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Szonya Durant, Michele Furlan; Measuring response saturation in human MT and MST as a function of motion density. Journal of Vision 2014;14(10):1013. doi: 10.1167/14.10.1013.
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© ARVO (1962-2015); The Authors (2016-present)
The response of neurons of human visual areas can be defined by two properties. The first is the functional selectivity, i.e. what is their preferred stimulus and what is not. The second is the rate of change of their response, i.e. how the response changes as a function of the preferred stimulus. Two of the best candidates to study these features are MT and MST. Although the functional selectivity of these two regions has been widely studied, the change in their response is still unclear. MT and MST response have been shown to increase linearly with motion coherence. In this work we measure the saturation function of these areas using a pure motion signal not embedded in noise. We used a 3T functional MRI to measure the hemodynamic activity in the human motion complex (MT, MST) and in primary visual cortex for comparison, while participants were exposed to different levels of motion density. We use spatially fixed apertures containing motion stimuli to manipulate the amount of area covered by motion, keeping local motion density constant and simultaneously stimulating over a wide area of the visual scene. We found that compared to the primary visual area, MT and MST responded above baseline to a very little amount of motion. We simulated population responses to our motion stimuli and found that the response function of the amount of motion versus static stimuli was well described by a simple model of divisive normalization. We then compared different types of motion and found no difference between coherent (uniform) and random motion at any motion density, suggesting that when combining response over several motion stimuli covering the visual field, a linear relationship of MT and MST population response as a function of motion coherence might not hold.
Meeting abstract presented at VSS 2014
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