Abstract
With each saccade towards a peripheral target, the retinal projection of the stationary object rapidly shifts from the periphery to the fovea. Optimal integration of peripheral and foveal information is believed to serve visual stability; but is such integration exclusive to saccades or can it also occur during fixation? Saccades differ from experimental, trans-retinal displacements implemented during fixation in two important aspects: first, the saccadic shift on the retina is continuous and the visual system can exploit the resulting motion to serve visual function (Schweitzer & Rolfs, 2021); second, saccades are self-initiated, so that there is little uncertainty as to when and where the target shifts across the retina. We tested if integration of peripheral and foveal information can be observed when participants maintain fixation and object information moves on a screen, and whether this depends on the availability of saccade-like continuous motion (Experiment 1), or on the self-initiation of the shift (Experiment 2). In Experiment 1, we moved an oriented Gabor either in a discrete step or in a continuous fashion, either following the peak-velocity-amplitude relation of saccades or deviating from it. In Experiment 2, the onset of a discrete shift was either automatic or actively initiated by the participant via a button press. In both experiments, we measured observers’ orientation discrimination performance to test for trans-retinal integration. In a control experiment, we tested whether our participants show integration across saccades (trans-saccadic integration). Neither the presence of continuous motion, whether saccade-like or not, nor the self-initiation of motion onset via a button press led to integration of peripheral and foveal information. We did, however, find trans-retinal integration when participants executed a saccade towards the target. These results suggest that trans-retinal integration is exclusive to saccades and is not mediated by the retinal consequences of saccades nor by self-initiation alone.