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A chimpanzee recognizes synthetic speech with significantly reduced acoustic cues to phonetic content.

ABSTRACT: A long-standing debate concerns whether humans are specialized for speech perception, which some researchers argue is demonstrated by the ability to understand synthetic speech with significantly reduced acoustic cues to phonetic content. We tested a chimpanzee (Pan troglodytes) that recognizes 128 spoken words, asking whether she could understand such speech. Three experiments presented 48 individual words, with the animal selecting a corresponding visuographic symbol from among four alternatives. Experiment 1 tested spectrally reduced, noise-vocoded (NV) synthesis, originally developed to simulate input received by human cochlear-implant users. Experiment 2 tested "impossibly unspeechlike" sine-wave (SW) synthesis, which reduces speech to just three moving tones. Although receiving only intermittent and noncontingent reward, the chimpanzee performed well above chance level, including when hearing synthetic versions for the first time. Recognition of SW words was least accurate but improved in experiment 3 when natural words in the same session were rewarded. The chimpanzee was more accurate with NV than SW versions, as were 32 human participants hearing these items. The chimpanzee's ability to spontaneously recognize acoustically reduced synthetic words suggests that experience rather than specialization is critical for speech-perception capabilities that some have suggested are uniquely human.

SUBMITTER: Heimbauer LA

PROVIDER: S-EPMC3143218 | biostudies-literature | 2011 Jul

REPOSITORIES: biostudies-literature

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A chimpanzee recognizes synthetic speech with significantly reduced acoustic cues to phonetic content.

Heimbauer Lisa A LA Beran Michael J MJ Owren Michael J MJ

Current biology : CB 20110630 14

A long-standing debate concerns whether humans are specialized for speech perception, which some researchers argue is demonstrated by the ability to understand synthetic speech with significantly reduced acoustic cues to phonetic content. We tested a chimpanzee (Pan troglodytes) that recognizes 128 spoken words, asking whether she could understand such speech. Three experiments presented 48 individual words, with the animal selecting a corresponding visuographic symbol from among four alternativ ...[more]

PMID: 21723125

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Project description:Efficient speech perception requires listeners to maintain an exquisite tension between stability of the language architecture and flexibility to accommodate variation in the input, such as that associated with individual talker differences in speech production. Achieving this tension can be guided by top-down learning mechanisms, wherein lexical information constrains interpretation of speech input, and by bottom-up learning mechanisms, in which distributional information in the speech signal is used to optimize the mapping to speech sound categories. An open question for theories of perceptual learning concerns the nature of the representations that are built for individual talkers: do these representations reflect long-term, global exposure to a talker or rather only short-term, local exposure? Recent research suggests that when lexical knowledge is used to resolve a talker's ambiguous productions, listeners disregard previous experience with a talker and instead rely on only recent experience, a finding that is contrary to predictions of Bayesian belief-updating accounts of perceptual adaptation. Here we use a distributional learning paradigm in which lexical information is not explicitly required to resolve ambiguous input to provide an additional test of global versus local exposure accounts. Listeners completed two blocks of phonetic categorization for stimuli that differed in voice-onset-time, a probabilistic cue to the voicing contrast in English stop consonants. In each block, two distributions were presented, one specifying /g/ and one specifying /k/. Across the two blocks, variance of the distributions was manipulated to be either narrow or wide. The critical manipulation was order of the two blocks; half of the listeners were first exposed to the narrow distributions followed by the wide distributions, with the order reversed for the other half of the listeners. The results showed that for earlier trials, the identification slope was steeper for the narrow-wide group compared to the wide-narrow group, but this difference was attenuated for later trials. The between-group convergence was driven by an asymmetry in learning between the two orders such that only those in the narrow-wide group showed slope movement during exposure, a pattern that was mirrored by computational simulations in which the distributional statistics of the present talker were integrated with prior experience with English. This pattern of results suggests that listeners did not disregard all prior experience with the talker, and instead used cumulative exposure to guide phonetic decisions, which raises the possibility that accommodating a talker's phonetic signature entails maintaining representations that reflect global experience.

Dataset Information

A chimpanzee recognizes synthetic speech with significantly reduced acoustic cues to phonetic content.

Publications

A chimpanzee recognizes synthetic speech with significantly reduced acoustic cues to phonetic content.

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