|Meaning and Mind in Monkeys|
|(revised November 15, 1997)|
Seyfarth, Robert M. and Dorothy L. Cheney (1992). Meaning and Mind
Nonhuman primates, such as vervet monkeys, seem to communicate in ways that resemble aspects of human speech. But they do not seem to recognize mental states in others. Scientific American, December 1992.
"In our studies, we have tried to determine whether monkeys have words
for things, such as predators, or understand, as we do, that particular
sounds represent features of their environment: in other words, do monkeys
think? We have also sought to examine whether monkeys have mental states
such as knowledge, belief or desire and, perhaps most important, if monkeys
do have mental states, whether they recognize that others do as well."
The common assumption has been that "Human words represented objects and events in the external world; the calls of monkeys and apes represented only an individual's emotional state or imminent behavior" (122).
Thomas Struhsaker reported in 1967 that vervets gave distinct alarm calls in response to spotting three predators (leopards, eagles, and snakes), and the listeners would appropriately in each case. The calls appear to function as "representational, or semantic, signals" (125).
"When one vervet hears another give an eagle alarm call, the listener responds as if it had seen the eagle itself. This behavior suggests that in the monkey's mind the call "stands for" or "conjures up images of" an avian predator even when the monkey has not yet see the eagle" (125). In the language of memory, Seyfarth and Cheney is making the proposition that vervets have evolved explicit categorical (semantic) recall (cf. On Memory).
After a series of habituation experiments designed to test if the vervets
responded to differences in relevant symbolic meaning rather than acoustic
similarity, Seyfarth and Cheney concludes, "Our findings suggest that when
one vervet monkey hears another vocalize, the listener forms a representation
of what that call means" (126).
Theory of Mind
Human beings make inferences about the knowledge, beliefs, and motives of others in order to understand and predict their behavior. There is some evidence that chimpanzees have an incipient theory of mind; however, monkeys apparently do not.
While "animals are clearly sensitive to the presence or lack of an audience,"
there is "considerable evidence suggests that animals cannot recognize
the distinction between an ignorant audience and a knowledgeable one" (126-7).
Infant vervets learn calls by observation, and often make mistakes. Some
errors are inconsequential; others, "such as that made by an infant who
looks up in the air when he or she hears a snake alarm, are more serious,
and they actually increase the infant's risk of being taken" (128).
Note that this is similar to human language learning: this is instinctual, learned by observation alone-you do not teach a child to speak through reward and punishment. This could be further evidence that the origins of language are older than ToMM, as suggested by the vervet data. Seyfarth and Cheney conclude,
Under these conditions, one might expect adults to intervene and help their infants learn about predators. Somewhat surprisingly, they do not. Despite extensive observations and experiments, we have found no evidence that adults selectively encourage infants who have given alarm calls appropriate to the predators, nor do adults correct infants who have responded to an alarm call inappropriately. Infant vervets learn by observation alone, without explicit tutelage. Such reliance on observational learning is widespread among animals and can, in our view, ultimately be traced to the adults' failure to recognize that their offspring's knowledge is different from their own. (128)
Although much of human communication is designed to influence the knowledge, beliefs and motives that underlie behavior, there is no evidence at present that monkeys ever communicate with the intent of influencing another animal's mental state. (128)