A binocular evaluation of pupil-size dependent deviation in measured gaze position J Drewes1, W Zhu2, Y Li2, Y Hu2, F Yang2, X Du2, X Hu2 |
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1Centre for Vision Research, York University, ON, Canada |
| Camera-based eye trackers are the mainstay of eye movement research and countless practical applications of eye tracking. Recently, a significant impact of changes in pupil size on gaze position as measured by camera-based eye trackers has been reported [Wyatt 2010], and a first attempt at compensating for this drift was proposed (Drewes et. al. 2012). While ground truth was presented (Drewes et al. 2012), all previous studies used very few subjects to demonstrate this effect (5 and 2 respectively), and only monocular measurements were performed. In an attempt to improve understanding of the magnitude and population-wise distribution of the pupil-size dependent shift in reported gaze position, we present the first collection of binocular pupil drift measurements recorded from 20 subjects (SR Research Eyelink 1000, subjects were ethnic Han-Chinese). The pupil-size dependent shift varied greatly between subjects (0.6 to 4.4 degree, mean 2.4 degree), but also between the eyes of individual subjects (0.16 to 1.7 degree difference, mean difference 0.8 degree). We observed a wide range of drift directions. We demonstrate a method to partially compensate the pupil-based shift using separate calibrations in pupil-constricted and pupil-dilated conditions, and evaluate an improved method of calibration based on multiple different pupil-dilation conditions. |
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