Alternation of primary task stimulus modality affects event-related brain potentials and secondary task signal detection performance

The effect of alternating primary task stimulus modality on event-related brain potentials and secondary signal detection performance was examined in a dual-task paradigm. An odd-ball paradigm with alternating pairs of auditory tones and visual lights was employed as the primary counting task. Primary task stimuli were classified by previous trial modality (same vs different), previous trial stimulus type (standard vs deviant), and current trial stimulus type. A signal detection task in which an auditory tone followed the primary task stimuli by 120 ms on 50 percent of the trials served as the secondary task. For all but one condition, deviant stimuli produced large P300 and decreased signal detection performance. When a deviant stimulus preceded a deviant in the same modality, however, signal detection performance was better than on standard trials preceded by a deviant. These results were interpreted using a two-parameter model of stimulus probability and subjective value of the stimulus sequence. Also examined were other effects of alternating modality of the primary task stimulus and the sequences defined by the modality and stimulus type of the current and previous trial on the event-related potentials elicited by the primary task stimuli.