A Chimpanzee Recognizes Synthetic Speech with Significantly Reduced Acoustic Cues to Phonetic Content

• Published in: Current biology Vol. 21; no. 14; pp. 1210 - 1214
• Main Authors: Heimbauer, Lisa A., Beran, Michael J., Owren, Michael J.
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 26.07.2011
• Subjects: Animals; Hearing; Language; Pan troglodytes - physiology; Pan troglodytes - psychology; Recognition, Psychology; Speech Perception
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2011.06.007

A long-standing debate concerns whether humans are specialized for speech perception [1–7], which some researchers argue is demonstrated by the ability to understand synthetic speech with significantly reduced acoustic cues to phonetic content [2–4, 7]. We tested a chimpanzee (Pan troglodytes) that recognizes 128 spoken words [8, 9], 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 [10]. Experiment 2 tested “impossibly unspeechlike” [3] sine-wave (SW) synthesis, which reduces speech to just three moving tones [11]. 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 [12–14]. ► Some argue that acoustically reduced synthetic speech requires specialized processing ► Two such forms were tested in a chimpanzee that recognizes spoken words ► The animal performed well above chance level, with parallels to human results ► Findings highlight the importance of experience in shaping speech perception