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Perception
Top-down processing
What do you see?
Perception is different from
sensation
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Wundt-Jastrow illusion
The oscillating window illusion
The horizontal-vertical illusion
The Muller-Lyer Illusion
The oblique effect
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
Other visual pathways
• To the SCN (suprachiasmatic nucleus) 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 of the tectum, for
control of visual attention
Information processing
• At each level in the visual pathways, more
complex information is drawn from the
stream
• Hubel and Wiesel’s method (1977):
Microelectrodes
• Receptive fields: On and Off
The Hermann Grid
Receptive fields
• The piece in the visual field to which a
given cell responds.
• Receptive fields for rods and cones are
simple and round.
Off
On
Examples of receptive fields
on
on
on
off
on
on
Center off-surround on
off
off
off on
off off
Center on-surround off
Center-surround Cells:
-Ganglion cells, LGN
cells (both M and P),
and layer IV of
striate cortex
Receptive fields and gray dots
Examples...
on
off
Simple cortical cells:
Line border responds
best to
-contrasting bars
-single straight edges
-at a particular angle
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
Complex cell fields
Note:
- the larger receptive field
- no subdivision on-off
-orientation responsiveness
-directional sensitivity
Visual association cortex
• Combines information from the primary
visual cortex to produce
– Orientation, movement, and color
– Three dimension views
– Spatial location of objects
Effects of damage
• Primary visual cortex: Sensory (Scotomas)
• Visual association cortex: Perceptual
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Achromatopsia
Loss of movement perception
Balint’s syndrome: Location
Visual agnosias
• Prosopagnosia
Agnosias
• Prosopagnosia
– Actually, an inability to identify particular
faces
– Duplicated as an inability to recognize
particular cows, doors, cars
– Problem is in distinguishing among similar
examples of complex visual stimuli
– Damage is inferior temporal
Other agnosias
• Apperceptive visual agnosias
– Prosopagnosia
– Achromatopsia
• Associative visual agnosias
– Inability to name seen objects, although they
can copy them and know the word (“anchor”)
– May get the word through circumlocutions (the
milking farmer)
Processes of organization
• Selective attention
– Reversible figures
– The cocktail party effect
– Dichotic listening experiments
• Perceptual illusions
– Visual capture
Principles of organization
• Gestalt psychology
• Form perception
– Figure-ground
– Grouping: Pragnanz
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Closure and completion
Proximity
Similarity
Continuation and Common Fate
Connectedness
Form perception: Figure-ground
Notice the effects
of continuous
boundaries on the
goodness of form
perception of the
vase figure.
Closing borders
An example of completion at
Mt. Rushmore
Subjective contours
Other subjective contours
Gestalt laws of perception
Pragnanz
Proximity
More Gestalt principles
CCCBCCC
CCCBCCC
BBBBBBB
CCCBCCC
CCCBCCC
CCCBCCC
CCCBCCC
CCCBCCC
Similarity
Continuation
More Gestalt Principles...
Common Fate
Connectedness
What principles here?
Form and pattern perception
• Templates?
• Prototypes
– Humphrey’s monkeys
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Interested in individual monkey pictures
Not interested in individual cows and pigs
Exposure increased interest in cows and pigs
Experience sharpens prototypes
Distinctive features
• Rule prototypes: Ulrich Neisser (1964)
EWAFTMX
LKZFECKH
EXNWKAE
AFLXZMW
SQPRDGB
OBCQJUG
SDBPNRQ
BPOSRGQ
• The man who mistook his wife for a hat
Perceiving distinctive features
• Context cues
• Biederman’s (1990) geons
• Cusps and joints
Principles of organization
• Depth perception
– Monocular cues
– Binocular cues
– Examples: Fingerpointing, hole in hand
• Motion perception
– Size and position
– Stroboscopic movement
– Phi phenomenon
The phi phenomenon
Monocular Depth cues: Height,
Interposition, and Relative Size
What cues are here?
Charles Sheeler, Classic Landscape, National Gallery, Feb. 26, 2000
Perception phenomena
• Perceptual constancy
– Size and shape: The swelling hand
– Brightness: Overhead
• Perception as interpretation
• The grasping visual illusion
Ebbinghaus figures and the
grasping illusion
Franz, Gegenfurter, Bulthoff, & Fahle, 2000
Perceptual Constancy and the
Moon Illusion
Expectations affect perceptions
• Perceptual set
– Expectations or schemas: Numbers and names
– Context:
TIME FLIES I CANT THEYRE TOO FAST
CHO
PHO
USE
CHOPHOUSE
More context effects
FOLK
CROAK
SOAK
THE WHITE OF AN EGG
Cognitive set
• LULB
• CALEM
• NUKKS
• SEUMO
• BAZER
• NORC
• NOONI
• MATOOT
• PREPPE
• TEBE
EAP
Social transmission of narrative
• Three men, masked and armed with pistols,
robbed the Glenwood State Bank yesterday
morning at 9:30 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.
Backmasking
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Queen, Another one bites the dust
Queen, backwards
Psalm 23, backwards
Excerpt: Jabberwocky, Lewis Carroll
More Jabberwocky