Abstract
When exposed to enhanced background noise, humans avoid signal masking by increasing the amplitude of the voice, a phenomenon termed the Lombard effect. This auditory feedback-mediated voice control has also been found in monkeys, bats, cetaceans, fish and some frogs and birds. We studied the Lombard effect for the first time in a phylogenetically basal primate, the grey mouse lemur, Microcebus murinus. When background noise was increased, mouse lemurs were able to raise the amplitude of the voice, comparable to monkeys, but they did not show this effect consistently across context/individuals. The Lombard effect, even if representing a generic vocal communication system property of mammals, may thus be affected by more complex mechanisms. The present findings emphasize an effect of context, and individual, and the need for further standardized approaches to disentangle the multiple system properties of mammalian vocal communication, important for understanding the evolution of the unique human faculty of speech and language.
Highlights
A cross-cultural phenomenon of human speech is the Lombard effect (Lombard, 1911), the capability to compensate masking in background noise by adjusting voice amplitude
We provide the first evidence for a moderate Lombard effect in a phylogenetically basal, nocturnal primate
The gray mouse lemur is able to adjust the voice amplitude of the short whistle call, i.e., the high frequency general disturbance call, when exposed to background noise, covering the call’s spectral content, in line with comparable findings in monkeys, e.g., for different call types given in social isolation by cotton-top tamarins (Egnor & Hauser, 2006; Hotchkin, Parks & Weiss, 2015) and marmosets (Brumm et al, 2004)
Summary
A cross-cultural phenomenon of human speech is the Lombard effect (Lombard, 1911), the capability to compensate masking in background noise by adjusting voice amplitude. A feedback-mediated control of voice amplitude has been described for non-human mammals such as monkeys, whales and dolphins, bats, rodents and cats (Hotchkin & Parks, 2013), and fish (Holt & Johnston, 2014), but not for all studied frogs (Schwartz & Bee, 2013), birds (Schuster et al, 2012) and mammals (Miksis-Olds & Tyack, 2009). The Lombard effect depended on the call type and the context, in which the call type was emitted. These conflicting findings in mammals and the fact that non-human mammals have been relatively poorly studied compared to frogs and birds (Hotchkin & Parks, 2013) reflect the need for studies of natural communication situations in other mammalian species
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