The role of language in executive function development: Evidence from oral deaf preschoolers.

Language and executive function (EF) are correlated in preschool years. However, whether language plays a causal role in supporting EF development remains unclear given that language development cannot be experimentally manipulated. The present study recognizes that deaf and hard-of-hearing (DHH) children's language development represents a natural quasi-experimental proxy, in the common case where children's access to spoken language is delayed until they receive an assistive hearing device. We investigated whether DHH children's delayed EF development, relative to typically hearing (TH) children, is accounted for by DHH children's delayed access to spoken language. Preschoolers (n = 108, 38 oral DHH and 70 TH, 3.0-6.5 years) completed an EF task that primarily indexes inhibitory control and a standardized receptive language assessment. We also computed each DHH child's length of language access as the time that had elapsed since receiving their first assistive hearing device (at ages that varied widely from 1.5 months to 48 months). Replicating prior findings, TH children outperformed DHH children in EF (η2p = .17). Crucially, a mediation model revealed that length of language access fully mediated the link between DHH/TH status and EF. A second mediation model indicated that receptive vocabulary also fully mediated this link, further supporting the claim that EF delays among DHH children reflect delayed access to language rather than any cognitive deficit. Results provide strong evidence that language facilitates EF development and highlight the importance of early intervention to support language and EF. Theoretical implications for the nature and development of EF are discussed alongside practical implications for supporting DHH children.