Sensation, Perception and Attention
This section distinguishes detecting stimulus energy from interpreting it, and tests the Gestalt rules, depth cues and attention models that CHSE papers favour. Expect definition questions and illusion-based applications.
Sensation
- Transduction converts physical energy into neural impulses.
- Absolute threshold: weakest stimulus detected 50 percent of the time. Difference threshold (JND): smallest detectable change. Weber's law: the JND is a constant proportion of the original stimulus.
- Sensory adaptation: sensitivity declines under constant stimulation.
- Signal detection theory separates sensitivity from response bias (hits, misses, false alarms, correct rejections).
Perception
- Organisation and interpretation of sensory input. Gestalt laws: figure-ground, proximity, similarity, closure, continuity.
- Constancies: size, shape, colour, brightness.
- Depth cues: binocular (retinal disparity, convergence); monocular (interposition, relative size, linear perspective, texture gradient, motion parallax).
- Perceptual set: expectations shape interpretation.
Attention
Selective attention filters input (Broadbent's filter model; cocktail-party effect); divided attention is capacity-limited; sustained attention is vigilance.
Worked example
In the Mueller-Lyer figure, equal lines with inward and outward arrows appear unequal. Reasoning: retinal images are identical (sensation), but the brain reads the arrows as depth cues (perception); the illusion is perceptual, not sensory.
Traps
- Sensation is detection; perception is interpretation.
- Weber's law concerns proportion, not a fixed amount.
- Attention is not the same as perception.