Intra-saccadic motion streaks as cues to linking object locations across saccades

Abstract

When visual objects shift rapidly across the retina, they produce motion blur. Intra-saccadic visual signals, caused incessantly by our own saccades, are thought to be eliminated at early stages of visual processing. Here we investigate whether they are still available to the visual system and could-in principle-be used as cues for localizing objects as they change locations on the retina. Using a high-speed projection system, we developed a trans-saccadic identification task in which brief but continuous intra-saccadic object motion was key to successful performance. Observers made a saccade to a target stimulus that moved rapidly either up or down, strictly during the eye movement. Just as the target reached its final position, an identical distractor stimulus appeared on the opposite side, resulting in a display of two identical stimuli upon saccade landing. Observers had to identify the original target using the only available clue: the target's intra-saccadic movement. In an additional replay condition, we presented the observers' own intra-saccadic retinal stimulus trajectories during fixation. Compared to the replay condition, task performance was impaired during saccades but recovered fully when a post-saccadic blank was introduced. Reverse regression analyses and confirmatory experiments showed that performance increased markedly when targets had long movement durations, low spatial frequencies, and orientations parallel to their retinal trajectory-features that promote intra-saccadic motion streaks. Although the potential functional role of intra-saccadic visual signals is still unclear, our results suggest that they could provide cues to tracking objects that rapidly change locations across saccades.

Intra-saccadic motion streaks jump-start gaze correction

“…Furthermore, we not only showed that the effect of intra-saccadic object motion is orthogonal to the effect of primary saccade landing positions (cf. Hollingworth et al, 2008), but also provided evidence for the benefit of effective temporal integration when stimulus orientations were aligned with their retinal motion trajectories -a typical signature of motion streaks (Schweitzer & Rolfs, 2020). In other words, the more effectively the combined movement of eye and target in a given trial generated a motion streak, the more often did a secondary saccade go to the target.…”

“…Most experiments thus far, in fact, were built on the premise that "vision is suppressed, creating a gap in perceptual input" (Richard et al, 2008, p. 66) and "people are virtually blind" (Hollingworth et al, 2008, p. 163) during saccades. In contrast to this premise, we have recently shown that observers can use intra-saccadic motion streaks to tell pre-saccadic objects from identical distractors upon saccade landing (Schweitzer & Rolfs, 2020). The crucial question -if intra-saccadic streaks could be used to establish object correspondence across saccades -remains unanswered, however.…”

“…This procedure inevitably led to some differences in spatial frequency and orientation for the two types of content in the pairs of noise patches. This effect was intended, as it allowed for both easier discrimination of the two types during trials and for reverse regression analyses involving stimulus features at a later stage (Schweitzer & Rolfs, 2020;Wyart et al, 2012). All noise patches were at full Michelson contrast to maximize their intra-saccadic visibility.…”

“…From retinal positions, retinal angles were computed, whose median was subsequently used to normalize each stimulus' orientation components for its respective retinal trajectory. Relative orientation is the angular difference between the retinal angle and the orientations contained in a given noise patch (Schweitzer & Rolfs, 2020). To achieve the equal-sized steps of relative orientations (in the face of retinal angles that naturally varied between trials), the filter responses for the defined orientation and SF levels were interpolated based on a full tensor product smooth (using cubic splines) of each stimulus' energy map.…”

“…We hypothesized, therefore, that the rapid movement of the target across the retina produced intra-saccadic motion streaks (Bedell & Yang, 2001;Brooks et al, 1980;Duyck et al, 2016;Geisler, 1999;Matin et al, 1972). In this case, secondary saccades to the target should be facilitated if stimulus features (incidentally) produced a distinctive streak, for instance if the orientation of a stimulus is parallel to its trajectory on the retina (Schweitzer & Rolfs, 2020).…”