The tendency for an activity to recur even when there is no apparent stimulus and the activity has no obvious usefulness.

Psychological events that do not seem to be explicable by known scientific principles; the subject matter of PARAPSYCHOLOGY.

BRAIN surgery directed at curing a severe psychological disorder.

A situation developed out of GAME THEORY and used by SOCIAL PSYCHOLOGISTS in the study of bargaining BEHAVIOUR. In the game two suspects are caught by the police and questioned separately about the crime. If one prisoner confesses and the other does not the squealer is set free and the fall guy takes the rap. If both confess, both are convicted but dealt with leniendy. If neither confesses, both benefit because they cannot then be convicted.

In STATISTICS, one-hundredth of the total number of scores in a ranked DISTRIBUTION. For example, the ninetieth percentile is the point below which lie 90 per cent of the scores.

The study of the relationship between external stimuli from the physical world and the subjective sensations they produce. The psychological processes involved are still as much a part of the subject matter of EXPERIMENTAL PSYCHOLOGY as they were when these problems were studied in the first psychological laboratories established in the 1870s. See WUNDT.

Someone who practises PSYCHOTHERAPY. He or she is usually a PSYCHIATRIST, a CLINICAL PSYCHOLOGIST or a psychiatric social worker but in many places where psychotherapy’ is practised no special qualifications are legally required.

The study of criminal BEHAVIOUR and its treatment.

Used in CONDITIONING as a way of increasing the strength of a given response by rewarding it.

A social group with which one associates on more or less equal terms. Used especially of CHILDHOOD and ADOLESCENCE.