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Glossary

abnormal psychology The scientific study of mental disorders and their treatment.

absolute threshold The minimum amount of energy in a sensory stimulus detected 50% of the time.

accommodation (1) In vision, the focusing of light waves from objects of different distances directly on the retina. (2) In Piagetian theory, Piaget’s term for the modification of present schemas to fit with new experiences.

acetylcholine (ACh) A neurotransmitter involved in learning, memory, and muscle movement.

acquisition (1) In classical conditioning, acquiring a new response (the conditioned response) to the conditioned stimulus. (2) In operant conditioning, the strengthening of a reinforced operant response.

actor-observer bias The tendency to overestimate situational influences on our own behavior, but to overestimate dispositional influences on the behavior of others.

additive mixtures Direct mixtures of different wavelengths of light in which all of the wavelengths reach the retina and are added together.

agonist A drug or poison that increases the activity of one or more neurotransmitters.

agoraphobia An anxiety disorder indicated by a marked and persistent fear of being in places or situations from which escape may be difficult or embarrassing.

algorithm A step-by-step problem-solving procedure that guarantees a correct answer to a problem.

amnesic A person with severe memory deficits following brain surgery or injury.

amplitude The amount of energy in a wave, its intensity, which is the height of the wave at its crest.

amygdala A part of the brain that is involved in emotions by influencing aggression, anger, and fear and by providing the emotional element of our memories and the interpretation of emotional expressions in others.

anal stage of psychosexual development The second stage in Freud’s theory (from 18 months to 3 years), in which the erogenous zone is the anus, and the child derives pleasure from stimulation of the anal region through having and withholding bowel movements.

anchoring and adjustment heuristic A heuristic for estimation problems in which one uses his or her initial estimate as an anchor estimate and then adjusts the anchor up or down (often insufficiently).

antagonist A drug or poison that decreases the activity of one or more neurotransmitters.

anterograde amnesia The inability to form new explicit long-term memories for events following surgery or trauma to the brain. Explicit memories formed before the surgery or trauma are left intact.

antianxiety drugs Drugs used to treat anxiety problems and disorders.

antidepressant drugs Drugs used to treat depressive disorders.

antipsychotic drugs Drugs used to treat psychotic disorders.

anxiety disorders Disorders that share features of excessive fear and anxiety and related behavioral disturbances, such as avoidance behaviors.

appetitive stimulus A stimulus that is pleasant.

arousal theory A theory of motivation that proposes that our behavior is motivated to maintain an optimal level of physiological arousal.

assimilation Piaget’s term for the interpretation of new experiences in terms of present schemas.

association cortex All of the cerebral cortex except those areas devoted to primary sensory processing or motor processing. This is where all the higher-level cognitive processing that requires the association (integration) of information, such as perception and language, occurs.

attachment The lifelong emotional bond between infants and their mothers or other caregivers, formed during the first 6 months of life.

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attitudes Evaluative reactions (positive or negative) toward objects, events, and other people.

attribution The process by which we explain our own behavior and that of others.

authoritarian parenting A style of parenting in which the parents are demanding, expect unquestioned obedience, are not responsive to their children’s desires, and communicate poorly with their children.

authoritative parenting A style of parenting in which the parents are demanding, but set rational limits for their children and communicate well with their children.

automatic processing Memory processing that occurs subconsciously and does not require attention.

autonomic nervous system The part of the peripheral nervous system that regulates the functioning of our internal environment (glands and organs like the heart, lungs, and stomach).

availability heuristic A heuristic for judging the probability of an event by how available examples of the event are in memory (the more available, the more probable).

aversive stimulus A stimulus that is unpleasant.

axon The long, singular fiber projecting out of the cell body of a neuron, whose function is to conduct the neural impulse from the cell body to the axon terminals, triggering chemical communication with other neurons.

babbling The rhythmic repetition of various syllables including both consonants and vowels.

baby talk (parentese) The different format of speech that adults use when talking with babies that involves the use of shorter sentences with a higher, more melodious pitch.

basal ganglia A part of the brain that is involved in the initiation and execution of movements.

Beck’s cognitive therapy A type of cognitive therapy, developed by Aaron Beck, in which the therapist works to develop a warm relationship with the person and has the person carefully consider the evidence for his or her beliefs in order to see the errors in his or her thinking.

behavior modification The application of classical and operant conditioning principles to eliminate undesirable behavior and to teach more desirable behavior.

behavioral perspective A research perspective whose major explanatory focus is how external environmental events condition observable behavior.

behavioral therapy A style of psychotherapy in which the therapist uses the principles of classical and operant conditioning to change the person’s behavior from maladaptive to adaptive.

belief perseverance The tendency to cling to one’s beliefs in the face of contradictory evidence.

biological perspective A research perspective whose major explanatory focus is how the brain, nervous system, and other physiological mechanisms produce behavior and mental processes.

biomedical therapy The use of biological interventions, such as drugs, to treat mental disorders.

biopsychosocial approach Explaining abnormality as the result of the interaction among biological, psychological (behavioral and cognitive), and socio-cultural factors.

bipolar disorder A disorder in which recurrent cycles of depressive and manic episodes occur.

blindsight A condition in which a blind person has some spared visual capacities in the absence of any visual awareness.

blood–brain barrier A protective mechanism by which the blood capillaries supplying the brain create a barrier that prevents dangerous substances access to the brain.

bottom-up processing The processing of incoming sensory information as it travels up from the sensory structures to the brain.

Broca’s area An area in the cerebral cortex responsible for fluent speech production. It is in the left frontal lobe of the majority of people, regardless of handedness.

bystander effect The probability of a person’s helping in an emergency is greater when there are no other bystanders than when there are other bystanders.

Cannon-Bard theory A theory of emotion proposing that an emotion is determined from simultaneously occurring physiological arousal, behavioral responses, and cognitive appraisal.

case study A descriptive research method in which the researcher studies an individual in depth over an extended period of time.

