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.
Highlights
Hypo- and Hyperarticulation in SpeechSpeech production is highly variable
We investigate the overall difference in vhh-index between infant-directed speech (IDS) and adult-directed speech (ADS), and compare the results with differences in vowel space area and mean formant values
The results show that when all vowels were considered, the range of Vowel hypo- and hyperarticulation (VHH) was not necessarily larger in IDS than in ADS, but both modal value and peak ratio were greater in IDS than in ADS, indicative of hyperarticulation in IDS
Summary
Hypo- and Hyperarticulation in SpeechSpeech production is highly variable. Depending on a multitude of factors, for example speech rate (Adams et al, 1993) and segmental context (Stevens and House, 1963), the precise articulation of a particular speech sound varies considerably, even within a single speaker. According to the H&H theory (Lindblom, 1990), articulation can be placed on a continuum between clear or exaggerated articulation (hyperarticulation) and more relaxed articulation with more reductions (hypoarticulation). The cause of this variability is the speaker’s adaptiveness, where he or she balances the listener’s need for a clear signal with preservation of energy in articulatory motor activity. When signal transmission is less than ideal, such as in noisy environments, the speaker tends to hyperarticulate, whereas under optimal transmission conditions the speaker defaults to hypoarticulation because it requires less energy (Lindblom, 1983).
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