MCAT Behavioral Sciences Review

Sensory Perception and Visual Processing

• Visual cues allow for perceptual organization based on depth, form, motion, and constancy.

• Binocular cues provide a sense of depth through retinal disparity and convergence.

  • Retinal Disparity: Eyes are approximately $2.5\,inches$ apart, providing slightly different views of the environment to gauge depth.

  • Convergence: Depth is sensed through eye muscle movements; muscles relax for distant objects and contract for close objects.

• Monocular cues provide a sense of form, motion, and constancy without requiring both eyes.

  • Relative Size: Closer objects are perceived as larger.

  • Interposition (Overlap): An object in front of another is perceived as closer.

  • Relative Height: Higher objects are perceived as farther away.

  • Shading and Contour: Light and shadows help perceive depth and form (e.g., distinguishing a crater from a mountain).

  • Motion Parallax (Relative Motion): Farther objects appear to move slower than closer objects.

• Constancy: Perception of an object remains the same even if the retinal image changes.

  • Size Constancy: Perceiving an object as the same size regardless of its distance.

  • Shape Constancy: An opening door changes retinal shape but is still perceived as a rectangle.

  • Color Constancy: Perceivng an object as the same color despite changes in lighting.

• Sensory Adaptation: Down-regulation involves sensory desensitization to constant stimuli.

  • Hearing: The inner ear muscle contracts to dampen loud noises (takes seconds; ineffective for immediate sounds like gunshots).

  • Proprioception: Adapting to the world being viewed through upside-down goggles.

  • Sight: In bright light, pupils constrict and rods/cones desensitize; in the dark, pupils dilate and rods/cones synthesize light-sensitive molecules.

• Weber’s Law establishes the relationship between the initial intensity of a stimulus ($I$) and the Just Noticeable Difference ($\Delta I$ or JND).

  • Formula: $\frac{\Delta I}{I} = k$

  • The relationship is linear: $\Delta I = Ik$.

• Absolute Threshold of Sensation: The minimum stimulus intensity needed for detection $50\,\%$ of the time. This is different from JND, which is the smallest difference detectable $50\,\%$ of the time.

  • Influenced by physiological and psychological states: expectations, experience, motivation, and alertness.

  • Subliminal Stimuli: Stimuli below the absolute threshold.

• Somatosensation encodes intensity (speed of neuronal firing), timing (non-adapting, slow-adapting, or fast-adapting), and location (based on dermatomes).

• The Vestibular System manages balance and spatial orientation using the inner ear and limbs.

  • Semicircular Canals: Posterior, lateral, and anterior canals filled with endolymph detect head direction and strength of rotation.

  • Otolithic Organs: The utricle and saccule detect linear acceleration and head positioning using $CaCO_3$ (calcium carbonate) crystals attached to hair cells in a viscous gel.

• Signal Detection Theory: Discerning important stimuli from "noise."

  • Outcomes: Hit (signal present, responded yes), False Alarm (signal absent, responded yes), Correct Rejection (signal absent, responded no), Miss (signal present, responded no).

  • Variables: $d'$ (signal strength; Hit > Miss is a strong signal) and $c$ (strategy).

  • Strategies: Conservative (always no unless $100\,\%$ sure) or Liberal (always yes). Ideal observer ($C=0$) minimizes misses and false alarms.

• Processing Models:

  • Bottom-Up Processing: Stimulus-driven, data-driven, and uses inductive reasoning. It begins with the stimulus itself.

  • Top-Down Processing: Theory-driven, goal-driven, and uses deductive reasoning. Background knowledge influences perception.

• Gestalt Principles (Laws of Grouping):

  • Similarity: Similar items are grouped together.

  • Pragnanz: Reality is organized into the simplest form possible (e.g., Olympic rings as five circles).

  • Proximity: Objects close together are grouped.

  • Continuity: Lines are seen following the smoothest path.

  • Closure: Objects grouped together are seen as a whole; the mind fills in gaps.

Anatomy and Physiology of the Eye

• Conjunctiva: Thin layer of cells lining the eyelids.

• Cornea: Transparent fibrous tissue (anterior $1/6th$) that bends light.

• Anterior Chamber: Filled with aqueous humor, providing pressure and nutrients.

• Pupil and Iris: The iris is the colored muscle that modulates the pupil size to control light entry.

• Lens: Bends light to focus it on the fovea of the retina.

• Retina: Contains photoreceptors that convert light into electrochemical impulses.

  • Macula: Part of the retina rich in cones and rods.

  • Fovea: The center of the macula, containing only cones (high detail).

• Choroid: A network of blood vessels behind the retina; pigmented black in humans to absorb light.

• Sclera: The thick, white fibrous tissue covering the posterior $5/6th$ of the eyeball.

• Photoreceptors: Rods ($120\,million$) for night vision; Cones ($6 - 7\,million$) for color vision (Red $60\,\%$, Green $30\,\%$, Blue $10\,\%$).

  • Rods contain rhodopsin; cones contain photopsin.

