Seeing on the fly: Physiological and behavioral evidence show that space-to-space representation and processing enable fast and efficient performance by the visual system.

Abstract

When we view the world, our eyes saccade quickly between points of interest. Even when fixating a target our eyes are not completely at rest but execute small fixational eye movements (FEMs). That vision is not blurred despite this ever-present jitter has seemingly motivated an increasingly popular theory denying the reliance of the visual system on pure spatial processing in favor of a space-to-time mechanism generated by the eye drifting across the image. Accordingly, FEMs are not detrimental but rather essential to good visibility. However, the space-to-time theory is incompatible with physiological data showing that all information is conveyed by the short neural volleys generated when the eyes land on a target, and with our faithful perception of briefly displayed objects, during which time FEMs have no effect. Another difficulty in rejecting the idea of image representation by the locations and nature of responding cells in favor of a timecode, is that somewhere, somehow, this code must be decoded into a parallel spatial one when reaching perception. Thus, in addition to the implausibility of generating meaningful responses during retinal drift, the space-to-time hypothesis calls for replacing efficient point-to-point parallel transmission with a cumbersome, delayed, space-to-time-to-space process. A novel physiological framework is presented here wherein the ability of the visual system to quickly process information is mediated by the short, powerful neural volleys generated by the landing saccades. These volleys are necessary and sufficient for normal perception without FEMs contribution. This mechanism enables our excellent perception of brief stimuli and explains that visibility is not blurred by FEMs because they do not generate useful information.