Sensory, Attentional and Perceptual Processes

How senses register stimuli, thresholds, the kinds and theories of attention, Gestalt organisation, depth cues, constancies and illusions.

Key ideas

Sensation is the first registration of a stimulus; attention selects some stimuli; perception gives them meaning.
The absolute threshold is the least stimulus that can be noticed; the difference threshold is the least change that can be told apart.
Attention can be selective, divided (possible for well-practised, automatic tasks) or sustained (vigilance).
Broadbent’s filter blocks unattended stimuli, Treisman’s only weakens them, and the multimode theory selects at three stages.
Gestalt principles group what we see into wholes: proximity, similarity, continuity, closure, smallness, symmetry, surroundedness.
Constancies keep size, shape and brightness stable as viewing conditions change; illusions are misperceptions of real stimuli.
Bottom-up processing builds from features to the whole; top-down uses knowledge and expectations; both work together.

Remember

Span of attention	seven plus or minus two items (Miller)
Properties of attention	alertness, concentration, search
Binocular depth cues	retinal disparity, convergence, accommodation
Monocular depth cues	relative size, interposition, linear and aerial perspective, light and shade, texture gradient, motion parallax
Deep senses	kinesthetic (body position) and vestibular (balance and movement)
Illusions	Müller-Lyer (equal lines look unequal); phi-phenomenon (still pictures seem to move)

Watch out

Mixing up the two thresholds: the absolute threshold is about noticing at all, the difference threshold about noticing a change.
Calling a monocular cue binocular: only retinal disparity, convergence and accommodation need both eyes.
Pairing the filter theory with Treisman: Broadbent gave the filter, Treisman the attenuation.

Worked example

Suppose plain water first tastes sweet after 5 grains of sugar, and tastes sweeter than before only after 9 more grains. What do the 5 and the 9 grains show, and how many grains are there in all?

Working: 5 + 9

Answer: 5 grains: the absolute threshold; 9 grains: the difference threshold; 14 grains in all