Sensory, Attentional and Perceptual Processes
Sensation is the detection of physical energy by sense organs; perception is the interpretation of that information. The exam tests thresholds, sensory systems, attention and Gestalt organisation.
Psychophysics
Absolute threshold: the weakest stimulus detected 50% of the time. Difference threshold (JND): the smallest detectable change. Weber's law: the JND is a constant fraction of the original stimulus. Signal detection theory separates sensory sensitivity from response bias; sensory adaptation is reduced sensitivity after constant stimulation.
Vision and audition
Light passes the cornea, pupil and lens and is transduced by rods and cones in the retina; cones cluster at the fovea and code colour, rods serve dim light. Trichromatic theory (Young-Helmholtz) explains colour mixing; opponent-process theory (Hering) explains afterimages. In hearing, sound travels through the outer and middle ear to the cochlea; place theory explains high pitches, frequency theory low pitches.
Attention
Selective attention filters input (Broadbent); divided attention shares capacity; sustained attention persists over time. External determinants: intensity, size, contrast, movement, novelty. Internal: needs, interests, mental set. Inattentional blindness shows that looking is not the same as seeing.
Perceptual organisation
Gestalt laws: proximity, similarity, continuity, closure, common fate, good form. Depth cues: binocular (retinal disparity, convergence) and monocular (linear perspective, relative size, interposition, texture gradient, motion parallax). Constancies keep size, shape and brightness stable.
Worked example
In the Muller-Lyer illusion the line with outward-turned arrows looks longer. Reasoning: the arrows act as depth cues, so size constancy scales the line perceived as farther away - an interpretation error, not an eye defect.
Traps
- Reversing rod and cone functions.
- Confusing absolute and difference thresholds.
- Treating attention as unlimited.
- Listing Gestalt laws as depth cues.