Data from: Vocal learning via social reinforcement by infant marmoset monkeys

For over half a century now, primate vocalizations have been thought to
undergo little or no experience-dependent acoustic changes during
development [ 1 ]. If any changes are apparent, then they are routinely
(and quite reasonably) attributed to the passive consequences of growth.
Indeed, previous experiments on squirrel monkeys and macaque monkeys
showed that social isolation [ 2, 3 ], deafness [ 2 ], cross-fostering [ 4
] and parental absence [ 5 ] have little or no effect on vocal
development. Here, we explicitly test in marmoset monkeys—a very vocal and
cooperatively breeding species [ 6 ]—whether the transformation of
immature into mature contact calls by infants is influenced by contingent
parental vocal feedback. Using a closed-loop design, we experimentally
provided more versus less contingent vocal feedback to twin infant
marmoset monkeys over their first 2 months of life, the interval during
which their contact calls transform from noisy, immature calls to tonal
adult-like “phee” calls [ 7, 8 ]. Infants who received more contingent
feedback had a faster rate of vocal development, producing mature-sounding
contact calls earlier than the other twin. The differential rate of vocal
development was not linked to genetics, perinatal experience, or body
growth; nor did the amount of contingency influence the overall rate of
spontaneous vocal production. Thus, we provide the first experimental
evidence for production-related vocal learning during the development of a
nonhuman primate.