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cell body The part of the neuron that contains its nucleus and the other biological machinery to keep the cell alive and that decides whether to generate a neural impulse in order to pass incoming information on to other neurons.

central nervous system (CNS) The brain and spinal cord.

centration The tendency to focus on only one aspect of a problem at a time.

cerebellum A part of the brain involved in the coordination of our movements, sense of balance, and motor learning.

cerebral cortex The layers of interconnected cells covering the brain’s two hemispheres. This is the control and information-processing center for the nervous system and where perception, memory, language, decision making, and all other higher-level cognitive processing occur.

chromosomes Molecules of DNA that hold the genetic instructions for every cell in the body.

chunk A meaningful unit in a person’s memory.

classical conditioning Acquiring a new response (the conditioned response) to a previously neutral stimulus (the conditioned stimulus) that reliably signals the arrival of an unconditioned stimulus.

client-centered therapy A style of psychotherapy, developed by Carl Rogers, in which the therapist uses unconditional positive regard, genuineness, and empathy to help the person to gain insight into his or her true self-concept.

closure The Gestalt perceptual organizational principle that the brain completes (closes) incomplete figures to form meaningful objects.

cochlea A snail-shaped structure in the inner ear that contains the receptor cells for hearing.

cognitive dissonance theory A theory, developed by Leon Festinger, that assumes people have a tendency to change their attitudes to reduce the cognitive discomfort created by inconsistencies between their attitudes and their behavior.

cognitive perspective A research perspective whose major explanatory focus is how mental processes, such as perception, memory, and problem solving, work and impact behavior.

cognitive therapy A style of psychotherapy in which the therapist attempts to change the person’s thinking from maladaptive to adaptive.

cohort effects People of a given age (cohorts) are affected by factors unique to their generation, leading to differences in performance between generations.

complementary colors Wavelengths of light that when added together produce white.

compliance Acting in accordance with a direct request from another person or group.

compulsion A repetitive and rigid behavior that a person feels compelled to perform in order to reduce anxiety.

concrete operational stage The third stage in Piaget’s theory of cognitive development, from age 6 to 12, during which children gain a fuller understanding of conservation and other mental operations that allow them to think logically, but only about concrete events.

conditioned response (CR) The response that is elicited by the conditioned stimulus in classical conditioning.

conditioned stimulus (CS) The stimulus that comes to elicit a new response (the conditioned response) in classical conditioning.

conditions of worth The behaviors and attitudes for which other people, starting with our parents, will give us positive regard.

conduction deafness Hearing loss created by damage to one of the structures in the ear responsible for mechanically conducting the auditory information to the inner ear.

cones Receptor cells in the retina that are principally responsible for bright light and color vision.

confirmation bias The tendency to seek evidence that confirms one’s beliefs.

conformity A change in behavior, belief, or both to conform to a group norm as a result of real or imagined group pressure.

conjunction fallacy Incorrectly judging the overlap of two uncertain events to be more probable than either of the two events.

conscious mind Freud’s term for what we are presently aware of.

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consciousness An individual’s subjective awareness of their inner thinking and feeling and their external environment.

conservation The knowledge that the quantitative properties of objects (such as mass and number) remain the same despite changes in appearance.

contextual effect The use of the present context of sensory information to determine its meaning.

continuous schedule of reinforcement In operant conditioning, reinforcing the desired operant response each time it is made.

control group In an experiment, the group not exposed to the independent variable.

conventional level of moral reasoning The second level of reasoning in Kohlberg’s theory of moral development in which moral reasoning is based on social rules and laws.

corpus callosum The bridge of neurons that connects the two cerebral hemispheres.

correlation coefficient A statistic that tells us the type and the strength of the relationship between two variables. The sign of the coefficient (+ or –) indicates the type of correlation—positive or negative, respectively. The absolute value of the coefficient (0.0 to 1.0) represents the strength of the correlation, with 1.0 being the maximum strength.

correlational study A research study in which two variables are measured to determine if they are related (how well either one predicts the other).

counterconditioning A type of behavioral therapy in which a maladaptive response is replaced by an incompatible adaptive response.

cross-sectional study A study in which the performances of groups of participants of different ages are compared with one another.

cue-dependent theory A theory of forgetting that proposes that forgetting is due to the unavailability of the retrieval cues necessary to locate the information in long-term memory.

cumulative record A record of the total number of operant responses over time that visually depicts the rate of responding.

dark adaptation The process by which the rods and cones through internal chemical changes become more and more sensitive to light in dim light conditions.

defense mechanism A process used by the ego to distort reality and protect a person from anxiety.

deindividuation The loss of self-awareness and self-restraint in a group situation that fosters arousal and anonymity.

delayed conditioning A classical conditioning procedure in which the conditioned stimulus precedes the unconditioned stimulus and remains present until after the unconditioned stimulus is presented so that the two stimuli occur together.

delusion A false belief.

demand characteristics Cues in the experimental environment that make participants aware of what the experimenters expect to find (their hypothesis) and how participants are expected to act.

dendrites Fibers projecting out of the cell body of a neuron whose function is to receive information from other neurons.

dependent variable In an experiment, a variable that is hypothesized to be affected by the independent variable and thus is measured by the experimenter.

depressive disorders Disorders that involve the presence of sad, empty, or irritable mood, accompanied by somatic and cognitive changes that significantly affect the individual’s capacity to function.

depth perception Our ability to perceive the distance of objects from us.

descriptive methods Research methods whose main purpose is to provide objective and detailed descriptions of behavior and mental processes.

descriptive statistics Statistics that describe the results of a research study in a concise fashion.

developmental psychology The scientific study of biological, cognitive, social, and personality development across the life span.

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deviation IQ score 100 plus or minus (15 × the number of standard deviations the person is from the raw score mean for their standardization group).

Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) The current version of the American Psychiatric Association’s diagnostic and classification guidelines for mental disorders.

difference threshold The minimum difference between two sensory stimuli detected 50% of the time. The difference threshold is also sometimes referred to as the just noticeable difference, or jnd.

diffusion of responsibility The lessening of individual responsibility for a task when responsibility for the task is spread across the members of a group.

discriminative stimulus In operant conditioning, the stimulus that has to be present for the operant response to be reinforced.

distractor task A memory task in which a small amount of information is briefly presented and then the participant is distracted from rehearsing the information for a variable period of time, after which the participant has to recall the information.

door-in-the-face technique Compliance is gained by starting with a large, unreasonable request that is turned down and following it with a more reasonable, smaller request.

dopamine A neurotransmitter involved in arousal and mood states, thought processes, and physical movement.

double-blind procedure A control measure in an experiment in which neither the experimenters nor the participants know which participants are in the experimental and control groups.

drive-reduction theory A theory of motivation that proposes that our behavior is motivated to reduce drives (bodily tension states) created by unsatisfied bodily needs in order to return the body to a balanced internal state.

effortful processing Memory processing that occurs consciously and requires attention.

