Abstract
The spike activity of single neurons of the primary visual cortex (V1) becomes more selective and reliable in response to wide-field natural scenes compared to smaller stimuli confined to the classical receptive field (RF). However, it is largely unknown what aspects of natural scenes increase the selectivity of V1 neurons. One hypothesis is that modulation by surround interaction is highly sensitive to small changes in spatiotemporal aspects of RF surround. Such a fine-tuned modulation would enable single neurons to hold information about spatiotemporal sequences of oriented stimuli, which extends the role of V1 neurons as a simple spatiotemporal filter confined to the RF. In the current study, we examined the hypothesis in the V1 of awake behaving monkeys, by testing whether the spike response of single V1 neurons is modulated by temporal interval of spatiotemporal stimulus sequence encompassing inside and outside the RF. We used two identical Gabor stimuli that were sequentially presented with a variable stimulus onset asynchrony (SOA): the preceding one (S1) outside the RF and the following one (S2) in the RF. This stimulus configuration enabled us to examine the spatiotemporal selectivity of response modulation from a focal surround region. Although S1 alone did not evoke spike responses, visual response to S2 was modulated for SOA in the range of tens of milliseconds. These results suggest that V1 neurons participate in processing spatiotemporal sequences of oriented stimuli extending outside the RF.
Highlights
The visual world is full of events laid out in space and time
We found that the activity of single V1 neurons in behaving macaques responded with a magnitude that varied with stimulus onset asynchrony (SOA) in non-monotonic ways, to an receptive field (RF) stimulus that followed a focal stimulus outside the RF
Summary In the current study, we assessed the possibility that V1 spike activity is involved in encoding spatiotemporal sequences of oriented stimuli encompassing spatial locations in and out of the classical receptive field
Summary
The visual world is full of events laid out in space and time. Identifying where and how spatiotemporal relations of event features are encoded in the brain is critical for understanding central visual processing. Perceptual organization of image volume can be based on discovering and organizing elementary relations of spatiotemporal sequences before object recognition is completed at a given instant [3] To apply these ideas to the early visual system, further imagine that a static contour at a given instant is discretized by spatially-confined and oriented filters, such as the classical receptive fields (RFs) of V1 neurons. The video world is represented as a spatiotemporal volume in which each contour segment exists over space and time with a changing orientation In this volume, oriented bars at different spatial locations at times t1 and t2 can represent a contour sequence of a common object, for example the bat, discretized by RFs at different times (Fig. 1B). The anatomical sites for processing global motion from spatiotemporal sequence stimuli are not known [4]
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