Cognitive Components of Vocal Communication: A Case Study

The 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