Caregivers' use of iconic words is associated with high positive engagement by both caregivers and infants

Iconic words are more frequent in infant-directed speech, but it is not known why. We examine whether caregivers use iconic words to engage infants in interaction. In two studies (Study 2 preregistered), involving five White American English-speaking 18-month-olds (three female; data collected between 2002 and 2005) and 45 American English-speaking 13- to 23-month-olds (23 female; 32 White, 10 Mixed Race, 1 Black/African American, and 2 Other; data collected between 2017 and 2020), we used iconicity ratings to identify the 10 most and least iconic 10-s windows (bouts) in caregiver speech. In high compared to low-iconicity bouts, infants gazed more at caregivers, gazed more at the subject of conversation, and more often smiled, laughed, gestured, and verbalized. Mothers' utterances within high-iconicity bouts were also higher in pitch and slower in speech rate than those in low-iconicity bouts.