DISSOZIATION VON EREIGNISKORRELIERTEN POTENTIALEN UND REAKTIONSZEIT IN EINER KATEGORISIERUNGSAUFGABE

The investigation was aimed at the question whether or not the N400-component of the event-related brain potential and reaction time index the same processes in semantic priming experiments. To this end, word lists comprised of exemplars of ten common taxonomic categories were constructed and structured such that words that came from the same category as their predecessor and words that came from a different category were equally probable. Furthermore the sequence of the preceding items was pseudo-randomized yielding equal numbers of each of sixteen possible sequences of four words. Subjects had to judge the category-membership of each word as compared to the preceding word (same/different category, speeded button press). Event-related potentials were obtained in twelve subjects from several scalp sites and averaged according to the sequences of preceding words. Reaction times varied systematically as a function of the preceding words whereas for the N400 amplitude only a difference for the 'category same' (amplitude low) and 'category different' (amplitude high) events was found. No effect of the sequence of preceding events was found. It is concluded that N400 and reaction time index are different processes in semantic priming experiments. Furthermore the constant N400 amplitude irrespective of the sequence of preceding events strongly supports the view that N400 is different from N2.