Infants’ Lexical Processing: Independent Contributions of Attentional and Clarity Cues

ABSTRACT

There is a long-standing debate in the literature about the benefits that acoustic components of Infant Directed Speech (IDS) might have for infants’ language acquisition. One of the highly contested features is vowel space expansion, which refers to the enlargement of the acoustic space between the corner vowels /i, u, a/ in IDS compared to Adult Directed Speech (ADS). Some evidence indicates that vowel space expansion in IDS facilitates infants’ speech perception, thus promoting language development, whereas other studies have questioned these benefits and have proposed that any processing benefits of IDS are due to its other prosodic features such as exaggerated and variable pitch. This study aimed to tease apart the effects of vowel space expansion and prosodic exaggeration in IDS on 18-month-old infants’ speech processing. Using a looking-while-listening paradigm, two between-subjects conditions were compared: Exaggerated Pitch (with exaggerated pitch height and range, but without vowel space expansion) and Expanded Vowel Space (with vowel space expansion, but no exaggeration in pitch height and range). Our results showed that infants recognized the meanings of the words more accurately in the Expanded Vowel Space compared to the Exaggerated Pitch condition. This suggests that vowel space expansion in IDS facilitates infants’ lexical processing even when it does not cooccur with the prosodic exaggeration typical of IDS.

Acknowledgments

We would like to thank the HEARing Cooperative Research Centre for the grant 82631, “The Seeds of Language Development,” to the 2^nd author. The 1^st author’s work was supported by World Premier International Research Center Initiative (WPI), MEXT, Japan. The 3^rd author’s work was supported by the Basque Government through the BERC 2018-2021 program, by the Spanish State Research Agency through BCBL Severo Ochoa excellence accreditation CEX2020-001010-S, and by the Spanish Ministry of Science and Innovation through the Ramon y Cajal Research Fellowship, RYC2018-024284-I. We thank the families for their valuable time.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data and analyses reported in this paper are freely available at the following link: https://osf.io/wb65q/?view_only=5c99b83d616d49c79c2ff5b89e388ed8.

Additional information

Funding

This work was supported by the HEARing Cooperative Research Centre [82631]; Spanish Ministry of Science and Innovation [Ramon y Cajal Research Fellowship, PID2019-105528G]; Spanish State Research Agency [BCBL Severo Ochoa excellence accreditation SEV-201]; Basque Government [BERC 2018-2021]; World Premier International Research Center Initiative (WPI), MEXT.