ego The part of the personality that starts developing in the first year or so of life in order to find realistic outlets for the id’s instinctual drives.

egocentrism The inability to distinguish one’s own perceptions, thoughts, and feelings from those of others.

elaborative rehearsal A type of rehearsal in short-term memory in which incoming information is related to information from long-term memory to encode it into long-term memory.

electroconvulsive therapy (ECT) A biomedical treatment for severe depression that involves electrically inducing a brief brain seizure.

emotion A complex psychological state that involves a state of physiological arousal, an outward behavioral expression of the emotion, and a cognitive appraisal of the situation to determine the specific emotion and its intensity.

encoding The process of moving information from one memory stage to the next (from sensory memory into short-term memory or from short-term memory to long-term memory).

encoding failure theory A theory of forgetting that proposes that forgetting is due to the failure to encode the information into long-term memory.

encoding specificity principle The principle that the environmental cues (both internal and external) present at the time information is encoded into long-term memory serve as the best retrieval cues for the information.

endocrine glandular system The body’s other major communication system, in addition to the nervous system. Communication is achieved through hormones that are secreted by the endocrine glands and travel through the bloodstream to their target sites.

endorphins A group of neurotransmitters that are involved in pain relief and feelings of pleasure.

episodic memory Explicit memory for personal experiences.

erogenous zone The area of the body where the id’s pleasure-seeking energies are focused during a particular stage of psychosexual development.

experiment A research method in which the researcher manipulates one or more independent variables and measures their effect on one or more dependent variables while controlling other potentially relevant variables.

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experimental group In an experiment, the group exposed to the independent variable.

experimenter bias A process in which the person performing the research influences the results in order to portray a certain outcome.

explicit (declarative) memory Long-term memory for factual knowledge and personal experiences. This type of memory requires a conscious effort to remember and entails making declarations about the information remembered.

external locus of control The perception that chance or external forces beyond one’s personal control determine one’s fate.

extinction (1) In classical conditioning, the diminishing of the conditioned response when the unconditioned stimulus no longer follows the conditioned stimulus. (2) In operant conditioning, the diminishing of the operant response when it is no longer reinforced.

extrinsic motivation The desire to perform a behavior for external reinforcement.

factor analysis A statistical technique that identifies clusters of test items that measure the same ability (factor).

false consensus effect The tendency to overestimate the commonality of one’s opinions and unsuccessful behaviors.

false memory An inaccurate memory that feels as real as an accurate memory.

false uniqueness effect The tendency to underestimate the commonality of one’s abilities and successful behaviors.

farsightedness A visual problem in which the light waves from nearby objects come into focus behind the retina, blurring the images of these objects.

fetal alcohol syndrome (FAS) A syndrome affecting infants whose mothers consumed large amounts of alcohol during pregnancy, resulting in a range of severe effects including intellectual disability and facial abnormalities.

figure-and-ground principle The Gestalt perceptual organizational principle that the brain organizes sensory information into a figure or figures (the center of attention) and ground (the less distinct background).

fixation (1) In problem solving, the inability to create a new interpretation of a problem. (2) In Freudian theory, some of the id’s pleasure-seeking energies remaining stuck in a psychosexual stage due to excessive gratification or frustration of instinctual needs.

fixed-interval schedule A partial schedule of reinforcement in which a reinforcer is delivered after the first response is given once a set interval of time has elapsed.

fixed-ratio schedule A partial schedule of reinforcement in which a reinforcer is delivered each time a fixed number of responses is made. The fixed number can be any number greater than one.

flooding A counterconditioning exposure therapy in which the patient is immediately exposed to a feared object or situation.

Flynn effect The finding that the average intelligence test score in the United States and other industrialized nations has improved steadily over the last century.

foot-in-the-door technique Compliance to a large request is gained by preceding it with a very small request.

formal operational stage The last stage in Piaget’s theory of cognitive development, starting at age 12 or so, during which a child gains the capacity for hypothetical-deductive thought.

fovea A tiny pit in the center of the retina filled with cones.

fraternal (dizygotic) twins Twins that originate from the fertilization of two eggs at approximately the same time (two zygotes).

free association A person spontaneously describes, without editing, all thoughts, feelings, or images that come to mind.

free recall task A memory task in which a list of items is presented one at a time and then the participant is free to recall them in any order.

frequency The number of times a wave cycles in one second.

frequency distribution A depiction, in a table or figure, of the number of participants (frequency) receiving each score for a variable.

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frequency theory A theory of pitch perception that assumes that the frequency of the sound wave is mimicked by the firing rate of the entire basilar membrane.

frontal lobe The area in each cerebral hemisphere in front of the central fissure and above the lateral fissure. The motor cortex is in this lobe.

functional fixedness The inability to see that an object can have a function other than its typical one in solving a problem.

functional magnetic resonance imaging (fMRI) A computerized image of the activity levels of various areas in the brain generated by detecting the amount of oxygen brought to each area.

fundamental attribution error The tendency as an observer to overestimate dispositional influences and underestimate situational influences on others’ behavior.

GABA (gamma-aminobutyric acid) The main inhibitory neurotransmitter in the nervous system. It is involved in lowering arousal and anxiety and regulating movement.

gambler’s fallacy Incorrectly believing that a chance process is self-correcting in that an event that has not occurred for a while is more likely to occur.

gene The basic unit of genetic instruction.

generalized anxiety disorder An anxiety disorder in which a person has excessive, global anxiety and worries that he cannot control, occurring more days than not for at least a period of 6 months.

genital stage of psychosexual development The fifth stage in Freud’s theory (from puberty through adulthood), in which the erogenous zone is at the genitals, and the child develops sexual relationships, moving toward intimate adult relationships.

glial cells (glia) Cells in the nervous system that comprise the support system for the neurons.

glutamate The main excitatory neurotransmitter in the nervous system. It is involved in memory storage, pain perception, strokes, and schizophrenia.

group polarization The strengthening of a group’s prevailing opinion about a topic following group discussion about the topic.

groupthink A mode of group thinking that impairs decision making, because the desire for group harmony overrides a realistic appraisal of the possible decision alternatives.

habituation A decrease in the physiological responding to a stimulus once it becomes familiar.

hair cells The receptor cells for hearing. They line the basilar membrane inside the cochlea.

hallucination A false sensory perception.

heritability An index of the degree that variation of a trait within a given population is due to heredity.

heuristic A problem-solving strategy that seems reasonable given one’s past experience with solving problems, especially similar problems, but does not guarantee a correct answer to a problem.