  • Rods have a slow recovery time; cones have a fast recovery time.

• Phototransduction Cascade (PTC): The process of turning a rod "OFF" when light hits.

  • Rhodopsin contains 11-cis retinal. Light converts it to 11-trans retinal.

  • Transducin alpha subunit breaks off and binds to phosphodiesterase (PDE).

  • PDE converts cGMP to GMP. Lower cGMP levels cause sodium channels to close.

  • Rod hyperpolarizes and turns "OFF," which activates ON-center bipolar cells and then retinal ganglion cells.

• Visual Field Processing: The right visual field is processed by the left side of the brain, and vice-versa.

  • Light from the nasal side of both eyes crosses the optic chiasm.

  • Light from the temporal side does not cross.

• Feature Detection Breakdown: Color (trichromatic theory), Form (Parvocellular pathway: high spatial resolution, poor temporal resolution), and Motion (Magnocellular pathway: high temporal resolution, poor spatial resolution).

Auditory and Chemical Senses

• Audition requires pressurized sound waves and hair cells in the cochlea.

• Auditory Path: Pinna -> External Auditory Meatus -> Tympanic Membrane -> MIS (Malleus, Incus, Stapes) -> Oval Window -> Cochlea -> Circular Window.

• Organ of Corti: Separates the cochlea into upper and lower membranes; contains hair cells (cilia) with kinocilia filaments.

  • Movement of endolymph pulls on tip links of kinocilia, opening $K+$ channels.

  • Calcium channels open, triggering an action potential in the spiral ganglion cell.

• Basilar Tuning: The brain uses the position of hair cell firing in the cochlea to distinguish pitch.

  • Base (start) of cochlea: High frequency ($1600\,Hz$).

  • Apex (end) of cochlea: Low frequency ($20\,Hz$).

• Somatosensory Receptors: Mechanoreceptors (position/vibration/touch), Nociceptors (pain), and Thermoreceptors (temperature).

  • TrypV1 Receptor: Sensitive to both heat and pain.

  • Nerve Fibers: A-beta (thick, myelinated, fast), A-delta (medium, less myelin), C (small, unmyelinated, slow/lingering pain).

• Olfaction: Molecules bind to GPCRs on olfactory epithelial cells in the nostril.

  • Signal moves through the cribriform plate to the glomerulus in the olfactory bulb, then to mitral/tufted cells, and then the amygdala.

  • Smell and Taste are ipsilateral, while other senses are contralateral.

• Gustation: Five main tastes: bitter, salty, sweet, sour, and umami (glutamate).

  • Papillae: Fungiform (front), Foliate (sides), and Circumvallate (back).

  • Sweet, Umami, and Bitter use GPCRs. Sour and Salty use ion channels.

Consciousness, Sleep, and Drugs

• States of Consciousness: Alertness (Beta waves $12-30\,Hz$), Daydreaming (Alpha waves $8-13\,Hz$), Drowsiness (Theta waves $4-7\,Hz$), and Sleep (Delta waves $0.5-3\,Hz$).

• Sleep Stages (90-minute cycles):

  • N1 (Stage 1): Theta waves, hypnagonic hallucinations, Tetris effect, and hypnic jerks.

  • N2 (Stage 2): More theta waves, sleep spindles (bursts of rapid activity), and K-complexes (memory consolidation and suppression of arousal).

  • N3 (Stage 3): Delta waves, slow-wave sleep. Where sleepwalking/talking occurs.

  • REM (Rapid Eye Movement): Paralyzed muscles, memorable dreaming, episodic memory consolidation. Brain looks awake (Beta/Alpha waves).

• Dream Theories: Freud (Unconscious desires; Manifest content is literal, Latent content is hidden meaning) and Activation-Synthesis Hypothesis (Brainstem activation interpreted by the cortex; dreams may be meaningless).

• Psychoactive Drugs:

  • Depressants: Lower CNS activity (Alcohol, Barbiturates, Benzodiazepines). Enhance GABA response.

  • Stimulants: Excite CNS, increase heart rate and glucose metabolism (Caffeine, Nicotine, Cocaine, Amphetamines). MDMA is a mix of stimulant/hallucinogen.

  • Hallucinogens: Distorted perceptions (LSD, Psilocybin, Marijuana).

  • Opiates/Opioids: Act on endorphin receptors to reduce pain and produce euphoria (Heroin, Morphine, Oxycodone).

• Reward Pathway: Dopamine is produced in the Ventral Tegmental Area (VTA) and sent to the amygdala, nucleus accumbens, prefrontal cortex, and hippocampus. Serotonin levels decrease, reducing satiation.

Memory and Information Processing

• Information Processing Model: Input -> Process -> Output.

• Sensory Memory: Iconic (visual, <0.5\,s) and Echoic (auditory, $3 - 4\,s$).

• Working Memory (Short-Term): Capacity is $7 \pm 2$ items. Components include the visuo-spatial sketchpad and phonological loop coordinated by the central executive.

