1,800+ MCAT terms, defined.

Meditation is a set of practices, such as focusing on the breath or observing thoughts without judgment, that produce a relaxed, awake, altered state of consciousness. The most testable point: EEG typically shows more alpha waves (someti...

Freud's psychosexual theory says personality forms through childhood stages (oral, anal, phallic, latency, genital), each centered on a body zone where libido is focused. Unresolved conflict at a stage can cause fixation that shapes adul...

Secure attachment is an infant's bond with a caregiver in which the child uses the caregiver as a secure base, is upset by separation, and is quickly comforted on reunion. In Ainsworth's Strange Situation it is the most common pattern an...

Homeostasis is the maintenance of a stable internal state around a set point. In psychology it underlies drive reduction theory: a need creates a drive, and behavior that reduces the drive restores balance. It fits hunger and thirst but...

Reaction formation is a psychoanalytic defense mechanism in which a person hides an unacceptable impulse or feeling by adopting the opposite attitude or behavior, often in an exaggerated way. The testable clue is an excessive, insistent...

Social identity theory (Tajfel and Turner) says part of your self-concept comes from the groups you belong to, and that people tend to raise self-esteem by favoring their ingroup over outgroups. Testable point: even arbitrary group membe...

A social script is a learned mental outline of the usual sequence of actions and roles in a familiar situation, such as ordering at a restaurant. It is a kind of event schema that guides expectations and behavior, and a departure from it...

Twin studies compare monozygotic (identical) twins, who share nearly all their genes, with dizygotic (fraternal) twins, who share about half, to separate genetic from environmental influence on a trait. If identical pairs match more ofte...

Crystallized intelligence is the knowledge and skill a person has accumulated through learning and experience, such as vocabulary and general facts. The testable point: it tends to be maintained or to grow into later adulthood, unlike fl...

Iconic memory is visual sensory memory: a brief, detailed image of what was just seen that lasts well under a second unless attention moves it into working memory. The most testable point is Sperling's partial-report experiment, which sh...

The pinna (auricle) is the visible, cartilage-based flap of the outer ear. It collects sound waves and funnels them into the ear canal toward the eardrum, and its folds help the brain judge a sound's elevation and whether it is in front...

Adulthood is the lifespan period after adolescence, usually split into early, middle, and late adulthood. Physical function generally peaks early and declines gradually. Most testable: Erikson's conflicts are intimacy vs isolation, gener...

Sleep stages are phases of the ~90-minute sleep cycle, identified by EEG: non-REM stages N1, N2, N3 (deepest, slow-wave) and REM. Most testable: from N1 to N3 EEG frequency falls and amplitude rises, while REM looks like waking brain act...

A cochlear implant is an electronic device that bypasses damaged hair cells and electrically stimulates the auditory nerve, so the brain still receives sound signals. It is used for many cases of sensorineural hearing loss, whereas a hea...

Long-term potentiation (LTP) is a lasting increase in the strength of a synapse after repeated or intense stimulation. It is the leading cellular model of how learning and memory are stored, notably in the hippocampus. Testable point: th...

Motion parallax is a monocular depth cue: when you move, nearby objects appear to sweep across your visual field faster than distant ones, and the brain uses that difference to judge distance. It works with one eye, unlike binocular cues...

Place theory says pitch is coded by where along the basilar membrane in the cochlea the vibration peaks and bends hair cells: high frequencies near the base, low frequencies near the apex. It explains high pitches well; frequency theory...

The theory of planned behavior (Ajzen) says the best direct predictor of a behavior is the intention to do it. Intention is shaped by attitude toward the behavior, subjective norms, and perceived behavioral control. Perceived control is...

The inner ear is the fluid-filled part of the ear that holds the cochlea, where hair cells transduce sound vibrations into neural signals, and the vestibular system, which senses balance and head position. Testable point: transduction ha...

Proximity is physical nearness between people, and it is a major factor in interpersonal attraction: people tend to form friendships and relationships with those who live, work or sit close to them. It works largely through repeated cont...

Selective attention is focusing on one stimulus while filtering out others. The exam often uses dichotic listening and the cocktail party effect, and models differ on where filtering happens: early (Broadbent, Treisman's attenuation) or...

Internalization is taking in a group's norms, values, or beliefs until they become one's own, held privately and not just shown in public. In Kelman's three responses to social influence, it is the deepest and most lasting, unlike compli...

The Cannon-Bard theory says the feeling of an emotion and the body's physiological arousal occur at the same time and independently, both triggered by thalamic signals after a stimulus. The key test point is timing: James-Lange puts arou...

The cocktail party effect is selective attention: you can focus on one conversation in a noisy room, yet often notice your own name in an ignored one. It shows unattended input gets some processing, as Treisman's attenuation model and la...

Intuition is a fast, automatic judgment reached without conscious step-by-step reasoning, the "gut feeling" of dual-process models (System 1). It can work well with expertise but is more prone to heuristic-driven bias than slow, delibera...

