ABSTRACT
Many animals use various “ special” (species-specific) mechanisms to enhance the processing of information in biologically relevant communication signals. While frogs use low-level peripheral filtering in decoding conspecific vocaliza tions (Capranica, Frishkopf, & Nevo, 1973), monkeys use higher-level mecha nisms that implicate semantic communication (Seyfarth, Cheney, & Marler, 1980) and selective attention (Petersen, 1982). As humans, we are most familiar with the special aspects of our own communication system, which uses internal cognitive structures (i.e., sentences) to impose grammatical relationships on speech (Chomsky, 1967; Miller, 1962). Human sentence formation is difficult, if at all possible, for nonhumans to acquire (Terrace, Petitto, Sanders, & Bever, 1979). Nevertheless, it seems appropriate from an evolutionary orientation to search for rudimentary internal cognitive structures in animals by examining the processing of their own conspecific communication signals.
