Infant directed speech and the development of speech perception: Enhancing development or an unintended consequence?

Abstract

Infant directed speech (IDS) is a speech register characterized by simpler sentences, a slower rate, and more variable prosody. Recent work has implicated it in more subtle aspects of language development. Kuhl et al. (1997) demonstrated that segmental cues for vowels are affected by IDS in a way that may enhance development: the average locations of the extreme “point” vowels (/a/, /i/ and /u/) are further apart in acoustic space. If infants learn speech categories, in part, from the statistical distributions of such cues, these changes may specifically enhance speech category learning. We revisited this by asking (1) if these findings extend to a new cue (Voice Onset Time, a cue for voicing); (2) whether they extend to the interior vowels which are much harder to learn and/or discriminate; and (3) whether these changes may be an unintended phonetic consequence of factors like speaking rate or prosodic changes associated with IDS. Eighteen caregivers were recorded reading a picture book including minimal pairs for voicing (e.g., beach/peach) and a variety of vowels to either an adult or their infant. Acoustic measurements suggested that VOT was different in IDS, but not in a way that necessarily supports better development, and that these changes are almost entirely due to slower rate of speech of IDS. Measurements of the vowel suggested that in addition to changes in the mean, there was also an increase in variance, and statistical modeling suggests that this may counteract the benefit of any expansion of the vowel space. As a whole this suggests that changes in segmental cues associated with IDS may be an unintended by-product of the slower rate of speech and different prosodic structure, and do not necessarily derive from a motivation to enhance development.

A communicative approach to early word learning

“…But we should not take evidence that speech is not optimal for learning as evidence that it is not better for learning than it would be if it were not communicative (Eaves Jr et al, 2016;McMurray et al, 2013). Coordinating in-the-moment is only a piece of the language learning puzzle, but it is an 365 important one (Tomasello, 2000).…”

Is infant-directed speech interesting because it is surprising? – Linking properties of IDS to statistical learning and attention at the prosodic level

“…This is concrete modeling support for the idea that the more variable IDS speaking style may boost prosodic learning in infants. In contrast, the previous studies on the potential benefits of higher acoustic variability of IDS in phonetic learning have been more mixed (e.g., de Boer & Kuhl, 2003;Kirchhoff & Schimmel, 2005;McMurray et al, 2013;Martin et al, 2015).…”

“…For instance, McMurray et al (2013) have suggested that the higher variability of voice onset times (VOTs) and formant frequencies in IDS may be counter-productive to phonetic learning from speech, as the variability does correspond to that observed in typical ADS (see also Kirchhoff & Schimmel, 2005).…”

Unnatural pedagogy : a computational analysis of children's learning to learn from other people.

“…This competition has inspired efforts to indirectly evaluate the optimality of IDS by asking whether machine learning algorithms learn better from infant-directed data than adult-directed data (de Boer & Kuhl, 2003;Kirchhoff & Schimmel, 2005;McMurray et al, 2013). However, the results are mixed.…”

“…Further research demonstrated that the trend of hyperarticulation in IDS is not constant across all phoneme pairs; some pairs are hypoarticulated (Cristia & Seidl, 2013). Additionally, the within-phoneme variability of some phoneme categories increases (de Boer & Kuhl, 2003;Cristia & Seidl, 2013;McMurray, Kovack-Lesh, Goodwin, & McEchron, 2013). The acoustical properties of IDS appear to compete with each other.…”