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      Smaller Is Better: Drift in Gaze Measurements due to Pupil Dynamics

      1 , 2 , * , 2 , 3 , 4 , 4 , 4

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          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. In an attempt to improve the 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 39 subjects. The pupil-size dependent shift varied greatly between subjects (from 0.3 to 5.2 deg of deviation, mean 2.6 deg), but also between the eyes of individual subjects (0.1 to 3.0 deg difference, mean difference 1.0 deg). We observed a wide range of drift direction, mostly downward and nasal. We demonstrate two methods to partially compensate the pupil-based shift using separate calibrations in pupil-constricted and pupil-dilated conditions, and evaluate an improved method of compensation based on individual look-up-tables, achieving up to 74% of compensation.

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          Most cited references 4

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          Task-evoked pupillary responses, processing load, and the structure of processing resources.

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            The pupillary light reflex in normal subjects.

             Matthew Ellis (1981)
            In 19 normal subjects the pupillary reflex to light was studied over a range of stimulus intensities by infrared electronic pupillography and analysed by a computer technique. Increasing stimulus intensity was associated with an increase in direct light reflex amplitude and maximum rate of constriction and redilatation. Latency from stimulus to onset of response-decreased with increasing stimulus intensity. The normal range for each of these parameters is given and the significance of these results in clinical pupillary assessment discussed.
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              The human pupil and the use of video-based eyetrackers.

              Video-based devices for measuring gaze direction are widespread. However, there is a built-in imprecision in such devices in the event that pupil diameter changes during the experiments. Data are presented to demonstrate this effect. The possibility of correcting eye-position records for the imprecision is discussed and preliminary examples of such correction are presented. Copyright 2010 Elsevier Ltd. All rights reserved.

                Author and article information

                Role: Editor
                PLoS One
                PLoS ONE
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                22 October 2014
                : 9
                : 10
                [1 ]Centre for Vision Research, York University, Toronto, Canada
                [2 ]Center for Mind/Brain Sciences, Trento University, Rovereto, Italy
                [3 ]School of Information Science, Yunnan University, Kunming, China
                [4 ]Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China
                Tokyo Metropolitan Institute of Medical Science, Japan
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: JD. Performed the experiments: JD WZ YH. Analyzed the data: JD WZ. Contributed reagents/materials/analysis tools: XH. Wrote the paper: JD WZ XH.


                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                Page count
                Pages: 6
                WZ was supported by the National Natural Science Foundation of China (62263042, 61005087). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Research Article
                Biology and Life Sciences
                Computational Biology
                Computational Neuroscience
                Sensory Perception
                Binocular Vision
                Monocular Vision
                Behavioral Neuroscience
                Cognitive Neuroscience
                Cognitive Science
                Social Sciences
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                The authors confirm that all data underlying the findings are fully available without restriction. Data are available from DRYAD using the doi doi:10.5061/dryad.3ts56.



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