Mothers’ and fathers’ infant-directed speech have similar acoustic properties, but these are not associated with direct or indirect measures of word comprehension in 8-month-old infants

Abstract

Previous research on infant-directed speech (IDS) and its role in infants’ language development has largely focused on mothers, with fathers being investigated scarcely. Here we examine the acoustics of IDS as compared to adult-directed speech (ADS) in Norwegian mothers and fathers to 8-month-old infants, and whether these relate to direct (eye-tracking) and indirect (parental report) measures of infants’ word comprehension. Forty-five parent-infant dyads participated in the study. Parents (24 mothers, 21 fathers) were recorded reading a picture book to their infant (IDS), and to an experimenter (ADS), ensuring identical linguistic context across speakers and registers. Results showed that both mothers’ and fathers’ IDS had exaggerated prosody, expanded vowel spaces, as well as more variable and less distinct vowels. We found no evidence that acoustic features of parents’ speech were associated with infants’ word comprehension. Potential reasons for the lack of such a relationship are discussed.

Longitudinal changes in consonant production in infant-directed speech and infants’ early speech production from 6 to 12 months

“…Finally, while gender-differences was not a primary focus of the current study, it is interesting that, irrespective of register, the fathers in our sample had overall more distinct consonant contrasts than mothers. This contradicts previous studies, albeit in other languages, that mostly report more contrastive VOT patterns in women than men (Li, 2013;Swartz, 1992;Whiteside & Irving, 1997), yet aligns with our results on vowels in IDS, which found that fathers had less variable and more distinctive vowel categories than mothers (Rosslund et al, 2023).…”

“…Given the so-far sparsity of evidence, whether a relationship between parents' VOT and infants' language outcomes exists or not need to be corroborated by future research. However, as it stands, our study join others that found no correlation between features of parents' IDS and infants' language outcomes (Rosslund et al, 2023;Song et al, 2018;Suttora et al, 2017), and studies that challenge the overall 'clarity' view of IDS (Benders et al, 2019;Cox et al, 2023;Ludusan et al, 2021;Miyazawa et al, 2017). While we do not refute IDS as a register that is beneficial for language acquisition, either directly (for example via vowel space expansion; Kalashnikova & Burnham, 2018) or indirectly (for example via its attentional, emotional, and/or social properties; Golinkoff et al, 2015), our results suggest that, within the context of VOT of Norwegian stop consonants, IDS is not a more distinctive and didactic register as compared to ADS, and its realisation might instead be motivated by attentional and affective goals.…”

“…With respect to the impact of VOT on infants' language outcomes, we took a similar approach as previous studies (e.g., Rosslund et al, 2023) and examined the impact of parents' speech operationalised as an adaptation -the IDS versus ADS (i.e., baseline-corrected IDS), and as the IDS input per se. We predicted, first, that if parents have longer VOTs for voiced and/or voiceless stop consonants in IDS as compared to ADS, then parents' enhanced VOT in IDS (register-difference between IDS vs ADS) and longer VOT in IDS themselves, 3 might translate into earlier production of these specific consonants in infants.…”

A longitudinal investigation of the acoustic properties of infant-directed speech from 6 to 18 months

“…In line with previous above-reviewed research and meta-analytic evidence (where available), and per our detailed preregistration (https://osf.io/8k3eh), we expected that parents' IDS, compared to ADS, would be characterised by overall higher pitch, wider pitch range, slower articulation rate, longer vowel duration, increased vowel spaces, and more variable and less distinct vowel categories (Cox et al, 2022;Lovcevic et al, 2023;McMurray et al, 2013;Miyazawa et al, 2017;Rosslund et al, 2022Rosslund et al, , 2023. Crucially, we expected that the predicted IDS-ADS differences in pitch, articulation rate, vowel duration, vowel category variability, and vowel distinctiveness would decrease with infants' age, attributed to IDS becoming more similar to ADS (Bernstein Ratner, 1984;Cox et al, 2022;Rosslund et al, 2022Rosslund et al, , 2023. In contrast, we expected that the IDS-ADS differences in pitch range and vowel space areas would remain stable with infants' age (Cox et al, 2022).…”

“…(3) to support infants' linguistic development (Cristia, 2013;Ferjan Ramirez et al, 2020;Golinkoff et al, 2015;Snow & Ferguson, 1977). While these functions are not mutually exclusive, 2 it has been suggested that their relative importance shifts with infants' age: IDS as a tool to capture attention and convey emotional valence might be the main function in speech directed to young infants, while its facilitating role in language learning might emerge later in development (Fernald, 1992;Rosslund et al, 2023;Song et al, 2010;Spinelli et al, 2017).…”