What is or isn't a theory of mind? Part 2: Theories of mind and theories of mind

I said a while ago I'd return to theories of mind after reading up a bit more on primate cognition.  I have, now, and so I shall.  But first, the one that got away.

When I first got started on this thread, I ran across a paper discussing what kind of experiment might show other primates to have a theory of mind.  There were two points: First, that existing experiments (at the time) could be explained away by simple rules like "Non-dominant chimps can follow the gaze of their dominants and associate taking food while the dominant is looking with getting the snot beat out of them."  Second, that there were experiments, in principle, in which positive results could not be plausibly explained away by such rules.

I haven't been able to dig up the paper, but as I recall the gist of the improved experiments was to produce, as I mentioned before, a combinatorial explosion of possibilities, which could be explained more simply by the primate subject having a theory of mind than by a large number of ad-hoc rules.  "Explained more simply" are, of course, three magic words in science.

The scenario involved a dominant chimp, a non-dominant one, food to be stolen, and various doors and windows by which the non-dominant chimp would be able to see what the dominant saw, with or without the dominant seeing that it saw it.

Um, yeah.

For example, the two chimps are in separate rooms, with a row of compartments between them.  The compartments have doors on both sides.  The experimenter places the food in the third of five compartments.  Both doors are open, both chimps can see the food and they can see each other.  The doors are closed (the dominant's first), and the food is moved to compartment one.  The non-dominant sees its door to compartment one open and then the other door.  Does it rush for the food or hang back?  What if it sees that the other door to compartment one was already open?

If we try several different randomly-chosen scenarios with such a setup, a subject with a theory of mind should behave differently with one without, and due to the sheer number of possibilities a "mindless" explanation would have to be hopelessly contrived.

Something like that.  I probably have the exact setup garbled, but the point was to go beyond "Did I see the dominant looking at the food?" to "Where does the dominant think the food is?"  Interesting stuff.


While trying to track that paper down again, I ran across a retrospective by Josep Call and Michael Tomasello entitled Does the chimpanzee have a theory of mind? 30 years later.  I'm not familiar with Call, but Tomasello turns up again and again in research on developmental psychology and the primate mind.  He also has quite a bit to say about language and its development in humans, but that's for a different post (or several).

As with well-written papers in general, the key points of the retrospective are in the abstract:

On the 30th anniversary of Premack and Woodruff’s seminal paper asking whether chimpanzees have a theory of mind, we review recent evidence that suggests in many respects they do, whereas in other respects they might not. Specifically, there is solid evidence from several different experimental paradigms that chimpanzees understand the goals and intentions of others, as well as the perception and knowledge of others. Nevertheless, despite several seemingly valid attempts, there is currently no evidence that chimpanzees understand false beliefs. Our conclusion for the moment is, thus, that chimpanzees understand others in terms of a perception–goal psychology, as opposed to a full-fledged, human-like belief–desire psychology.

In other words, chimps appear to understand that others (both other chimps and those funny-looking furless creatures) can have goals and knowledge, but they don't appear to understand that others have beliefs based on knowledge behind those goals.  For example, if a human is reaching for something inaccessible, a chimp will reach it down for them (at least if the human has been a reliable source of goodies).  If a human is flips a light switch by foot -- an unusual act for a creature lacking prehensile toes -- a chimp is likely to try the same, unless the human's hands were full at the time, suggesting that the chimp is aware that the human had to use their foot in the second case but wanted to in the first.

Naturally, any of the ten cases given in the paper could be explained by other means.  Call and Tomasello argue that the simplest explanation for the results taken together is that chimps understand intention.

Likewise, there is good evidence that chimps understand that others see and know things.  For example, they are more likely to gesture when someone (again, normal or furless) is looking, and they will take close account of who is looking where when trying to steal food.

On the other hand, chimps fail several tests that young humans pass in largely similar form.  For example, if there are two boxes that may contain food, and a dominant and a non-dominant subject both see food placed in it, the subject will not try to take food from the box with food in it.  Makes sense.  The subject knows the dominant knows where the food is.

If they both see the food moved to a second box, the subject will still leave it alone.  If the dominant doesn't see the food moved but the subject does, the subject ought to know that the dominant thinks the food is still in the first box and that it's safe to go for the second (the experiment is set up so that the dominant can effectively only guard one box).

However, it doesn't go for the box with the food in it.  This and other experiments suggest that the subject doesn't know that the dominant doesn't know what it knows.

Um, yeah.

In other words, the subject appears to assume that that, because it knows the food is in the second box, so does the dominant.  "Because" might be a bit strong here ... try again: Chimps understand that others may have their own intentions different from theirs, and that others can know things, but not that others can have knowledge different from theirs.


Call and Tomasello conclude:

It is time for humans to quit thinking that their nearest primate relatives only read and react to overt behavior.   Obviously, chimpanzees’ social understanding begins with the observation of others’ behavior, as it does for humans, but it does not end there. Even if chimpanzees do not understand false beliefs, they clearly do not just perceive the surface behavior of others and learn mindless behavioral rules as a result. All of the evidence reviewed here suggests that chimpanzees understand both the goals and intentions of others as well as the perception and knowledge of others. 

[...]

In a broad construal of the phrase ‘theory of mind’, then, the answer to Premack and Woodruff’s pregnant question of 30 years ago is a definite yes, chimpanzees do have a theory of mind. But chimpanzees probably do not understand others in terms of a fully human-like belief–desire psychology in which they appreciate that others have mental representations of the world that drive their actions even when those do not correspond to reality [I'd argue for "their own perception of reality" here].  And so in a more narrow definition of theory of mind as an understanding of false beliefs, the answer to Premack  and Woodruff’s question might be no, they do not.

I suppose this might sound wishy-washy (chimps have a theory of mind, except no, they don't), but for my money it's insightful, not just concerning the minds of chimps, but the notion that there can be more than one kind of theory of mind.