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      Is the eye-movement field confused about fixations and saccades? A survey among 124 researchers

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          Abstract

          Eye movements have been extensively studied in a wide range of research fields. While new methods such as mobile eye tracking and eye tracking in virtual/augmented realities are emerging quickly, the eye-movement terminology has scarcely been revised. We assert that this may cause confusion about two of the main concepts: fixations and saccades. In this study, we assessed the definitions of fixations and saccades held in the eye-movement field, by surveying 124 eye-movement researchers. These eye-movement researchers held a variety of definitions of fixations and saccades, of which the breadth seems even wider than what is reported in the literature. Moreover, these definitions did not seem to be related to researcher background or experience. We urge researchers to make their definitions more explicit by specifying all the relevant components of the eye movement under investigation: (i) the oculomotor component: e.g. whether the eye moves slow or fast; (ii) the functional component: what purposes does the eye movement (or lack thereof) serve; (iii) the coordinate system used: relative to what does the eye move; (iv) the computational definition: how is the event represented in the eye-tracker signal. This should enable eye-movement researchers from different fields to have a discussion without misunderstandings.

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          An adaptive algorithm for fixation, saccade, and glissade detection in eyetracking data.

          Event detection is used to classify recorded gaze points into periods of fixation, saccade, smooth pursuit, blink, and noise. Although there is an overall consensus that current algorithms for event detection have serious flaws and that a de facto standard for event detection does not exist, surprisingly little work has been done to remedy this problem. We suggest a new velocity-based algorithm that takes several of the previously known limitations into account. Most important, the new algorithm identifies so-called glissades, a wobbling movement at the end of many saccades, as a separate class of eye movements. Part of the solution involves designing an adaptive velocity threshold that makes the event detection less sensitive to variations in noise level and the algorithm settings-free for the user. We demonstrate the performance of the new algorithm on eye movements recorded during reading and scene perception and compare it with two of the most commonly used algorithms today. Results show that, unlike the currently used algorithms, fixations, saccades, and glissades are robustly identified by the new algorithm. Using this algorithm, we found that glissades occur in about half of the saccades, during both reading and scene perception, and that they have an average duration close to 24 msec. Due to the high prevalence and long durations of glissades, we argue that researchers must actively choose whether to assign the glissades to saccades or fixations; the choice affects dependent variables such as fixation and saccade duration significantly. Current algorithms do not offer this choice, and their assignments of each glissade are largely arbitrary.
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            The brainstem control of saccadic eye movements.

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              The Roles of Vision and Eye Movements in the Control of Activities of Daily Living

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                Author and article information

                Journal
                R Soc Open Sci
                R Soc Open Sci
                RSOS
                royopensci
                Royal Society Open Science
                The Royal Society
                2054-5703
                August 2018
                29 August 2018
                29 August 2018
                : 5
                : 8
                : 180502
                Affiliations
                [1 ]Experimental Psychology, Helmholtz Institute, Utrecht University , Utrecht, The Netherlands
                [2 ]Developmental Psychology, Utrecht University , Utrecht, The Netherlands
                [3 ]Lund University Humanities Lab, Lund University , Lund, Sweden
                [4 ]Department of Psychology, Lund University , Lund, Sweden
                [5 ]Tobii AB, Stockholm, Sweden
                Author notes
                Author for correspondence: Roy S. Hessels e-mail: royhessels@ 123456gmail.com

                Electronic supplementary material is available online at https://dx.doi.org/10.6084/m9.figshare.c.4203068.

                Author information
                http://orcid.org/0000-0002-4907-1067
                http://orcid.org/0000-0002-4672-8756
                Article
                rsos180502
                10.1098/rsos.180502
                6124022
                30225041
                b28bc015-9442-4ac0-8cae-5a5ece741117
                © 2018 The Authors.

                Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

                History
                : 30 March 2018
                : 6 August 2018
                Funding
                Funded by: Gravitation program of the Dutch Ministry of Education, Culture, and Science and the NWO;
                Award ID: 024.001.003
                Categories
                1001
                205
                133
                42
                Psychology and Cognitive Neuroscience
                Research Article
                Custom metadata
                August, 2018

                eye movements,fixation,saccade,eye tracking,definitions
                eye movements, fixation, saccade, eye tracking, definitions

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