Visual Attention neural mechanisms Arash Afraz

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Visual Attention (neural mechanisms)Arash
Afraz
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• Large receptive fields of extrastriate cortex
  ? Significant computational problems (multiple
  stimuli in a single field)

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• AMI (attended-ignored)/(attendedignored)
• 1 gt AMI gt -1

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Cue set

• 24 complex multicolor pictures
• 1 x 1 to 2 x 2 degrees size
• Good and Poor stimuli were defined after a simple
  fixation task

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Saccade task

• Two-stimulus array
• One-stimulus array
• Fixation only task
• Three and Five stimulus arrays

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Lever release task

• Two-stimulus array
• One-stimulus array
• Fixation only task

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Random cue design
Blocked cue design
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• A significant target effect on 10-ms bins of
  the population histogram began 70-80ms before the
  eye movement toward target (paired t-test)

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Visuomotor Origins of Covert Spatial Attention
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Important stimuli are generally the targets of
head and eye movements

• Visual Attention

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• The ability of primates to dissociate the point
  of gaze from the point of interest does not
  preclude a common mechanism of attention and eye
  movement control.

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Control of eye movements and spatial attention

• Is there a common mechanism?!?!?

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• A Staircase procedure was used to determine
  the luminance change threshold for the
  stimulation and control conditions.
• Electrical stimulation consisted of a 100-ms
  train of biphasic current pulses (0.2 ms, 200 Hz)
  

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• Stimulation of the FEF with currents below the
  movement threshold does not evoke saccades, but
  nonetheless biases the selection of targets for
  eye movements

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• Modulation of activity in area V4 during both
  overt and covert spatial attention tasks has
  previously been observed.

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• It should be possible to induce a
  spatial-attention-like modulation of V4 activity
  in passively fixating monkeys!?

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• The effect of stimulation seemed to depend on
  how well the V4 neuron was visually driven.

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