No evidence for a late locus of task switch effects.

When participants are asked to switch from one task to another, reaction time is longer than in task repetition trials. Current models assume that switch costs are located either at the perceptual stage or at the response selection stage. Contrary to this assumption, Hsieh and Liu ([2005. The nature of switch cost: task set configuration or carry-over effect? Cogn. Brain Res. 22,165-175]) found that task switching affects the response-locked lateralized readiness potential and thus provided evidence for a motor locus of switch costs. We hypothesized that this finding may have been due to methodological artefacts. In order to test this hypothesis, we replicated the experiment by Hsieh and Liu (2005) but avoided some potential methodological artefacts of their study. Our results showed a clear effect of task switching on the stimulus-locked lateralized readiness potential but no effect on the response-locked lateralized readiness potential. Thus, the present study questions the evidence for a late, motor locus of task switch effects but rather indicates a locus at the response selection stage.