Sensory, Attentional and Perceptual Processes
Sensation, attention and perception questions test psychophysical thresholds, attention types, Gestalt grouping and depth cues.
Sensation and thresholds
Sensation is detection by sense organs; perception is interpretation. The absolute threshold is the weakest stimulus detected 50% of the time. The difference threshold (just noticeable difference) is the smallest detectable change. Weber's law says the JND is a constant proportion of the original stimulus. Signal detection theory separates sensitivity from response bias (hits, misses, false alarms).
Attention
Selective attention focuses on one input, as in the cocktail-party effect. Divided attention shares capacity across tasks; sustained attention is vigilance over time. Broadbent's filter model proposed early selection.
Gestalt and depth
Gestalt principles: proximity, similarity, continuity, closure and figure-ground. Monocular depth cues include relative size, interposition, linear perspective, texture gradient and motion parallax. Binocular cues are retinal disparity and convergence. Perceptual constancy keeps size, shape and brightness stable despite changing retinal images.
Worked example
In the Müller-Lyer illusion two equal lines look different because of the arrowheads. Reasoning: the outward fins suggest a nearer corner and the inward fins a farther corner; the brain applies size constancy and perceives the farther line as longer. The error occurs in interpretation, not in the eye.
Traps
- Absolute threshold and difference threshold are not the same.
- Sensation is raw detection; perception adds meaning.
- Constancy explains why we do not see the world changing as we move.