Gustison Morgan L, Bergman Thore J
Department of Psychology, University of Michigan.
Department of Ecology and Evolutionary Biology, University of Michigan.
J Lang Evol. 2017 Jan;2(1):20-36. doi: 10.1093/jole/lzx015. Epub 2017 Jun 26.
Human speech has many complex spectral and temporal features traditionally thought to be absent in the vocalizations of other primates. Recent explorations of the vocal capabilities of non-human primates are challenging this view. Here, we continue this trend by exploring the spectro-temporal properties of gelada () vocalizations. First, we made cross-species comparisons of geladas, chacma baboons, and human vowel space area. We found that adult male and female gelada exhaled grunts-a call type shared with baboons-have formant profiles that overlap more with human vowel space than do baboon grunts. These gelada grunts also contained more modulation of fundamental and formant frequencies than did baboon grunts. Second, we compared formant profiles and modulation of exhaled grunts to the derived call types (those not shared with baboons) produced by gelada males. These derived calls contained divergent formant profiles, and a subset of them, notably wobbles and vocalized yawns, were more modulated than grunts. Third, we investigated the rhythmic patterns of wobbles, a call type shown previously to contain cycles that match the 3-8 Hz tempo of speech. We use a larger dataset to show that the wobble rhythm overlaps more with speech rhythm than previously thought. We also found that variation in cycle duration depends on the production modality; specifically, exhaled wobbles were produced at a slower tempo than inhaled wobbles. Moreover, the variability in cycle duration within wobbles aligns with a linguistic property known as 'Menzerath's law' in that there was a negative association between cycle duration and wobble size (i.e. the number of cycles). Taken together, our results add to growing evidence that non-human primates are anatomically capable of producing modulated sounds. Our results also support and expand on current hypotheses of speech evolution, including the 'neural hypothesis' and the 'bimodal speech rhythm hypothesis'.
人类语音具有许多复杂的频谱和时间特征，传统观点认为这些特征在其他灵长类动物的发声中并不存在。最近对非人类灵长类动物发声能力的探索正在挑战这一观点。在这里，我们通过探索狮尾狒（）发声的频谱-时间特性延续了这一趋势。首先，我们对狮尾狒、东非狒狒和人类的元音空间区域进行了跨物种比较。我们发现成年雄性和雌性狮尾狒呼出的呼噜声——一种与狒狒共有的叫声类型——其共振峰分布比狒狒的呼噜声与人类元音空间的重叠更多。这些狮尾狒的呼噜声在基频和共振峰频率上的调制也比狒狒的呼噜声更多。其次，我们将呼出的呼噜声的共振峰分布和调制与狮尾狒雄性发出的派生叫声类型（那些与狒狒不共有的叫声）进行了比较。这些派生叫声具有不同的共振峰分布，其中一部分，特别是颤音和发声哈欠，比呼噜声的调制更多。第三，我们研究了颤音的节奏模式，之前的研究表明这种叫声类型包含与3-8赫兹语音节奏相匹配的周期。我们使用了一个更大的数据集来表明，颤音节奏与语音节奏的重叠比之前认为的更多。我们还发现周期持续时间的变化取决于发声方式；具体来说，呼出的颤音比吸入的颤音产生的节奏更慢。此外，颤音内周期持续时间的变异性与一种被称为“门泽拉斯定律”的语言特性相符，即周期持续时间与颤音大小（即周期数量）之间存在负相关。综上所述，我们的结果进一步证明了非人类灵长类动物在解剖学上能够发出调制声音。我们的结果还支持并扩展了当前关于语音进化的假设，包括“神经假设”和“双峰语音节奏假设”。
