The influence of calibration method and eye physiology on eyetracking data quality

Nyström, Maria; Andersson, Richard; Holmqvist, Kenneth; Weijer, Joost van de

doi:10.3758/s13428-012-0247-4

Cited by 221 publications

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“…For instance, Nyström, Andersson, Holmqvist, and van de Weijer (2013) showed that when recorded using a SensoMotoric Instruments (SMI) HiSpeed 1250 tower eye-tracker, blue eyes result in data with a poorer RMS(S2S) precision than brown eyes, and that data recorded from participants with glasses are more imprecise than data from uncorrected eyes in this particular eye-tracker. Increasing the pixel resolution at the eye (e.g., by using a higherresolution camera or placing it closer to the eye) makes precision better [lower RMS(S2S) or SD].…”

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A study of artificial eyes for the measurement of precision in eye-trackers

et al. 2016

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The precision of an eye-tracker is critical to the correct identification of eye movements and their properties. To measure a system's precision, artificial eyes (AEs) are often used, to exclude eye movements influencing the measurements. A possible issue, however, is that it is virtually impossible to construct AEs with sufficient complexity to fully represent the human eye. To examine the consequences of this limitation, we tested currently used AEs from three manufacturers of eye-trackers and compared them to a more complex model, using 12 commercial eye-trackers. Because precision can be measured in various ways, we compared different metrics in the spatial domain and analyzed the power-spectral densities in the frequency domain. To assess how precision measurements compare in artificial and human eyes, we also measured precision using human recordings on the same eyetrackers. Our results show that the modified eye model presented can cope with all eye-trackers tested and acts as a promising candidate for further development of a set of AEs with varying pupil size and pupil-iris contrast. The spectral analysis of both the AE and human data revealed that human eye data have different frequencies that likely reflect the physiological characteristics of human eye movements. We also report the effects of sample selection methods for precision calculations. This study is part of the EMRA/COGAIN Eye Data Quality Standardization Project.Keywords Eye movements . Artificial eye . Precision . Data quality . Eye-tracker noise . Power-spectral density High-quality eye movement data are a prerequisite for the valid measurement of fixation durations, saccade amplitudes and velocities, and many other behavioral measures in eye movement research. Spatial accuracy and precision are two of the most important aspects of eye data quality. Accuracy is defined as the difference between the tracker-estimated gaze position and the actual gaze position, whereas precision is defined as the ability to reliably reproduce a measurement, given a fixating eye (ideally, a stable eye)-see Fig. 1. Accuracy and precision are two independent measurements of eye-tracking data quality-that is, they can be both good or poor, or one good and the other poor. The most commonly used measures of precision in eye-trackers are the sample-tosample root mean square angular displacement [RMS(S2S)] and the standard deviation (SD) of samples in a given time window. These values will change not only dependent on the actual precision level of the tracker but also on the calculation used, and the samples or time period included in that calculation. Longer periods increase the probability of fixational eye movements (tremor, microsaccades, and drift), which in turn will increase imprecision. Holmqvist, Nyström, and Mulvey (2012) showed that artificially increasing imprecision via the addition of Gaussian noise from 0.03°to 0.30°results in an increase of up to 200 ms in calculated fixation durations. If this range of noise, as measured by RMS(S2S) precis...

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A study of artificial eyes for the measurement of precision in eye-trackers

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“…Las métricas que usualmente se utilizan para evaluar estos dispositivos son la precisión y la exactitud, expresadas en grados angulares. Estas medidas se llevan a cabo bajo condiciones controladas de luz y restringiendo los movimientos de la cabeza (Nyström, Andersson, Holmqvist, & van de Weijer, 2013). La evaluación con estas dos métricas está centrada en medir la calidad del dispositivo, que sirve de interfaz de acceso al ordenador.…”

Section: Evaluación De La Interacción: Un Problema No Resueltounclassified

Metodología de Evaluación de Eye-trackers como Dispositivos de Acceso Alternativo para Personas con Parálisis Cerebral

