Limiting parental feedback disrupts vocal development in marmoset monkeys.

Vocalizations of human infants undergo dramatic changes across the first year by becoming increasingly mature and speech-like. Human vocal development is partially dependent on learning by imitation through social feedback between infants and caregivers. Recent studies revealed similar developmental processes being influenced by parental feedback in marmoset monkeys for apparently innate vocalizations. Marmosets produce infant-specific vocalizations that disappear after the first postnatal months. However, it is yet unclear whether parental feedback is an obligate requirement for proper vocal development. Using quantitative measures to compare call parameters and vocal sequence structure we show that, in contrast to normally raised marmosets, marmosets that were separated from parents after the third postnatal month still produced infant-specific vocal behaviour at subadult stages. These findings suggest a significant role of social feedback on primate vocal development until the subadult stages and further show that marmoset monkeys are a compelling model system for early human vocal development.