The Role of Parent Responsiveness and Vocal Complexity in Expressive Language Outcome: Intervention Effects in Toddlers at Risk for ASD and Language Impairment

Abstract

Up to 40% of later-born siblings of children with autism spectrum disorder (ASD) are diagnosed with: a) ASD (7-19%), which is defined by social communication impairments; or b) other language and/or cognitive delays (14-20%) by age three. Vocal complexity, a measure of the quality and maturity of vocal communication, seems to be a strong predictor of later expressive language in typically developing (TD) and children with ASD, but no studies have examined this relation for these toddlers at high familial risk for ASD (high risk; HR toddlers). Also, previous studies have not examined the role of vocal complexity occurring within preverbal (non-word) vocalizations, distinct from that occurring within words. Low preverbal vocal complexity may signal early language difficulties and need for intervention in HR toddlers. Vocal complexity may be malleable with intervention. This study examined vocally complex communication within an ongoing longitudinal randomized controlled trial (RCT) of the ImPACT intervention (compared to business as usual; BAU) in 54 12-27-month-old HR toddlers. It found that: 1) nonword vocal complexity was a value-added predictor of later expressive language ability in HR toddlers; 2) families in the ImPACT condition did not display greater parent verbal responsiveness (PVR) to toddlers’ vocally complex communication acts, greater toddler vocal complexity, or greater toddler expressive language outcome compared to families in the BAU condition; and 3) for toddlers in both treatment conditions, there was an indirect effect of parents’ verbal responsiveness on toddlers’ later expressive language ability through toddlers’ midpoint vocal complexity. This study provides insight into the role of vocal complexity as a risk indicator of language delay and discusses the mechanisms by which vocal complexity may or may not be malleable in response to a parent-implemented social communication intervention.