Head-Mounted Eye Tracking of a Chimpanzee under Naturalistic Conditions

Abstract

This study offers a new method for examining the bodily, manual, and eye movements of a chimpanzee at the micro-level. A female chimpanzee wore a lightweight head-mounted eye tracker (60 Hz) on her head while engaging in daily interactions with the human experimenter. The eye tracker recorded her eye movements accurately while the chimpanzee freely moved her head, hands, and body. Three video cameras recorded the bodily and manual movements of the chimpanzee from multiple angles. We examined how the chimpanzee viewed the experimenter in this interactive setting and how the eye movements were related to the ongoing interactive contexts and actions. We prepared two experimentally defined contexts in each session: a face-to-face greeting phase upon the appearance of the experimenter in the experimental room, and a subsequent face-to-face task phase that included manual gestures and fruit rewards. Overall, the general viewing pattern of the chimpanzee, measured in terms of duration of individual fixations, length of individual saccades, and total viewing duration of the experimenter’s face/body, was very similar to that observed in previous eye-tracking studies that used non-interactive situations, despite the differences in the experimental settings. However, the chimpanzee viewed the experimenter and the scene objects differently depending on the ongoing context and actions. The chimpanzee viewed the experimenter’s face and body during the greeting phase, but viewed the experimenter’s face and hands as well as the fruit reward during the task phase. These differences can be explained by the differential bodily/manual actions produced by the chimpanzee and the experimenter during each experimental phase (i.e., greeting gestures, task cueing). Additionally, the chimpanzee’s viewing pattern varied depending on the identity of the experimenter (i.e., the chimpanzee’s prior experience with the experimenter). These methods and results offer new possibilities for examining the natural gaze behavior of chimpanzees.

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“…Head-mounted systems are advantageous in that they can track eye gaze patterns in moving subjects, but they also require that hardware be physically attached to subjects, which is not always feasible. Head-mounted eye tracking systems have been developed for a variety of species, including chickens (Schwartz et al 2013), peahens (Yorzinski et al 2013), starlings (Tyrrell et al 2014), rats (Wallace et al 2013, dogs , and chimpanzees (Kano & Tomonaga 2013). Externally mounted devices allow eye gaze to be tracked without handling subjects, but require that subjects remain relatively stationary throughout trials and generally involve a calibration session to set subject specific eye parameters before each trial.…”

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