O

obedience Following the specific commands of a person in authority. 18

obesity An excess of body weight. 12

object permanence The ability to represent objects “in the head”—to know that things exist even when they cannot be physically sensed. 9

object relations theory An approach to the ego that emphasizes the importance of early attachments to the development of the child’s ego, the child’s feelings about the self, and later interpersonal relationships. 13

observational learning The process of learning how to act by watching the behavior of others. 6, 13

obsession An unwanted thought or image that keeps intruding into consciousness, despite a person’s efforts to dismiss it. 15

occipital lobes A rear portion of each cerebral hemisphere that is concerned with the reception and analysis of visual information. 3

Oedipus conflict According to Freud, the tendency of children to see themselves as rivals of the same-sex parent for the affection of the parent of the opposite sex. When resolved, the conflict leads to adoption of the values of the same-sex parent. 10

olfaction The sense of smell. 4

operant conditioning Learning to either make or withhold a particular response because of its consequences. 6

opiates Narcotics such as morphine and heroin that mimic the action of endorphins, thus modulating pain and pleasure. 3

opponent-process theory Proposed by Ewald Hering, the theory of color vision stating that there are four primary colors which, when linked in complementary pairs in the brain, form “opponent” systems. One opponent system contains cells that are stimulated by red and inhibited by green, and others that are stimulated by green and inhibited by red. In a second opponent system, yellow and blue similarly act in opposition to each other. A third opponent system is achromatic and enables the perception of brightness. 4

optic nerve The nerve that carries visual information from the eye to the brain. 4

optimal arousal theory The view that humans are motivated to maintain a comfortable level of arousal. If they are understimulated, they act to increase their arousal. If overstimulated, they act to bring their level of arousal down. 11

oral stage According to Freud, the first psychosexual stage (occurring during the first year of life) in which sexual pleasure is focused on the mouth’s activities. 13

orgasmic phase The third stage of Masters and Johnson’s sexual response cycle, characterized by strong muscle contractions, rise in blood pressure and heartbeat, and extremely heightened arousal accompanied by feelings of intense pleasure as muscle tension is released. 11

out-groups Those groups to which one does not belong. 17

oval window A membrane between the middle ear and the inner ear that transmits sound to the cochlea. 4

overextension The phenomenon that occurs when a young child uses a word to describe many similar things. For example, the word dada is used in reference to every male person the child encounters. 9

overregularization The tendency of preschoolers to overextend a grammatical rule to instances where it does not apply. 9