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David C. Lyon, Jitendra Sharma, James Schummers, Mriganka Sur; Non Linear Modulation of Contextual Influences by Attention in Awake Monkey V1. Journal of Vision 2004;4(8):620. doi: 10.1167/4.8.620.
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© ARVO (1962-2015); The Authors (2016-present)
Responses of V1 neurons to oriented gratings can vary depending on the context of the stimulus, such as size and contrast. This modulation of the neuronal response is thought to derive from long-range lateral connections within V1. The center-surround stimulus is useful for ascertaining the relative influence of these lateral interactions. Surround stimuli presented outside of the classical receptive field (CRF) of the neuron may suppress or facilitate responses to the stimulus placed within the CRF depending upon its orientation. To determine whether behavioral state can modulate contextual influence in V1 we examined the influence of attention on V1 neurons in 2 alert monkeys. We measured the component effects of center-surround receptive field organization on neuronal firing while the monkey attended to the CRF or attended away (the opposite hemifield). For the majority of neurons, presenting a surround stimulus of high contrast and a center stimulus of relatively low contrast, iso-orientation suppression is further enhanced when the monkey attends towards the CRF. Interestingly, we also find that attention modulates the neurons response when the center stimulus is presented alone. The effect of attention is non-linear and seems most pronounced at the preferred orientation of the neuron. Specifically, for a subset of cells, when the monkey attends towards the CRF, the response to the preferred orientation is enhanced thereby sharpening the orientation tuning, compared to when the monkey attends away from the CRF. These results show that attentional mechanisms play a role in the processing of visual information early in the visual hierarchy, serving to accentuate response properties of V1 neurons.
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