An adaptive algorithm for fast and reliable online saccade detection
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An adaptive algorithm for fast and reliable online saccade detection Richard Schweitzer 1,2,3
&
Martin Rolfs 1,2
# The Psychonomic Society, Inc. 2019
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, because 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 weaknesses: late detections and false alarms, respectively. 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 the detection criteria. Inspired by the Engbert–Kliegl algorithm for microsaccade detection, our algorithm computes two-dimensional velocity thresholds from variance in the 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 ms. High accuracy was maintained even under simulated high-noise conditions. To demonstrate that purely intrasaccadic presentations are technically feasible, we devised an experimental test in which a Gabor patch drifted at saccadic peak velocities. Whereas this stimulus was invisible when presented during fixation, observers reliably detected it during saccades. Photodiode measurements verified that—including all system delays—the stimuli were physically displayed on average 20 ms after saccade onset. Thus, the proposed algorithm provides a valuable tool for gaze-contingent paradigms. Keywords Saccade detection . Eye movements . Intrasaccadic perception . Gaze-contingent presentation
In the field of active vision, most eyetracking experiments study visual perception around goal-directed rapid eye movements, so-called saccades. Specifically, when investigating trans-saccadic or intrasaccadic perception, an experimental paradigm has to be implemented in a way that a stimulus or the configuration of stimuli is manipulated online (i.e., in real time) and gaze-contingently, starting with the onset of a saccade (Higgins & Rayner, 2015; Hollingworth, Richard, & Luck, 2008; Melcher & Colby, 2008; Prime, Vesia, & Crawford, 2011; Wolf & Schütz, 2015). Because saccades are rapid and brief events, often with a skewed velocity profile
* Richard Schweitzer [email protected] 1
Department of Psychology, Humboldt-Universität zu Berlin, Berlin, Germany
2
Bernstein Center for Computational Neuroscience Berlin, Berlin, Germany
3
Berlin School of Mind and Brain, Humboldt-Universität zu Berlin, Berlin, Germany
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