Audio-visual speech perception off the top of the head.

The study examined whether people can extract speech related information from the talker's upper face that was presented using either normally textured videos (Experiments 1 and 3) or videos showing only the outlined of the head (Experiments 2 and 4). Experiments 1 and 2 used within- and cross-modal matching tasks. In the within-modal task, observers were presented two pairs of short silent video clips that showed the top part of a talker's head. In the cross-modal task, pairs of audio and silent video clips were presented. The task was to determine the pair in which the talker said the same sentence. Performance on both tasks was better than chance for the outline as well as textured presentation suggesting that judgments were primarily based on head movements. Experiments 3 and 4 tested if observing the talker's upper face would help identify speech in noise. The results showed the viewing the talker's moving upper head produced a small but reliable improvement in speech intelligibility, however, this effect was only secure for the expressive sentences that involved greater head movements. The results suggest that people are sensitive to speech related head movements that extend beyond the mouth area and can use these to assist in language processing.