Rhesus macaques spontaneously perceive formants in conspecific vocalizations

Abstract

We provide a direct demonstration that nonhuman primates spontaneously perceive changes in formant frequencies in their own species-typical vocalizations, without training or reinforcement. Formants are vocal tract resonances leading to distinctive spectral prominences in the vocal signal, and provide the acoustic determinant of many key phonetic distinctions in human languages. We developed algorithms for manipulating formants in rhesus macaque calls. Using the resulting computer-manipulated calls in a habituation/dishabituation paradigm, with blind video scoring, we show that rhesus macaques spontaneously respond to a change in formant frequencies within the normal macaque vocal range. Lack of dishabituation to a "synthetic replica" signal demonstrates that dishabituation was not due to an artificial quality of synthetic calls, but to the formant shift itself. These results indicate that formant perception, a significant component of human voice and speech perception, is a perceptual ability shared with other primates.

Vocal Tract Morphology Determines Species-Specific Features in Vocal Signals of Lemurs (Eulemur)

“…Our findings demonstrate that vocal cues discriminate species, in agreement with previous studies on the oral "meows" of felids (Nicastro 2004). Indirectly, our data support the hypothesis that formants can be perceived spontaneously in Strepsirrhini, as demonstrated in macaques (Fitch and Fritz 2006). It is interesting to evaluate our results in relation to the perceptual abilities of lemurs.…”

Morphing rhesus monkey vocalizations

“…The procedure can now be used to morph between many different types of vocalizations, such as those from different individuals, different genders and across species or call types. This broadens the scope of the questions that can be asked in behavioral and neurophysiological studies of vocal recognition, and has the potential to bridge approaches that manipulate the features of natural and ethologically relevant vocalizations (e.g., Fitch and Fritz, 2006;Ghazanfar et al, 2007;Gifford et al, 2005;Smith et al, 2005) with the more common approach of using controlled acoustical stimuli to probe the function of the auditory system.…”

“…Scientists have been using various algorithms and software packages to automate the analysis, extraction and independent manipulation of the different frequency components of 'voiced' sounds (Fitch and Fritz, 2006;Ghazanfar et al, 2007;Smith et al, 2005;von Kriegstein et al, 2007), also see the Praat software at http://www.fon.hum.uva.nl/praat/. This work suggests that the gradual morphing of vocalizations is possible if 'voiced' sounds are used which have prominent frequency and harmonic structure.…”

Bilateral Speech Comprehension Reflects Differential Sensitivity to Spectral and Temporal Features

“…The assumption upheld, though, was that low-level effects bear direct relevance to meaningful material, especially speech and music. Related research in nonhuman species (Rauschecker et al, 1995;Wang et al, 1995;Read et al, 2002;Fitch and Fritz, 2006;Petkov et al, 2006;Pandya et al, 2008) has limitations in generalizing to human speech processing. This gap between meaningless stimuli and a proclaimed role in the decoding of speech or music has not been closed yet (with the notable exception of intelligibilitymodulating speech chimeras with varied temporal detail) (Luo and Poeppel, 2007).…”