Central and parietal event-related lateralizations in a flanker task.

Recently Wascher et al. (1999) reported that in a flanker task with arrow stimuli not only the known lateralized readiness potential (LRP) that reflects lateralized response activation was induced, but also a parietal lateralized activation (direction encoding lateralization; DEL) that was interpreted as reflecting an earlier coding of a response side. However, the Wascher study did not exclude that the DEL could have also been due to lateralized stimulus- or attention-related factors. In the present study we used vertically directed arrow stimuli, and had our subjects perform responses in the vertical dimension. To separate flanker-induced from target-induced lateralizations the delay between the presentations of irrelevant and relevant stimuli (stimulus onset asynchrony; SOA) was manipulated. Apart from the usual LRPs we obtained clear DELs that varied in a similar way with the experimental variables, but peaked earlier and had a more posterior topography than the LRP. These results indicate that the DEL reflects premotor response representation.