The capacity of audiovisual integration is limited to one item.

The human visual attention system is geared toward detecting the most salient and relevant events in an overwhelming stream of information. There has been great interest in measuring how many visual events can be processed at a time, and most of the work has suggested that the limit is three to four. However, attention to a visual stimulus can also be driven by a synchronous auditory event. The present work indicates that a fundamentally different limit applies to audiovisual processing, such that at most only a single audiovisual event can be processed at a time. This limited capacity is not due to a limitation in visual selection; participants were able to process about four visual objects simultaneously. Instead, we propose that audiovisual orienting is subject to a fundamentally different capacity limit than pure visual selection is.