Improving gaze accuracy and predicting fixation in real time with video based eye trackers

Ivanov, Paul; Blanche, Tim

doi:10.1167/11.11.505

Cited by 3 publications

(1 citation statement)

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“…Prior work has shown that eye-tracker estimates of gaze direction are affected by fluctuations in pupil size (Choe, Blake, & Lee, 2016 ; Ivanov & Blanche, 2011 ). These effects are contingent on gaze direction and thus are difficult to correct systematically.…”

Section: Natural Statistics Experimentsmentioning

confidence: 99%

The natural statistics of blur

et al. 2016

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Blur from defocus can be both useful and detrimental for visual perception: It can be useful as a source of depth information and detrimental because it degrades image quality. We examined these aspects of blur by measuring the natural statistics of defocus blur across the visual field. Participants wore an eye-and-scene tracker that measured gaze direction, pupil diameter, and scene distances as they performed everyday tasks. We found that blur magnitude increases with increasing eccentricity. There is a vertical gradient in the distances that generate defocus blur: Blur below the fovea is generally due to scene points nearer than fixation; blur above the fovea is mostly due to points farther than fixation. There is no systematic horizontal gradient. Large blurs are generally caused by points farther rather than nearer than fixation. Consistent with the statistics, participants in a perceptual experiment perceived vertical blur gradients as slanted top-back whereas horizontal gradients were perceived equally as left-back and right-back. The tendency for people to see sharp as near and blurred as far is also consistent with the observed statistics. We calculated how many observations will be perceived as unsharp and found that perceptible blur is rare. Finally, we found that eye shape in ground-dwelling animals conforms to that required to put likely distances in best focus.

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Section: Natural Statistics Experimentsmentioning

confidence: 99%

The natural statistics of blur

et al. 2016

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Analysis of microsaccades and pupil dilation reveals a common decisional origin during visual search

et al. 2014

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During free viewing visual search, observers often refixate the same locations several times before and after target detection is reported with a button press. We analyzed the rate of microsaccades in the sequence of refixations made during visual search and found two important components. One related to the visual content of the region being fixated; fixations on targets generate more microsaccades and more microsaccades are generated for those targets that are more difficult to disambiguate. The other empathizes non-visual decisional processes; fixations containing the button press generate more microsaccades than those made on the same target but without the button press. Pupil dilation during the same refixations reveals a similar modulation. We inferred that generic sympathetic arousal mechanisms are part of the articulated complex of perceptual processes governing fixational eye movements.

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Pupil size dynamics during fixation impact the accuracy and precision of video-based gaze estimation

2016

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Video-based eye tracking relies on locating pupil center to measure gaze positions. Although widely used, the technique is known to generate spurious gaze position shifts up to several degrees in visual angle because pupil centration can change without eye movement during pupil constriction or dilation. Since pupil size can fluctuate markedly from moment to moment, reflecting arousal state and cognitive processing during human behavioral and neuroimaging experiments, the pupil size artifact is prevalent and thus weakens the quality of the video-based eye tracking measurements reliant on small fixational eye movements. Moreover, the artifact may lead to erroneous conclusions if the spurious signal is taken as an actual eye movement. Here, we measured pupil size and gaze position from 23 human observers performing a fixation task and examined the relationship between these two measures. Results disclosed that the pupils contracted as fixation was prolonged, at both small (<16s) and large (∼4min) time scales, and these pupil contractions were accompanied by systematic errors in gaze position estimation, in both the ellipse and the centroid methods of pupil tracking. When pupil size was regressed out, the accuracy and reliability of gaze position measurements were substantially improved, enabling differentiation of 0.1° difference in eye position. We confirmed the presence of systematic changes in pupil size, again at both small and large scales, and its tight relationship with gaze position estimates when observers were engaged in a demanding visual discrimination task.

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Improving gaze accuracy and predicting fixation in real time with video based eye trackers

Cited by 3 publications

References 0 publications

The natural statistics of blur

The natural statistics of blur

Analysis of microsaccades and pupil dilation reveals a common decisional origin during visual search

Pupil size dynamics during fixation impact the accuracy and precision of video-based gaze estimation

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