Visual Attention (neural mechanisms) Arash Afraz.

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Presentation transcript:

Visual Attention (neural mechanisms) Arash Afraz

Large receptive fields of extrastriate cortex  Significant computational problems (multiple stimuli in a single field) Large receptive fields of extrastriate cortex  Significant computational problems (multiple stimuli in a single field)

AMI = (attended- ignored)/(attended+ignored) 1 > AMI > -1

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

“ Saccade task ” Two-stimulus array Two-stimulus array One-stimulus array One-stimulus array Fixation only task Fixation only task Three and Five stimulus arrays Three and Five stimulus arrays

“ Lever release task ” Two-stimulus array Two-stimulus array One-stimulus array One-stimulus array Fixation only task Fixation only task

Random cue design Blocked cue design Random cue design Blocked cue design

A significant target effect on 10-ms bins of the population histogram began ms before the eye movement toward target (paired t-test) A significant target effect on 10-ms bins of the population histogram began ms before the eye movement toward target (paired t-test)

Visuomotor Origins of Covert Spatial Attention

Important stimuli are generally the targets of head and eye movements Visual Attention

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.

Control of eye movements and spatial attention Is there a common mechanism?!?!?

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)

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

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

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

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