Unit 3: Sensation and Perception
AP Psychology: 60 practice questions with detailed explanations.
Unit Study Guide
Executive Summary
Unit 3 separates detection (sensation) from interpretation (perception) and explains how the brain constructs our experienced world.
Sensation
Sensory receptors transduce physical energy into neural signals. Absolute threshold: the minimum stimulus detected 50% of the time. Difference threshold (just noticeable difference) follows Weber's law — the JND is a constant proportion of stimulus intensity. Signal detection theory adds response criteria and noise.
Vision
Light enters the cornea and pupil, focuses through the lens onto the retina. Rods (dim light, black/white, periphery) and cones (color, detail, fovea) transduce it. The optic nerve exits at the blind spot. Opponent-process theory explains afterimages via red-green and blue-yellow pairs; trichromatic theory explains color mixing via three cone types.
Perception
Top-down processing uses expectations; bottom-up builds from raw features. Gestalt principles group stimuli: proximity, similarity, continuity, closure. Depth perception uses binocular (retinal disparity, convergence) and monocular cues (relative size, interposition, linear perspective). Perceptual constancy keeps objects stable despite changing input.
Hearing
Sound waves vibrate the eardrum and ossicles; the cochlea's hair cells transduce pitch and loudness. Place theory explains high pitches; frequency theory explains low ones.
Other senses
Taste (sweet, sour, salty, bitter, umami), smell (olfaction — the only sense that bypasses the thalamus), touch, kinesthesis (body position), and the vestibular sense (balance).
Exam traps
Sensation is physical; perception is psychological. Absolute threshold is 50% detection, not any detection. Top-down processing is expectation-driven — the same stimulus can be perceived differently by different people.