Eye tracking: empirical foundations for a minimal reporting guideline.

In this paper, we present a review of how the various aspects of any study using an eye tracker (such as the instrument, methodology, environment, participant, etc.) affect the quality of the recorded eye-tracking data and the obtained eye-movement and gaze measures. We take this review to represent the empirical foundation for reporting guidelines of any study involving an eye tracker. We compare this empirical foundation to five existing reporting guidelines and to a database of 207 published eye-tracking studies. We find that reporting guidelines vary substantially and do not match with actual reporting practices. We end by deriving a minimal, flexible reporting guideline based on empirical research (Section "An empirically based minimal reporting guideline").

High-Accuracy Gaze Estimation for Interpolation-Based Eye-Tracking Methods.

This study investigates the influence of the eye-camera location associated with the accuracy and precision of interpolation-based eye-tracking methods. Several factors can negatively influence gaze estimation methods when building a commercial or off-the-shelf eye tracker device, including the eye-camera location in uncalibrated setups. Our experiments show that the eye-camera location combined with the non-coplanarity of the eye plane deforms the eye feature distribution when the eye-camera is far from the eye's optical axis. This paper proposes geometric transformation methods to reshape the eye feature distribution based on the virtual alignment of the eye-camera in the center of the eye's optical axis. The data analysis uses eye-tracking data from a simulated environment and an experiment with 83 volunteer participants (55 males and 28 females). We evaluate the improvements achieved with the proposed methods using Gaussian analysis, which defines a range for high-accuracy gaze estimation between -0.5∘ and 0.5∘. Compared to traditional polynomial-based and homography-based gaze estimation methods, the proposed methods increase the number of gaze estimations in the high-accuracy range.

The impact of physiological fatigue and gaze behavior on shooting performance in expert biathletes.

OBJECTIVES: Biathlon is a discipline that combines cross country skiing with rifle shooting. It demands high shooting accuracy and fast shooting times under increasing levels of physiological fatigue. Building on Vickers and Williams (2007), the current study aimed at scrutinizing the impact of physiological fatigue and gaze behavior on shooting performance in elite and sub-elite biathletes. DESIGN: Ten members of the German national senior team (elite) and 13 members of the German national junior team (sub-elite) participated in a performance test. They conducted a roller skiing test on a treadmill including four increasing intensity levels followed by shooting blocks of five shots in both prone and standing position. METHODS: Physiological measurements consisted of heart rate and blood lactate, shooting performance data included shooting accuracy and time. Eye movements were assessed, i.e. the duration of the final fixation, using a gun-mounted eye tracking system. RESULTS: Physiological fatigue systematically increased across intensity levels. There were no differences between elite and sub-elite biathletes in percentage shooting accuracy. However, elites needed shorter shooting times than sub-elites. Both groups showed increased range times with increased workload levels in prone and standing positions. Yet, there was no effect on shooting accuracy. Finally, analyses of a subset of data did not show any effect of final fixation duration on shooting accuracy. CONCLUSIONS: Physiological fatigue seems to have no impact on shooting accuracy, but rather affects shooting times in expert biathletes. Furthermore, the duration of the final fixation does not seem to moderate shooting accuracy in elite biathletes.

Why have microsaccades become larger? Investigating eye deformations and detection algorithms.

The reported size of microsaccades is considerably larger today compared to the initial era of microsaccade studies during the 1950s and 1960s. We investigate whether this increase in size is related to the fact that the eye-trackers of today measure different ocular structures than the older techniques, and that the movements of these structures may differ during a microsaccade. In addition, we explore the impact such differences have on subsequent analyzes of the eye-tracker signals. In Experiment I, the movement of the pupil as well as the first and fourth Purkinje reflections were extracted from series of eye images recorded during a fixation task. Results show that the different ocular structures produce different microsaccade signatures. In Experiment II, we found that microsaccade amplitudes computed with a common detection algorithm were larger compared to those reported by two human experts. The main reason was that the overshoots were not systematically detected by the algorithm and therefore not accurately accounted for. We conclude that one reason to why the reported size of microsaccades has increased is due to the larger overshoots produced by the modern pupil-based eye-trackers compared to the systems used in the classical studies, in combination with the lack of a systematic algorithmic treatment of the overshoot. We hope that awareness of these discrepancies in microsaccade dynamics across eye structures will lead to more generally accepted definitions of microsaccades.

In the eye of the beholder: a survey of models for eyes and gaze.

Despite active research and significant progress in the last 30 years, eye detection and tracking remains challenging due to the individuality of eyes, occlusion, variability in scale, location, and light conditions. Data on eye location and details of eye movements have numerous applications and are essential in face detection, biometric identification, and particular human-computer interaction tasks. This paper reviews current progress and state of the art in video-based eye detection and tracking in order to identify promising techniques as well as issues to be further addressed. We present a detailed review of recent eye models and techniques for eye detection and tracking. We also survey methods for gaze estimation and compare them based on their geometric properties and reported accuracies. This review shows that, despite their apparent simplicity, the development of a general eye detection technique involves addressing many challenges, requires further theoretical developments, and is consequently of interest to many other domains problems in computer vision and beyond.