Crossmodal attention effects on brain responses to different stimulus classes

Background: Attending to a point in space in one modality may facilitate processing to information from the same region in another modality. The involvement of sensory-specific cortical areas in intramodal and crossmodal selective spatial attention can be assessed with event-related brain potentials (ERPs). ERPs were recorded in two groups of young participants (each n = 11). Stimulus sequences comprised visual standard stimuli (p = 0.4, a white square), visual deviant stimuli (p = 0.05, a white square with small black rectangle) and visual novel stimuli (p = 0.05, different multicolored checkerboards) as well as auditory standard (p = 0.4,800 Hz tone), deviant (p = 0.05, 900 Hz tone), and novel (p = 0.05, random combination of three sine-wave tones) stimuli, occurring in random order at locations 30 degrees left and right of a fixation point. The "auditory group" of participants attended either to the left or to the right speaker in order to respond to the infrequent auditory deviants at that location by a speeded button press. Visual stimuli were irrelevant for this group. The "visual group" had the analogue task for the visual modality. For these participants auditory stimuli were irrelevant throughout the experiment. Results: ERPs showed a typical enhancement of early sensory specific components by intramodal spatial attention (visual group: visual PI and NI; auditory group: auditory Nd). Crossmodal spatial attention effects included a modulation of the Nd to auditory standards in the visual group and a modulation of the PI to visual novels and NI for visual standards for the auditory group. Similar to previous studies crossmodal spatial attention effects on visual standard and novel stimuli also included a frontocentral positivity in the 200-400 ms range that was not seen for intramodal spatial visual attention suggesting involvement of later supramodal areas. Conclusion: These findings are consistent with an action of crossmodal spatial attention on early, sensory specific processing stages.