Cognitive Components of Vocal Communication: A Case Study.

Abstract

Simple SummaryThe pygmy marmoset is the world’s smallest true monkey with a mean brain size of 4.5 g. I review the cognitive and pre-linguistic skills that these monkeys show in their vocal communication. Pygmy marmosets have several types of calls used to maintain contact with one another, and they use calls that are cryptic when they are close to group members, and calls that more easily detected when they are farther away. They take turns in contact calling. They modify their call structure when in a new social setting to match the structure of other group members or of mates. Infants display babbling behavior similar to human infants, and adult caretakers provide social reinforcement that lead infants to develop adult like calls. Thus, pygmy marmosets modify vocal structure and learn through social interactions. This contrasts sharply with the general view that most nonhuman primates do not display vocal learning or an ability to modify call structure. Pygmy marmosets signal other group members when they find food using specialized calls but inhibit these calls with living prey. These complex cognitive skills in communication indicate that brain size may not be a good predictor of cognitive ability.Communication among nonhuman animals is often presented as rigid and inflexible, reflecting emotional states rather than having any cognitive basis. Using the world’s smallest monkey, the pygmy marmoset (Cebuella pygmaea), with the smallest absolute brain size amongst simian primates as a case study, I review the role of cognition in the development and usage of vocalizations in pygmy marmosets and present new data on the instrumental use of babbling and of food associated vocalizations. Pygmy marmosets have several contact calls that differ in the psychoacoustic properties for sound localization as well as the distance at which they carry through the rainforest. Marmosets use these calls strategically based on distance from neighbors. Marmosets alter spectral and temporal aspects of call structure when exposed to new groups and when newly mated. They display population specific vocal dialects. Young pygmy marmosets engage in extensive babbling behavior rewarded by parents that helps the young develop adult vocal structures, but older monkeys also use babbling instrumentally in conflict situations. Specific food referential calls generally relate to food preferences, but food calls are suppressed in the presence of animate prey. Unmated animals systematically combine a long distance call with food calls as though advertising for mates. Taken together, these examples show that even small brained primates use their vocal signals flexibly and strategically in response to a variety of environmental and social conditions.