Compensatory mechanisms affect sensorimotor integration during ongoing vocal-motor acts in marmoset monkeys

In vertebrates, any transmission of vocal signals faces the challenge of acoustic interferences such as heavy rain, wind, animal, or urban sounds. Consequently, several mechanisms and strategies have evolved to optimize the signal-to-noise ratio. Examples to increase detectability are the Lombard effect, an involuntary rise in call amplitude in response to masking ambient noise, which is often associated with several other vocal changes such as call frequency and duration, as well as the animals capability of limiting calling to periods where noise perturbation is absent. Previous studies revealed rapid vocal flexibility and various audio-vocal integration mechanisms in marmoset monkeys. Using acoustic perturbation triggered by vocal behavior, we investigated whether marmoset monkeys are capable of exhibiting changes in call structure when perturbing noise starts after call onset or whether such effects only occur if noise perturbation starts prior to call onset. We show that marmoset monkeys are capable of rapidly modulating call amplitude and frequency in response to such perturbing noise bursts. Vocalizations swiftly increased call frequency after noise onset indicating a rapid effect of perturbing noise on vocal motor pattern production. Call amplitudes were also affected. Interestingly, however, the marmosets did not exhibit the Lombard effect as previously reported but decreased their call intensity in response to perturbing noise. Our findings indicate that marmosets possess a general avoidance strategy to call in the presences of ambient noise and suggest that these animals are capable of counteracting a previously thought involuntary audio-vocal mechanism, the Lombard effect, presumably via cognitive control processes.