historical term for a mania taking the form of periodic, uncontrollable cravings for alcohol; unlike chronic alcoholism, the person is not dependent on daily drinking, and the episodic bouts were thought to reflect an underlying emotional disturbance.
Discourse analysis
The analysis of spoken or written communication using units of meaning longer than a single sentence, examining how language constructs meaning, identity and social relations across a text or conversation.
Discrimination
In its core psychological sense, simply the ability to perceive a difference between two sensory stimuli. In social and political contexts, the term instead refers to acting unfairly against people on the basis of a perceived difference, such as race, sex or age.
Disinhibition
A phenomenon first observed in classical conditioning: if a conditioned response (such as salivating to a stimulus) has been inhibited by withdrawing the reward, introducing a new, unrelated stimulus can suddenly restore the response — as though the inhibition itself has been temporarily suppressed.
Disintegration
Literally, the loss of integration or organisation among parts that would normally function harmoniously together. In psychology, most often applied to personality, whose components of thought, feeling and action can disintegrate under the stress of severe psychological disturbance. See also: psychosis.
Displacement
In psychoanalysis, the unconscious shifting of an emotional response from its true object onto a substitute object that feels less threatening to the ego — for example, venting frustration at a television rather than confronting one's employer. This mechanism is considered central to dream symbolism. See also: dream wish, dream work.
Display
In ethology, the tendency of an animal, typically a male, to present itself to best advantage — whether to intimidate a rival or attract a mate — in response to the appropriate stimulus of another animal of the same species. The concept has sometimes been applied, loosely, to human adolescent social behaviour.
Display rules
A concept, drawn partly from sociology, for the socially learned norms governing how genuine feelings are masked or modified in favour of an outwardly appropriate expression — for example, smiling politely while frustrated.
Dissociation
A state in which a set of otherwise integrated psychological processes splits off from the rest of a person's personality and appears to function with a degree of independence. Occurs in certain forms of amnesia and underlies what is now called dissociative identity disorder, historically termed multiple personality.
Distributed cognition
The idea that many complex goals can only be achieved through the collaboration of multiple people who pool their distinct knowledge, skills and perspectives, rather than by any one individual's cognition alone. Compare with parallel distributed processing, a related concept from computational modelling of the mind.
Distributed practice
A learning technique in which study or practice sessions are spread out over the available time, rather than concentrated together; generally shown to produce more durable learning than massed, or “crammed,” practice.
Distribution
A statistical term for the way a set of data is arranged across categories or values, often displayed as a graph or table — for example, a normal distribution.
Distributive justice
A situation in which rewards or resources are allocated fairly according to merit or need. Although rarely fully realised in practice, people are thought to need to believe such fairness generally prevails, consistent with the just-world hypothesis.
Divergent thinking
Creative, exploratory thinking that moves away from the obvious or conventional to generate multiple possible solutions to a problem. Contrasted with convergent thinking, which narrows toward one correct answer. See also: lateral thinking.
Dizygotic twins
Commonly known as fraternal twins: twins who develop from two separate fertilised eggs (zygotes), and are therefore genetically no more similar than ordinary siblings, may differ in sex, and need not closely resemble one another. Contrast with monozygotic twins.
Dominance
Describes a person with a strong need to control others or to be regarded as more important than them. See also: dominant gene, cerebral dominance, which use the term in unrelated biological senses.
Dominant gene
A gene that determines the appearance of a particular physical characteristic in an offspring by overriding, or “dominating,” the effect of the alternative (recessive) version of that gene inherited from the other parent.
Doppler effect
The apparent increase or decrease in the frequency of light or sound waves as their source moves toward or away from an observer — for example, the change in pitch heard as a train's whistle passes by.
Double-bind theory
The theory that contradictory messages or conflicting demands, particularly within an intense, dependent relationship such as that between parent and child, can induce severe stress and, in some formulations, contribute to conditions such as schizophrenia — particularly where the person can neither resolve nor escape the underlying dilemma. See also: experimental neurosis.
Double-blind technique
An experimental method, especially common in drug trials, in which neither the participant nor the person administering the treatment knows which condition (such as active drug or placebo) is being given at any point, in order to guard against both conscious and unconscious experimenter bias.
Down's syndrome
A form of congenital intellectual disability caused by a genetic abnormality (an extra copy of chromosome 21), accompanied by characteristic facial features and, often, particular health considerations. Named after physician John Langdon Down; the older term “mongolism,” based on a since-discredited comparison of facial features, is no longer used. The likelihood of Down's syndrome increases with maternal age.
Draw-a-Person Test
A projective technique in which a child is asked to draw a person, used both as a rough measure of intellectual development and, in research contexts, to explore self-concept.
Dream
Imagery, thought and sensation occurring during sleep, usually possessing some internal coherence but often including bizarre, fragmented or confusing elements as well.
Dream interpretation
A foundational technique of psychoanalysis, in which a patient's free association to elements of a recalled dream is used to uncover its hidden meaning. Freud described dreams as “the royal road to the unconscious,” holding that no unconscious activity is random, and that dream symbolism offers a crucial clue to a patient's underlying motivations. See also: latent content, manifest content.
Dream wish
In psychoanalysis, the disguised form in which a repressed wish emerges within the content of a dream.
Drive
A general term for a strong underlying urge in an animal or human, including urges sometimes described as instinctive. See also: instinct, motivation.
Dual personality
The simplest form of what is now called dissociative identity disorder (historically, multiple personality) — the coexistence of two distinct personality states within one individual, as in the fictional case of Jekyll and Hyde.
Dyad
A sociological term for a group consisting of exactly two people, the smallest possible social group, with its own distinct dynamics of interaction.
Dynamic psychology
A term for the aspects of psychology primarily concerned with motivation and with uncovering the underlying causes of behaviour. Psychoanalysis and related approaches are the leading examples, though Gestalt psychology and other approaches concerned with underlying psychological forces also qualify.
Dyslexia
A developmental impairment of word perception involving significant difficulty learning to read or to process written language accurately, despite otherwise normal intelligence. Contrast with alexia, which is an acquired reading impairment resulting from brain injury.
