Vocal tract elongation, which uniformly lowers vocal tract resonances (formant frequencies) in animal vocalizations, has evolved independently in several vertebrate groups as a means for vocalizers to exaggerate their apparent body size. Here, we propose that smaller speech-like articulatory movements that alter only individual formants can serve a similar yet less energetically costly size-exaggerating function. To test this, we examine whether uneven formant spacing alters the perceived body size of vocalizers in synthesized human vowels and animal calls. Among six synthetic vowel patterns, those characterized by the lowest first and second formant (the vowel /u/ as in ‘boot’) are consistently perceived as produced by the largest vocalizer. Crucially, lowering only one or two formants in animal-like calls also conveys the impression of a larger body size, and lowering the second and third formants simultaneously exaggerates perceived size to a similar extent as rescaling all formants. As the articulatory movements required for individual formant shifts are minor compared to full vocal tract extension, they represent a rapid and energetically efficient mechanism for acoustic size exaggeration. We suggest that, by favouring the evolution of uneven formant patterns in vocal communication, this deceptive strategy may have contributed to the origins of the phonemic diversification required for articulated speech.

This article is part of the theme issue ‘Voice modulation: from origin and mechanism to social impact (Part II)’.

声道伸长可以均匀降低动物发声中的声道共振（共振峰频率），它在多个脊椎动物群体中独立进化，作为发声者夸大其表观身体尺寸的一种手段。在这里，我们提出，仅改变单个共振峰的较小的类似语音的发音运动可以起到类似但能量消耗较小的尺寸夸大功能。为了测试这一点，我们检查了不均匀的共振峰间距是否会改变合成人类元音和动物叫声中发声者的体型大小。在六种合成元音模式中，那些以最低的第一和第二共振峰（元音 /u/ 如“boot”中的元音）为特征的模式始终被认为是由最大的发声者产生的。至关重要的是，在类似动物的叫声中仅降低一两个共振峰也会传达出体型较大的印象，而降低第二个和第三个共振峰同时会夸大感知的尺寸，其程度与重新调整所有共振峰的程度相似。由于与完整声道延伸相比，单个共振峰转变所需的发音运动较小，因此它们代表了一种快速且高效的声学尺寸夸大机制。我们认为，通过促进声音交流中不均匀共振峰模式的演变，这种欺骗性策略可能促成了清晰语音所需的音素多样化的起源。

本文是“声音调制：从起源、机制到社会影响（下）”主题的一部分。