Perception
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Transcript of Perception
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Perception
Top-down processing
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What do you see?
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Perception is different from sensation
• Wundt-Jastrow illusion• The oscillating window illusion• The horizontal-vertical illusion• The Muller-Lyer Illusion
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The oblique effect
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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 (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
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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
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The Hermann Grid
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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.
Off
On
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Examples of receptive fieldson
on
on on
onoff
off
offoff off
offon
Center off-surround on
Center on-surround off
Center-surround Cells:-Ganglion cells, LGN cells (both M and P), and layer IV of striate cortex
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Receptive fields and gray dots
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Examples...
onoff on
off
Simple cortical cells:Line border respondsbest to -contrasting bars -single straight edges -at a particular angle
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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 fieldsNote:- 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– Balint’s syndrome: Location– Visual agnosias
• Prosopagnosia
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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
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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)
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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: Pragnanz
• Closure and completion• Proximity• Similarity• Continuation and Common Fate• Connectedness
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Form perception: Figure-ground
Notice the effects of continuous boundaries on the goodness of form perception of thevase figure.
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Closing borders
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An example of completion at Mt. Rushmore
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Subjective contours
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Other subjective contours
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Gestalt laws of perception
Pragnanz Proximity
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More Gestalt principles
C C C B C C CC C C B C C CB B B B B B BC C C B C C CC C C B C C CC C C B C C CC C C B C C CC C C B C C C
Similarity Continuation
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More Gestalt Principles...
Common Fate Connectedness
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What principles here?
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Form and pattern perception
• Templates?• Prototypes
– Humphrey’s monkeys• Interested in individual monkey pictures• Not interested in individual cows and pigs• Exposure increased interest in cows and pigs• Experience sharpens prototypes
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Distinctive features
• Rule prototypes: Ulrich Neisser (1964)
EWAFTMX SQPRDGBLKZFECKH OBCQJUGEXNWKAE SDBPNRQAFLXZMW BPOSRGQ
• The man who mistook his wife for a hat
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Perceiving distinctive features
• Context cues• Biederman’s (1990) geons• Cusps and joints
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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
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The phi phenomenon
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Monocular Depth cues: Height, Interposition, and Relative Size
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What cues are here?
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Charles Sheeler, Classic Landscape, National Gallery, Feb. 26, 2000
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Perception phenomena
• Perceptual constancy– Size and shape: The swelling hand– Brightness: Overhead
• Perception as interpretation• The grasping visual illusion
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Ebbinghaus figures and the grasping illusion
Franz, Gegenfurter, Bulthoff, & Fahle, 2000
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Perceptual Constancy and the Moon Illusion
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Expectations affect perceptions
• Perceptual set– Expectations or schemas: Numbers and names– Context:
TIME FLIES I CANT THEYRE TOO FASTCHOPHOUSECHOPHOUSE
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More context effects
FOLKCROAKSOAK
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 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.
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Backmasking
• Queen, Another one bites the dust• Queen, backwards• Psalm 23, backwards• Excerpt: Jabberwocky, Lewis Carroll• More Jabberwocky
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