A critical parameter of brain-computer interfaces (BCIs) is the number of dimensions a user can control independently. One way to increment this number without increasing the mental effort required to operate the system is to stimulate several sensory modalities simultaneously, and to distinguish brain activity patterns when the user focuses attention to different elements of this multisensory input. In this article we show how shifting attention between simultaneously presented tactile and visual stimuli affects the electrical brain activity of human subjects, and that this signal can be used to augment the control information from the two uni-modal BCI subsystems.