Clemotte

Velasco

Raya

et al. 2017

Revista Iberoamericana de Automática e Informática Industrial R

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ResumenLos procedimientos de evaluación de los sistemas alternativos de acceso al ordenador son poco rigurosos, sistemáticos y formales. Este trabajo presenta una metodología para la valoración de la interacción usuario-ordenador, cuando los sistemas de eye-tracking son utilizados como herramienta de acceso alternativo al ordenador por personas con Parálisis Cerebral (PC). Para ello, proponemos tres métricas de evaluación: tasa de fallos de calibración, tasa de error en el clic y tiempo de clic. Validamos la metodología, comparando 3 (tres) eyetrackers, con 9 (nueve) participantes con PC con trastornos motores severos. Los resultados indican que la calibración es un proceso crítico en estos escenarios como refleja la alta tasa de fallos de calibración medida. Los participantes con PC también tienen una alta tasa de error del clic, lo que indica que el uso de eye-trackers para alcanzar un objeto en pantalla es un proceso complejo para estos niveles de discapacidad motriz. Los tiempos de clics son similares entre todos los eye-trackers y participantes. Este trabajo pretende establecer líneas metodológicas para la efectiva evaluación de estos dispositivos, que pueden llegar a ser una interesante alternativa de acceso al ordenador para esta población. Palabras Clave:Acceso alternativo, eye-trackers, metodología, evaluación, valoración, parálisis cerebral, ley de Fitts. Introducción La parálisis cerebral y los sistemas de comunicación aumentativos alternativosLa parálisis cerebral (PC) es una de las discapacidades más severas de los niños (McIntyre, Morgan, Walker, & Novak, 2011). La definición más citada de PC es la que la describe como "un trastorno de la postura y el movimiento debido a un defecto o lesión en el cerebro inmaduro (Bax et al., 2005)'', en los periodos perinatales principalmente. Los sistemas de comunicación aumentativa y alternativa (AAC, acrónimo en su terminología anglosajona Augmentative and Alternative Communication) son un medio eficaz para complementar y mejorar las habilidades de comunicación funcional e interacción con el entorno de las personas con PC (Clarke & Price, 2012;Fager, Bardach, Russell, & Higginbotham, 2012;Pennington, 2008;Wilkinson & Mitchell, 2014). Sin embargo, existe un grupo de personas con PC, severamente afectadas por esta discapacidad que presentan serias dificultades para interactuar con sistemas AAC basados en ordenadores, controlados con un ratón o un teclado. En este sentido, Davies et al. (Davies, Chau, Fehlings, Ameratunga, & Stott, 2010) encontraron que un 65% de personas afectadas por la PC no podían usar ni un ratón ni el teclado estándar, quedando por ende inhabilitados para utilizar herramientas AAC. Una alternativa para estos casos tan severos son los seguidores de la mirada o eyetrackers (ET).Estos dispositivos son capaces de estimar el punto de la mirada en la pantalla de un computador (Duchowski, 2007), permitiendo a las personas controlar un ordenador con los ojos. Los ETs aprovechan una de las escasas habilidades residuales de los casos más graves de la ...

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“…Calibration was executed before starting the experiment, as this has great importance for examining vergence (see, e.g., Nyström et al, 2013). Using video-based eye tracking, estimates of the gaze position always relate to the calibrated positions.…”

Section: Methodsmentioning

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“…359-365. DOI: 10.1515/prolas-2017 eyelashes...) were already mentioned as possible sources of variation in other studies (Nyström et al 2013). Kirkby et al (2013) investigated the hypothesis that one potential source for the contradictory findings may be related to different devices used to collect the data as well as the different methods used for analysis.…”

Section: Introductionmentioning

confidence: 99%

Binocular Coordination in Reading When Changing Background Brightness

Köpsel

Huckauf²

2017

Proceedings of the Latvian Academy of Sciences. Section B. Natural, Exact, and Applied Sciences.

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INTRODUCTIONWhen we look, we fixate on an object of interest with both eyes. The process of aligning both focus points is referred to as binocular coordination, the result of this process is termed vergence. That is, a vergence point is defined as the position where both lines of sight meet. Understanding the alignment of both lines of sight is important also for the understanding of binocular vision, that is, the motor coordination of the eyes as well as the perceptual coordination like, for example, in image fusion. In visual tasks, vergence points are expected to occur where an image is depicted. Therefore, when presenting images on a screen, the fixation location of both eyes is measured on the screen. The resulting difference between fixation locations of both eyes is referred to as fixation disparity. That is, fixation disparity is the difference between the two lines of sight at a given distance, which informs about the spatial accuracy of aligning both lines of sight.Binocular coordination is performed also in seemingly two-dimensional tasks like, for example, in reading. This raises the question of whether two eyes are better than one, as Radach and Heller (1999) put it. With regard to fixation disparity in reading, there are contradictory results. Liversedge et al. (2006) reported that about half of the fixations accompanying reading are unaligned. The authors characterised these fixations as crossed or uncrossed, depending on their disparity: fixations were counted as crossed when the right eye fixated more than one character left of the left eye, and as uncrossed when the right eye fixated more than one character right of the left eye. Expressed as vergence, crossed fixations were described as a vergence point spatially in front of the screen, and uncrossed fixations as a vergence point behind the screen. Liversedge et al. (2006) found more uncrossed fixation disparities than crossed ones, that is, a mean vergence point behind the screen.In contrast, a dominance of crossed fixations and hence, vergence points, which are typically in front of the screen, was reported by Nuthmann and Kliegl (2009). With regard to binocular coordination, one might wonder how image fusion can take place on the basis of such huge amounts of not aligned fixations. In order to understand binocular visual functioning, it is therefore important to distinguish systematic variations of fixation alignments from random variability.There were already various reasons suggested as potentially being responsible for the differences in the findings of Nuthmann and Kliegl (2009) as compared to : differing eye-trackers, calibration procedures, viewing distances and also letter sizes. The former used a chin rest, the latter a bite bar, and participants had to read in different languages (German vs. English). These differences and several more (e.g., glasses, contact lenses, eye colour, PROCEEDINGS OF THE LATVIAN ACADEMY OF SCIENCES. Section B, Vol. 71 (2017)

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The influence of calibration method and eye physiology on eyetracking data quality

Cited by 221 publications

References 31 publications

A study of artificial eyes for the measurement of precision in eye-trackers

A study of artificial eyes for the measurement of precision in eye-trackers

Metodología de Evaluación de Eye-trackers como Dispositivos de Acceso Alternativo para Personas con Parálisis Cerebral

Binocular Coordination in Reading When Changing Background Brightness

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