Abstract
Recent studies purported to demonstrate that chimpanzees, monkeys and corvids possess a basic Theory of Mind, the ability to attribute mental states like seeing to others. However, these studies remain controversial because they share a common confound: the conspecific's line of gaze, which could serve as an associative cue. Here, we show that ravens Corvus corax take into account the visual access of others, even when they cannot see a conspecific. Specifically, we find that ravens guard their caches against discovery in response to the sounds of conspecifics when a peephole is open but not when it is closed. Our results suggest that ravens can generalize from their own perceptual experience to infer the possibility of being seen. These findings confirm and unite previous work, providing strong evidence that ravens are more than mere behaviour-readers.
Highlights
Recent studies purported to demonstrate that chimpanzees, monkeys and corvids possess a basic Theory of Mind, the ability to attribute mental states like seeing to others
It did not control for a memory of past gaze cues, as the competitor was present during the initial caching episode—and so even this elegant design can be explained by appeal to representations of previously observed gaze cues alone[7,8]
Stulp et al.[19] and Shaw and Clayton[20,21] have recently shown that jays can infer the presence of unseen conspecifics on the basis of auditory cues. These findings point the way towards the experimental design reported here, which aims to overcome the line-of-gaze interpretation by controlling for both (i) gaze cues in the test, by relying only on sounds to indicate the presence of a possible competitor and (ii) memories of gaze cues previously observed in the training, by denying the subjects prior access to any competitor’s gaze in contexts resembling the test
Summary
Recent studies purported to demonstrate that chimpanzees, monkeys and corvids possess a basic Theory of Mind, the ability to attribute mental states like seeing to others. Stulp et al.[19] and Shaw and Clayton[20,21] have recently shown that jays can infer the presence of unseen conspecifics on the basis of auditory cues These findings point the way towards the experimental design reported here, which aims to overcome the line-of-gaze interpretation by controlling for both (i) gaze cues in the test, by relying only on sounds to indicate the presence of a possible competitor and (ii) memories of gaze cues previously observed in the training, by denying the subjects prior access to any competitor’s gaze in contexts resembling the test. Rather than another raven being present in the test, the observation room was empty, and a hidden loudspeaker was used to play a series of sounds that were recorded from a competitor raven in the observation chamber during the non-observed condition
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