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Carrie J. McAdams, R. Clay Reid; The receptive field strength of simple cells can be modulated by attention.. Journal of Vision 2004;4(8):183. doi: 10.1167/4.8.183.
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© ARVO (1962-2015); The Authors (2016-present)
We examined the effects of attention on the receptive fields of simple cells in the primary visual cortex of two macaques. Receptive fields (RFs) were mapped using a white-noise stimulus that consisted of a grid of square pixels (0.2–0.3 ) randomly set to be white or black every 20–35 ms. A second, identical stimulus was also presented on the screen at an equal but opposite eccentricity from the one used to map the receptive field. The monkey was directed to pay attention to only one of the two stimulus grids on any given trial, while maintaining fixation within a 1 window. At random points in the trial (60–2900 ms), a single pixel of either or both grids might change to either red or green for 250–350 ms. The animal was required to report his detection and discrimination of the color by making a saccade to a target of the same color. On 1/3 of the trials, no color pixel appeared and the animal was rewarded for maintaining fixation throughout the trial. While the animal performed these tasks, we recorded the responses of single neurons in primary visual cortex. We compared the RF maps under two conditions: when the animal's attention was directed to the stimulus covering the RF of the neuron being recorded versus when the animal's attention was directed to the other, distant stimulus. We found that focal attention increased the strength (in spikes/s) of the RFs of simple cells by a mean of 13% (n = 46; t-test, p < 0.001). Interestingly, the average spike rate of the neurons did not change (mean spike rate unattended 16.3 spikes/s, attended 16.3 spikes/s, paired t-test, p = 0.85). These results indicate that attention improves the coherence between stimulus and response at an early stage of visual cortical processing.
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