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Visual Perception in the Brain (Early Visual Information Processing (fovea…
Visual Perception in the Brain
big neural investment in processing visual information
50% brains to visual processing
brain damage
visual agnosia
not blind
but unable to recognize anything visually
sensory system able to register visual information
inability to transform visual information into perceptual experience
apperceptive agnosia
unable to recognize simple shapes / draw shapes as shown
problem with early processing
shapes and objects are extracted from the visual scene
associative agnosia
able to recognize shapes and copy drawing
unable to recognize complex objects
problem with pattern recognition (later processing)
shapes and objects are recognized
Early Visual Information Processing
light passes lens and vitreous humor
falls on retina at back of eye
retina contains photoreceptor cells
light-sensitive molecules
a photochemical process converts light into neural signals
two kinds of photoreceptors
cones
color
high resolution
rods
poor resolution
less acute, black-and-white
function
sharpen image - good shape
fovea
a small area in retina
highly concentrated cones
high resolution
fine details
periphery
detects global information, movement
optic nerve
receptor cell -> bipolar cell -> ganglion cell -> form optic nerve -> brain -> subcortical structures -> primary visual cortex
ganglion cell encodes information from a small region of retina called the cell's receptive field
light encoded as firing rate
left hemisphere processes information about right part of part; right hemisphere processes information about left part
upper part of vision field in lower part of visual cortex;
lower part of vision in upper region
two pathways
“what"
temporal cortex
identifying objects
"where"
parietal region
spacial information
coordinating vision with action
Information Coding in Visual Cells
edge detector
specific to position, orientation, and width
bar detector
specific to position, orientation, and width
nervous system processing information in terms of patterns of neural activation
hypercolumn representation