Unit 2 covers how we take in information (sensation), how we interpret it (perception), and how our awareness shifts (states of consciousness). The MCQ frequently tests threshold distinctions and perceptual principles; the FRQ sometimes asks you to apply sleep or learning concepts to a scenario.
Sensation
Absolute threshold — minimum stimulus intensity detectable 50% of the time. Difference threshold / JND (Just Noticeable Difference) — smallest detectable change between two stimuli. Weber's Law — the JND is a constant proportion of the original stimulus (e.g., you need a bigger weight increase to notice a difference when lifting 50 lbs than when lifting 1 lb). Sensory adaptation — diminished sensitivity to unchanging stimuli over time (you stop noticing the smell of your own home). Signal detection theory — detecting a stimulus depends on both sensory sensitivity AND psychological factors (expectations, distractions); accounts for why context changes what we "hear."
Perception
Perceptual constancy — we perceive objects as stable even when sensory input changes: size constancy (car looks same size even as it moves away), shape constancy (door still looks rectangular when partly open). Gestalt principles — the mind organizes sensory data into meaningful patterns: figure-ground (separating object from background), proximity (close objects grouped together), similarity, continuity, closure (filling in gaps). Depth perception — binocular cues (retinal disparity, convergence) and monocular cues (linear perspective, interposition, texture gradient, relative size). Top-down processing — prior knowledge and expectations shape perception (recognizing your name in a noisy room). Bottom-up processing — sensation builds up to perception from raw sensory data.
States of Consciousness
Sleep stages: NREM Stage 1 (light sleep, hypnic jerk), NREM Stage 2 (sleep spindles, harder to wake), NREM Stage 3 (slow-wave/deep sleep, most restorative), REM (rapid eye movement — vivid dreams, muscle paralysis, memory consolidation, brain active). Sleep cycles ~90 min; REM increases in later cycles. REM sleep behavior disorder — muscle paralysis fails; person acts out dreams. Insomnia (can't sleep), sleep apnea (breathing stops), narcolepsy (sudden sleep attacks/cataplexy). Circadian rhythm — ~24-hour biological clock; disrupted by jet lag or shift work. Dreams: Freudian view (wish fulfillment, manifest vs. latent content); activation-synthesis (random neural firing interpreted by waking mind); memory consolidation view (most supported).
Psychoactive drugs: Depressants (alcohol, barbiturates, benzodiazepines — slow CNS, enhance GABA). Stimulants (caffeine, cocaine, amphetamines — speed CNS, flood dopamine). Opiates (heroin, morphine — mimic endorphins). Hallucinogens (LSD, psilocybin — distort perception). Tolerance (need more for same effect), withdrawal (physical symptoms when stopping).
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