hierarchy of needs The motivational component in Maslow’s theory of personality, in which our innate needs that motivate our behavior are hierarchically arranged in a pyramid shape. From bottom to top, the needs are physiological, safety, belonging and love, esteem, and self-actualization.

hindsight bias (I-knew-it-all-along phenomenon) The tendency, after learning about an outcome, to be overconfident in one’s ability to have predicted it.

hippocampus A part of the brain involved in the formation of memories.

holophrase A word used by an infant to express a complete idea.

hormone A chemical messenger that is produced by an endocrine gland and carried by the bloodstream to target tissues throughout the body.

hypothalamus A part of the brain that is involved in regulating basic drives such as eating, drinking, and having sex. It also directs the endocrine glandular system through its control of the pituitary gland and the autonomic nervous system to maintain the body’s internal environment.

iconic memory The visual sensory register that holds an exact copy of the incoming visual input but only for a brief period of time, less than 1 second.

id The part of the personality that a person is born with, where the biological instinctual drives reside, and that is located totally in the unconscious mind.

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identical (monozygotic) twins Twins that originate from the same zygote.

identification The process by which children adopt the characteristics of the same-sex parent and learn their gender role and sense of morality.

ill-defined problem A problem lacking clear specification of either the start state, goal state, or the processes for reaching the goal state.

illusory correlation The erroneous belief that two variables are statistically related when they actually are not.

implicit (nondeclarative) memory Long-term memory for procedural tasks, classical conditioning, and priming effects. This type of memory does not require conscious awareness or the need to make declarations about the information remembered.

incentive theory A theory of motivation that proposes that our behavior is motivated by incentives, external stimuli that we have learned to associate with reinforcement.

independent variable In an experiment, the variable that is a hypothesized cause and thus is manipulated by the experimenter.

infantile/child amnesia Our inability as adults to remember events that occurred in our lives before about 3 years of age.

inferential statistical analyses Statistical analyses that allow researchers to draw conclusions about the results of a study by determining the probability that the results are due to random variation (chance). The results are statistically significant if this probability is .05 or less.

informational social influence Influence stemming from the need for information in situations in which the correct action or judgment is uncertain.

information-processing approach to cognitive development An approach to studying cognitive development that assumes cognitive development is continuous and improves as children become more adept at processing information (taking in, storing, and using information).

insecure-ambivalent attachment The type of attachment indicated by the infant not exploring but seeking closeness to the mother in the Ainsworth strange situation procedure, showing high levels of distress when the mother leaves, and ambivalent behavior when she returns—by alternately clinging to and pushing away from her.

insecure-avoidant attachment The type of attachment indicated by the infant exploring with little interest in the mother in the Ainsworth strange situation procedure, showing only minimal distress when the mother leaves, and avoiding her when she returns.

insecure-disorganized (disoriented) attachment The type of attachment indicated by the infant’s confusion when the mother leaves and returns in the Ainsworth strange situation procedure. The infant acts disoriented, seems overwhelmed by the situation, and does not demonstrate a consistent way of coping with it.

insight A new way to interpret a problem that immediately yields the solution.

instinctual drift The tendency for an animal to drift back from a learned operant response to an innate, instinctual response to an object.

intelligence quotient (IQ) (mental age/chronological age) × 100.

interference theory A theory of forgetting that proposes that forgetting is due to other information in memory interfering and thereby making the to-be-remembered information inaccessible.

internal locus of control The perception that one controls one’s own individual fate.

interneurons Neurons that integrate information within the central nervous system through their communication with each other and between sensory and motor neurons in the spinal cord.

interposition A monocular depth cue referring to the fact that if one object partially blocks our view of another, we perceive it as closer to us.

intrinsic motivation The desire to perform a behavior for its own sake.

James-Lange theory A theory of emotion proposing that an emotion is determined from a cognitive appraisal of the physiological arousal and behavioral responses, which occur first.

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just-world hypothesis The assumption that the world is just and that people get what they deserve.

L-dopa A drug for Parkinson’s disease that contains the precursors to dopamine so that once it is in the brain, it will be converted to dopamine.

latency stage of psychosexual development The fourth stage in Freud’s theory (from 6 years old to puberty), in which there is no erogenous zone, sexual feelings are repressed, and the focus is on cognitive and social development.

latent content Freud’s term for the underlying true meaning of a dream.

latent learning Learning that occurs but is not demonstrated until there is incentive to do so.

law of effect A principle developed by Edward Thorndike that says that any behavior that results in satisfying consequences tends to be repeated and that any behavior that results in unsatisfying consequences tends not to be repeated.

learned helplessness A sense of hopelessness in which a person thinks that he is unable to prevent aversive events.

left-skewed distribution An asymmetric frequency distribution in which there are some unusually low scores that distort the mean to be less than the median.

levels-of-processing theory A theory of information processing in memory that assumes that semantic processing, especially elaborative semantic processing, leads to better long-term memory.

limbic system A group of brain structures (hypothalamus, hippocampus, and amygdala) that play an important role in our survival, memory, and emotions.

linear perspective A monocular depth cue referring to the fact that as parallel lines recede away from us, they appear to converge—the greater the distance, the more they seem to converge. Sometimes referred to as perspective convergence.

lithium A naturally occurring element (a mineral salt) that is used to treat bipolar disorder.

lobotomy A type of psychosurgery in which the neuronal connections of the frontal lobes to lower brain areas are severed.

long-term memory (LTM) The memory stage in which information is stored for a long period of time (perhaps permanently) and whose capacity is essentially unlimited.

longitudinal study A study in which performance of the same group of participants is examined at different ages.

low-ball technique Compliance to a costly request is gained by first getting compliance to an attractive, less costly request but then reneging on it.

maintenance rehearsal A type of rehearsal in short-term memory in which the information is repeated over and over again in order to maintain it.

major depressive disorder A depressive disorder in which the person has experienced one or more major depressive episodes.

major depressive episode An episode characterized by symptoms such as feelings of intense hopelessness, low self-esteem and worthlessness, extreme fatigue, dramatic changes in eating and sleeping behavior, inability to concentrate, and greatly diminished interest in family, friends, and activities for a period of 2 weeks or more.

manic episode An episode characterized by abnormally elevated mood in which the person experiences symptoms such as inflated self-esteem with grandiose delusions, a decreased need for sleep, constant talking, distractibility, restlessness, and poor judgment for a period of at least a week.

manifest content Freud’s term for the literal surface meaning of a dream.

mean The numerical average of a distribution of scores.

means–end analysis heuristic A problem-solving heuristic in which the distance to the goal state is decreased systematically by breaking the problem down into subgoals and achieving these subgoals.

median The score positioned in the middle of a distribution of scores when all of the scores are arranged from lowest to highest.

medulla A brain stem structure involved in many essential body functions, such as heartbeat, breathing, blood pressure, digestion, and swallowing.

