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Vision: Perception & Pattern Recognition

Kimberley A. Clow

kclow2@uwo.cahttp://instruct.uwo.ca/psychology/130/

Outline Welcome to the EyeHow Long Do We Remember What We See?Perception

How do we perceive depth?How do we perceive form?

How Do We Identify Objects?Template TheoriesFeature TheoriesComponent Theories

Perceptual DevelopmentThe effects of experience

The Effects of Drugs

Welcome to the Eye

Why two eyes?Stereopsis

Basic anatomySee diagram

Rods and conesLocationAcuityDark adaptation

Eye Movements

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How Long Do We Remember What We See?

LightningSeries of separate bolts

Each lasts about 1ms with 50ms of darkness in between

Perception of LightningA half-second to a second duration of light

SperlingC 2 L E6 R P 5S 9 1 T

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So What Is Perception?

The means by which information acquired from the environment via the sense organs is transformed into experiences of objects

SightsSoundsTastes, etc.

How Do We Perceive Depth?Monocular Cues

Pictorial CuesFamiliar SizeLinear PerspectiveTexture GradientsInterposition or OverlapShadingAtmospheric Haze or Aerial PerspectiveRelative Height

Kinetic CuesMotion ParallaxKinetic Depth Effect

Binocular CuesPhysiological Cues

Binocular DisparityAccommodationConvergenceDivergence

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Pictorial Cues

Shape Constancy

Size Constancy

Familiar Size

Linear Perspective Texture Gradient

Size, Linear Perspective, and Texture

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Shading

Original Reversed

Atmospheric Hazeor

Aerial Perspective

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Allows for Depth Perception Can Create Illusions

Relative Height

Kinetic Cues

Motion Parallax

Physiological Cues

Binocular Disparity

Accommodation

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How Do We Perceive Form?

Change as a requirement for perceiving form

Snow BlindnessStabilized Retinal Images

Figure-Ground RelationsOrganization occurs in the mind, not on the retinaSmaller shapes more likely to become figure than ground

Gestalt Psychology

The whole is greater than the sum of its partsLaws of Perception

Figural OrganizationProximitySimilarityGood ContinuationClosureSymmetrySubjective Contours

How Are They Organized?

Similarity

Proximity

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Good ContinuationViolation

Closure

Symmetry Subjective Contours

How Do We Identify Objects?

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Template Theories

We identify objects by matching the current stimulus to a template (or model) in memory

Stimulus Templates

Feature Theories

Can You Identify This Shape?

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Component Theories

These Theories Are Not Enough

These theories are all data drivenbottom-up processing

Need to allow for the effects of context as welltop-down processing

In real life, we have expectancies and these exert an influence on what we perceive

The pile of clothes that looks like a person out of the corner of our eyeThe school classmate you don’t recognise in the mall

Perceptual Development

Testing Children2-3 Weeks

Blink when object approaches

4 MonthsBinocular depth cuesMonocular dependent on exp.

6-7 MonthsLinear perspectiveFamiliar size

3 YearsRelative heightShadingAdult acuity

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The Effects of Experience

The effects of deprivation and altering perception

Kittens reared with only vertical linesDark reared chimps Prism glasses

At birth, infants can perceive and discriminate between all human sounds

By 10-12 monthscannot differentiate between different phonemes that don’t exist in own language

Effects of Drugs