Comparative Bioacoustics Group, Max Planck Institute for Psycholinguistics, Wundtlaan 1, 6525 XD Nijmegen, The Netherlands.
Research Department, Sealcentre Pieterburen, Hoofdstraat 94-A, 9968 AG Pieterburen, The Netherlands.
Philos Trans R Soc Lond B Biol Sci. 2021 Dec 20;376(1840):20200456. doi: 10.1098/rstb.2020.0456. Epub 2021 Nov 1.
Vocal plasticity can occur in response to environmental and biological factors, including conspecifics' vocalizations and noise. Pinnipeds are one of the few mammalian groups capable of vocal learning, and are therefore relevant to understanding the evolution of vocal plasticity in humans and other animals. Here, we investigate the vocal plasticity of harbour seals (), a species with vocal learning abilities observed in adulthood but not puppyhood. To evaluate early mammalian vocal development, we tested 1-3 weeks-old seal pups. We tailored noise playbacks to this species and age to induce seal pups to shift their fundamental frequency (), rather than adapt call amplitude or temporal characteristics. We exposed individual pups to low- and high-intensity bandpass-filtered noise, which spanned-and masked-their typical range of ; simultaneously, we recorded pups' spontaneous calls. Unlike most mammals, pups modified their vocalizations by lowering their in response to increased noise. This modulation was precise and adapted to the particular experimental manipulation of the noise condition. In addition, higher levels of noise induced less dispersion around the mean , suggesting that pups may have actively focused their phonatory efforts to target lower frequencies. Noise did not seem to affect call amplitude. However, one seal showed two characteristics of the Lombard effect known for human speech in noise: significant increase in call amplitude and flattening of spectral tilt. Our relatively low noise levels may have favoured modulation while inhibiting amplitude adjustments. This lowering of is unusual, as most animals commonly display no such shift. Our data represent a relatively rare case in mammalian neonates, and have implications for the evolution of vocal plasticity and vocal learning across species, including humans. This article is part of the theme issue 'Voice modulation: from origin and mechanism to social impact (Part I)'.
发声可塑性可以响应环境和生物因素而发生，包括同种动物的发声和噪声。鳍足类动物是少数几种具有发声学习能力的哺乳动物之一，因此对于理解人类和其他动物发声可塑性的进化具有重要意义。在这里，我们研究了港海豹（）的发声可塑性，这种动物在成年期具有发声学习能力，但在幼年期则没有。为了评估早期哺乳动物的发声发育，我们测试了 1-3 周大的海豹幼崽。我们根据该物种和年龄定制了噪声回放，以诱导海豹幼崽改变其基频（），而不是适应叫声幅度或时间特征。我们将个体幼崽暴露于低强度和高强度带通滤波噪声中，这些噪声涵盖并掩盖了它们典型的范围；同时，我们记录了幼崽的自发叫声。与大多数哺乳动物不同，幼崽通过降低来响应增加的噪声来改变它们的发声。这种调制是精确的，并适应于噪声条件的特定实验操作。此外，更高水平的噪声导致的平均降低幅度较小，这表明幼崽可能积极集中发声努力以达到更低的频率。噪声似乎没有影响叫声幅度。然而，一只海豹表现出了两个在人类噪声中的言语 Lombard 效应的特征：叫声幅度显著增加和频谱倾斜变平。我们相对较低的噪声水平可能有利于基频调制，而抑制幅度调整。这种基频降低是不寻常的，因为大多数动物通常不会表现出这种基频变化。我们的数据代表了哺乳动物新生儿中相对罕见的情况，对于物种间发声可塑性和发声学习的进化具有重要意义，包括人类。本文是主题为“声音调制：从起源和机制到社会影响（第一部分）”的系列文章的一部分。
