Abstract
Integrated eye tracking in virtual reality is a crucial tool for the field of vision science, and one that frees the stimulus from the stationary 2D plane defined by conventional desktop displays, allowing for the monitoring of task-coordinated movements of the eyes, head, and body, interaction via gaze, and the use of gaze-contingent displays. The Pupil Labs integration into the HTC Vive and Vive Pro is a notable solution, because it is extremely cost effective, and completely open source. One notable limitation, however is that the lack of space between the user’s face and the helmet optics has required that clip-on eye cameras are positioned below the helmet optics, looking up at the eyes at an extreme angle, and this affects the quality of the Pupil Labs eye tracking algorithm. Here, we present the results of a DIY hardware modification that replaces the large 120 Hz eye cameras positioned outside the optics with smaller 200 Hz eye cameras positioned behind the optics, inside the body of the Vive or Vive Pro, and aimed at a specially coated “hot” mirror positioned between the lens and the display. This mirror allows the visible light from the display to pass through to the viewer while reflecting an infrared image of the eye to the eye cameras above. This design provides a clear an on-axis eye image that is well-suited for computer-vision detection of the pupil, a key feature used by Pupil Labs’ eye tracking software. Here, we report on the accuracy and precision of the integrated eye tracking system, and provide instruction and resources to interested researchers looking to modify their own integrations.