-A-
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 in Piaget’s development theory
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.
Acculturation
The process of acquiring the values, beliefs, attitudes, and behavior of a new culture.
Acetylcholine
One of the most common neurotransmitters in the human nervous system, it is manufactured and delivered by motor neurons.
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.
Active touch
The manipulation of an object, which produces information about the shape, weight, length and other characteristics of the object.

Actor observer effect
The tendency to attribute the behavior of others to internal causes while attributing one’s own behavior to situational causes.
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.
Adrenal glands , adrenals
The endocrine glands responsible for secreting the hormones adrenaline (epinephrine) and noradrenaline (norepinephrine), which regulate bodily functions and affect mood and emotion, blood pressure, blood sugar level, and redistribution of blood between internal organs and voluntary muscles
Adulthood
The period of development that takes place from puberty to death
Afterimage
A sensory impression that lasts after removal of the stimulus that caused it
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.
Agonists
A group of psychoactive drugs that cause neurotransmitters to be released, prevent deactivation of neurotransmitters, or mimic the effects of neurotransmitters by binding to their receptors, drugs such as nicotine and cocaine are examples
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.
Allergens
Substances, such as pollen, household dust, tobacco smoke, fabric softener, and perfume, that trigger allergic responses.
All-or-none law (Principle)
The rule that the size of the action potential is unaffected by increases in the intensity of stimulation beyond the threshold level.
Altered state of consciousness
A condition r state that is considered outside the realm of normal consciousness, resulting from any number of different conditions, such as sensory deprivation or overstimulation, hypnosis, meditation, or the use of psychoactive drugs.
Altruism
Pro-social behaviors a