Can free-ranging rhesus monkeys (Macaca mulatta) extract artificially created rules comprised of natural vocalizations?

Though nonhuman animals lack anything like a set of grammatical structures in their natural vocalizations, studies now suggest that at least some animals can extract patterns from a structured input that appear abstract and rule-like. The authors continue this line of research by adding three new methodological contributions, specifically, tests of (1) a free-ranging animal population (as opposed to captive laboratory subjects), (2) a new taxonomic group (i.e., Old World monkeys: rhesus macaques, Macaca mulatta), and (3), the presentation of artificially sequenced strings of species-specific vocalizations (as opposed to artificial symbols or speech stimuli). Specifically, the authors created artificial strings of rhesus vocalizations in the pattern notated as AAB (i.e., two identical calls [AA] followed by a different one [B]) or ABB. Following habituation to AAB strings, rhesus monkeys showed significantly more orienting responses to novel ABB strings than to novel AAB strings. Further, following habituation to an ABB pattern, rhesus responded more in test trials to AAB than ABB. These results, combined with other parallel studies, suggest that animals can extract an identity relationship from an artificial sequence of sounds, and can do so even though the tokens are species-specific vocalizations that are never produced in this sequence.