Sensation, Perception, and Attention (Foundational Concept 6)
The core distinction
Sensation is the transduction of stimulus energy into neural signals; perception is the selection, organization, and interpretation of those signals. Almost every question here is easier if you first ask which of the two the stem describes.
Psychophysics
Know the absolute threshold (detected about half the time), the difference threshold or just-noticeable difference (JND), and Weber's law: the JND is a constant proportion of the original stimulus, so the same ratio, not the same amount, applies across intensities. Fechner modeled this logarithmically; Stevens proposed a power function. Signal detection theory separates sensitivity (d-prime) from response criterion: a liberal criterion raises hits and false alarms together, so more hits alone do not prove better sensitivity. Add sensory adaptation.
Organization and attention
Bottom-up processing is stimulus-driven; top-down processing is expectation-, context-, and knowledge-driven. The Gestalt principles (proximity, similarity, continuity, closure, figure-ground) describe top-down grouping. Selective attention, divided attention, the cocktail-party effect, and inattentional blindness are frequent targets.
Sensory systems
Rods (dim light, periphery, high convergence, no color) versus cones (acuity, color, fovea). Trichromatic coding operates at the receptor level and opponent-process coding at later ganglion and thalamic levels; both are correct at different stages. Feature detectors code edges and orientation. In audition, place theory handles high frequencies and frequency/volley accounts handle low ones. Somatosensation includes gate control theory, in which non-painful input can reduce pain transmission.
Traps
Confusing adaptation (receptor-level) with habituation (learning-based response decline); presenting opponent-process and trichromatic theories as rivals; equating a lower threshold with a stricter criterion.
Worked rule
If the JND for weight is 1/50 of the standard, a 100 g standard needs +2 g and a 200 g standard needs +4 g. Weber's law is always a ratio.