Crossmodal and intermodal attention modulate event-related brain potentials to tactile and auditory stimuli

An increasing number of animal and human studies suggests that different sensory systems share spatial representations in the brain. The aim of the present study was to test whether attending to auditory stimuli presented at a particular spatial location influences the processing of tactile stimuli at that position and vice versa (crossmodal attention). Moreover, it was investigated which processing stages are influenced by orienting attention to a certain stimulus modality (intermodal attention). Event-related brain potentials (ERPs) were recorded from 15 participants while tactile and auditory stimuli were presented at the left or right side of the body midline. The task of the participants was to attend to either the auditory or to the tactile modality, and to respond to infrequent double-stimuli of either the left or right side. Results showed that spatial attention modulated both early and late somatosensory and auditory ERPs when touch and tones were relevant, respectively. Moreover, early somatosensory (N70-100, N125-175) and auditory (N100-170) potentials, but not later deflections, were affected by spatial attention to the other modality, suggesting bi-directional crossmodal links between hearing and touch. Additionally, ERPs were modulated by intermodal selection mechanisms: stimuli elicited enhanced negative early and late ERPs when they belonged to the attended modality compared to those that belonged to the unattended modality. The present results provide evidence for the parallel influence of spatial and intermodal selection mechanisms at early processing stages while later processing steps are restricted to the relevant modality.