Visual load does not modulate neural processing of audiovisual speech integration

A long-standing controversial issue in speech perception concerns the automatic nature of audiovisual speech integration, independent of attentional and cognitive load. From this question, the present EEG study aimed to determine whether visual load and associated task difficulty can modulate audiovisual speech integration and, if so, at what stage of neural processing. To this end, four syllable discrimination tasks differing in the degree of visual discrimination and speaker variability were performed in auditory, visual, and audiovisual modalities. Early and late effects of audiovisual integration, as well as late effects of visual load, were observed on auditory evoked responses. Crucially, the neural binding of acoustic and visual speech signals was not modulated by either visual discrimination or speaker variability. These results support an automatic integration of acoustic and visual speech cues, independent of visual load, during audiovisual syllable discrimination.