Compliance is changing your behavior because someone directly asked you to, often without changing your private beliefs. The MCAT contrasts it with conformity (matching group norms, often unspoken) and obedience (following an order from...

Confirmation bias is the tendency to seek, notice, interpret, and remember information in ways that support what one already believes, while discounting evidence that contradicts it. It is a cognitive bias in judgment, and it often helps...

Kin selection is the evolutionary idea that a behavior costly to the individual can spread if it helps genetic relatives survive and reproduce, raising inclusive fitness. Testable point: help is predicted to be greater toward closer kin,...

A behaviorist explains behavior as learned from the environment and treats only observable behavior as the proper subject of psychology. The most testable point: behaviorist explanations rely on classical and operant conditioning (Pavlov...

Piaget's stages are four steps of cognitive development, taken in a fixed order: sensorimotor, preoperational, concrete operational, formal operational. Ages are approximate. The testable skill is matching a behavior to a stage, such as...

Sigmund Freud founded psychoanalysis, the view that much behavior comes from unconscious conflict among the id, ego, and superego, shaped by childhood psychosexual stages. Most testable: match each structure and each defense mechanism to...

Appraisal is the cognitive evaluation of what an event means for you and whether you can cope with it. In Lazarus's model, primary appraisal judges whether an event is irrelevant, benign-positive, or stressful, and secondary appraisal ju...

The central executive is the component of Baddeley's working memory model that directs attention and coordinates the other parts. It allocates limited attentional resources between the phonological loop, visuospatial sketchpad and episod...

Psychosocial refers to the interaction of psychological factors (thoughts, emotions) and social factors (relationships, culture, income) in shaping behavior and health. Testable: Erikson's psychosocial stages each center on a conflict, a...

Competence is the sense of being capable of handling tasks and reaching goals effectively. It appears as a basic psychological need in self-determination theory and as the virtue gained from Erikson's industry versus inferiority stage. S...

Cranial nerves are 12 pairs of peripheral nerves that connect directly to the brain instead of the spinal cord; each is sensory, motor, or mixed. Testable points: they belong to the PNS, not the CNS, and the vagus nerve (X) carries paras...

Hypomania is a milder elevated or irritable mood state with high energy and reduced need for sleep, lasting at least four days in DSM-5 criteria. Unlike mania, it causes no marked impairment and no psychosis. Hypomania plus major depress...

A hypnic jerk (sleep start) is a brief, involuntary muscle twitch, often with a sensation of falling, that happens as a person drifts into sleep. The testable point: it occurs in stage 1 non-REM sleep, when theta waves replace alpha wave...

A shadowing task is a dichotic listening method in which a person repeats aloud the message in one ear while a different message plays in the other. It studies selective attention: people usually notice physical features of the ignored m...

The tetris effect is the carryover of a long, repetitive, pattern-based activity into later thoughts, mental images and dreams, often at sleep onset. The testable point is that it can occur in amnesic patients who cannot recall the activ...

Trichromatic theory (Young-Helmholtz) says color vision comes from three cone types, most sensitive to short (blue), medium (green), and long (red) wavelengths, with each color coded by their relative activity. It explains the receptor s...

A K-complex is a brief, large EEG wave, a sharp negative peak followed by a slower positive swing, that is a hallmark of stage 2 (N2) non-REM sleep along with sleep spindles. On the MCAT, spindles plus K-complexes on a theta background p...

Rationalization is a defense mechanism in which a person explains a behavior or outcome with logical, socially acceptable reasons that hide the real, anxiety-provoking motive. Testable point: the facts are admitted but reinterpreted, unl...

Endolymph is the fluid inside the membranous labyrinth of the inner ear, which includes the cochlear duct and the semicircular canals. Its movement bends hair-ority stereocilia, turning sound vibration (cochlea) or head motion (vestibula...

Semantic means relating to meaning. Semantic memory is explicit long-term memory for general facts, concepts, and word meanings, not tied to a personal time or place. Semantic encoding (processing meaning) generally gives better recall t...

Impulse control is the ability to resist an urge or delay a reward instead of acting on it right away. It depends heavily on the prefrontal cortex, and in Freud's model on the ego restraining the id. Frontal lobe damage, as in Phineas Ga...

The just noticeable difference (difference threshold) is the smallest change in a stimulus that a person detects half the time. By Weber's law, it is roughly a constant fraction of the starting intensity, so heavier or brighter baselines...

Exhaustion is the third and last stage of Selye's general adaptation syndrome (alarm, resistance, exhaustion). When a stressor lasts long enough, the body's coping resources tend to run down, and vulnerability to illness rises. Chronic s...

Psychoticism is one of the three dimensions in Eysenck's trait theory, along with extraversion and neuroticism. High scorers tend to be aggressive, cold, impulsive, and nonconforming. It is a personality trait on a continuum, not psychos...

Basilar tuning is the frequency selectivity of the basilar membrane: each location along the cochlea vibrates most for a particular pitch, high near the base and low near the apex. Place theory explains this; frequency theory also contri...