lecture 16 Flashcards
visual field
total area in which objects can be seen in peripheral vision when eyes r fixed on a point
- left and right visual fields (info goes to opposite hemisphere)
coding location
light falling on one place on the retina will activate one ganglion cell and light falling on another will activate a different cell
- each RGC responds to stimulation on just 1 patch of retina
receptive field hierarchy
ganglion cell < LGN cell < V1
where is acuity best
central part of visual field- fovea sends information to a disproportionately large part of occipital cortex
where is acuity best
central part of visual field- fovea sends information to a disproportionately large part of occipital cortex
retinal ganglion cells
respond to prescence or abscence of light but not shape
- receptive fields are circular
on/off center cells
on- excited when light falls on center of receptive field and inhibited in surround (weak excitation)
off- excited when light falls on sorround and inhibited when light falls of center (weak inhibition)
how does brain go from on-off receptivity to shape
RGCs tell brain amount of light. hitting a certain spot relative to the average in the surrounding area
luminance contrast
amount of light reflected by an object relative to its surroundings
V1 cell processing
respond to more complex stimuli than light because they receive input from multiple RGC
- orientation detectors: excited by orientation in particular directions
simple cells- V1
receptive field with rectangular on/off layout
- respond best to stimulation in specific orientation
complex cells- V1
maximally excited by bars of light moving in particular direction through receptive field
0 direction of movement
hypercomplex cells (end-stopped)- V1
maximally respond to moving bars (like complex)
also have strong inhibitory area at one side of receptive field
how do we go from circular receptive fields to rectangular ones
bars of light strike the receptive field of many RGC input comes from a gorup of ganglion cells aligned in a row, V1 is activated when a bar of light hits retina in particular row of ganglion cels
ocular dominance columns
neurons are organized into functional columns
- neurons with similar functions
- inputs arrive in layer 4 then connect vertically
- input from left or right eye
trichromatic theory
receptor level0 explanation of color vision based on the coding of three primary colors (red, green and blue)
color is determined by relative responses of diff cone types
what can trichromatic theory not explain
what about yellow
cannot explain afterimages: red-green and blue-yellow
opponent proces theory
neural level-
explanation of color vision that emphasizes importance of opposite colors (R-G, B-Y)
occurs in retinal ganglion cells
injury to ventral stream
what pathway- agnosia
visual form: inability to recognize objects or drawings
face agnosia: ianbility to recognize faces
- cannot recognize objects but can copy objects and shape hands to grasp
injury to the how pathway
optic ataxia- deficit in the visual control of reaching and other movements
parietal cortex
- retention of ability to recognize objects normally
