Chapter 6: Sensation and Perception 1

Some Definitions: Sensation - process used by sense receptors to receive and store information from environment Perception - process of organizing and interpreting sensory information allowing us to make sense of and recognize objects. 2

Perceptual psychologists - often study illusions Illusions – misperceptions; when we get it wrong, when we misperceive Ex. - lines This is also on page 240 in textbook 3 Which line is longer A - B or B - C?

4 Look at the following. What do you see?

Gestalt psychologists studied perceptual organization Gestalt - German word for “form” or “whole” Gestalt psychologists - “the whole may differ from the sum of its parts” Some Gestalt principles. 5

Gestalt Principles of Organization: Figure-ground effect 6

7 Gestalt Principles of Grouping: Proximity Continuity Closure Similarity

Depth Perception Depth Perception - the ability to see objects in three dimensions, although, the image that strikes the retina is two dimensional Allows us to judge distance, to see some objects as close and other objects as far away. 8

Gibson and Walk - depth perception and young children Is depth perception innate? 6 to 14 month old infants Designed a visual cliff Placed infants on the visual cliff - observed behavior. 9

Visual Cliff 10

Findings - depth perception may be partly innate Infants would not crawl out on the glass to get to their mother - perceived the drop off But, by six to fourteen months … Perhaps depth perception is due to experience. Yet, newborn animals (kittens, chicks) would not walk on the glass area 11

How do we perceive depth and distance from a two dimensional retinal image? We have depth cues Depth cues - binocular and monocular. 12

Binocular Cues Depth and distance cues - depend on the use of two eyes Retinal disparity - each eye perceives a slightly different world because … We usually do not realize this. Yet, this fact provides an important cue to depth and distance. 13

An Example Retinal disparity is built into the viewmaster How? You are seeing two pictures - one in your right eye, the other in your left What is the difference between pictures? Convergence - the extent to which the eyes converge inward when looking at an object. 14

Monocular Cues Cues to depth and distance available to either eye alone First, some information Some examples...

16 Relative Size If we assume that two objects are similar in size, we perceive the one that casts a smaller retinal image as farther away. (p.246)

17 Relative Clarity Because light from distant objects passes through more atmosphere we perceive hazy objects as farther away than clear objects (effect of fog on judging distance). (p. 247)

18 Interposition If one object partially blocks the view of another we perceive it as closer. (p. 246)

19 A gradual change from a coarse, distinct texture to a fine indistinct texture signals increasing distance. (p. 247) Perceives objects higher in our field as farther away. (p. 247) Texture Gradient Relative Height

Parallel lines, such as railroad tracks and cabbage rows, appear to converge with distance. (p.248) The more the lines converge the greater their perceived distance. 20 Linear Perspective

Perceptual Constancy Perceptual Constancy - perceiving objects as unchanging, even though retinal images change Ex. - size constancy It’s fortunate that our retina does not talk and have decision-making ability. Why? 21

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Shape and Size Constancy 23

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25 The size/distance relationship is often related to misperception.

26 Another Example...

Perceptual Interpretation Sensory Deprivation and Restored Vision Born blind, operation corrects vision in adulthood Can person see normally? Cataracts removed… distinguish figure from ground, but could not learn to recognize by sight objects that were familiar by touch Critical period. 27

Perceptual Adaptation. Can we adapt to an artificially displaced or inverted visual field? When subjects wear glasses that shift the apparent location of object 40 degrees to the left, can they adapt? Yes, within a few minutes and with practice experience brief aftereffect. 28

If you wore goggles which completely inverted your perception, could you adapt and respond normally? 29 If you wore goggles which completely inverted your perception, could you adapt and respond normally? After a period of adjustment, people wearing the inverted goggles have been able to ride a motorcycle, ski, and fly an airplane.

Perceptual Set and Context Effects This is a mental predisposition to perceive one thing and not another. 30

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Extrasensory Perception (ESP) The controversial claim that perception can occur apart from sensory input. 35