Enhancing eye tracking for nonhuman primates and other subjects unable to follow instructions: Adaptive calibration and validation of Tobii eye trackers with the Titta toolbox

Accurate eye tracking is crucial for gaze-dependent research, but calibrating eye trackers in subjects who cannot follow instructions, such as human infants and nonhuman primates, presents a challenge. Traditional calibration methods rely on verbal instructions, which are ineffective for these populations. To address this, researchers often use attention-grabbing stimuli in known locations; however, existing software for video-based calibration is often proprietary and inflexible. We introduce an extension to the open-source toolbox Titta-a software package integrating desktop Tobii eye trackers with PsychToolbox experiments-to facilitate custom video-based calibration. This toolbox extension offers a flexible platform for attracting attention, calibrating using flexible point selection, and validating the calibration. The toolbox has been refined through extensive use with chimpanzees, baboons, and macaques, demonstrating its effectiveness across species. Our adaptive calibration and validation procedures provide a standardized method for achieving more accurate gaze tracking, enhancing gaze accuracy across diverse species.