Abnormal behavior—behavior that is statistically
unusual, maladaptive, and personally distressing to
the individual.
Absolute threshold—the weakest level of a stimulus
that can be correctly detected at least half the time.
Abstract learning—learning in which the relation-
ship between and among stimuli is more impor-
tant than the physical features of the stimuli.
Accommodation—process by which we modify
our schemas to fit new information; process of
changing the curvature of the lens to focus light
rays on the retina of the eye.
Acetylcholine (ACh)—a neurotransmitter that causes
contraction of skeletal muscles, helps regulate heart
muscles, is involved in memory, and also transmits
messages between the brain and spinal cord. Lack
of ACh is associated with Alzheimer’s disease.
Achievement motive—the desire to accomplish some-
thing, to excel, or reach a standard of excellence.
Achievement tests—tests that measure our current
mastery of a subject or specific program of study.
Acoustic encoding—the encoding of sound, espe-
cially the sound of words.
Acquisition—learning a new behavior; refers to the
initial stage of conditioning in which the new
response is established and gradually strengthened.
Action potential—also called an impulse, the “firing”
of a neuron; a net flow of sodium ions into the cell
that causes a rapid change in potential across the
membrane when stimulation reaches threshold.
Activation-synthesis theory—during REM sleep the
brainstem stimulates the forebrain with random
neural activity, which we interpret as a dream.
Active listening—Rogers’s term for hearing another
person with complete attention to what he or she
says and means through acknowledging feelings,
echoing, restating, and seeking clarification.
Actor-observer bias—tendency to focus on our own
situations and the other person, rather than his or
her situation, when we interpret behavior.
Acuity—ability to detect fine details; sharpness of
vision. Can be affected by small distortions in the
shape of the eye.
Adaptations—structures or behaviors that increase
chances of survival.Addiction—physiological dependence on a drug that
has changed brain chemistry, necessitating taking
the drug to avoid withdrawal symptoms.
Adrenal glands—endocrine glands atop kidneys.
Adrenal cortex, the outer layer, produces ste-
roid hormones such as cortisol, which is a stress
hormone. Adrenal medulla, the core, secretes
adrenaline (epinephrine) and noradrenaline
(norepinephrine), which prepare the body for
“fight or flight” like the sympathetic nervous
system does.
Affective (mood) disorder—disorder characterized
by significant shifts or disturbances in mood that
affect normal perception, thought, and behavior;
e.g., depression and bipolar disorders.
Afferent neuron—also called sensory neuron, nerve
cell in our PNS that transmits impulses from
receptors to the brain or spinal cord.
Affiliation motive—the need to be with others.
Age of viability—the end of the second trimester in
pregnancy; the point at which there is a reasonable
chance the fetus will survive if born prematurely.
Aggression—any behavior intended to hurt some-
one, either physically or psychologically.
Alarm response—first stage of Selye’s General
Adaptation Syndrome (GAS) to stress; involves
increasing activity of the sympathetic nervous
system speeding up heart rate and blood pressure,
and releasing adrenaline.
Albinism—recessive trait that produces lack of pig-
ment and involves quivering eyes and inability to
perceive depth with both eyes.
Algorithm—problem-solving strategy that involves
a slow, step-by-step procedure that guarantees a
solution to certain types of problems.
All-or-none principle—the law that the neuron
either generates an action potential when the stim-
ulation reaches threshold or it doesn’t fire when
stimulation is below threshold. The strength of the
action potential is constant whenever it occurs.
Altruism—an unselfish interest in helping others.
Alzheimer’s disease—a fatal neurocognitive disease
in which brain neurons progressively die, causing
loss of memory, reasoning, emotion, control of
bodily functions, then death.Glossary
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