American Scientist

MINDREADING ANIMALS: The Debate over What Animals Know about Other Minds. Robert W. Lurz. xviii + 245 pp. The MIT Press, 2011. $35.

Does your dog know what you are thinking? Can a chimpanzee understand what another sees? In the three and a half decades since David Premack and Guy Woodruff first asked whether chimpanzees have a “theory of mind,” a considerable empirical and philosophical literature has sprung up around what has come to be called “mind reading” in animals. Theory of mind, as Premack and Woodruff defined it, is the ability to attribute perceptual and cognitive states to others. This is not about telepathy, but about whether any animals besides humans have the capacity to attribute such states to others. Numerous experimental tests and other observations have been offered in favor of animal mind reading, and although many scientists are skeptical, others assert that humans are not the only species capable of representing what others do and don’t perceive and know.

Robert Lurz, a philosopher at Brooklyn College, CUNY, surveys the experiments at the heart of the debate and finds that not one of them solves what he calls “the logical problem” in animal mind-reading research. The logical problem is that for any mind-reading hypothesis, it seems possible to construct a complementary “behavior-reading” hypothesis that makes exactly the same predictions but is assumed to be less cognitively demanding. The basic point is that whatever mind reading is, it is not magic, and thus depends on ordinary, perceivable cues—but these same cues are then available as a basis for expectations about actions that an animal might take without making any mental attribution. If you see me gazing at a piece of cake with a certain look on my face, you may infer that I’m thinking about eating it, or you might instead directly form some expectations about my cake-directed behavior without imagining what I might be thinking about it.

Lurz argues that all previous experiments conducted or proposed to test mind reading in animals suffer from some version of this problem. For example, he notes, Brian Hare and colleagues ran an experiment in which a subordinate and a dominant chimpanzee could compete for two pieces of food. One of the pieces was hidden so that the dominant animal could not see it because of an opaque barrier blocking the line of gaze to the food item. The subordinate chimpanzee, who had an unobstructed view from the other side of the barrier, preferentially went for the piece that the dominant could not see, leading the researchers to argue that the subordinate chimpanzee attributed to the dominant a state of ignorance about the presence of this food item. But Lurz points out that the subordinate need only make the behavioral prediction that the dominant will not attempt to retrieve a piece of food for which it lacks a direct line of gaze. The subordinate animal does not need to attribute any states of seeing or knowing to the dominant to make this behavioral prediction.

The fact that Lurz finds all prior experiments lacking does not, however, make him an outright skeptic about animal mind reading. In the second half of the book he offers a number of experiments, variously designed to be appropriate for some of the species that have been tested for mind reading so far: chimpanzees, dogs, ravens and scrub jays. To solve the logical problem, Lurz must devise situations in which the mind-reading hypothesis makes a different prediction than does the complementary behavior-reading hypothesis. Because his proposed experiments are somewhat complex, it is not possible to spell them out in detail in this short review. But they all turn on the possibility that members of these species might be capable of making basic appearance-reality distinctions. For instance, one suggested experiment involves chimpanzees; real, yellow bananas; orange-colored fake bananas; and a red translucent barrier that makes yellow bananas appear orange. Lurz speculates that a mind-reading chimpanzee who has been familiarized with the effects of the red barrier on how bananas appear could use its knowledge to predict how a dominant animal might act. To wit, a dominant animal who is unfamiliar with the red barrier and whose line of gaze passes through it to a yellow banana would be unlikely to compete for that apparently orange banana. The subordinate chimpanzee would therefore try to retrieve the banana that lies behind the red filter. According to Lurz, a chimpanzee that is using a complementary behavioral strategy would not make the same prediction because its experience is that dominants always attempt to retrieve yellow bananas to which they have a direct line of gaze. That is, to predict that the dominant would not try to retrieve the banana behind the colored barrier, the subordinate chimp would have to know that the dominant saw the banana through the barrier and that its view of the banana was colored by it. A chimpanzee lacking this knowledge and relying on a behavioral strategy would not try to retrieve the banana.

Lurz does not claim that this experiment eliminates every alternative behavior-reading hypothesis, mentioning, for example, that experiments based on something other than the dominant’s line of gaze might still apply. Indeed, he thinks that no single experiment can eliminate all possibility that a behavior-reading hypothesis might explain the chimpanzee’s actions. Rather, his point is that such experiments could be used to distinguish between a specific mind-reading hypothesis and its complementary behavior-reading hypothesis.

Complicated as the experiments proposed for mind-reading perceptual states may be, at least they don’t depend on the kind of heavy philosophical machinery that Lurz is forced to bring out for the notion of belief that is pursued in chapter 4. One issue here is that most philosophers treat beliefs as the relationship of a believer to an abstract “proposition” (corresponding to the meaning of a declarative sentence that can be true or false), whereas Lurz argues the better model is a relationship between believer and “states of affairs” (equally abstract, but less tied to sentences and the concepts of truth and falsity). As a philosopher who has tried to defend belief attributions to nonhuman animals, I am sympathetic to Lurz’s motivations here, but I suspect that most scientists will think that the philosophical abstractions are too murky to admit clear empirical tests.

There is much to be learned from reading this book, especially from the clarity that Lurz brings to his discussion of the logical problem. Nevertheless, the book feels incomplete. Chapter 3, on attribution of perceptual states, has as its very last sentence, “The issue is now in the hands of the experimentalists—and, of course, the animals.” Chapter 4, on attributing beliefs, ends almost identically: “The rest is now in the hands of empirical researchers—and, of course, the animals.” I applaud philosophers’ desire to contribute to empirical research, but I suspect that many scientists will wonder why it is acceptable for a philosopher to publish what is essentially a research proposal, rather than doing what scientists do: Apply for funding to carry out the experiments, or find collaborators willing to do them. My suspicion is that Lurz’s designs are rather more complicated and the inferences rather more fraught than would make funding agencies or experimentalists comfortable committing time and resources. He mentions in the preface that he has begun working with other researchers to test them in pilot studies. It will be interesting to see the results of this work. In the meantime, we can expect the steady flow of more-typical scientific studies of animal mind reading to continue. Lurz has provided a valuable guide to assessing a critical aspect of such experiments. But even if the logical problem remains experimentally unsolved, more tractable experiments, including those conducted in natural social conditions, may still contribute to scientific understanding of how animals exploit cues relevant to what others do and don’t know.

Colin Allen is professor in the Cognitive Science Program and the Department of History and Philosophy of Science at Indiana University. His research interests include animal cognition, the philosophical foundations of cognitive science and digital applications for the humanities.