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memory span The average number of items an individual can remember across a series of memory span trials.

memory span task A memory task in which the participant is given a series of items one at a time and then has to recall the items in the order in which they were presented.

mental set The tendency to use previously successful problem-solving strategies without considering others that are more appropriate for the current problem.

meta-analysis A statistical technique that combines the results of a large number of studies on one experimental question into one analysis to arrive at an overall conclusion.

method of loci A mnemonic in which sequential pieces of information to be remembered are encoded by associating them with sequential locations in a very familiar room or place and then the pieces of information are retrieved by mentally going around the room (place) and retrieving the piece at each location.

mirror neurons Neurons that fire both when performing an action and when observing another person perform that same action.

misinformation effect The distortion of a memory by exposure to misleading information.

mnemonic A memory aid.

mode The most frequently occurring score in a distribution of scores.

mood-congruence effect Tendency to retrieve experiences and information that are congruent with a person’s current mood.

mood-dependent memory Long-term memory retrieval is best when a person’s mood state at the time of encoding and retrieval of the information is the same.

motivation The set of internal and external factors that energize our behavior and direct it toward goals.

motor cortex The strip of cortex in each cerebral hemisphere in the frontal lobe directly in front of the central fissure, which allows us to move different parts of our body.

motor neurons Neurons in the peripheral nervous system that carry movement commands from the central nervous system out to the rest of the body.

myelin sheath An insulating layer covering an axon that allows for faster neural impulses.

naturalistic observation A descriptive research method in which the behavior of interest is observed in its natural setting, and the researcher does not intervene in the behavior being observed.

nearsightedness A visual problem in which the light waves from distant objects come into focus in front of the retina, blurring the images of these objects.

negative correlation An inverse relationship between two variables.

negative punishment Punishment in which an appetitive stimulus is removed.

negative reinforcement Reinforcement in which an aversive stimulus is removed.

nerve deafness Hearing loss created by damage to the hair cells or the auditory nerve fibers in the inner ear.

neurogenesis theory of depression An explanation of depression that proposes that neurogenesis, the growth of new neurons, in the hippocampus stops during depression, and when it resumes, the depression lifts.

neurons Cells that transmit information within the nervous system.

neuroscience The scientific study of the brain and nervous system.

neurotransmitter A naturally occurring chemical in the nervous system that specializes in transmitting information between neurons.

nocebo effect A negative placebo effect due to the expectation of adverse consequences from receiving treatment.

normal distribution A frequency distribution that is shaped like a bell. About 68% of the scores fall within 1 standard deviation of the mean, about 95% within 2 standard deviations of the mean, and over 99% within 3 standard deviations of the mean.

normative social influence Influence stemming from our desire to gain the approval and to avoid the disapproval of others.

obedience Following the commands of a person in authority.

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object permanence The knowledge that an object exists independent of perceptual contact with it.

observational learning (modeling) Learning by observing others and imitating their behavior.

obsession A persistent intrusive thought, idea, impulse, or image that causes anxiety.

obsessive-compulsive disorder A disorder in which the person experiences recurrent obsessions or compulsions that are perceived by the person as excessive or unreasonable, but cause significant distress and disruption in the person’s daily life.

occipital lobe The area located in the lower back of each cerebral hemisphere. The primary visual cortex is in this lobe.

Oedipus conflict A phallic stage conflict for a boy in which the boy becomes sexually attracted to his mother and fears his father will find out and castrate him.

operant conditioning Learning to associate behaviors with their consequences. Behaviors that are reinforced (lead to satisfying consequences) will be strengthened, and behaviors that are punished (lead to unsatisfying consequences) will be weakened.

operational definition A description of the operations or procedures that a researcher uses to manipulate or measure a variable.

opponent-process theory A theory of color vision that assumes that there are three opponent-process cell systems (red-green, blue-yellow, and black-white) that process color information after it has been processed by the cones. The colors in each system oppose one another in that if one color is stimulated, the other is inhibited.

oral stage of psychosexual development The first stage in Freud’s theory (from birth to 18 months), in which the erogenous zones are the mouth, lips, and tongue, and the child derives pleasure from oral activities such as sucking, biting, and chewing.

overextension The application of a newly learned word to objects that are not included in the meaning of the word.

overjustification effect A decrease in an intrinsically motivated behavior after the behavior is extrinsically reinforced and then the reinforcement is discontinued.

panic disorder An anxiety disorder in which a person experiences recurrent panic attacks.

parasympathetic nervous system The part of the autonomic nervous system that returns the body to its normal resting state after having been highly aroused, as in an emergency.

parietal lobe The area in each cerebral hemisphere in back of the central fissure and above the lateral fissure. The somatosensory cortex is in this lobe.

Parkinson’s disease A disease in which the person has movement problems such as muscle tremors, difficulty initiating movements, and rigidity of movement. These movement problems stem from a scarcity of dopamine in the basal ganglia.

partial-reinforcement effect The finding that operant responses that are reinforced on partial schedules are more resistant to extinction than those reinforced on a continuous schedule.

partial schedule of reinforcement In operant conditioning, reinforcing the desired operant response only part of the time.

participant observation A descriptive research method in which the observer becomes part of the group being observed.

peg-word system A mnemonic in which the items in a list to be remembered are associated with the sequential items in a memorized jingle and then the list is retrieved by going through the jingle and retrieving the associated items.

percentile rank The percentage of scores below a specific score in a distribution of scores.

perception The interpretation by the brain of sensory information.

perceptual constancy The perceptual stability of the size, shape, brightness, and color for familiar objects seen at varying distances, different angles, and under different lighting conditions.

perceptual set The interpretation of ambiguous sensory information in terms of how our past experiences have set us to perceive it.

peripheral nervous system (PNS) The part of the nervous system that links the central nervous system with the body’s sensory receptors, muscles, and glands.

