Great Apes' Understanding of Other Individuals' Line of Sight

Abstract

Previous research has shown that many social animals follow the gaze of other individuals. However, knowledge about how this skill differs between species and whether it shows a relationship with genetic distance from humans is still fragmentary. In the present study of gaze following in great apes, we manipulated the nature of a visual obstruction and the presence/absence of a target. We found that bonobos, chimpanzees, and gorillas followed gaze significantly more often when the obstruction had a window than when it did not, just as human infants do. Additionally, bonobos and chimpanzees looked at the experimenter's side of a windowless obstruction more often than the other species. Moreover, bonobos produced more double looks when the barrier was opaque than when it had a window, indicating an understanding of what other individuals see. The most distant human relatives studied, orangutans, showed few signs of understanding what another individual saw. Instead, they were attracted to the target's location by the target's presence, but not by the experimenter's gaze. Great apes' perspective-taking skills seem to have increased in the evolutionary lineage leading to bonobos, chimpanzees, and humans.

The goggles experiment: can chimpanzees use self-experience to infer what a competitor can see?

“…On top of that, subjects did not get training with the exact test situation (while they received an average of six sessions of experience with the requirements in the training). However, previous studies (Hare, Call, & Tomasello, 2006;Melis et al 2006;Okamoto-Barth et al 2007;Tomasello et al 1999) and ours consistently support the view that chimpanzees know what others can and cannot see in various situations, and that they can use this knowledge strategically in competitive or food-begging contexts (see also Br€ auer, Bulloch, Boysen, & Furlong, 2008;Hostetter, Cantero, & Hopkins, 2001;Hostetter, Russell, Freeman, & Hopkins, 2007;Tempelmann, Kaminski, & Liebal, 2011).…”

“…One reason for this might be that our subjects face more ecological challenges (e.g. snakes, more food competition) than the zoo animals in the study by Okamoto-Barth et al (2007), and they might thus be more sensitive to gaze. It could also be that a flat barrier close to one's face is rather rare and its effect less often experienced in everyday life (and thus more likely not be taken into account) than gaze-obscuring obstacles at some distance from another individual's eyes.…”

“…they take into account the presence of barriers, Okamoto-Barth et al 2007), and stop following the gaze of someone who repeatedly looks towards nothing , in experiment 2 chimpanzees had unlimited time to think about which box to choose. Although in humans, sociocognitive processes such as perspective taking have been proven to be fast and sometimes even involuntary (e.g.…”

Knowledge as a Mental State

“…Nonhuman primates can be very responsive to each others' behavior. For example, they track where their conspecifics are looking, following the direction of their gaze (Tomasello, Call, & Hare, 1998) in a way that is sensitive to the presence or absence of opaque barriers blocking the gazer's line of sight (Okamoto--Barth, Call, & Tomasello, 2007). The question of whether they are capable of mental state recognition is however difficult to assess.…”

Rhesus monkeys show human-like changes in gaze following across the lifespan

“…First, we examined whether monkeys co-oriented by looking upwards. Such co-orienting behaviours can stem from different underlying psychological processes-from reflexive response to others' orientation, to more complex inferences about others' line of sight and perceptual experience [21,22,55,56]. We, therefore, also examined two additional features of their behaviour to disentangle the cognitive mechanisms mediating their responses.…”