Concentrated in periphery of retina many rods to one

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concentrated in periphery of retina many rods to one ganglion Cones: detect color (high light) concentrated in fovea few cones to one ganglion (1:1) provide highest resolution in vision Horizontal and Amacrine cell modulate connections between the photoreceptors and the ganglion cells Lateral inhibition point: boundary distinction bigger stimulus for lighter colors, smaller stimulus for darker colors less inhibition = brighter percept Center-surround photoreceptors in the middle have a different excitatory/inhibitory response than the outer photoreceptors excitatory center, inhibitory surround on-center : photoreceptors in the center that send an excitatory signal off-surround: photoreceptors around the center send an inhibitory signal off-center/on-surround: photoreceptors in the center send an inhibitory signal II. Receptive Fields: bipolar and ganglion cells Receptive fields: area of sensory apparatus (e.g., retina, skin) that responds to external stimulus receptive field of a cortical neuron part of the retina to which a “higher neuron” is connected the visual field is divided into thousands of such receptive fields which are overlapping at each level beyond the retina is a map or a series of maps of the retina representations differ with reference to: precision (i.e. ability to localize; small receptive fields) attributes coded (e.g., color/form) amount of cortex which responds to that input more territory → better acuity point-to-point topographic organization point on skin (or retina) projects to a specific point in cortex larger the cortical region, the greater the acuity a huge amount of V1 is dedicated to input from the fovea III. LGN and the Visual Cortices Visual pathway axons of retinal ganglion cells → optic nerve → two different pathways Superior Colliculus (localizes information) Lateral Geniculate Nucleus (LGN – Thalamus) → primary visual cortex (V1) Basic principles: Left brain “sees” Right visual field Nasal “sees” lateral Temporal “sees” medial Nasal contra/temporal ipsilateral both eyes “see” LVF & RVF Simple Cells respond to a line at one particular location
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one specific orientation small receptive field Located in V1 (primary visual cortex) Complex Cells Respond to a bar of light in a specific orientation anywhere in the receptive field Located in V1 and V2 Have medium and large sized receptive fields November 9, 2012: Sensory Systems (Vision) cont. IV. Magnocellular and Parvocellular Streams Patient DF Titchener Circles center circles are the same size Streams of visual processing Dorsal stream (magnocellular): V1 through posterior parietal to frontal Derives from periphery of eye where rods are fast transmission “where/how” pathway function: use visual information in the service of action
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