Sign Duration in Infant-Directed Signing: Evidence from Deaf Mother–Hearing Infant Dyads in Israeli Sign Language

This longitudinal study examined how sign duration in Israeli Sign Language infant-directed input is shaped by linguistic and developmental factors. Two Deaf mothers were video-recorded interacting naturally with their hearing children between 10 and 36 months of age. Sign duration decreased with child age, reflecting a shift from pedagogically enriched to more compact input. Iconic signs were elongated relative to non-iconic signs, particularly at younger ages, suggesting a perceptual scaffolding function. Lexical category was the strongest predictor: object and attribute signs were consistently produced with longer durations than action or function signs. Lexical frequency had no significant effect on sign duration. Qualitative observations identified prosodic strategies—such as final holds and enlarged movement—to enhance visual salience during early input. These findings underscore how Deaf caregivers adapt their signing to the child’s developmental level, using prosodic modulation informed by iconic and lexical features. Sign duration thus emerges as a dynamic and communicatively motivated feature of infant-directed signing, supporting early language acquisition in the visual-manual modality.