Great apes can use self-experience to anticipate others’ actions, providing yet more evidence of a theory of mind in non-human animals.
Theory of mind is the ability to understand and anticipate the thoughts of others, even when they conflict with one’s own.
The skill, long thought to be unique to humans, underpins many important aspects of human communication, cooperation and culture, according to the researchers.
Lead author Fumihiro Kano, of Kyoto University, Japan, and colleagues had previously shown that great apes are capable of a key feature of theory of mind – false belief. Even if they know a hidden item is no longer in a given location, apes can correctly anticipate where human actors will look for it.
“We initially created a movie based on an established psychological test, especially exciting for apes, and combined this with eye-tracking technology to record gaze patterns indicating anticipation of an agent’s behaviour based on an understanding of the agent’s false belief.” Kano explains.
Theory of mind in apes and other animals is hotly contested, despite mounting evidence. One of the untested alternative explanations for the previous research is that the apes are simply applying a behaviour rule, which is that agents (humans, animals) tend to search for things where they last saw them.
In this latest study, published in the journal PNAS, Kano and colleagues challenged the behaviour rule account by building upon the same video model, adding in a visual barrier.
The test, known as “goggles test” or “trick blindfold task” had been successfully used when studying theory of mind in 18-month-old human children.
To carry out the study, great apes of three species: chimpanzee (Pan troglodytes), bonobo (Pan paniscus), and orangutan (Pongo abelii) were separated into two groups, and exposed to different visual barriers – one opaque, the other translucent or partly see-through.
After familiarisation, all apes were shown the same video footage while hooked up to visual tracking tech gear and sucking juice from a specially developed straw.
The video shows an actor hiding an object in a box. The actor then scuttles behind a barrier. A man dressed in a Kong suit moves the object to another box, then removes the object completely. The actor returns from behind the barrier and reaches slowly towards the two boxes. The visual tracking tech follows the eye movement of the apes.
The team observed that those apes who had been familiarised with the opaque barrier anticipated that the actor would go to the location based on their false belief – as the barrier indicated the actor had not seen the object removal.
Conversely, the apes exposed to the translucent barrier anticipated that the actor would go to neither location, correctly attributing a belief to the actor that the object had been removed entirely.
The researchers conclude that their findings rule out a purely behavioural explanation, because the two groups of apes anticipated the agent’s behaviour based on their own experiences with the barriers, even when both groups had observed the actor acting in an identical manner.
“We are excited to find that great apes actually passed this difficult test,” says Kano. “The results suggest that we share this ability with our evolutionary cousins.” He adds that they plan to continue testing other non-cognitive alternatives to the theory of mind in nonhuman animals.