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Jan Churan, Farhan A. Khawaja, James M.G. Tsui, Christopher C. Pack; Neuronal and psychophysical responses to brief motion stimuli. Journal of Vision 2009;9(8):670. doi: https://doi.org/10.1167/9.8.670.
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© ARVO (1962-2015); The Authors (2016-present)
Recent psychophysical work has shown that performance in a direction discrimination task decreases with increasing stimulus size for brief, high-contrast stimuli (Tadin et al., 2003). This psychophysical surround suppression has been linked to the inhibitory spatial surrounds that have been observed in motion-sensitive visual area MT. However, many cells in MT lack surround suppression, and so it is not clear why the surround-suppressed cells would be the sole determinant of visual perception.
We have recorded from 88 neurons in area MT of the alert macaque, using brief ([[lt]]40 ms) motion stimuli for which psychophysical surround suppression was shown to be strong. Remarkably, we find that MT neurons that lack surround suppression fail to respond to such stimuli, while the responses of surround-suppressed neurons are robust and direction-selective. Thus psychophysical surround suppression for brief stimuli can be attributed to a link between the spatial and temporal properties of MT neurons.
We extended this finding by introducing a delay between the appearance of the stimulus and its subsequent motion. When the stimulus was presented foveally, this motion onset delay improved discrimination performance for large stimuli, thus eliminating psychophysical surround suppression. However, poor performance for large stimuli returned as the stimulus was moved farther into the visual periphery. Recordings in MT confirmed that, for eccentric receptive fields, direction selectivity decreased with increasing onset delays. Thus these results reveal a complex interaction between stimulus size, duration, and eccentricity that may be linked to mechanisms of short-term adaptation in the visual system.
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