  • Dual Coding Hypothesis: Easier to remember words associated with images.

• Long-Term Memory: Unlimited capacity.

  • Explicit (Declarative): Semantic (facts) and Episodic (events/experiences).

  • Implicit (Non-declarative): Procedural (motor skills/habits) and Priming.

• Encoding Strategies: Rote rehearsal (least effective), Chunking, Mnemonic devices (Imagery, Pegword system, Method of Loci, Acronyms), Self-referencing, and Spacing.

• Retrieval Cues: Free recall (primacy and recency effects), Cued recall, and Recognition (easiest).

• Memory Problems:

  • Decay: The pathway between cue and memory weakens over time.

  • Interference: Retroactive (new learning impairs old info) and Proactive (old learning impairs new info).

  • Alzheimer’s Disease: Progressive loss of memory and cognitive function, characterized by beta-amyloid plaques and neurofibrillary tau tangles.

  • Korsakoff’s Syndrome: Caused by Vitamin B1 (thiamine) deficiency (malnutrition or alcoholism). Preceded by Wernicke’s encephalopathy. Characterized by severe memory loss and confabulation.

Cognition and Intelligence

• Piaget’s Stages of Cognitive Development:

  • Sensorimotor (0-2y): Object permanence develops.

  • Preoperational (2-7y): Egocentric, pretend play, and use of symbols.

  • Concrete Operational (7-11y): Conservation and empathy develop; logical reasoning regarding real events.

  • Formal Operational (12y+): Abstract thinking and moral reasoning.

• Problem Solving Methods: Trial and Error, Algorithms, Heuristics (Means-end analysis, Working backwards), and Intuition.

  • Biases: Overconfidence, Belief Perseverance, and Confirmation Bias.

• Intelligence:

  • Spearman: General Intelligence (g factor).

  • Sternberg: Triarchic Theory (Analytical, Creative, Practical).

  • Gardner: Multiple Intelligences (originally 7, then 9 independent areas).

  • Thurnstone: 7 Primary Mental Abilities.

  • Fluid Intelligence: Ability to reason quickly and abstractly; decreases with age.

  • Crystallized Intelligence: Accumulated knowledge and verbal skills; increases or stays stable with age.

Language, Emotion, and Stress

• Language Brain Areas:

  • Broca’s Area: Language expression/production (frontal lobe). Broca’s Aphasia = broken speech.

  • Wernicke’s Area: Language understanding/processing (temporal lobe). Wernicke’s Aphasia = word salad.

  • Arcuate Fasciculus: Connects the two areas. Damage causes conduction aphasia.

• Theories of Language and Cognition: Universalism (thought dictates language), Piaget (cognition develops then language), Vygotsky (language and thought are independent), Linguistic Determinism (Weak relativism vs. Strong Sapir-Whorfian).

• Components of Emotion: Physiological (arousal), Cognitive (appraisal), and Behavioral (body language).

  • Universal Emotions (Ekman): Happiness, Sadness, Fear, Disgust, Anger, Surprise.

  • James-Lange Theory: Event -> Physiological Response -> Interpretation -> Emotion.

  • Cannon-Bard Theory: Event -> Physiological Response + Emotion simultaneously.

  • Schachter-Singer Theory: Event -> Physiological Response + Cognition (Label) -> Emotion.

  • Lazarus Theory: Event -> Cognitive Appraisal -> Emotion + Physiological Response.

• Stress: Process of appraising and coping with challenges.

  • Richard Lazarus Appraisal Theory: Primary Appraisal (irrelevant, benign/positive, or stressful/negative). Secondary Appraisal (harm, threat, and challenge).

  • General Adaptation Syndrome (GAS): Alarm, Resistance, and Exhaustion phases.

Social Structure, Demographics, and Inequality

• Social Theories:

  • Functionalism: Society is a system of institutions maintaining stability/equilibrium (Durkheim).

  • Conflict Theory: Society is made of groups competing for resources and power (Marx, Weber).

  • Social Constructionism: Reality is a social product created by human agreement.

  • Symbolic Interactionism: Micro-scale social interactions and meanings given to symbols (Mead, Blumer).

  • Rational Choice/Exchange Theory: People weigh costs and benefits to maximize personal gain.

• Demographic Structure:

  • Age Cohorts: GI Generation (1901-1924), Silent Generation (1925-1945), Baby Boomers (1946-1964), Gen X (1965-1980), Millennials (1980-2000s), Gen Z (1995-2003).

  • Demographic Transition Model: 5 stages showing shift from high birth/death rates to low birth/death rates as a country industrializes.

• Social Inequality:

  • Social Mobility: Horizontal vs. Vertical (upward/downward). Caste (none) vs. Class (some) vs. Meritocracy (idealized; based on achievement).

  • Social Reproduction: Inequality replicating across generations via financial, social, and cultural capital.

  • Absolute Poverty (survival threatened) vs. Relative Poverty (excluded from society).

  • Intersectionality: Multiple layers of discrimination (race, gender, etc.) compounding for an individual.