Cognitive Connie
What is perception?
Perception is the process by which the brain interprets and organises sensory information to construct a coherent representation of the world. It is not a passive recording of reality but an active, constructive process: the brain uses prior knowledge, expectations, and context to resolve the inherently ambiguous sensory input it receives.
Key concepts
Gestalt principles
Rules by which the visual system groups elements into organised percepts. Proximity: nearby elements are grouped together. Similarity: like elements are grouped. Continuity: contours are perceived as continuous. Closure: incomplete figures are perceptually completed. Figure-ground: the visual field is organised into a figure (the object of attention) and ground (the background). These reflect the brain's tendency to impose structure on ambiguous input.
Perceptual constancies
The tendency to perceive stable object properties despite changing sensory signals. Size constancy: we see a person as the same size whether near or far, even though retinal image size changes. Shape constancy: a door appears rectangular whether viewed straight-on or at an angle. Lightness constancy: surfaces maintain their apparent brightness across changes in illumination. Constancies require the brain to "factor out" viewing conditions from raw sensory data.
Visual pathways
The visual cortex processes information in two major streams from primary visual cortex (V1). The ventral ("what") stream runs to the inferior temporal cortex and processes object identity, colour, and face recognition. The dorsal ("where/how") stream runs to the posterior parietal cortex and processes spatial location, motion, and the guidance of action. Double dissociations in patients with selective lesions of each pathway confirm their functional independence.
Top-down processing
The influence of higher-level knowledge, expectations, and context on the interpretation of sensory input. We perceive what we expect as much as what is "out there." Context effects, priming, and the resolution of perceptual ambiguity all involve top-down processing. Distinguished from bottom-up (data-driven) processing, which begins with sensory features and builds to perception.
Test your knowledge
Sources
Last reviewed July 2025- 1.
Gibson, J. J. (1966). The Senses Considered as Perceptual Systems. Houghton Mifflin.
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Ecological approach to perception proposing direct pickup of affordances from the environment without internal representation.
- 2.
Gregory, R. L. (1970). The Intelligent Eye. Weidenfeld & Nicolson.
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Constructivist account of perception arguing that percepts are hypotheses about the external world built from ambiguous sensory data.
- 3.
Rock, I. (1983). The Logic of Perception. MIT Press.
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Comprehensive account of indirect, constructive perception including perceptual constancies and the role of Gestalt principles.