Maternal input, not transient elevated depression and anxiety symptoms, predicts 2-year-olds’ vocabulary development

Both the quantity and quality of the maternal language input are important for early language development. However, depression and anxiety can negatively impact mothers’ engagement with their infants and their infants’ expressive language abilities. Australian mother-infant dyads (N = 30) participated in a longitudinal study examining the effect of maternal language input when infants were 24 and 30 months and maternal depression and anxiety symptoms on vocabulary size. Half the mothers had elevated depression and anxiety symptoms during at least one point in the study (at 6, 12, 18, 24, or 30 months). The results showed that only maternal input measures (word tokens, types, and mean length of utterance) predicted vocabulary size. While no evidence was found that brief periods of maternal depression and anxiety negatively impacted early vocabulary development, the findings highlight the critical importance and possible mitigating effects of maintaining good quality mother–infant interactions during early development.