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permissive parenting A style of parenting in which the parents make few demands and are overly responsive to their children’s desires, letting their children do pretty much as they please.

person-who reasoning Questioning a well-established research finding because one knows a person who violates the finding.

personality A person’s internally based characteristic ways of acting and thinking.

personality disorder A disorder characterized by inflexible, long-standing personality traits that lead to behavior that impairs social functioning and deviates from cultural norms.

personality inventory An objective personality test that uses a series of questions or statements for which the test taker must indicate whether they apply to her or not.

phallic stage of psychosexual development The third stage in Freud’s theory (from 3 to 6 years), in which the erogenous zone is located at the genitals, and the child derives pleasure from genital stimulation.

phonemes The smallest distinctive speech sounds in a language.

pituitary gland The most influential gland in the endocrine glandular system. It releases hormones for human growth and hormones that direct other endocrine glands to release their hormones.

place theory A theory of pitch perception that assumes that there is a specific location along the basilar membrane that will maximally respond to a particular frequency, thereby indicating the pitch to the brain. As this location goes down the basilar membrane from the oval window, the pitch goes down from 20,000 Hz to 20 Hz.

placebo An inactive pill or a treatment that has no known effects.

placebo effect Improvement due to the expectation of improving because of receiving treatment.

placebo group A control group of participants who believe they are receiving treatment, but who are only receiving a placebo.

pleasure principle The principle of seeking immediate gratification for instinctual drives without concern for the consequences.

pons A brain stem structure that serves as a bridge between the cerebellum and the rest of the brain and is involved in sleep and dreaming.

population The entire group of people that a researcher is studying.

positive correlation A direct relationship between two variables.

positive punishment Punishment in which an aversive stimulus is presented.

positive reinforcement Reinforcement in which an appetitive stimulus is presented.

positron emission tomography (PET) scans A visual display of the activity levels in various areas in the brain generated by detecting the amount of positron emission created by the metabolization of radioactive glucose in each area.

postconventional level of moral reasoning The last level of reasoning in Kohlberg’s theory of moral development in which moral reasoning is based on self-chosen universal ethical principles (with human rights taking precedence over laws) and the avoidance of self-condemnation for violating such principles.

preconscious mind Freud’s term for what is stored in one’s memory that one is not presently aware of but can access.

preconventional level of moral reasoning The first level of reasoning in Kohlberg’s theory of moral development in which moral reasoning is based on avoiding punishment and looking out for your own welfare and needs.

Premack principle The principle that the opportunity to perform a highly frequent behavior can reinforce a less frequent behavior.

preoperational stage The second stage in Piaget’s theory of cognitive development, from age 2 to 6, during which the child’s thinking becomes more symbolic and language-based, but remains egocentric and lacks the mental operations that allow logical thinking.

primacy effect (1) In memory, the superior recall of the early portion of a list relative to the middle of the list in a one-trial free recall task. (2) In impression formation, information gathered early is weighted more heavily than information gathered later in forming an impression of another person.

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primary reinforcer A stimulus that is innately reinforcing.

priming The implicit influence of an earlier presented stimulus on the response to a later stimulus. This influence is independent of conscious memory for the earlier stimulus.

proactive interference The disruptive effect of prior learning on the retrieval of new information.

procedural memory Implicit memory for cognitive and motor tasks that have a physical procedural aspect to them.

projective test A personality test that uses a series of ambiguous stimuli to which the test taker must respond about her perceptions of the stimuli.

psychoanalysis A style of psychotherapy, originally developed by Sigmund Freud, in which the therapist helps the person gain insight into the unconscious sources of his or her problems.

psychology The science of behavior and mental processes.

psychosurgery A biomedical treatment in which specific areas of the brain are destroyed.

psychotherapy The use of psychological interventions to treat mental disorders.

psychotic disorder A disorder characterized by a loss of contact with reality.

punisher A stimulus that decreases the probability of a prior response.

punishment The process by which the probability of a response is decreased by the presentation of a punisher.

random assignment A control measure in which participants are randomly assigned to groups in order to equalize participant characteristics across the various groups in an experiment.

random sampling A sampling technique that obtains a representative sample of a population by ensuring that each individual in a population has an equal opportunity to be in the sample.

range The difference between the highest and lowest scores in a distribution of scores.

rational-emotive therapy A type of cognitive therapy, developed by Albert Ellis, in which the therapist directly confronts and challenges the person’s unrealistic thoughts and beliefs to show that they are irrational.

reaction range The genetically determined limits for an individual’s intelligence.

reality principle The principle of finding gratification for instinctual drives within the constraints of reality (norms of society).

recall A measure of long-term memory retrieval that requires the reproduction of the information with essentially no retrieval cues.

recency effect The superior recall of the latter portion of a list relative to the middle of the list in a one-trial free recall task.

recognition A measure of long-term memory retrieval that only requires the identification of the information in the presence of retrieval cues.

reflex A stimulus-response pair in which the stimulus (the unconditioned stimulus) automatically elicits the response (the unconditioned response).

regression toward the mean The tendency for extreme or unusual values on one variable to be matched on average with less extreme values on the other variable when the two variables are not perfectly correlated.

reinforcement The process by which the probability of a response is increased by the presentation of a reinforcer.

reinforcer A stimulus that increases the probability of a prior response.

relearning The savings method of measuring long-term memory retrieval in which the measure is the amount of time saved when learning information for the second time.

reliability The extent to which the scores for a test are consistent.

REM (rapid eye movement) sleep The stage of sleep that is characterized by rapid eye movements and brain wave patterns that resemble those for an awake state and in which most dreaming occurs. REM sleep is sometimes referred to as paradoxical sleep because the bodily muscles are immobilized but much of the brain is highly active.

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representativeness heuristic A heuristic for judging the probability of membership in a category by how well an object resembles (is representative of) that category (the more representative, the more probable).

resistance A person’s unwillingness to discuss a particular topic during therapy.

reticular formation A network of neurons running up the center of the brain stem that is responsible for our different levels of arousal and consciousness.

retina The light-sensitive layer of the eye that is composed of three layers of cells—ganglion, bipolar, and receptor (rods and cones).

retinal disparity A binocular depth cue referring to the fact that as the disparity (difference) between the two retinal images of an object increases, the distance of the object from us decreases.

retrieval The process of bringing information stored in long-term memory into short-term memory.

retroactive interference The disruptive effect of new learning on the retrieval of old information.

retrograde amnesia The disruption of memory for the past, especially episodic information for events before, especially just before, surgery or trauma to the brain.

reversibility The knowledge that reversing a transformation brings about the conditions that existed before the transformation.

right-skewed distribution An asymmetric frequency distribution in which there are some unusually high scores that distort the mean to be greater than the median.

rods Receptor cells in the retina that are principally responsible for dim light and achromatic vision.

rooting reflex An innate human reflex that leads infants to turn their mouth toward anything that touches their cheeks and search for something to suck on.

sample The subset of a population that actually participates in a research study.

scaffolding According to Vygotsky, a style of teaching in which the teacher adjusts the level of help in relation to the child’s level of performance while orienting the child’s learning toward the upper level of his or her zone of proximal development.

scatterplot A visual depiction of correlational data in which each data point represents the scores on the two variables for each participant.

