Obedience -  Compliance with commands given by an authority figure.

Objective personality tests -  Tests that usually consist of self-report inventories. Commonly used objective tests include the MMPI-2, the 16PF, and the NEO Personality Inventory.

Objective test -  Generally a pencil-and-paper-type standardized test used to assess a psychological disorder.

Object permanence -  The ability to recognize that an object exists even when the object is not present and not perceived.

Object relations -  The relationships that people have with others, who are represented mentally as objects with certain attributes.

Observational learning -  A change in behavior or knowledge that happens by watching others. It can also be called vicarious conditioning.

Obsessions -  Persistent ideas, thoughts, impulses, or images that cause anxiety or distress.

Obsessive-compulsive disorder -  A disorder involving obsessions, compulsions, or both.

Occam’s razor -  See principle of parsimony.

Oedipus complex -  In psychoanalytic theory, a male child’s sexual desire for his mother and his hostility toward his father, whom he considers to be a rival for his mother’s love.

Operant conditioning -  A type of learning in which responses come to be controlled by their consequences.

Operational definition -  A way of stating precisely how a variable will be measured.

Opponent process theory -  A theory of color vision that states that the visual system has receptors responding in opposite ways to wavelengths associated with three pairs of colors.

Optic disk -  The point in the retina at which the optic nerve leaves the eye. This point is also called the blind spot.

Optic nerve -  A bundle of ganglion cell axons that originate in the retina.

Optimism -  The tendency to expect positive outcomes.

Ossicles -  Three bones in the middle ear called the hammer, the anvil, and the stirrup.

Outgroup -  A group to which one does not belong.

Overlearning -  Continuing to practice material even after it is learned in order to increase retention.

Overcompensation -  According to Alfred Adler, the attempt to cover up a sense of inferiority by focusing on outward signs of superiority such as status, wealth, and power.

Overconfidence effect -  The tendency for people to be too certain that their beliefs, decisions, estimates, and accuracy of recall are correct.