Chapter 6: Sensation and Perception

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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.

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• 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

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• Which line is longer A - B or B - C?

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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.

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Gestalt Principles of Organization:• Figure-ground effect

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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.

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• 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.

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Visual Cliff

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• 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

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• How do we perceive depth and distance from a two dimensional retinal image?

• We have depth cues • Depth cues - binocular and monocular.

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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.

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• 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.

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Monocular Cues• Cues to depth and distance available to either eye

alone• First, some information . . .

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• Some examples . . .

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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)

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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)

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Interposition

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

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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.

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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?

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Shape and Size Constancy

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The size/distance relationship is often related to misperception.

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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.

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• 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?

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• 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.

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Extrasensory Perception (ESP)

• The controversial claim that perception can occur apart from sensory input.

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