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Abstract Words in infant-directed speech (IDS) are often phonetically reduced. This likely renders words harder for infants to learn and recognize. This difficulty might be mitigated by the repetitive nature of IDS, in particular if reduced instances are often preceded by clear instances (i.e., the first-mention effect). To characterize phonetic clarity in American English word repetitions, words were extracted from the IDS of eight mothers and presented to adults (n = 36) who judged their clarity. First mentions of repeated words were found to be clearer than second mentions, though this effect was small. Clarity was rated as greater for less common words and for utterance-final words. Clarity was also greater for words parents thought their child knew. The results help guide intuitions about the phonetic problem infants face when learning their first words. 

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. 

The speech young children hear is highly variable. For example, reduced pronunciations, where some sounds in the canonical pronunciation are naturally dropped or altered, are common even in speech to children. The present study employed a new story-guided looking method (a variation on language-guided looking) to create felicitous conditions for testing young children’s recognition of reduced pronunciations of familiar words. Experiment 1 (18-24 months, n=32) found that toddlers succeeded at recognizing clear pronunciations, but failed to recognize reduced pronunciations, even in repetition trials when target words were preceded by a clear mention of the same word in the previous sentence. In Experiment 2, 3-year-olds (35-39 months, n=17 out of 44 pre- registered, ongoing) succeeded at recognizing reduced pronunciations, and benefited from preceding repetition. Overall, these results demonstrate a powerful new method for studying children’s language comprehension under more naturalistic conditions, and highlight an important psycholinguistic development over the 2-3 year span. 

Stimuli and data for Swingley, D. (2025), The intelligibility of consonants in American English infant-directed speech, Cognitive Psychology. doi.org/10.1016/j.cogpsych.2025.101766 

Subject data - interim results as reported in CogSci Proceedings 

Data and readme file corresponding to Swingley, D. (2025). The clarity of word repetitions in American English infant-directed speech. Journal of Child Language. doi:10.1017/S0305000925100263