Perception

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Perception

• Top-down processing

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Brain pathways and perception

• From the retina, axons of ganglion cells travel
  as the optic nerve to the lateral geniculate
  nucleus (LGN) of the thalamus
• From LGN cells, axons travel to the primary
  visual cortex, in the occipital lobe
• From the primary visual cortex, axons project to
  visual association cortex, in the parietal and
  inferior temporal lobes

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Other visual pathways

• To the SCN of hypothalamus
• To accessory optic nuclei of brainstem and to
  cerebellum Synchronize eye and head movements
• To pretectum to control pupil diameter
• To superior colliculi, for control of visual
  attention
• To ventral LGN, as a relay

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Information processing

• At each level in the visual pathways, more
  complex information is drawn from the stream
• Hubel and Wiesels method (1977) Microelectrodes
• Receptive fields On and Off

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Receptive fields

• The piece in the visual field to which a given
  cell responds.
• Receptive fields for rods and cones are simple
  and round.
• Receptive fields for ganglion cells, LGN cells,
  and cortical cells are complex.

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Examples of receptive fields
Center-surround Cells -Ganglion cells, LGN
cells (both M and P), and layer IV of striate
cortex
Center off-surround on
Center on-surround off
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Examples...
Simple cortical cells Line border responds best
to -contrasting bars -single straight edges
-at a particular angle
off
on
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Complex cortical cells

• Merge inputs from simple cells to detect
• Stimuli over a larger area of the visual field
• An edge at a particular angle anywhere in the
  field (not on-off)
• Movement, often directionally
• About half are binocular
• Half of the binocular cells show ocular dominance
• Some are retinal disparity detectors

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Complex cell fields
Note - the larger receptive field
- no subdivision on-off
-orientation responsiveness
-directional sensitivity
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Visual association cortex

• Combines information from the primary visual
  cortex to produce
• Orientation, movement, and color
• Three dimension views
• Spatial location of objects

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Effects of damage

• Primary visual cortex Sensory (Scotomas)
• Visual association cortex Perceptual
• Achromatopsia
• Loss of movement perception
• Balints syndrome Location
• Visual agnosias
• Prosopagnosia

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Processes of organization

• Selective attention
• Reversible figures
• The cocktail party effect
• Dichotic listening experiments
• Perceptual illusions
• Visual capture

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Principles of organization

• Gestalt psychology
• Form perception
• Figure-ground
• Grouping
• Proximity
• Similarity
• Continuity
• Closure
• Connectedness

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Principles of organization

• Depth perception
• Monocular cues
• Binocular cues
• Examples Fingerpointing, hole in hand
• Motion perception
• Size and position
• Stroboscopic movement
• Phi phenomenon
• Example Troxler effect

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Perception phenomena

• Perceptual constancy
• Size and shape The swelling hand
• Lightness Transparency
• Perception as interpretation
• Study sensory restriction effects p. 203
• Perceptual adaptation-Videotape

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Expectations affect perceptions

• Perceptual set
• Expectations or schemas Numbers and names
• Context
• TIME FLIES I CANT THEYRE TOO FAST
• CHO
• PHO
• USE
• CHOPHOUSE

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More context effects

• FOLK
• CROAK
• SOAK
• THE WHITE OF AN EGG

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Cognitive set

• LULB
• CALEM
• NUKKS
• SEUMO
• BAZER

• NORC
• NOONI
• MATOOT
• PREPPE
• TEBE

EAP
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Social transmission of narrative

• Three men, masked and armed with pistols, robbed
  the Glenwood State Bank yesterday morning at 930
  a.m. They escaped in a Ford two-door bearing a
  1971 Connecticut license plate, taking 647 in
  coins and 2,190 in five-dollar bills. A
  lieutenant in the Marines claims he saw the car
  going north at noon yesterday.

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