Abstract
Simon effect using movement related brain potentials. The present study was aimed to diagnosis the locus of interference in the Simon effect (before or during the response-preparation stage) using movement-related brain potentials (the lateralized readiness potential, LRP). Arrowheads pointing left or right, were presented at either side of fixation and subjects pressed a key to indicate the direction of the arrow. The RTs showed the typical Simon effect and the spatial S-R incompatibility produced an early motor activation of the incorrect response. These results are in agreement with models which posit an automatic activation of the ipsilateral response (e.g., Craft and Simon, 1970; Kornblum et al., 1990) and in contradiction with perceptual interference models such as Hasbroucq and Guiard (1991) or Chen-Hui and Proctor (1994). However, we doubt that the LRP between 100 and 200 ms poststimulus is indexing response preparation, at least in this experiment. The reason is that lateralized presentation of visual stimuli produces amplitude asymetries in the same temporal range (N100) at parietal and occipital sites, and we have gather preliminary evidence supporting that these interhemispheric amplitude differences might contaminated the ERPs recorded at central sites.
