Parallel Processing

Parallel Processing

1. Motion

   • Orientation Selectivity: centre surround receptive field of simple cells
     • bar of light in middle = firing of simple cell
       • how this occurs - many ganglion cells with centre surround arrangement input onto simple cells
         • receptive fields align along one axis
           • receptive fields properties are refined by
             • inhibitory interneurones
             • horizontal connections within cortex
     • light on either side = inhibition
   • Direction Selectivity
     • 3 models
       • intracortical model = one V1 input to direction selective cell, other input goes through another neurones in V1 = delay
       • thalamocortical model = delay in thalamus
         • Lien and Scanziani 2018 showed that this is the predominant model
           • blocked local cortical connections = still direction selectivity
       • retinal model = processing in retina direction - thalamus - cortex
     • Enhancing
       • directionally selective feedforward inhibition
       • interneurones
         • Lee et al 2010 - random activation of GABA interneurones
         • interneurones that are themselves directionally selective = matched input from similarly selective interneurones

2. Colour

   • Blob colour sensitive receptive fields = cells are monocular
     • colour opponent antagonistic centre surround organisation
       • red in centre = excitation
         • reduced by green in the surround
           • green by itself in the surround = inhibtion
     • central colour opponency, no surround
       • green or blue in middle = excitation
     • colour opponent centre and colour opponent surround (coc cos)
       • yellow in middle = excitation
       • blue in surround = excitation
   • colour channels
     • green vs red integrated antagonisitically
     • yellow vs blue integrated antagonistically
     • lumosity
     • integration of all these channels = can see any colour

3. Shape

   • cells in interblob region have binocular receptive fields = complex cells
     • cells with similar orientation selectivity neighboured = orientation columns: layer 2/3 interblob neurones receive converging input from layer 4c beta cells with the same orientation selectivity
       • doesn't have antagonistic surround = doesn't matter where the bar is in the receptive field - will respond to prescence not location

4. Blindsight

   • Boyer et al 2005
     • subject with V1 inactivation guesses object in front of them correctly, this may be due to
       • direct projections from LGN to higher visual area
       • retinal input to superior colliculus

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