Perception: Revision and Exam Practice

This lesson brings together all the key concepts from the perception topic, providing a comprehensive revision resource and exam-style practice for AQA GCSE Psychology.

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Key Concepts Summary

Sensation vs Perception

	Sensation	Perception
Process	Detection of stimuli	Interpretation of stimuli
Direction	Bottom-up	Can be top-down or bottom-up
Involves	Sensory receptors	Brain and cognitive processes

Depth Cues

Monocular cues (one eye): relative size, overlap, height in plane, linear perspective, texture gradient

Binocular cues (two eyes): retinal disparity, convergence

Perceptual Constancies

• Size constancy — objects perceived as same size despite changing retinal image
• Shape constancy — objects perceived as same shape despite viewing angle changes
• Colour constancy — objects perceived as same colour despite lighting changes

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Theories of Perception: Comparison

flowchart TD
    P[Perception]
    P --> BU["Bottom-Up<br/>Gibson 1979"]
    P --> TD["Top-Down<br/>Gregory 1970"]
    BU --> OA[Optic array]
    BU --> OF[Optic flow]
    BU --> AF[Affordances]
    TD --> UI["Unconscious<br/>inference"]
    TD --> HY["Perceptual<br/>hypothesis"]
    TD --> PS[Perceptual set]
    OA --> EV["Everyday<br/>accurate perception"]
    HY --> IL["Visual illusions<br/>Muller-Lyer / Ponzo / Rubin"]

Feature	Gibson's Direct Theory (1979)	Gregory's Constructivist Theory (1970)
Type of processing	Bottom-up	Top-down
Key idea	Environment provides sufficient information	Brain constructs perception using knowledge
Role of experience	Minimal	Central
Key concepts	Optic array, optic flow, affordances	Unconscious inference, hypotheses
Explains illusions?	Poorly	Well
Explains everyday perception?	Well	Less well (overestimates errors)
Key evidence	Optic flow, Lee and Lishman (1975)	Müller-Lyer, Ponzo, hollow face, Bruner and Minturn
Ecological validity	High (real-world focus)	Lower (lab-based illusions)

Exam Tip: When asked to compare the two theories, structure your answer around their key differences and use specific evidence for each. A balanced evaluation acknowledges that both contribute to our understanding of perception.

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Visual Illusions Summary

Illusion	Type	Description	Explanation
Müller-Lyer	Distortion	Lines with fins appear different lengths	Misapplied size constancy (Gregory)
Ponzo	Distortion	Lines between converging lines appear different sizes	Misapplied size constancy (Gregory)
Rubin's vase	Ambiguous	Seen as vase or two faces	Competing hypotheses/figure-ground
Ames room	Distortion	People appear different sizes	Misapplied size constancy
Kanizsa triangle	Fictional	See a triangle that is not drawn	Brain fills in missing information

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Factors Affecting Perception

Factor	Effect	Key Study
Motivation	Needs influence what we perceive	Gilchrist and Nesberg (1952) — hungry people saw food as brighter
Expectation	Context creates perceptual set	Bruner and Minturn (1955) — B vs 13
Emotion	Mood affects interpretation	McGinnies (1949) — perceptual defence
Culture	Visual environment shapes perception	Segall et al. (1963) — Müller-Lyer cross-cultural

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Key Studies in Detail

Segall et al. (1963)

• Aim: To investigate whether susceptibility to visual illusions varies across cultures
• Method: Tested participants from 14 cultures on the Müller-Lyer and other illusions
• Results: Western participants (carpentered environments) more susceptible to Müller-Lyer
• Conclusion: Cultural experience affects perception — supports Gregory's theory
• Evaluation: Methodological issues with using 2D drawings across cultures; supports carpentered world hypothesis

Bruner and Minturn (1955)

• Aim: To test whether context affects perception of an ambiguous figure
• Method: Showed B/13 figure in letter or number context
• Results: Perceived as B in letter context, 13 in number context
• Conclusion: Context creates perceptual set — supports top-down processing
• Evaluation: Artificial task; may test interpretation rather than perception

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Common Exam Questions and How to Answer Them

"Describe Gibson's direct theory of perception." (4 marks)

A strong answer should include:

1. It is a bottom-up theory — perception is driven by environmental stimuli
2. The optic array provides rich information about the world
3. Optic flow provides information about speed and direction of movement
4. Affordances — we perceive what objects offer for action

"Explain one difference between Gibson's and Gregory's theories." (3 marks)

Gibson argues that perception is a direct, bottom-up process driven by information in the environment (e.g. optic flow), while Gregory argues that perception is an indirect, top-down process where the brain uses stored knowledge to construct a hypothesis about what is being perceived. For example, Gregory can explain visual illusions (where perception is inaccurate) but Gibson cannot fully account for why they occur.

"Evaluate the use of visual illusions as evidence for Gregory's theory." (4 marks)

For: Illusions such as the Müller-Lyer show that perception can be inaccurate, supporting the idea that the brain constructs perception rather than directly detecting reality. Cross-cultural differences in susceptibility (Segall et al.) show that experience influences this construction.

Against: Illusions are artificial stimuli that do not represent real-world perception. Gibson would argue that illusions only occur with impoverished stimuli — in natural, dynamic environments, perception is generally accurate because sufficient information is available.

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Revision Checklist

• I can explain the difference between sensation and perception
• I can describe monocular and binocular depth cues
• I can explain size, shape, and colour constancy
• I can describe and evaluate Gibson's direct theory
• I can describe and evaluate Gregory's constructivist theory
• I can compare Gibson's and Gregory's theories
• I can explain the Müller-Lyer illusion and Ponzo illusion
• I can describe Rubin's vase and explain why it is important
• I can describe factors affecting perception (motivation, expectation, emotion, culture)
• I can describe and evaluate the Bruner and Minturn (1955) study
• I can describe and evaluate the Segall et al. (1963) study

Final Exam Tip: Always link your answer to a specific theory (Gibson or Gregory) and use named research studies as evidence. The highest marks go to answers that evaluate using both supporting and contradicting evidence.

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Key Points