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Michele Rucci, Martina Poletti, Jonathan Victor, Marco Boi; Why do the response properties of magnocellular and parvocellular neurons differ both in space and time?. Journal of Vision 2016;16(12):564. doi: 10.1167/16.12.564.
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© 2017 Association for Research in Vision and Ophthalmology.
Magnocellular and parvocellular neurons in the retina and lateral geniculate nucleus tend to prefer complementary spatial frequency ranges, with magnocellular neurons sensitive to lower frequencies than parvocellular ones. Interestingly, these neurons also exhibit different temporal preferences: magnocellular neurons tend to be more responsive to temporal transients than parvocellular neurons. Why do neurons sensitive to separate spatial frequency ranges also differ in their temporal characteristics? To address this question, we combined three approaches: spectral analysis of retinal input, neural modeling, and visual psychophysics. We recorded eye movements at high resolution while human observers freely examined pictures of natural scenes and examined how different types of eye movements affect the frequency content of luminance signals on the retina. We made predictions of contrast sensitivity by passing these signals through linear-nonlinear neural models and a standard decision stage. Finally, we compared the predictions to psychophysical measurements obtained with an apparatus that allowed for control of retinal image motion. We found that saccades and fixational eye movements lead to strikingly different transformations of spatial patterns into temporal modulations. As a consequence, detection of a low spatial frequency stimulus tends to be more reliable immediately following a saccade than later during fixation, whereas a high spatial frequency stimulus maintains similar levels of detectability throughout fixation. In a model that optimally integrates information during post-saccadic fixation, these dynamics predict an oculomotor-driven coarse-to-fine dynamics of contrast sensitivity, which we confirm psychophysically. Magnocellular neurons capture the transient modulations that saccades produce from low spatial frequencies, while parvocellular neurons capture the sustained modulations that fixational movements produce from high spatial frequencies. Thus, a coupling between spatial and temporal response characteristics similar to that observed in retinal ganglion cells emerges as an experimentally-confirmed prediction of a model of contrast sensitivity that takes oculomotor transients into account.
Meeting abstract presented at VSS 2016
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