Gaze behaviour in audiovisual speech perception: asymmetrical distribution of face-directed fixations.

Speech perception under natural conditions entails integration of auditory and visual information. Understanding how visual and auditory speech information are integrated requires detailed descriptions of the nature and processing of visual speech information. To understand better the process of gathering visual information, we studied the distribution of face-directed fixations of humans performing an audiovisual speech perception task to characterise the degree of asymmetrical viewing and its relationship to speech intelligibility. Participants showed stronger gaze fixation asymmetries while viewing dynamic faces, compared to static faces or face-like objects, especially when gaze was directed to the talkers' eyes. Although speech perception accuracy was significantly enhanced by the viewing of congruent, dynamic faces, we found no correlation between task performance and gaze fixation asymmetry. Most participants preferentially fixated the right side of the faces and their preferences persisted while viewing horizontally mirrored stimuli, different talkers, or static faces. These results suggest that the asymmetrical distributions of gaze fixations reflect the participants' viewing preferences, rather than being a product of asymmetrical faces, but that this behavioural bias does not predict correct audiovisual speech perception.