VII. Perception

VII. Perception

• Sensation:

- “raw” material for perception

- started at “entry level”, data driven

“bottom-up processing”

• Perception: “top-down processing”

- concept driven, use preexisting knowledge

to interpret information.

VII. PERCEPTION

• Recall – we are bombarded with possible “energy” from environment...

• A. To what sensations do we attend?• In order to perceive something, we must attend or pay

attention to it (consciousness).Selective Attention:• Ability to focus awareness on a single stimulus to the

exclusion of other stimuli.(We focus our awareness on only a limited aspect of all that we are capable of experiencing.)

B. How do we organize stimuli?

• We tend to organize stimuli into “wholes”.• Origin: Gestalt Psychology

– “Gestalt”: means “whole” or “form” in German.

• Proposed nervous system is predisposed to respond to patterns in stimuli according to certain rules.

• “Whole is different from its parts”• Example from video – wooden “triangle”

C. FORM PERCEPTION• One of these basic rules...

• 1. Figure vs. Ground– To see an image, need to be able to distinguish

between figure and ground.– Sometimes, they can be reversible.– But, at one time, we can focus on only one or other.

Judging Distance

Which is closer, the manor the house?

How can you tell?

-- Interposition

-- Relative size

-- Relative height

-- Linear perspective

-- Relative Clarity

C. FORM PERCEPTION

• What stimuli are grouped together?

• 2. Grouping

- We automatically imply order by grouping

things together according to certain rules.

D. DEPTH & DISTANCE PERCEPTION

• How do we perceive depth/distance?- Image on retina is 2-d.- Need the brain – uses certain cues.

1. Depth perception:• a. Binocular Cues:

Cues for perceiving depth that require both eyes.- Retinas receive slightly different images of world.- Brain compares those 2 images.- Retinal Disparity: difference between 2 images.- Key to judging depth – SHORT DISTANCES.

D. DEPTH OR DISTANCE PERCEPTION

• But, when at a distance, there is very little retinal disparity.

• 2. Distance perception

• a. Monocular Cues Cues for distance that require one eye.

Example from video.

Judging Distance

Which is closer, the manor the house?

How can you tell?

-- Interposition

-- Relative size

-- Relative height

-- Linear perspective

-- Relative Clarity

• Linear Perspective

D. DEPTH OR DISTANCE PERCEPTION

• 3. Nature or nurture?– When would ability to perceive depth be

important in terms of development?– Gibson & Walk (1960):

• “Visual Cliff” Experiments

– But, is evidence for nurture also.• “Use it or lose it”

E. MOTION PERCEPTION

• Another possible innate ability.

• Speculated to have evolved more for survival than other types of perception. Why?

• Brain makes sense of cues:– Shrinking objects are retreating.– Enlarging objects are approaching.

Perceptual Constancy

• Perceptual constancy:

We perceive objects as unchanging even though the stimuli we receive about those objects change. – Importance of experience and expectations?– babies vs. Pygmies

• Connecting the cues....

– Distance– Size– Motion– Perceptual Constancy

• Insert slide of Muller-Lyers Illusion

INTERPRETATION IN PERCEPTION

• Folk, croak, soak...

• 1. Perceptual Set:

A mental predisposition to perceive one thing and not another.

- Power of our expectations, predisposition – particularly when interpreting ambiguous stimuli.

• 2. Review – importance of expectations– Efficiency– Can not resist imposing patterns on unpatterned

stimuli (“gestalt”).– When we see a pattern, difficult to see a

different pattern.– Even if we formed an incorrect image, difficult

to form a correct one.

• 3. Where do our expectations (schemas) come from?– a. Experience – b. Culture

• Vulnerability to illusions

G. INTERPRETATION AND PERCEPTION

c. Context

- Context Effects: We often discern the

meaning of something by using the context in which it is placed.

- rat/man study

- Kulechov effect

Importance of EXPECTATIONS

G. Interpretation in Perception

• How adaptive is our ability to interpret and organize stimuli into perceptions?

• 4. Perceptual Adaptation:In vision, the ability to adjust to an artificially displaced or even inverted visual field.

Conclusions• Perception: The top-down part of understanding

environment and processing information. Brain interprets and organizes information.– Amazing feats of grouping stimuli & using cues.

• But that can also cause illusions...

– Individual differences based on experience and expectations.

• All of these rely on taking in physical energy from environment – sensations.

• Assumption: our experiences are tied to actual, physical events occurring in environment.... see text

H. Perception without Sensation?

• ESP -Extrasensory perception: • Perception without sensory input. • Types of ESP:• Telepathy, Clairvoyance, Precognition • More than ½ Americans believe in some type of

ESP.• Parapsychologists: • Psychologists who study psychic phenomena

through case studies and experiments.

H. Perception without Sensation?

• Rhine’s Research

• Conclusion about ESP:

• No sound evidence for para-psychological phenomena

• No single individual who can demonstrate psychic powers to independent investigators

•  

Impossible FiguresImpossible Figures

• Example:

• Cocktail Party Effect:

The ability to selectively attend to one voice among many.