Effects of horizontal viewing angle on visual and audiovisual speech recognition

The authors investigated the effects of changes in horizontal viewing angle on visual and audiovisual speech recognition in 4 experiments, using a talker's face viewed full face, three quarters, and in profile. When only experimental items were shown (Experiments 1 and 2), identification of unimodal visual speech and visual speech influences on congruent and incongruent auditory speech were unaffected by viewing angle changes. However, when experimental items were intermingled with distractor items (Experiments 3 and 4), identification of unimodal visual speech decreased with profile views, whereas visual speech influences on congruent and incongruent auditory speech remained unaffected by viewing angle changes. These findings indicate that audiovisual speech recognition withstands substantial changes in horizontal viewing angle, but explicit identification of visual speech is less robust. Implications of this distinction for understanding the processes underlying visual and audiovisual speech recognition are discussed.