An ERP investigation of task switching using a flanker paradigm

To investigate whether a task rule carried over from the preceding trial modifies an early portion of the stimulus-locked lateralized readiness potential (sLRP), participants were asked to perform two different flanker tasks that were switched. One task required a left-hand response for a central letter "H" in a five-letter array, and a right-hand response for "S." The stimulus-response rule was reversed for the other task. Reaction times (RTs) were prolonged for switch trials as compared to repeat trials, irrespective of whether stimuli in the five-letter array were congruent or incongruent flankers. For the incongruent stimuli, the onset latency of the sLRP was shorter on switch trials compared to repeat trials although the onset for congruent stimuli was delayed on the switch trials. These different sLRP effects as a function of congruent versus incongruent stimuli were interpreted as a manifestation that automatic response activation, dependent on a task rule carried over from a preceding trial, was induced by the early transmission of flanker-related information from stimulus evaluation processes. The finding that the earlier sLRP onset for incongruent stimuli on switch trials did not shorten RTs suggests that RT switch costs are not attributable simply to passive processes.