Abstract
In social animals, identifying sounds is critical for communication. In humans, the acoustic parameters involved in speech recognition, such as the formant frequencies derived from the resonance of the supralaryngeal vocal tract, have been well documented. However, how formants contribute to recognizing learned sounds in non-human primates remains unclear. To determine this, we trained two rhesus monkeys to discriminate target and non-target sounds presented in sequences of 1–3 sounds. After training, we performed three experiments: (1) We tested the monkeys’ accuracy and reaction times during the discrimination of various acoustic categories; (2) their ability to discriminate morphing sounds; and (3) their ability to identify sounds consisting of formant 1 (F1), formant 2 (F2), or F1 and F2 (F1F2) pass filters. Our results indicate that macaques can learn diverse sounds and discriminate from morphs and formants F1 and F2, suggesting that information from few acoustic parameters suffice for recognizing complex sounds. We anticipate that future neurophysiological experiments in this paradigm may help elucidate how formants contribute to the recognition of sounds.
Highlights
Non-human primates (NHP) identify conspecific vocalizations (Rendall et al, 1996; Jovanovic et al, 2000; Ceugniet and Izumi, 2004; Belin, 2006) that inform troop members about food quality (Hauser, 1998; Slocombe and Zuberbühler, 2006) or nearby predators (Seyfarth et al, 1980b)
We presented the monkeys with formant 1 (F1), formant 2 (F2), and F1 and F2 (F1F2)-pass filters synthesized from the learned sounds (Figure 3A)
Performance was significantly lower than during the discrimination of the learned sounds: Learned > F1F2 > F2 > F1 (Benjamini-Hochberg and FDR correction for multiple Wilcoxon signed-rank test comparisons; q-value = 0.01; Figure 3D). These results suggest that formants F1 and F2 provide relevant information about sounds
Summary
Non-human primates (NHP) identify conspecific vocalizations (Rendall et al, 1996; Jovanovic et al, 2000; Ceugniet and Izumi, 2004; Belin, 2006) that inform troop members about food quality (Hauser, 1998; Slocombe and Zuberbühler, 2006) or nearby predators (Seyfarth et al, 1980b) These communication abilities are likely to rely on the activity of vocal recognition brain areas, homologous in humans and macaques (Petkov et al, 2008; Leaver and Rauschecker, 2010; OrtizRios et al, 2015; Belin et al, 2018). Recognition of Sounds in Macaques and the length of the individuals’ vocal tract (Remez et al, 1981; Lieberman and Blumstein, 1988; Rendall et al, 2004; Ghazanfar and Rendall, 2008; Ackermann et al, 2014)
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