Effects of saccade-like image shifts on retinal processing: Phenomena, mechanisms, and relation to visual processing in higher brain centers

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During natural viewing, image flow on the retina is determined primarily by the behavior of the observer. Eye movements during active visual exploration are particularly dominating in this regard, especially because they incessantly occur 3-5 times per second. Despite this, retinal image processing has in the past often been studied with isolated stimuli, ignoring the highly dynamic aspects of natural viewing.In this project, we will explore the effects of eye-movement induced image motion on signal processing in the retina. We will characterize saccade-related response modulations in the retina in great detail, and we will correlate the effects seen in the retinal output to well-described phenomena in retina-recipient brain areas. Importantly, we will investigate the cellular mechanisms underlying saccadic response modulation in the retina. Based on preliminary data, we anticipate that retinal responses to "test stimuli" presented in the context of saccades will be strongly modulated in comparison to responses to the same stimuli presented in isolation. Moreover, we will show that saccades exude their modulatory effects for up to 1 second, suggesting a highly relevant role of eye-movement induced effects under natural conditions with short inter-saccadic fixations. Importantly, we will show that saccade-related retinal modulation critically depends on the statistical properties of the background scene present during the saccade, on the ambient luminance level, and on the specific retinal cell type. For example, the responses of OFF ganglion cells, but not ON ganglion cells, can be positively modulated after saccades. This suggests that the different pathways within the retina are distinct with respect to the properties of saccadic modulation. Thus, the diversity of modulations known from higher visual areas might be, at least in part, caused by the diverse modulations seen in the retina.This project is unique in that it will investigate retinal signal processing under conditions of natural viewing, while taking an integrated look at the saccade-initiated response modulation of visual neurons from retina to brain.