Prosodic Modification and Vocal Adjustments in Mothers' Speech During Face-to-face Interaction with Their Two- to Four-month-old Infants: A Double Video Study

The purpose of this study was to examine 32 mothers' sensitivity to social contingency during face-to-face interaction with their two- to four-month-old infants in a closed circuit TV set-up. Prosodic qualities and vocal sounds in mother's infant-directed (ID) speech during sequences of live interaction were compared to sequences where expressive behaviours were decoupled by presenting either the mothers (Replay 2) or the infants (Replay 1) with a replay record of the partners' former behaviour in a Live 1-Replay 1-Live 2-Replay 2-Live 3 design. Overall, the mothers produced significantly higher amount of ID speech during the live sequences. Compared to the Live 1 sequence, there was a significant reduction in mothers' ID speech during both replay sequences. However, the mothers only recovered ID speech after the Replay 2 sequence, not after the Replay 1. These findings suggest that the emotions signalled by the mothers' ID speech is affected by the contingency of the infant responses.