Perception: Key Concepts and Theories

Perception, Sensation
Visual Cues, Visual Constancies
Monocular Depth Cues, Height in Plane, Relative Size, Occlusion, Linear Perspective
Binocular Depth Cues, Retinal Disparity, Convergence
Constructivist Theory, Motivation, Expectation

Height in plane: objects higher in the visual field appear farther away.
Relative Size: smaller retinal image → perceived farther away; larger image → perceived closer.
Occlusion: obscured objects are perceived as further away.
Linear Perspective: parallel lines converge in the distance to a point.

Retinal Disparity: due to eyes being $6\text{ cm}$ apart; differences between the two images inform distance; closer objects produce larger disparity; farther objects produce less.
Convergence: as objects get nearer, the eyes rotate inward; greater convergence signals depth.

Perception is innate and not learned (nature).
Sensory information available from the environment is sufficient; no need to fill in gaps.
Eyes detect small changes in light, texture, movement, and depth; supports distance perception (e.g., color gradient: nearer colours appear brighter, farther colours paler).
Motion Parallax: depth cues combine with movement to judge distance (closer objects move faster when in motion).

Perception uses past experiences to interpret the world (nurture).
Much of what we see is incomplete/ambiguous; the brain fills gaps with inferences from cues.
Visual cues help determine size, shape, depth, and distance; perceptual judgments are usually accurate but can be mistaken (mistaken hypotheses).
Visual Illusions (e.g., Muller-Lyer) illustrate context-driven interpretation.

Size Constancy: brain maintains a constant perception of an object’s size despite retinal image changes.
Misinterpreted depth cues can lead to illusions.
Ponzo Illusion: converging lines create a sense of distance, causing the top line to look longer due to size constancy.
Müller-Lyer Illusion: outward vs inward corners cue depth; one line appears longer due to contextual cues.
Ames Room: room shape distorts perceived size through depth cues.
Ambiguity: Necker Cube, Rubin’s Vase – more than one valid interpretation.
Kanizsa Triangle: illusory contours hint at a triangle that isn’t physically present.

Ambiguity: images can be interpreted in more than one way.
Example: Necker Cube (two possible orientations); Rubin’s Vase (vase vs two faces).
Kanizsa Triangle: illusory contour suggesting a triangle.

Aim: investigate how culture affects interpretation of depth cues.
Sample: comparison across schooled/unschooled, black South Africans and white Europeans.
Result: schooling and culture affect depth cue interpretation; exposure to 2D images and books/magazines influences perception.
Conclusion: culture and schooling shape perceptual set.

Aim: whether words with emotional content affect recognition speed.
Method: participants identifed neutral vs taboo words while GSR measured.
Result: slower recognition for taboo words; larger GSR changes.
Conclusion: emotion influences perceptual set; heightened arousal can slow recognition of aversive stimuli.

Aim: effect of hunger on perception of food imagery.
Method: deprived vs non-deprived groups; slides of meals; adjust lighting to match initial brightness.
Result: hungry participants increased brightness of food pictures; control group showed no change.
Conclusion: hunger heightens perceptual sensitivity to food-related stimuli.

Aim: effect of context on interpretation of an ambiguous figure.
Method: ambiguous figure shown after sequences of letters vs numbers; participants drew what they saw.
Result: figure perceived as a B after letters; as 13 after numbers.
Conclusion: expectation (context) shapes perceptual interpretation.

Culture: strengths—standardized procedures; weaknesses—cultural/language differences may affect comprehension; limited temporal validity.
Emotion: strengths—objective GSR data; weaknesses—small sample; artificial task; potential ethical concerns.
Motivation: strengths—clear demonstration of hunger effect; weaknesses—artificial task; possible ethical concerns.
Expectation: strengths—illustrates context effects; weaknesses—ambiguous real-world applicability; artificial task.