Symbolic Representation by Pigeons

The capacity for symbolic representation is a prerequisite for the development of human language because words, the basic units of language, are symbols that represent things. But symbolic representation may also serve a nonlinguistic role of organizing events into categories having the same meaning, and such a capacity could have considerable survival value for many species. In a number of experiments, my co-workers and I have found that pigeons that are trained to treat two different stimuli similarly also learn that those stimuli are commonly represented and, thus, that they have the same meaning. We have demonstrated evidence for such common representations in a number of ways, but perhaps the most convincing is when pigeons learn a new association involving one of the presumed commonly represented stimuli, and without further training demonstrate that they have learned a similar association involving the other stimulus. Furthermore, we have found that when pigeons are trained to treat two stimuli similarly, one of those stimuli is represented in terms of the other. These results have implications not only for the generality of cognitive processes across species, but also for the generality of symbolic representation beyond language use.