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object permanence The conviction that an object remains perceptually constant over time and exists even when it is out of sight. According to Piaget, this does not develop until infants are eight months old or more.
observational learning A mechanism of socialization whereby a child observes another person who serves as a model and then proceeds to imitate what that model does.
observational study A study in which the investigator does not manipulate any of the variables but simply observes their relationship as they occur naturally.
obsessive-compulsive disorder (OCD) A disorder whose symptoms are obsessions (persistent and irrational thoughts or wishes) and compulsions (uncontrollable, repetitive acts), which seem to be defenses against anxiety. A member of a diagnostic category called anxiety disorders, which also includes generalized anxiety disorder and phobias.
occipital lobe The rearmost lobe in each cerebral hemisphere, which includes the primary visual projection area.
OCD See obsessive-compulsive disorder.
OCD spectrum disorders A family of disorders believed to derive from the same genetic inheritance, and involving the basal ganglia and frontal lobes. All involve some form of obsessive and compulsive symptoms and may benefit from the same kinds of medications as OCD.
Oedipus complex In psychoanalytic theory, a general term for the cluster of impulses and conflicts hypothesized to occur during the phallic phase, at around age five. In boys, a fantasized form of intense, possessive sexual love is directed at the mother, which is soon followed by hatred for and fear of the father. As the fear mounts, the sexual feelings are pushed underground and the boy identifies with the father. An equivalent process is hypothesized in girls and is called the Electra complex.
one-trial learning In classical conditioning, the establishment of a conditioned response (CR) after only one pairing of conditioned stimulus (CS) and unconditioned stimulus (US).
operant In Skinner's system, an instrumental response, defined by the effect it has (the way it "operates") on the environment. See also instrumental conditioning.
operant conditioning See instrumental conditioning.
operations According to Piaget, the mental transformations and relationships that underlie logical thought.
opponent-process theory (1) A theory of color vision that proposes three pairs of color antagonists: red-green, blue-yellow, and white-black. Excitation of one member of a pair automatically inhibits the other member. (2) A theory of motivation that asserts that the nervous system tends to counteract any deviation from the neutral point on the pain-pleasure dimension. If the original stimulus is maintained, there is an attenuation of the emotional state one is in; if it is withdrawn, the opponent process reveals itself, and the emotional state swings sharply in the opposite direction.
optic flow The phenomenon wherein an object's retinal image enlarges as we approach the object and shrinks as we retreat from it. It is used as a depth cue by the visual system.
optic nerve The bundle of fibers that proceeds from each eyeball to the brain, made up of axons whose cell bodies are retinal ganglion cells.
oral character According to Freud, a personality type based on a fixation at the oral stage of development and whose manifestations can include passive dependency or "biting" hostility. See also oral stage.
oral stage In psychoanalytic theory, the earliest stage of psychosexual development during which the primary source of bodily pleasure is stimulation of the mouth and lips, as in sucking at the breast.
ordinal scale A scale in which responses are rank-ordered by relative magnitude but in which the intervals between successive ranks are not necessarily equal. See also categorical scale, interval scale, nominal scale, ratio scale.
orexins Hormones synthesized in the lateral hypothalamus that are potent elicitors of eating.
organic brain syndromes Mental disorders that are reliably associated with definitive brain damage (e.g., Alzheimer's disease).
orgasm A brief episode during sexual activity when the organism experiences involuntary muscle contractions throughout the body. In males, rhythmic contractions of the urethra expel semen during orgasm.
orienting The tendency of an organism to shift its attention and sensory surfaces (e.g., by moving the eyes or turning the ears) to inspect a novel or unexpected stimulus.
oscilloscope An electronic monitoring device that uses a cathode ray tube (CRT) to display electrical signals such as electrocardiograph signals or action potentials.
outcome expectations A set of beliefs, drawn from experience, about what the consequences (rewards or punishments) of certain actions are likely to be.
outer ear The portion of the structures of the ear that includes the earflap, the auditory canal, and the outer surface of the eardrum.
out-group A social group with which one does not identify or to which one does not belong.
out-group homogeneity effect A phenomenon related to stereotyping in which a member of a group (the in-group) tends to view members of another group (the out-group) as more alike (less varied) than are members of his or her own group.
oval window The membrane separating the middle ear from the inner ear.
overregularization errors A pattern of mistakes in which a person treats irregular cases as though they followed the rules, for example, saying "goed" instead of "went," or "foots" instead of "feet."
oxytocin A hormone manufactured mostly in the hypothalamus that plays an important role in regulating sexual activity, nesting, and breast-feeding.
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