Abstract

Saccade detection is a critical step in the analysis of gaze data. A common method for saccade detection is to use a simple threshold for velocity or acceleration values, which can be estimated from the data using the mean and standard deviation. However, this method has the downside of being influenced by the very signal it is trying to detect, the outlying velocities or accelerations that occur during saccades. We propose instead to use the median absolute deviation (MAD), a robust estimator of dispersion that is not influenced by outliers. We modify an algorithm proposed by Nyström and colleagues, and quantify saccade detection performance in both simulated and human data. Our modified algorithm shows a significant and marked improvement in saccade detection - showing both more true positives and less false negatives – especially under higher noise levels. We conclude that robust estimators can be widely adopted in other common, automatic gaze classification algorithms due to their ease of implementation.

Highlights

  • The analysis of gaze behaviour yields critical insights into processes underlying visual attention, perception, and executive control, as well as their mechanistic underpinnings (Bahill et al, 1975; Engbert & Kliegl, 2003; OteroMillan et al, 2008)

  • One prominent component of gaze behaviour is saccades, ballistic eye movements that rapidly re-orient the eye and the image impinging on the retina

  • We find that robust threshold estimation leads to improved saccade detection, at higher noise levels, and is robust to varying threshold confidence levels

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Summary

Introduction

The analysis of gaze behaviour yields critical insights into processes underlying visual attention, perception, and executive control, as well as their mechanistic underpinnings (Bahill et al, 1975; Engbert & Kliegl, 2003; OteroMillan et al, 2008). One prominent component of gaze behaviour is saccades, ballistic eye movements that rapidly re-orient the eye and the image impinging on the retina. Saccades typically last between 20 and 100 ms, depending on the amplitude of the saccade (Bahill et al, 1975; Bargary et al, 2017; Inchinglo, 1985). Because of their ballistic nature, saccades can be differentiated from.

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