Schachter-Singer two-factor theory A theory of emotion proposing that an emotion is determined by cognitive appraisal of the physiological arousal and the entire environmental situation.

schemas Frameworks for our knowledge about people, objects, events, and actions that allow us to organize and interpret information about our world.

schizophrenia A psychotic disorder in which at least two of the following symptoms are present most of the time during a 1-month period— hallucinations, delusions, disorganized speech, disorganized or catatonic behavior, or negative symptoms such as loss of emotion.

secondary reinforcer A stimulus that gains its reinforcing property through learning.

secure attachment The type of attachment indicated by the infant exploring freely in the presence of the mother in the Ainsworth strange situation procedure, displaying distress when the mother leaves, and responding enthusiastically when she returns.

selective serotonin and norepinephrine reuptake inhibitors (SSNRIs) Antidepressant drugs that achieve their agonistic effect on serotonin and norepinephrine by selectively blocking their reuptake.

selective serotonin reuptake inhibitors (SSRIs) Antidepressant drugs that achieve their agonistic effect on serotonin by selectively blocking its reuptake.

self-actualization The fullest realization of a person’s potential.

self-efficacy A judgment of one’s effectiveness in dealing with particular situations.

self-fulfilling prophecy Our behavior leads a person to act in accordance with our expectations for that person.

self-perception theory A theory, developed by Daryl Bem, that assumes that when we are unsure of our attitudes, we infer them by examining our behavior and the context in which it occurs.

self-reference effect The superior long-term memory for information related to oneself at time of encoding into long-term memory.

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self-serving bias The tendency to make attributions so that one can perceive oneself favorably.

self-system The set of cognitive processes by which a person observes, evaluates, and regulates her behavior.

semantic memory Explicit memory for factual knowledge.

sensation The initial information gathering and recoding by the sensory structures.

sensorimotor stage The first stage in Piaget’s theory of cognitive development, from birth to about age 2, during which infants learn about the world through their sensory and motor interactions with it and develop object permanence.

sensory adaptation Our sensitivity to unchanging and repetitious stimuli disappears over time.

sensory memory (SM) The set of sensory registers, one for each of our senses, that serve as holding places for incoming sensory information until it can be attended to, interpreted, and encoded into short-term memory.

sensory neurons Neurons in the peripheral nervous system that carry information to the central nervous system from sensory receptors, muscles, and glands.

serotonin and norepinephrine Neurotransmitters involved in levels of arousal and mood, sleep, and eating.

shaping Training a human or animal to make an operant response by reinforcing successive approximations of the desired response.

short-term memory (STM) The memory stage with a small capacity (7 ± 2 chunks) and brief duration (< 30 seconds) that we are consciously aware of and in which we do our problem solving, reasoning, and decision making.

signal detection theory A theory that assumes that the detection of faint sensory stimuli depends not only upon a person’s physiological sensitivity to a stimulus but also upon his decision criterion for detection, which is based on nonsensory factors.

social anxiety disorder An anxiety disorder indicated by a marked and persistent fear of one or more social performance situations in which embarrassment may occur and in which there is exposure to unfamiliar people or scrutiny by others.

social facilitation Facilitation of a dominant response on a task due to social arousal, leading to improved performance on simple or well-learned tasks and worse performance on complex or unlearned tasks when other people are present.

social loafing The tendency to exert less effort when working in a group toward a common goal than when individually working toward the goal.

social psychology The scientific study of how we influence one another’s behavior and thinking.

sociocultural perspective A research perspective whose major explanatory focus is how other people and the cultural context impact behavior and mental processes.

somatic (skeletal) nervous system The part of the peripheral nervous system that carries sensory input from receptors to the central nervous system and relays commands from the central nervous system to skeletal muscles to control their movement.

somatosensory cortex The strip of cortex in each cerebral hemisphere in the parietal lobe directly in back of the central fissure, which allows us to sense pressure, temperature, and pain in different parts of our body as well as the position of our body parts.

source misattribution Attributing a memory to the wrong source, resulting in a false memory.

spacing (distributed study) effect Superior long-term memory for spaced study versus massed study (cramming).

specific phobia An anxiety disorder indicated by a marked and persistent fear of specific objects or situations that is excessive and unreasonable.

Sperling’s full-report procedure An experimental procedure in which, following the brief presentation of a matrix of unrelated consonants, the participant has to attempt to recall all of the letters in the matrix.

Sperling’s partial-report procedure An experimental procedure in which, following the brief presentation of a matrix of unrelated consonants, the participant is given an auditory cue about which row of the matrix to recall.

spinal cord The conduit between the brain and the peripheral nervous system for incoming sensory data and outgoing movement commands to the muscles.

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spinal reflex A simple automatic action of the spinal cord not requiring involvement of the brain, such as the knee-jerk reflex.

spontaneous recovery (1) In classical conditioning, a partial recovery in strength of the conditioned response following a break during extinction training. (2) In operant conditioning, the temporary recovery of the operant response following a break during extinction training.

spontaneous remission Getting better with the passage of time without receiving any therapy.

spurious correlation A correlation in which the variables are related through their relationship with one or more other variables but not through a causal mechanism.

standard deviation The average extent that the scores vary from the mean for a distribution of scores.

standardization The process that allows test scores to be interpreted by providing test norms.

state-dependent memory Long-term memory retrieval is best when a person’s physiological state at the time of encoding and retrieval of the information is the same.

