The McGurk effect: An investigation of attentional capacity employing response times

This paper proposes a novel approach to assess audiovisual integration for both congruent and incongruent speech stimuli using reaction times (RT). The experiments are based on the McGurk effect, in which a listener is presented with incongruent audiovisual speech signals. A typical example involves the auditory consonant/b/combined with a visually articulated/g/, often yielding a perception of/d/. We quantify the amount of integration relative to the predictions of a parallel independent model as a function of attention and congruency between auditory and visual signals. We assessed RT distributions for congruent and incongruent auditory and visual signals in a within-subjects signal detection paradigm under conditions of divided versus focused attention. Results showed that listeners often received only minimal benefit from congruent auditory visual stimuli, even when such information could have improved performance. Incongruent stimuli adversely affected performance in divided and focused attention conditions. Our findings support a parallel model of auditory-visual integration with interactions between auditory and visual channels.