The application of noninvasive, restraint-free eye-tracking methods for use with nonhuman primates

Abstract

Over the past 50 years there has been a strong interest in applying eye-tracking techniques to study a myriad of questions related to human and nonhuman primate psychological processes. Eye movements and fixations can provide qualitative and quantitative insights into cognitive processes of nonverbal populations such as nonhuman primates, clarifying the evolutionary, physiological, and representational underpinnings of human cognition. While early attempts at nonhuman primate eye tracking were relatively crude, later, more sophisticated and sensitive techniques required invasive protocols and the use of restraint. In the past decade, technology has advanced to a point where noninvasive eye-tracking techniques, developed for use with human participants, can be applied for use with nonhuman primates in a restraint-free manner. Here we review the corpus of recent studies (N=32) that take such an approach. Despite the growing interest in eye-tracking research, there is still little consensus on "best practices," both in terms of deploying test protocols or reporting methods and results. Therefore, we look to advances made in the field of developmental psychology, as well as our own collective experiences using eye trackers with nonhuman primates, to highlight key elements that researchers should consider when designing noninvasive restraint-free eye-tracking research protocols for use with nonhuman primates. Beyond promoting best practices for research protocols, we also outline an ideal approach for reporting such research and highlight future directions for the field.

Where Is Ethology Heading? An Invitation for Collective Metadisciplinary Discussion

“…However, the arrival of eye tracker techniques, which allowed for following the gaze of subjects with a minimal margin error, allowed to incorporate new ways to explore the existence of theory of mind in apes with a simple experimental design based on the anticipatory look on others’ movement [ 59 , 60 ]. Plus, the method is non-invasive and restraint-free [ 61 ]. Another milestone of technology in our discipline has been the use of drones in marine studies, because “behavioural observations are typically limited to records of animal surfacings obtained from a horizontal perspective” but “drones UAS provided three times more observational capacity than boat-based observations alone (300 vs. 103 min); provided more and longer observations plus enable documentation of multiple novel gray whale foraging tactics and social events not identified from boat-based observation” ([ 62 ], p. 359).…”

Does male mate choice select for female colouration in a promiscuous primate species?

“…The lack of effect of female colouration on male sexual behaviours -or in other words, the lack of male choice for darker/redder females-is surprising given that previous studies suggested a potential role of female colouration on male mate choice in Japanese macaques over-estimated due to the binary choice, the lack of familiarity with the stimuli which significantly matters in communication (e.g., visual trait: Higham et al, 2011;odorant trait: Setchell et al, 2010;auditory trait: Townsend et al, 2011), or the lack of precise measure of attention such as tracking fine-scale eye movements (Hopper et al, 2020;Yorzinski et al, 2013).…”

Testing the Relationship Between Looking Time and Choice Preference in Long-tailed Macaques

“…An additional avenue of research that now shows promise for a number of species, such as primates (Hopper et al, 2020) and dogs (Somppi et al, 2012), is the use of eye tracking. Eye tracking can be conducted non-invasively and thus is of increasing application to a wider scope of research setups such as in zoos (Hopper et al, 2020).…”

“…An additional avenue of research that now shows promise for a number of species, such as primates (Hopper et al, 2020) and dogs (Somppi et al, 2012), is the use of eye tracking. Eye tracking can be conducted non-invasively and thus is of increasing application to a wider scope of research setups such as in zoos (Hopper et al, 2020). The benefit of this approach is that it allows one to examine in detail gaze responses to social stimuli, such as how species explore facial images (Kano et al, 2012;Wilson et al, 2020).…”