Stevens’s power law The perceived magnitude of a stimulus is equal to its actual physical intensity raised to some constant power. The constant power is different for each type of sensory judgment.

stimulus discrimination (1) In classical conditioning, the elicitation of the conditioned response only by the conditioned stimulus or only by a small set of highly similar stimuli that includes the conditioned stimulus. (2) In operant conditioning, learning to give the operant response only in the presence of the discriminative stimulus.

stimulus generalization (1) In classical conditioning, the elicitation of the conditioned response to stimuli that are similar to the conditioned stimulus. The more similar the stimulus is to the conditioned stimulus, the stronger the response. (2) In operant conditioning, giving the operant response in the presence of stimuli similar to the discriminative stimulus. The more similar the stimulus is to the discriminative stimulus, the higher the operant response rate.

storage The process of maintaining information in a memory stage.

storage decay theory A theory of forgetting that proposes that forgetting is due to the decay of the biological representation of the information and that periodic usage of the information will help to maintain it in storage.

subjective contour A line or shape that is perceived to be present but does not really exist. The brain creates it during perception.

subtractive mixtures Mixtures of wavelengths of light in which some wavelengths are absorbed (subtracted) and so do not get reflected from the mixtures to the retina.

sucking reflex An innate human reflex that leads infants to suck anything that touches their lips.

superego The part of the personality that represents one’s conscience and idealized standards of behavior.

survey research A descriptive research method in which the researcher uses questionnaires and interviews to collect information about the behavior, beliefs, and attitudes of particular groups of people.

sympathetic nervous system The part of the autonomic nervous system that is in control when we are highly aroused, as in an emergency, and need to prepare for defensive action.

synaptic gap (synapse) The microscopic gap between neurons across which neurotransmitters travel to carry their messages to other neurons.

systematic desensitization A counterconditioning exposure therapy in which a fear response to an object or situation is replaced with a relaxation response in a series of progressively increasing fear-arousing steps.

tardive dyskinesia A side effect of long-term use of traditional antipsychotic drugs causing the person to have uncontrollable facial tics, grimaces, and other involuntary movements of the lips, jaw, and tongue.

telegraphic speech Using two-word sentences with mainly nouns and verbs.

temperament The set of innate tendencies or dispositions that lead a person to behave in certain ways.

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temporal integration procedure An experimental procedure in which two meaningless visual patterns that produce a meaningful pattern if integrated are presented sequentially with the time delay between their presentations varied.

temporal lobe The area in each cerebral hemisphere located beneath the lateral fissure. The primary auditory cortex is in this lobe.

teratogens Environmental agents such as drugs and viruses, diseases, and physical conditions that impair prenatal development and lead to birth defects and sometimes death.

thalamus A part of the brain that serves as a relay station for incoming sensory information.

that’s-not-all technique Compliance to a planned second request with additional benefits is gained by presenting this request before a response can be made to a first request.

theory of mind The understanding of the mental and emotional states of both ourselves and others.

thinking The processing of information to solve problems and make judgments and decisions.

third-variable problem An explanation of a correlation between two variables in terms of another (third) variable that could possibly be responsible for the observed relationship between the two variables.

tip-of-the-tongue (TOT) phenomenon The failure to recall specific information from memory combined with partial recall and the feeling that recall is imminent.

top-down processing The brain’s use of knowledge, beliefs, and expectations to interpret sensory information.

trace conditioning A classical conditioning procedure in which the conditioned stimulus precedes the unconditioned stimulus but is removed before the unconditioned stimulus is presented so that the two stimuli do not occur together.

traits The relatively stable internally based characteristics that describe a person.

transcranial magnetic stimulation (TMS) A neurostimulation therapy in which the left frontal lobe is stimulated with magnetic pulses via an electromagnetic coil placed on the patient’s scalp. It is only cleared for use in cases of severe depression for which traditional treatment has not helped.

transduction The conversion of physical energy into neural signals that the brain can understand.

transference When a person undergoing therapy acts toward the therapist as he or she did or does toward important figures in his or her life, such as his or her parents.

trichromatic theory A theory of color vision that assumes that there are three types of cones, each only activated by wavelength ranges of light corresponding roughly to blue, green, and red. It further assumes that all of the various colors that we can see are mixtures of various levels of activation of the three types of cones. If all three are equally activated, we see white.

unconditional positive regard Unconditional acceptance and approval of a person by others.

unconditioned response (UCR) The response in a reflex that is automatically elicited by the unconditioned stimulus.

unconditioned stimulus (UCS) The stimulus in a reflex that automatically elicits an unconditioned response.

unconscious mind Freud’s term for the part of our mind that we cannot become aware of.

underextension The failure to apply a new word more generally to objects that are included within the meaning of the word.

uninvolved parenting A style of parenting in which the parents minimize both the time they spend with their children and their emotional involvement with them and provide for their children’s basic needs, but little else.

validity The extent to which a test measures what it is supposed to measure or predicts what it is supposed to predict.

variable Any factor that can take on more than one value.

variable-interval schedule A partial schedule of reinforcement in which the time that must elapse on each trial before a response will lead to the delivery of a reinforcer varies from trial to trial but averages to a set time across trials.

variable-ratio schedule A partial schedule of reinforcement in which the number of responses it takes to obtain a reinforcer varies on each trial but averages to a set number across trials.

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virtual reality therapy A counterconditioning exposure therapy in which the patient is exposed in graduated steps to computer simulations of a feared object or situation.

volley principle Cells taking turns firing will increase the maximum firing rate for a group of cells.

vulnerability–stress model A biopsychosocial explanation of schizophrenia that proposes that genetic, prenatal, and postnatal biological factors render a person vulnerable to schizophrenia, but environmental stress determines whether it develops or not.

wavelength The distance in one cycle of a wave, from one crest to the next.

Weber’s law For each type of sensory judgment that we can make, the measured difference threshold is a constant fraction of the standard stimulus value used to measure it. This constant fraction is different for each type of sensory judgment.

well-defined problem A problem with clear specifications of the start state, goal state, and the processes for reaching the goal state.

Wernicke’s area An area in the cerebral cortex responsible for comprehension of speech and text. It is in the left temporal lobe of the majority of people, regardless of handedness.

working backward heuristic A problem-solving heuristic in which one attempts to solve a problem by working from the goal state back to the start state.

working memory A more detailed version of short-term memory that includes the mechanisms that allow short-term memory to accomplish its tasks.

Yerkes-Dodson law A law describing the relationship between the amount of arousal and the performance quality on a task—increasing arousal up to some optimal level increases performance quality on a task, but increasing arousal past this point is detrimental to performance.

zone of proximal development According to Vygotsky, the difference between what a child can actually do and what the child could do with the help of others.

zygote The fertilized egg that is formed from the union of the sperm and egg cells in human reproduction.