Attending to tactile, visual or bimodal targets: effects on the P3 and the relevance for brain machine interfaces

The P3 is a peak in EEG occurring after the presentation of a target. Research has focused on visual and auditory P3s. However, for controlling brain machine interfaces, tactile P3s are more suitable since tactile stimuli are not noticed by others and keep the user's eyes and ears free. We investigated P3s in response to tactile and visual stimuli unimodally, and bimodally. The tactile stimulus was a burst of vibration delivered by one of eight tactors around the waist. The analogous visual stimulus was a flashed circle in a schematic representation of the tactor layout. Participants attended to the vibrations and/or flashes of the target presented amongst non-targets. Tactile targets evoke stronger P3s than visual targets on frontal and central electrodes; the opposite happens on the occipital channel. Visuo-tactile stimuli only modestly strengthened the P3. We conclude that tactile stimuli applied to the waist are suitable to elicit P3s and have great potential for use in BMIs. In a follow-up study, we demonstrate this by building an example BMI.