The Dynamics of Vowel Hypo- and Hyperarticulation in Swedish Infant-Directed Speech to 12-Month-Olds

Abstract

Vowel hypo-and hyperarticulation (VHH) was investigated in Swedish infant-directed speech (IDS) to Swedish 12-month-olds using a measure that normalizes across speakers and vowels: the vhh-index. The vhh-index gives the degree of VHH for each individual vowel token, which allows for analysis of the dynamics of VHH within a conversation. Using both the vhh-index and traditional measures of VHH, the degree of VHH was compared between Swedish IDS and ADS. The vowel space area was larger in IDS than in ADS, and the average vhh-index as well as the modal value was higher in IDS than in ADS. Further, the proportion of vowel tokens that were highly hyperarticulated (vhh-index > 75th percentile) were fewer in ADS than in IDS. Vowels in Swedish IDS to 12-month-olds are thus concluded to be hyperarticulated compared to vowels in Swedish ADS, both in terms of degree and frequency. Findings are in line with previous reports on VHH in Swedish IDS as well as on VHH in IDS to infants around 12 months in other languages. The study considers the importance of robust formant estimation, highlights the need for replication of studies on VHH in IDS on previously studied languages and ages, and discusses the benefits of the vhh-index. Those benefits include that it normalizes across speakers and vowels, can be used for dynamic measures within speech samples, and permits analyses on token-level.

An Association Between Phonetic Complexity of Infant Vocalizations and Parent Vowel Hyperarticulation

“…Estimation of VH in parent’s IDS and ADS was performed as a part of a previous study, and detailed information about the procedure can be found there ( Marklund and Gustavsson, 2020 ). In brief, parent speech was quasi-orthographically transcribed using ELAN 4.6.2-5.3 ( Sloetjes and Wittenburg, 2008 ).…”

“…Since reliability of formant estimations decreases with higher fundamental frequency ( f o ), vowels with a median f o exceeding 350 Hz were excluded ( Lindblom, 1962 ; Monsen and Engebretson, 1983 ). To reduce the impact of coarticulation, the mid 40% of the vowel was used in the analysis ( Marklund and Gustavsson, 2020 ). Each parents’ average F 1 and F 2 for the point vowels /i/, /ɑ/, and /u/ in IDS and ADS were extracted and used for calculations of VSA.…”

“…Infant-directed speech (IDS), the speech style commonly used when speaking to infants and small children (e.g., Soderstrom, 2007 ; Golinkoff et al, 2015 ), has been reported to facilitate or promote various aspects of early language development (e.g., Trainor and Desjardins, 2002 ; Singh et al, 2009 ; Ma et al, 2011 ; Bosseler et al, 2016 ; Foursha-Stevenson et al, 2017 ). One specific characteristic commonly found in IDS, clear or exaggerated vowel articulation (for a review, see Marklund and Gustavsson, 2020 ) compared to adult-directed speech (ADS), has been linked to better speech sound discrimination ( Liu et al, 2003 ; García-Sierra et al, 2021 ), better word-recognition ( Song et al, 2010 ), as well as larger receptive and productive vocabulary sizes ( Hartman et al, 2017 ; Kalashnikova and Burnham, 2018 ). The present study focuses on the relationship between parents’ articulation and children’s own productions.…”

“…These adaptations mean that individual speech sounds are realized on a continuum that ranges from exaggerated articulation (i.e., hyperarticulation) to relaxed articulation (i.e., hypoarticulation). IDS has been reported to be more hyperarticulated overall than ADS in some cases (vowels: Kuhl et al, 1997 ; see Marklund and Gustavsson, 2020 for a review; consonants: Cristià, 2010 ; McMurray et al, 2013 ) and more hypoarticulated than ADS overall in other cases (vowels: Englund and Behne, 2005 , 2006 ; Benders, 2013 ; Englund, 2018 ; consonants: Sundberg and Lacerda, 1999 ; Benders et al, 2019 ). In this study, the focus is articulatory adaptation of vowels, and it will be referred to as vowel hyperarticulation (VH), since vowels in IDS to Swedish 12-month-old infants has previously been shown to be more hyperarticulated overall than vowels in Swedish ADS ( Marklund and Gustavsson, 2020 ).…”

“…In the present study, parents’ articulatory adaptations in terms of VH is quantified using the difference in of vowel space area (VSA), that is, the area between the point vowel formant means in F 1 - F 2 space, between IDS and ADS ( Kuhl et al, 1997 ; Marklund and Gustavsson, 2020 ). Phonetic complexity of children’s productions is measured using the Swedish adaptation of the Word-Complexity Measure (WCM-SE).…”