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Alexandria Marino, James Mazer; The footprint of spatial attention in V4 receptive fields. Journal of Vision 2015;15(12):226. doi: 10.1167/15.12.226.
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© ARVO (1962-2015); The Authors (2016-present)
Spatial attention modulates responses of visual neurons at virtually all levels of cortical processing. Studies of attentional modulation of neural selectivity for stimulus properties like orientation and contrast have found that directing attention into a V4 receptive field (RF) alters neuronal gain. Little, however, is known about how attention affects the spatial structure of V4 RFs. Nor do we know how, or even if, attentional modulation is constrained to neurons with RFs within the attentional focus (AF). To address these questions we recorded from V4 neurons in monkeys performing a spatiotopic attention task where they responded to targets appearing at a cued location in space. On alternating blocks of trials, the attended location was either in the lower or upper visual field. One of three fixation points was chosen at random on each trial to control the spatial relationship between the RF and AF. Ignored low contrast probe stimuli were displayed in and around RFs during trials. Neuronal responses to probe stimuli were used to characterize the spatiotemporal RF. Over half of V4 neurons showed significant attentional modulation (attend-in vs -out), with 70% of neurons showing facilitation and 30% suppression. We observed both multiplicative and additive modulatory effects. Interestingly, the sign of these effects were often in opposite directions. About half of the attentionally modulated neurons were modulated only when the RF fell inside the AF, consistent with behavioral performance. The remaining neurons were modulated even when the RF was located more than one diameter outside the AF, suggesting that at the neuronal level attention can spread beyond the AF, as defined by enhanced behavioral performance. Consistent with proposed ventral stream contributions to spatiotopic processing, we found activity in >70% of the V4 neurons studied was also modulated by gaze angle position, reminiscent of dorsal stream gain fields.
Meeting abstract presented at VSS 2015
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