Saccadic suppression: from zebrafish to primates
Aristides Arrenberg - Eberhard Karls Universität TübingenZiad Hafed - Eberhard Karls Universität Tübingen
Active sensation is the mode of operation for most behaving organisms. While there are a multitude of computational advantages to active sensation, moving the sensor, such as the eyes for the visual modality, invariably introduces complexities in processing of the input sensory streams. This is so because, during active sensation, information may be sensed by the organism that is the consequence of the sensor movement itself, as opposed to being a result of a genuine novel event in the outside world. Here, we focus on vision and eye movements. We study a robust perceptual phenomenon, called “saccadic suppression”, in which perceptual detection thresholds for brief visual stimulus presentations are dramatically elevated when the brief visual stimuli appear near the time of rapid saccadic eye movements. Despite the robustness of saccadic suppression as a phenomenon, countless debates have emerged, and remain, about its mechanisms and origins. Our goal in the proposed research is to approach saccadic suppression from the perspective of evolutionary convergence and optimization, and we do so by studying saccadic suppression in two organisms that are almost at two opposite ends of the evolutionary spectrum: zebrafish on the one hand and non-human primates on the other. While saccadic suppression has been observed in the latter, this phenomenon is completely unexplored in the former. We will exploit the known similarities in the oculomotor systems of zebrafish larvae and non-human primates to demonstrate the existence of saccadic suppression in the fish. We will focus on the optic tectum (OT) in fish and the homologous superior colliculus (SC) in non-human primates. The OT of larval zebrafish only contains a few thousand neurons. We will therefore characterize saccade-dependent changes of visual responses for all tectal neurons and relate saccadic suppression to the concept of efficient sensorimotor estimation, in which the OT shares computational resources for both motor control and visual perception. The identification of anatomically and functionally defined cell types involved in saccadic suppression in the fish will help resolve outstanding debates about this phenomenon in primates.
