Abstract
Eye movements routinely induce motion streaks as they shift visual projections across the retina at high speeds. To investigate the visual consequences of intra-saccadic motion streaks, we co-registered eye tracking and EEG while gaze-contingently shifting target objects during saccades, presenting either continuous, ‘streaky’ or apparent, step-like motion in four directions. We found significant reductions of secondary saccade latency, as well as improved decoding of the post-saccadic target location from the EEG signal when motion streaks were available. These signals arose as early as 50 ms after saccade offset and had a clear occipital topography. Using a physiologically plausible visual processing model, we provide evidence that the target’s motion trajectory is coded in orientation-selective channels and that speed of gaze correction was linked to the visual dynamics arising from the combination of saccadic and target motion, providing a parsimonious explanation of the behavioral benefits of intra-saccadic motion streaks.
To efficiently explore our visual environment, we humans incessantly make brief and rapid eye movements. These so-called saccades inevitably shift the entire visual image across the retina, thereby inducing - like a moving camera with long exposure duration - a significant amount of motion blur, transforming single objects into elongated smeared motion streaks. While simultaneously recording electroencephalography and eye tracking, we asked human observers to make saccades to a target stimulus which then rapidly changed location while their eyes were in mid-flight. Critically, we compared smooth target motion to a simple jump, thus isolating neural responses and behavioral benefits specific to motion streaks: For continuous motion (i.e., when streaks were available), the post-saccadic target location could be decoded earlier from electrophysiological data and secondary saccades went more quickly to the new target location. Indeed, decoding of target location succeeded immediately after the end of the saccade and was most efficient on occipital sensors, suggesting that saccade-induced motion streaks are represented in visual cortex. Computational modeling of saccades as a consequence of early visual processes suggests that fast motion could be efficiently coded in orientation-selective channels, providing a parsimonious mechanism by which the brain exploits motion streaks for goal-directed behavior.
Richard Schweitzer
Postdoc in Vision Science
Passionate about psychophysics, eye tracking, M/EEG, and computational modeling.