Cognitive Components of Vocal Communication: A Case Study

Abstract

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.

Keywords: babbling; cognition; communication; development; dialects; food calls; pygmy marmosets; sound localization; vocalization.

Figure 1

Wild pygmy marmoset feeding on exudate (Photo: Pablo Yepez).

Figure 2

Instrumental use of babbling to deter aggression as a function of age (binomial test p = 0.046).

Figure 3

Squeal series were produced almost exclusively in feeding contexts (p < 0.001), whereas single squeals were given as well to nonfood items and in the absence of any objects.

Figure 4

Mean rate of squeal series calling (+S.E.M.) in response to food is unrelated to food preference (R_S = 0.30). Foods are ordered from most preferred on left to least preferred on right.

Figure 5

More squeal series given to high preference portable foods but to low preference non portable food (F = 36.99, p < 0.001).

Figure 6

Both alerting calls alone and alerting calls combined with food calls given by unmated compared with mated marmosets (p’s < 0.04).