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Modulation of V1 spike response by temporal interval of spatiotemporal stimulus sequence.

Kim T, Kim HR, Kim K, Lee C - PLoS ONE (2012)

Bottom Line: 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).This stimulus configuration enabled us to examine the spatiotemporal selectivity of response modulation from a focal surround region.These results suggest that V1 neurons participate in processing spatiotemporal sequences of oriented stimuli extending outside the RF.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Seoul National University, Kwanak, Seoul, Korea.

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.

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An image volume.A: Spatiotemporal volume of an exemplary visual world. Each rectangle represents a topographically organized unit space corresponding to known receptive field of a single neuron of central visual system such as V1. B: Bars represent oriented line segment of simplified contours of visual events such as a swinging bat at instantaneous moments, t1 and t2.
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pone-0047543-g001: An image volume.A: Spatiotemporal volume of an exemplary visual world. Each rectangle represents a topographically organized unit space corresponding to known receptive field of a single neuron of central visual system such as V1. B: Bars represent oriented line segment of simplified contours of visual events such as a swinging bat at instantaneous moments, t1 and t2.

Mentions: 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. Imagine that you are watching a video screen in which a baseball player hits a ball (Fig. 1A). Understanding the video can be accomplished by the recognition of spatial features at a given instant and by subsequent detection of changes in static features across time to derive full motion [1]. Physiological evidence bearing on contour integration support reconstruction of object models at a given time frame; for example, the response magnitude of V1 single neurons modulate depending on detection of line segments belonging to a common contour that were simultaneously presented inside and outside RF [2]. Additionally, 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 now 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). An oriented and discretized feature at t1 can be first integrated with other discretized features at t1 for reconstructing an object contour at t1, or alternatively, it can be first integrated with another feature at t2 into a spatiotemporal sequence, and then based on resulting sequences, objects and their global motions (as opposed to local motions that are confined within RFs) are simultaneously derived. Note that the combination of locations, orientations and temporal interval of the two oriented stimuli constitutes a unique spatiotemporal sequence. The anatomical sites for processing global motion from spatiotemporal sequence stimuli are not known [4].


Modulation of V1 spike response by temporal interval of spatiotemporal stimulus sequence.

Kim T, Kim HR, Kim K, Lee C - PLoS ONE (2012)

An image volume.A: Spatiotemporal volume of an exemplary visual world. Each rectangle represents a topographically organized unit space corresponding to known receptive field of a single neuron of central visual system such as V1. B: Bars represent oriented line segment of simplified contours of visual events such as a swinging bat at instantaneous moments, t1 and t2.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3472985&req=5

pone-0047543-g001: An image volume.A: Spatiotemporal volume of an exemplary visual world. Each rectangle represents a topographically organized unit space corresponding to known receptive field of a single neuron of central visual system such as V1. B: Bars represent oriented line segment of simplified contours of visual events such as a swinging bat at instantaneous moments, t1 and t2.
Mentions: 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. Imagine that you are watching a video screen in which a baseball player hits a ball (Fig. 1A). Understanding the video can be accomplished by the recognition of spatial features at a given instant and by subsequent detection of changes in static features across time to derive full motion [1]. Physiological evidence bearing on contour integration support reconstruction of object models at a given time frame; for example, the response magnitude of V1 single neurons modulate depending on detection of line segments belonging to a common contour that were simultaneously presented inside and outside RF [2]. Additionally, 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 now 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). An oriented and discretized feature at t1 can be first integrated with other discretized features at t1 for reconstructing an object contour at t1, or alternatively, it can be first integrated with another feature at t2 into a spatiotemporal sequence, and then based on resulting sequences, objects and their global motions (as opposed to local motions that are confined within RFs) are simultaneously derived. Note that the combination of locations, orientations and temporal interval of the two oriented stimuli constitutes a unique spatiotemporal sequence. The anatomical sites for processing global motion from spatiotemporal sequence stimuli are not known [4].

Bottom Line: 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).This stimulus configuration enabled us to examine the spatiotemporal selectivity of response modulation from a focal surround region.These results suggest that V1 neurons participate in processing spatiotemporal sequences of oriented stimuli extending outside the RF.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Seoul National University, Kwanak, Seoul, Korea.

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.

Show MeSH
Related in: MedlinePlus