An adaptive algorithm for fast and reliable online saccade detection

Abstract

To investigate visual perception around the time of eye movements, vision scientists manipulate stimuli contingent upon the onset of a saccade. For these experimental paradigms, timing is especially crucial, as saccade offset imposes a deadline on the display change. Although efficient online saccade detection can greatly improve timing, most algorithms rely on spatialboundary techniques or absolute-velocity thresholds, which both suffer from their respective weaknesses: late detections and false alarms. We propose an adaptive, velocity-based algorithm for online saccade detection that surpasses both standard techniques in speed and accuracy and allows the user to freely define detection criteria. Inspired by the Engbert-Kliegl-algorithm for microsaccade detection, our algorithm computes two-dimensional velocity thresholds from variance in preceding fixation samples, while compensating for noisy or missing data samples. An optional direction criterion limits detection to the instructed saccade direction, further increasing robustness.We validated the algorithm by simulating its performance on a large saccade dataset and found that high detection accuracy (false-alarm rates of <1%) could be achieved with detection latencies of only 3 milliseconds. High accuracy was maintained even under simulated high-noise conditions. To demonstrate that purely intra-saccadic presentations are technically feasible, we devised an experimental test, in which a Gabor patch drifted at saccadic peak velocities. While this stimulus was invisible when presented during fixation, observers reliably detected it during saccades.Photodiode measurements verified that -including all system delays -stimuli were physically displayed on average 20 ms after saccade onset. Thus, the proposed algorithm provides valuable tool for gaze-contingent paradigms.

Intrasaccadic motion streaks jump-start gaze correction

“…After successful fixation, an exogenous cue was presented to indicate the saccade target: The target stimulus-one of the six presented stimuli and one of the two types of noise patches-was enlarged linearly up to twice its initial size for 25 ms and then decreased for 25 ms until the initial size was restored. Saccades were detected online using the algorithm described in (38) with parameters k = 2,  = 10, and ϑ = 40, on both eyes. In one-third of all trials, the target remained in its presaccadic location.…”

“…Last, to establish which stimulus features drive secondary saccades to the target stimulus, we performed a planned, large-scale reverse regression analysis (see Materials and Methods). Both contrast sensitivity for moving stimuli and motion perception-especially of high-spatial frequency (SF) stimuli-are known to dissipate at saccadic velocities (34)(35)(36)(37)(38). We hypothesized, therefore, that the rapid movement of the target across the retina produced intrasaccadic motion streaks (12)(13)(14)(15)17).…”

“…Third, on average, 10.1% (SD = 7.4) of the remaining trials in experiment 1 and 5.0% (SD = 3.8) of the remaining trials in experiment 2 were excluded because they failed to satisfy the following criteria: (i) no missing data within the relevant trial interval (see above), (ii) detection of one single primary saccade that reached the 2-dva area around the presaccadic target location (see the "Procedure and task" section), (iii) primary saccade metrics compatible with the instructed 10-dva saccade (i.e., amplitude 6 to 15 dva, peak velocity below 600 dva/s, duration below 75 ms), and (iv) strictly intrasaccadic stimulus motion (i.e., motion onset after saccade onset and motion offset before saccade offset, regardless of whether continuous motion was present or not), taking into account a deterministic 8.3-ms video delay of the PROPixx projection system [see (38)].…”

Limits of subjective and objective vection for ultra-high frame rate visual displays

“…The stimulus was back-projected onto the screen using a DLP LED projector (PROPixx, VPixx Technologies Inc., Montreal, Canada). The PROPixx operated in a specialized high refresh rate video sequencer mode called QUAD4X developed by VPixx Technologies (Alais et al, 2016;Balsdon et al, 2018;DeSimone & Schneider, 2019;Schweitzer & Rolfs, 2019;Zhang et al, 2019;Zhigalov et al, 2019). In short, the computer's graphic card (Titan V, Nvidia, Santa Clara, CA) transmits a 1920 x 1080 pixels image at 120 FPS.…”