Babies can differentiate most sounds soon after birth, and by the age of one year, they become language-specific listeners. But researchers are still trying to understand how babies recognize which acoustic dimensions of their language are contrastive, a linguistic term that describes differences between speech sounds that can change the meaning of words. For example, in English, [b] i [d] are contrasts, because changing the [b] in ‘ball’ aa [d] makes it a different word, “doll”.
A recent paper in The Proceedings of the National Academy of Sciences (PNAS) by two computational linguists affiliated with the University of Maryland offers new insight on this topic, which is essential to better understanding how infants learn what sounds are in their native language. they are
Their research shows that an infant’s ability to interpret acoustic differences as contrastive or non-contrastive can come from the contexts in which the different sounds occur.
For a long time, researchers believed that there would be obvious differences between how contrasting sounds, such as short and long vowels, are pronounced in Japanese. However, although the pronunciations of these two sounds are different in careful speech, the acoustics are often much more ambiguous in more natural settings.
This is one of the first accounts of phonetic learning to be shown to work with spontaneous data, suggesting that infants might be learning which acoustic dimensions are contrastive after all.”
Kasia Hitczenko, lead author of the paper
Hitczenko graduated from the University of Maryland in 2019 with a PhD in Linguistics. She is currently a postdoctoral researcher at the Laboratory of Cognitive and Psycholinguistic Sciences at the Ecole Normale Supérieure in Paris.
Hitczenko’s work shows that infants can differentiate between acoustic sounds based on context clues, such as neighboring sounds. His team tested their theory in two case studies with two different definitions of context, comparing data on Japanese, Dutch and French.
The researchers collected speech that occurred in different contexts and made plots summarizing what the vowel durations were in each context. In Japanese, they found that these vowel length graphs varied markedly in different contexts, because some contexts had more short vowels, while other contexts had more long vowels. In French, these vowel duration diagrams were similar in all contexts.
“We believe this work presents a compelling account of how infants learn the speech contrasts of their language and demonstrates that the necessary signal is present in naturalistic speech, advancing our understanding of early language learning.” says co-author Naomi Feldman, associate. professor of linguistics with an appointment at the University of Maryland Institute for Advanced Computing Studies (UMIACS).
Feldman adds that the signal they studied is true in most languages, and it is likely that their result can be generalized to other contrasts.
The recently published research is an extension of Hitczenko’s Ph.D. thesis, which examined how to use context for phonetic learning and perception from naturalistic speech.
Feldman was Hitczenko’s academic advisor at Maryland, where the two completed much of their research at the UMIACS-supported Computational Linguistics and Information Processing Laboratory.
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Journal reference:
Hitczenko, K and Feldman, NH, (2022) Naturalistic discourse supports distributive learning across contexts. PNAS. doi.org/10.1073/pnas.2123230119.