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      Development and Calibration of an Eye-Tracking Fixation Identification Algorithm for Immersive Virtual Reality

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          Abstract

          Fixation identification is an essential task in the extraction of relevant information from gaze patterns; various algorithms are used in the identification process. However, the thresholds used in the algorithms greatly affect their sensitivity. Moreover, the application of these algorithm to eye-tracking technologies integrated into head-mounted displays, where the subject’s head position is unrestricted, is still an open issue. Therefore, the adaptation of eye-tracking algorithms and their thresholds to immersive virtual reality frameworks needs to be validated. This study presents the development of a dispersion-threshold identification algorithm applied to data obtained from an eye-tracking system integrated into a head-mounted display. Rules-based criteria are proposed to calibrate the thresholds of the algorithm through different features, such as number of fixations and the percentage of points which belong to a fixation. The results show that distance-dispersion thresholds between 1–1.6° and time windows between 0.25 0.4 s are the acceptable range parameters, with 1° and 0.25 s being the optimum. The work presents a calibrated algorithm to be applied in future experiments with eye-tracking integrated into head-mounted displays and guidelines for calibrating fixation identification algorithms

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          Most cited references29

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          Eye Tracking in Virtual Reality

          The intent of this paper is to provide an introduction into the bourgeoning field of eye tracking in Virtual Reality (VR). VR itself is an emerging technology on the consumer market, which will create many new opportunities in research. It offers a lab environment with high immersion and close alignment with reality. An experiment which is using VR takes place in a highly controlled environment and allows for a more in-depth amount of information to be gathered about the actions of a subject. Techniques for eye tracking were introduced more than a century ago and are now an established technique in psychological experiments, yet recent development makes it versatile and affordable. In combination, these two techniques allow unprecedented monitoring and control of human behavior in semi-realistic conditions. This paper will explore the methods and tools which can be applied in the implementation of experiments using eye tracking in VR following the example of one case study. Accompanying the technical descriptions, we present research that displays the effectiveness of the technology and show what kind of results can be obtained when using eye tracking in VR. It is meant to guide the reader through the process of bringing VR in combination with eye tracking into the lab and to inspire ideas for new experiments.
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            Is the eye-movement field confused about fixations and saccades? A survey among 124 researchers

            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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              Cortical correlate of spatial presence in 2D and 3D interactive virtual reality: an EEG study.

              The present study is the first that examined neuronal underpinnings of spatial presence using multi-channel EEG in an interactive virtual reality (VR). We compared two VR-systems: a highly immersive Single-Wall-VR-system (three-dimensional view, large screen) and a less immersive Desktop-VR-system (two-dimensional view, small screen). Twenty-nine participants performed a spatial navigation task in a virtual maze and had to state their sensation of "being there" on a 5-point rating scale. Task-related power decrease/increase (TRPD/TRPI) in the Alpha band (8-12Hz) and coherence analyses in different frequency bands were used to analyze the EEG data. The Single-Wall-VR-system caused a more intense presence experience than the Desktop-VR-system. This increased feeling of presence in the Single-Wall-VR-condition was accompanied by an increased parietal TRPD in the Alpha band, which is associated with cortical activation. The lower presence experience in the Desktop-VR-group was accompanied by a stronger functional connectivity between frontal and parietal brain regions indicating that the communication between these two brain areas is crucial for the presence experience. Hence, we found a positive relationship between presence and parietal brain activation and a negative relationship between presence and frontal brain activation in an interactive VR-paradigm, supporting the results of passive non-interactive VR-studies. Copyright © 2011 Elsevier B.V. All rights reserved.
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                Author and article information

                Journal
                Sensors (Basel)
                Sensors (Basel)
                sensors
                Sensors (Basel, Switzerland)
                MDPI
                1424-8220
                01 September 2020
                September 2020
                : 20
                : 17
                : 4956
                Affiliations
                Instituto de Investigación e Innovación en Bioingeniería (i3B), Universitat Politècnica de València, 46022 Valencia, Spain; jamarmo@ 123456i3b.upv.es (J.M.-M.); jaiguipr@ 123456i3b.upv.es (J.G.); malcaniz@ 123456i3b.upv.es (M.A.)
                Author notes
                [* ]Correspondence: jllajur@ 123456i3b.upv.es
                Author information
                https://orcid.org/0000-0001-9207-0636
                Article
                sensors-20-04956
                10.3390/s20174956
                7547381
                32883026
                58fa1155-fa9a-4189-90f2-42d1e830aed8
                © 2020 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 29 June 2020
                : 26 August 2020
                Categories
                Article

                Biomedical engineering
                eye-tracking,fixation identification,virtual reality,immersive virtual reality,head-mounted display,calibration,area of interest

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