Speech development in toddlers at high and low risk for autism
Chenausky, Karen Virginia
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Speech development in autism spectrum disorder (ASD) has rarely been studied, yet residual speech sound errors are over 30 times more common in children with ASD than in the general population. Two main theories could explain this. The Social Feedback Loop proposes that toddlers with ASD vocalize less often and so have fewer opportunities to benefit from adult feedback. Thus, fewer vocalizations and perceptible differences in those vocalizations should be found in toddlers with ASD. The Speech Attunement Framework proposes that while toddlers with ASD “tune in” to their native languages well enough to acquire language normally, they lack the ability to “tune up” their articulation to the same level of precision as typically-developing children. Thus, differences in the vocalizations of toddlers with ASD may be perceptible or not, and should exist irrespective of differences in vocalization rate. This study longitudinally examines vocalization rate, consonant inventory size, and voice-onset time (VOT) in syllable-initial bilabial stops using 30-minute speech samples from toddlers in three groups: those at low risk for ASD (LRC), those at high risk for ASD with ASD themselves (HRA+), and those at high risk for ASD without ASD (HRA ) . Transient delays in consonant development were found in both HRA- and HRA+, but only HRA+ toddlers vocalized less often. Further, the relationship between vocalization rate and consonant inventory was significantly different from LRC only for HRA-. VOT development was similar across groups, except that fewer HRA+ 36-month-olds produced distinct /b/ and /p/ populations, as measured by t-test and by Cohen’s d ≥ 0.8 between mean VOTs in the two populations of stops. Results support the Speech Attunement Framework. Consonant acquisition delays are not related to differences in vocalization rate and are not found only in toddlers who develop ASD. The finding of sub-perceptual acoustic differences in stop production in toddlers who develop ASD, with no accompanying differences in production rate, also supports the Speech Attunement Framework. This suggests that the Social Feedback Loop is not diminished in ASD by lower vocalization rate, but that toddlers with ASD may have diminished ability to monitor their own speech.