VII. Perception

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VII. Perception
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• 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.

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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.)

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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

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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.

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C. FORM PERCEPTION

• What stimuli are grouped together?
• 2. Grouping
• - We automatically imply order by grouping
• things together according to certain rules.

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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.

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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.

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• Linear Perspective

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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

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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.

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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

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• Connecting the cues....
• Distance
• Size
• Motion
• Perceptual Constancy

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• Insert slide of Muller-Lyers Illusion

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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.

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• 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.

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

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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

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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.

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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

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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.

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H. Perception without Sensation?

• Rhines Research
• Conclusion about ESP
• No sound evidence for para-psychological
  phenomena
• No single individual who can demonstrate psychic
  powers to independent investigators
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Impossible Figures
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• Example
• Cocktail Party Effect
• The ability to selectively attend to one voice
  among many.

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