PSYC1011 Chap.5 Perception: From Sensation to Inference

Perception: From Sensation to Inference

Perception begins with physical energy but ends with an organised experience and decision. Sensation refers to detection and early encoding; perception refers to interpretation and organisation. The distinction is analytical rather than a clean temporal border.

At every stage the system preserves some information, transforms other information and operates under uncertainty.

Transduction converts light, sound or other energy into neural activity. Sensitivity varies with receptor properties, adaptation and noise. An absolute threshold is not a fixed cliff inside one person; performance changes with criterion, expectation and consequence.

Difference thresholds and Weber-like relations describe discrimination under defined ranges, not a universal percentage that applies to every stimulus and context.

Signal detection theory separates sensitivity from response criterion. Hits and misses occur when a signal is present; false alarms and correct rejections occur when it is absent.

Moving the criterion can raise both hit and false-alarm rates without changing sensory sensitivity. Comparing accuracy alone can therefore confuse improved detection with a greater willingness to say present.

Perceptual organisation uses grouping relations such as proximity, similarity, continuation and common fate. Figure–ground assignment determines which region is treated as object and which as background.

These principles describe regularities in organisation; they are not magic rules that always force one result. Competing cues and task goals can change the outcome.

Depth and object perception combine multiple sources. Binocular disparity, motion, occlusion, relative size, perspective and texture can support distance.

Perceptual constancies compensate for changing retinal size, shape or illumination to maintain useful object properties. A visual illusion is valuable because it reveals the assumptions normally supporting accurate perception under typical environments.

Top-down information includes expectation, context and prior knowledge. It can resolve ambiguous input efficiently but can also bias reports.

Bottom-up constraint prevents expectation from making any experience possible. Strong accounts state how sensory evidence and prior information are weighted, then predict where a changed cue will shift perception. Merely labelling an effect top-down does not explain the mechanism.

Worked detection case: two observers view the same noisy trials.

Both discriminate signal from noise equally well, but one reports present more often, producing more hits and more false alarms. The difference is criterion, perhaps due to unequal costs of misses. A treatment that reduces false alarms while also reducing hits has not necessarily improved sensitivity; the full response pattern is required.

Revision should alternate demonstrations with analysis.

For each illusion or detection result, identify the proximal input, relevant cues, comparison, criterion and inference. Change context while holding input constant, or change signal strength while holding payoff constant. Explain which result supports sensitivity, organisation or expectation.

The lesson is not that perception is unreliable, but that useful inference can be systematically tested.

Attention and perception interact without becoming identical. Attention can prioritise locations, features or objects and alter detection, while perceptual organisation can determine what counts as the selected object. A change in report can therefore arise at sensory sensitivity, organisation, selection or decision.

Use timing, task contrast and signal-detection outcomes to distinguish these possibilities. A single faster response does not identify which stage changed, even when the visual demonstration feels intuitively clear.

When a perceptual claim changes, identify whether the physical signal, organising context, attentional priority or reporting payoff actually changed.

What this chapter covers

• 01

  transduction

• 02

  signal detection

• 03

  perceptual constancy

• 04

  explain perceptual experience as the integration of sensory information, organisation and context-sensitive inference

• 05

  A compelling perceptual experience is evidence about the system's interpretation, not a direct copy of the external world.

Separate sensitivity from criterion

Key terms

transduction

Conversion of physical energy into neural activity by sensory receptors.

signal detection

A framework separating sensitivity to information from the criterion used to report its presence.

perceptual constancy

Relatively stable perception of an object despite changes in the proximal sensory pattern.

Perception: From Sensation to Inference FAQ

Exam move

Build a construct–operation–comparison–inference map, then change one cue, contingency, measure or design feature and predict the revised result.

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