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Qasim Zaidi, Robert Ennis, Dingcai Cao, Barry Lee; Eye-movements and the neural basis of context effects on temporal sensitivity . Journal of Vision 2014;14(10):201. doi: 10.1167/14.10.201.
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© ARVO (1962-2015); The Authors (2016-present)
It is well established that visual sensitivity is affected by context. The luminance of a surround region substantially affects the detection of luminance flicker at low frequencies, so that the Temporal Contrast Sensitivity Function is band-pass on dark or light surrounds, but low-pass on surrounds at the mean-level of the flicker. The cause of the effect remains controversial. Some explanations invoke enhancement of edge responses by lateral inhibition, others rely on transients caused by the miniature eye-movements involved in maintaining fixation. We replicated the psychophysical luminance results, and found that they also held for chromatic conditions: the TCSF for equiluminant red-green flicker was low-pass on mean-level surrounds, but was surprisingly band-pass on red or green surrounds. To identify the neural basis of the context effects, we used in vivo electrophysiological recordings of primate MC and PC ganglion cell responses to luminance and red-green modulations respectively. We measured cell responses at various distances from the modulation edge to test neuronal sensitivity to stationary edge contrast. To simulate the effects of eye movements, we measured cell responses to abruptly displaced target patches. Effects of stationary edge-contrasts on MC and PC cell responses were found to be minimal on all surrounds, excluding lateral inhibition as a mechanism for enhancement of responses to stationary edges. Abruptly displaced edges, however, evoked transient bursts or suppression of spikes. On mean-level surrounds, transient neural responses depended on the modulation phase, but responses were equal across all modulation phases on the polarized surrounds. Eye-movements thus enhanced detection of low-frequency flicker on mean-level surrounds, and a neurometric analysis supported a primary role for eye movements in the context effects on temporal sensitivity. These results also reveal that the transformation of spatial edges to transient retinal responses provides the neuronal substrate for detecting chromatic and luminance edges in natural scenes.
Meeting abstract presented at VSS 2014
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