The impact of slippage on the data quality of head-worn eye trackers

Abstract

Mobile head-worn eye trackers allow researchers to record eye-movement data as participants freely move around and interact with their surroundings. However, participant behavior may cause the eye tracker to slip on the participant's head, potentially strongly affecting data quality. To investigate how this eye-tracker slippage affects data quality, we designed experiments in which participants mimic behaviors that can cause a mobile eye tracker to move. Specifically, we investigated data quality when participants speak, make facial expressions, and move the eye tracker. Four head-worn eye-tracking setups were used: (i) Tobii Pro Glasses 2 in 50 Hz mode, (ii) SMI Eye Tracking Glasses 2.0 60 Hz, (iii) Pupil-Labs' Pupil in 3D mode, and (iv) Pupil-Labs' Pupil with the Grip gaze estimation algorithm as implemented in the EyeRecToo software. Our results show that whereas gaze estimates of the Tobii and Grip remained stable when the eye tracker moved, the other systems exhibited significant errors (0.8-3.1 • increase in gaze deviation over baseline) even for the small amounts of glasses movement that occurred during the speech and facial expressions tasks. We conclude that some of the tested eye-tracking setups may not be suitable for investigating gaze behavior when high accuracy is required, such as during face-to-face interaction scenarios. We recommend that users of mobile head-worn eye trackers perform similar tests with their setups to become aware of its characteristics. This will enable researchers to design experiments that are robust to the limitations of their particular eye-tracking setup. Keywords Head-mounted eye tracking • Wearable eye tracking • Mobile eye tracking • Eye movements • Natural behavior • Data quality Diederick C. Niehorster and Thiago Santini contributed equally and should be considered co-first authors.

Looking behavior and potential human interactions during locomotion

“…Participants' eye movements were measured with the Tobii Pro Glasses 2 (firmware version 1.25.3-citronkola) and the Tobii Pro Glasses Controller (version 1.95.14258) running on an HP Pavilion X2 with Windows 10. The Tobii Pro Glasses 2 were, apart from practical reasons of availability, used as the data quality of this device is less susceptible to slippage of the eye tracker with respect to the head compared with other wearable eye trackers (Niehorster, Santini, et al, 2020). The Tobii Pro Glasses 2 recorded eye movements at 50 Hz.…”

“…At the largest participant-walker distances that we were interested in, the systematic error in the gaze position signal may not allow us to determine whether the participant looks directly at the face of the walker. For example, previous research has established that one cannot generally distinguish gaze on facial features using wearable eye trackers at conversation distance (Niehorster, Santini, et al, 2020). Here we investigate gaze on walkers at larger interpersonal distances and thus choose a cruder AOI division, which includes a larger AOI for the face/head area (upper body).…”

Exploring the awe-some: Mobile eye-tracking insights into awe in a science museum

“…Once informed written consent was given, guests were guided through the Tobii Pro Glasses fitting procedure in which the Tobii Pro Glasses were placed and secured on their faces and the recording unit was secured to their clothing. Researchers [22] have noted issues with data quality when eye-tracker slippage occurs (e.g., participant removes or adjusts the Glasses on their face); we provided instructions to avoid these occurrences and guests were monitored as they were wearing the Glasses in the exhibit space. This fitting was followed by a fast calibration period in which guests focus their gaze on a bulls-eye pattern at arms-length while wearing the Tobii Pro Glasses.…”

Age-Related Differences in Fixation Pattern on a Companion Robot

“…None of the participants had any history of ocular diseases. All participants had normal or corrected-to-normal visual acuity [ 33 , 45 , 46 ]. They volunteered to participate in the study and provided informed consent.…”