Previous experimental research has suggested that chimpanzees may understand some of the epistemological aspects of visual perception, such as how the perceptual act of seeing can have internal mental consequences for an individual's state of knowledge. Other research suggests that chimpanzees and other nonhuman primates may understand visual perception at a simpler level; that is, they may at least understand seeing as a mental event that subjectively anchors organisms to the external world. However, these results are ambiguous and are open to several interpretations. In this Monograph, we report the results of 15 studies that we conducted with chimpanzees and preschool children to explore their knowledge about visual perception. The central goal of these studies was to determine whether young chimpanzees appreciate that visual perception subjectively links organisms to the external world. In order to achieve this goal, our research incorporated three methodological objectives. First, we sought to overcome limitations of previous comparative theory of mind research by using a fairly large sample of well-trained chimpanzees (six to seven animals in all studies) who were all within 8 months of age of each other. In contrast, previous research has typically relied on the results of one to four animals ranging widely in age. Second, we designed our studies in order to allow for a very sensitive diagnosis of whether the animals possessed immediate dispositions to act in a fashion predicted by a theory of mind view of their psychology or whether their successful performances could be better explained by learning theory. Finally, using fairly well-established transitions in preschool children's understanding of visual perception, we sought to establish the validity of our nonverbal methods by testing predictions about how children of various ages ought to perform. Collectively, our findings provide little evidence that young chimpanzees understand seeing as a mental event. Although our results establish that young chimpanzees both (a) develop algorithms for tracking the visual gaze of other organisms and (b) quickly learn rules about the configurations of faces and eyes, on the one hand, and subsequent events, on the other, they provide no clear evidence that these algorithms and rules are grounded in a matrix of intentionality. Particularly striking, our results demonstrate that, even though young chimpanzee subjects spontaneously attend to and follow the visual gaze of others, they simultaneously appear oblivious to the attentional significance of that gaze. Thus, young chimpanzees possess and learn rules about visual perception, but these rules do not necessarily incorporate the notion that seeing is "about" something. The general pattern of our results is consistent with three different possibilities. First, the potential existence of a general developmental delay in psychological development in chimpanzees (or, more likely, an acceleration in humans) leaves open the possibility that older chimpanzees may display e...

Gaze folloll'ing is a behal'ior that drall's the human infant into perceptual colltact lI'ith objects or evellts in the 1I'0rld to II'hich others are attending. One interpretation of the development of this phenomenon is that it signals the emergence ofjoint or shared attention, II'hich may be critical to the developmellt oftheory of mind. An alternatil'e interpretation is that gaze folloll'ing is a noncognitive mechanism that exploits social stimuli in order to orient the infant (or adult) to importall1 evell1s in the world. We report experimental results that chimpanzees display the effect in response to both mOl'ement ofthe head and eyes in concert and eye mOl'emellt alone. Additional tests indicate that chimpanzees appear able to (a) project all imaginary line of sight through inl'isible space and (b) understand hall' that line of sight can be impeded by solid. opaque objects. This capacity may hm'e arisen because ofits reproductive payoffs in the context of social competition with conspecifics. predation avoidance, or both.

Subjects were asked to indicate the likelihood that each of 30 animals (chosen as exemplars of the major phylogenetic classes) could engage in three complex cognitive tasks. Subjects were also asked to rate the extent to which they felt each animal was similar to themselves and whether they felt the animal experienced the world in a manner similar to the way they experienced it. The results showed that in all cases the perceived similarity and inferred cognitive abilities of animals proceeded from lesser to greater in the following order: invertebrates, fish, amphibians, reptiles, birds, mammals (excluding dogs, cats, and primates). For pets (dogs and cats) and primates, there was a marked increase in perceived similarity and in the tendency to make attributions about complex cognitive characteristics. The data are discussed in the context of viewing anthropomorphism as a derivative of our ability to infer the mental states of conspecifics-an ability that evolved as a consequence of the need to take into account the experience and intentions of other humans. Although we routinely generalize this capacity to species other than our own, the evidence that the effects are reciprocal is extremely limited.

No abstract