A-B-A design Experimental design in which participants first experience the baseline condition (A), then experience the experimental treatment (B), and then return to the baseline (A).
Abnormal psychology The area of psychological investigation concerned with understanding the nature of individual pathologies of mind, mood, and behavior.
Absolute threshold The minimum amount of physical energy needed to produce a reliable sensory experience; operationally defined as the stimulus level at which a sensory signal is detected half the time.
Accommodation The process by which the ciliary muscles change the thickness of the lens of the eye to permit variable focusing on near and distant objects.
Accommodation According to Piaget, the process of restructuring or modifying cognitive structures so that new information can fit into them more easily; this process works in tandem with assimilation.
Acquisition The stage in a classical conditioning experiment during which the conditioned response is first elicited by the conditioned stimulus.
Action potential The nerve impulse activated in a neuron that travels down the axon and causes neurotransmitters to be released into a synapse.
Acute stress A transient state of arousal with typically clear onset and offset patterns.
Addiction A condition in which the body requires a drug in order to function without physical and psychological reactions to its absence; often the outcome of tolerance and dependence.
Ageism Prejudice against older people, similar to racism and sexism in its negative stereotypes.
Aggression Behaviors that cause psychological or physical harm to another individual.
Agoraphobia An extreme fear of being in public places or open spaces from which escape may be difficult or embarrassing.
AIDS Acronym for acquired immune deficiency syndrome, a syndrome caused by a virus that damages the immune system and weakens the body's ability to fight infection.
Algorithm A step-by-step procedure that always provides the right answer for a particular type of problem.
All-or-none law The rule that the size of the action potential is unaffected by increases in the intensity of stimulation beyond the threshold level.
Altruism Prosocial behaviors a person carries out without considering his or her own safety or interests.
Alzheimer's disease A chronic organic brain syndrome characterized by gradual loss of memory, decline in intellectual ability, and deterioration of personality.
Amacrine cells Cells that integrate information across the retina; rather than sending signals toward the brain, amacrine cells link bipolar cells to other bipolar cells and ganglion cells to other ganglion cells.
Ambiguity A perceptual object that may have more than "one interpretation.
Amnesia A failure of memory caused by physical injury, disease, drug use, or psychological trauma.
Amygdala The part of the limbic system that controls emotion, aggression, and the formation of emotional memory.
Analytic psychology A branch of psychology that views the person as a constellation of compensatory internal forces in a dynamic balance.
Anchoring heuristic An insufficient adjustment up or down from an original starting value when judging the probable value of some event or outcome.
Animal cognition The cognitive capabilities of nonhuman animals; researchers trace the development of cognitive capabilities across species and the continuity of capabilities from nonhuman to human animals.
Anorexia nervosa An eating disorder in which an individual weighs less than 85 percent of her or his expected weight but still controls eating because of a self-perception of obesity.
Anticipatory coping Efforts made in advance of a potentially stressful event to overcome, reduce, or tolerate the imbalance between perceived demands and available resources.
Anxiety An intense emotional response caused by the preconscious recognition that a repressed conflict is about to emerge into consciousness.
Anxiety disorders Mental disorders marked by physiological arousal, feelings of tension, and intense apprehension without apparent reason.
Apparent motion A movement illusion in which one or more stationary lights going on and off in succession are perceived as a single moving light; the simplest form of apparent motion is the phi phenomenon.
Archetype A universal, inherited, primitive, and symbolic representation of a particular experience or object.
Assimilation According to Piaget, the process whereby new cognitive elements are fitted in with old elements or modified to fit more easily; this process works in tandem with accommodation.
Association cortex The parts of the cerebral cortex in which many high-level brain processes occur.
Attachment Emotional relationship between a child and the "regular caregiver.
Attention A state of focused awareness on a subset of the available perceptual information.
Attitude The learned, relatively stable tendency to respond to people, concepts, and events in an evaluative way.
Attribution theory A social-cognitive approach to describing the ways the social perceiver uses information to generate causal explanations.
Attributions Judgments about the causes of outcomes.
Audience design The process of shaping a message depending on the audience for which it is intended.
Auditory cortex The area of the temporal lobes that receives and processes auditory information.
Auditory nerve The nerve that carries impulses from the cochlea to the cochlear nucleus of the brain.
Automatic processes Processes that do not require attention; they can often be performed along with other tasks without interference.
Autonomic nervous system (ANS) The subdivision of the peripheral nervous system that controls the body's involuntary motor responses by connecting the sensory receptors to the central nervous system (CNS) and the CNS to the smooth muscle, cardiac muscle, and glands.
Availability heuristic A judgment based on the information readily available in memory.
Aversion therapy A type of behavioral therapy used to treat individuals attracted to harmful stimuli; an attractive stimulus is paired with a noxious stimulus in order to elicit a negative reaction to the target stimulus.
Axon The extended fiber of a neuron through which nerve impulses travel from the soma to the terminal buttons.