How do human observers establish object correspondence when the objects rapidly change locations on the retina with each saccade? There is strong evidence that the visual system encodes pre-saccadic object features in visual short-term memory, which are subsequently matched to the post-saccadic retinal image. In a new paper, to appear in Science Advances, we provide evidence that spatiotemporal continuity of visual information throughout the eye movement — the motion of the stimulus across the retina — provides an additional cue to object correspondence.
During fixation a major source of object correspondence is spatiotemporal continuity, or motion. In the context of trans-saccadic vision, this source has been largely neglected, as the ability to perceive motion is strongly impaired (albeit not eliminated) throughout the saccade. In a previous study, we have shown that some visual information, especially low spatial frequencies and orientations parallel to an object’s retinal motion trajectory, remain well resolvable even at saccadic eye velocities. That study, however, left open the crucial question whether intra-saccadic motion information in fact facilitates the establishment of object correspondence across saccades.
To answer this question, we adapted a classic gaze correction paradigm, prompting secondary saccades to a post-saccadic location by rapidly displacing target objects during saccades. Crucially, we used a high-speed projection system, running at 1440 frames per second, to display rapid, continuous, and strictly intra-saccadic target motion for only 14.6 ms, thus inducing motion streaks. We found that the presence of these motion streaks significantly increased the proportion of secondary saccades to the correct post-saccadic target location and reduced the latency of secondary saccades. This effect of intra-saccadic motion was independent of the saccade’s landing position, as well as the amount of object feature information available after each saccade, and was driven by low-level visual features that could efficiently be used by the visual system’s motion-streak detectors. Finally, motion streaks had to carry the inducing object’s features to efficiently drive gaze correction. In other words, facilitation of secondary saccades occurred only if both motion direction and surface features of the intra-saccadic target were congruent with the target’s post-saccadic location, which would almost exclusively be the case in natural vision.
Taken together, these results suggest that the intra-saccadic interval, during which the entire world is rapidly shifted across the retina, may not simply be a “gap in perceptual input”, as often assumed. Instead, motion information from objects undergoing these high-speed shifts — and potentially self-induced visual consequences in general — provide additional cues to support the visual system’s everyday tasks, such as gaze correction.
The paper is expected to appear soon in Science Advances:
Schweitzer, R. & Rolfs, M. (2021). Intra-saccadic motion streaks jump-start gaze correction. Science Advances, in press. [pdf]