Anemone's Research Emporium

A Brief History of Theory of Mind (ToM)

Part 1: Do apes think?

Anemone Cerridwen
April 17, 2009

Theory of mind (ToM) got its start with a 1978 paper by David Premack and Guy Woodruff, in which they asked: do chimpanzees impute mental states to themselves and others?

Behaviourism had dominated English-language psychology for many decades by this point, with its emphasis on reflexive learning (Pavlovian or operant conditioning) and pure behaviour over thinking (mentalism) in humans and other animals. Now, we know that we think (at least some of the time), but for years many people were perfectly happy to think of humans and other species as being purely empty-headed behaviourists, mindlessly behaving the way they do, or even thinking they way they do, because of positive reinforcement resulting from trial and error ("it worked the last time") rather than analyzing their environment and choosing which action to take - for example rats in mazes. Rats run mazes to get cheese, so they take the route that gets them the cheese. It becomes automatic: if the rat turns right here, it gets the cheese, so it turns right here reflexively once it learns that this is the correct route. Turning right is reinforced by getting cheese, and it becomes a mindless habit. (But rats will sometimes choose an alternate route just to check it out, instead of restricting themselves to tried and true routes. This is adaptive in the wild.) And if animals didn't think about what they did, they certainly didn't think about what other animals did, and why they did it. Premack and Woodruff took a sharp break from this tradition when they suggested that chimpanzees have a theory of mind.

"An individual has a theory of mind if he imputes mental states to himself and others."
[Premack and Woodruff: 515, in abstract]

That is, a theory of mind is the ability to theorize about what's going on inside the mind of another being. The theory does not need to be correct, it just needs to exist as a theory about another being's mental state. What does this other being think? feel? believe? want? fear? What are its intentions or motivations?

Premack and Woodruff were not interested in exploring whether chimps can master complex imbedded inferences: "Mary knows that John thinks he will win," "Harry doubts that Mary knows that John thinks he will win" (Premack and Woodruff: 515). People get uncomfortable by about four steps (except in The Princess Bride, when it's comedy). The authors didn't expect apes to manage even that many, but even if they did, how would you test it? Instead, they kept it fairly simple.

They were able to demonstrate that chimpanzees have a basic theory of mind by showing a chimp named Sarah videos of an actor trying to solve problems, then showing her photos of various possible solutions. She chose the correct solution often enough to indicate she knew that the actor was trying to get the bananas that were out of reach, etc. In other words, she knew what was going on in the actor's mind.

Premack and Woodruff considered this theory of mind to be very basic, found in children and chimps, but perhaps not in well educated adult humans who know better. It is normal to assign meaning to situations in describing them (the man is trying to reach the bananas), except when people are trained to be purely descriptive (the man is standing under the bananas with his arms up, and is jumping up and down). Young children even assign meaning when there is none: for example, when an inanimate object moves, they assume it has purpose (the wind is trying to move those leaves).

"The important point here is that assigning mental states to another individual is not a sophisticated or advanced act, but a primitive one." [Premack and Woodruff: 525]

A lively discussion ensued (comments in same journal issue) and some critiquers suggested the false belief test: put something in a container with two chimps watching, then move it when one chimp is watching and the other one isn't. Then somehow see if you can figure out if the chimp in the know is aware the other chimp isn't - not easy without language. If the chimp in the know laughs, you know it sees the discrepancy, but if it doesn't react, then you haven't learned anything either way. However, if animals could talk, they could tell you what was going on in their minds.

From here it was only logical to try it out on children.

Reference

David Premack and Guy Woodruff, 1978. Does the chimpanzee have a theory of mind? Behavioral and Brain Sciences 4:515-526. See also comments and reply pages 555-629 in the same journal issue.