Multisensory Integration Is Modulated by Auditory Sound Frequency and Visual Spatial Frequency

Accurate integration of auditory and visual information is essential for our ability to communicate with others. Previous studies have shown that the temporal discrepancies over which audiovisual speech stimuli will be integrated into a coherent percept are much wider than those typically observed for simple stimuli like beeps and flashes of light. However, our sensitivity to the low-level features of simple stimuli is not constant. We hypothesized that part of the enhanced integration of audiovisual speech may be due to it consisting predominantly of the sound frequencies and visual spatial frequencies that humans are most sensitive to. Here, we examined integration behaviors for pure tones across the sound frequency spectrum and visual gratings across the spatial frequency spectrum to examine how these low-level features modulate integration. The temporal window of integration was modulated by both sound frequency and visual spatial frequency, with the widest integration window occurring when both stimuli fell within their respective peak sensitivity ranges. These results suggest that part of the increased tolerance for temporal asynchrony typically observed for audiovisual speech may be due to the differential integration of low-level stimulus features that are dominant within complex audiovisual speech.