Four-Month-Olds' Discrimination of Voice Changes in Multimodal Displays as a Function of Discrimination Protocol.

Past studies have found equivocal support for the ability of young infants to discriminate infant-directed (ID) speech information in the presence of auditory-only versus auditory + visual displays (faces + voices). Generally, younger infants appear to have more difficulty discriminating a change in the vocal properties of ID speech when they are accompanied by faces. Forty 4-month-old infants were tested using either an infant-controlled habituation procedure (Experiment 1) or a fixed-trial habituation procedure (Experiment 2).