Development of an untethered, mobile, low-cost head-mounted eye tracker

Head-mounted eye-tracking systems allow us to observe participants' gaze behaviors in largely unconstrained, real-world settings. We have developed novel, untethered, mobile, low-cost, lightweight, easily-assembled head-mounted eye-tracking devices, comprised entirely of off-the-shelf components, including untethered, point-of-view, sports cameras. In total, the parts we have used cost ~$153, and we suggest untested alternative components that reduce the cost of parts to ~$31. Our device can be easily assembled using hobbying skills and techniques. We have developed hardware, software, and methodological techniques to perform point-of-regard estimation, and to temporally align scene and eye videos in the face of variable frame rate, which plagues low-cost, lightweight, untethered cameras. We describe an innovative technique for synchronizing eye and scene videos using synchronized flashing lights. Our hardware, software, and calibration designs will be made publicly available, and we describe them in detail here, to facilitate replication of our system. We also describe novel smooth-pursuit-based calibration methodology, which affords rich sampling of calibration data while compensating for lack of information regarding the extent of visibility on participants' scene recordings. Validation experiments indicate accuracy within 0.752 degrees of visual angle on average.