Figure 1

Experimental design. The task consisted of a man or a woman (pictured) articulating the vowel /a/. On each trial, infants were presented with three consecutive /a/ while the fourth vowel could be either /a/ or /i/. The sound lasted 200 ms, in synchrony with the first frame (mouth opened). Following the end of the sound, two frames of a mouth gradually closing were presented (60 ms). Finally, during the last 280 ms, a face with a closed mouth was presented. *Informed consent to publish identifying images was obtained.