Listener sensitivity to formant amplitude variations in the perception of both within- and between-vowel-category differences was examined for two isolated synthetic vowels, /i/ and /ɪ/. The relative amplitudes of F2 and F4 were varied in steps along acoustic continua which were created in accord with formant amplitude patterns found in natural speech. The results showed that vowel-specific patterns of formant amplitude variation affected listeners’ judgments of “naturalness” of each vowel token, as well as its phonetic quality.

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