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SUMMARY:Is the code in ferret V1 a 'sparse code'? - David Tolhurst\, Depar
 tment of Physiology\, University of Cambridge
DTSTART:20061113T130000Z
DTEND:20061113T140000Z
UID:TALK5753@talks.cam.ac.uk
CONTACT:Cordula Becker
DESCRIPTION:It has been proposed that the primary visual cortex provides a
  “sparse code” for the information in natural scenes. It has been diff
 icult to pin down quite what a sparse code would look like! One measure is
  “life-time sparseness”: how few natural scenes does a given neuron re
 spond to. We investigated how neurons in ferret V1 responded to flashed pr
 esentations of digitised photos of natural scenes. Some neurons showed ver
 y sparse responses: i.e. they responded to very few photos. The degree of 
 sparseness was correlated with whether the neurons were simple or complex\
 , with the sharpness of their tuning for sinewave gratings and with their 
 general responsivity to gratings. In a sparse code\, a neuron would respon
 d weakly to most stimuli but would respond well to a few\, giving a leptok
 urtic response distribution. In V1\, response variance increases with incr
 easing response. If a response distribution is replotted against equally-d
 iscriminable response steps\, the distribution becomes much less kurtotic!
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LOCATION:Seminar Room (ground floor)\, Craik-Marshall Building
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