Event-related potential response to attended and unattended locations in an interference task

Event-related potentials were measured in response to an interference task in which unattended stimulus items were compatible, incompatible a neutral with regard to the attended stimulus items. Two stimulus items were presented simultaneously and bilaterally--one in each visual field. This allowed examination of the event-related potential waveform according to whether recording sites were contralateral to the attended or unattended location. The first experiment used sustained cueing with 3.5 degrees separation between attended and unattended locations. Attentional modulation of the N1 was observed but not for the P1. In the second experiment, separation between attended and unattended locations was increased to 11.5 degrees. In both experiments, the hemisphere contralateral to the unattended material (unattended hemisphere) showed a greater negativity in the N2 latency range in the temporal regions to compatible and incompatible conditions compared to a neutral condition. These data are inconsistent with findings suggesting the filtering of material early in visual processing.