The intelligibility of consonants in American English infant-directed speech

To begin learning their language, infants must locate words in the speech signal. Some models of word discovery presuppose that the discovery process depends on identifying phonetic segments (phones) in speech. To test the plausibility of models arguing that infants can reliably categorize consonants in speech, adult native speakers were asked to identify the consonant in vowel-consonant-vowel sequences extracted from spontaneous English infant-directed speech. Listeners could consistently identify some instances of consonants (for example, correctly indicating that an /s/ was an /s/). But many tokens (about half) were not consistently identifiable. Performance was significantly worse for codas than onsets. Providing the full utterance context in low-pass-filtered form did not aid recognition, nor did familiarization with the talker. In a second task, listeners were barely above chance in guessing whether a consonant was a word onset or a word-final coda. Performance on infant-directed speech was not markedly better than performance on a comparison set of adult-directed speech consonants. Erroneous responses frequently had little systematic resemblance to the correct answer. The results suggest that it is not plausible that infants can parse most utterances exhaustively into strings of uttered speech sounds and feed those strings into a statistical clustering mechanism.