N400, the reference electrode, and the semantic activation in prime-task experiments: A reply to Dombrowski and Heil (2006)

In two recent papers, Heil et al. [Heil, M., Rolke, B., Pecchinenda, A., 2004. Automatic semantic activation is no myth: semantic context effects on the N400 in the Letter-Search task in the absence of response time effects. Psychol. Sci., 15 (12), 852–857] and Marí-Beffa et al. [Marí-Beffa, P., Valdés, B., Cullen, D.J.D., Catena, A., Houghton, G., 2005. ERP analyses of task effects on semantic processing from words. Cogn. Brain Res., 23, 293–305] found opposite ERP effects of semantic priming following letter search (as measured by the N400). Dombrowski and Heil [Dombrowski, J.H., Heil, M., 2006. Semantic activation, letter search and N400: a reply to Marí-Beffa, Valdés, Cullen, Catena and Houghton (2005). Brain Res., 1073–1074, 440–443] have argued that the N400 modulation associated to semantic priming found by Marí-Beffa et al. [Marí-Beffa, P., Valdés, B., Cullen, D.J.D., Catena, A., Houghton, G., 2005. ERP analyses of task effects on semantic processing from words. Cogn. Brain Res., 23, 293–305] is due to the use of electrode Cz as reference, rather than to the task manipulation being studied (letter search vs. categorisation). In the current article we argue that the conclusions of Dombrowski and Heil are mistaken and are due in part on a misreading of Marí-Beffa et al. [Marí-Beffa, P., Valdés, B., Cullen, D.J.D., Catena, A., Houghton, G., 2005. ERP analyses of task effects on semantic processing from words. Cogn. Brain Res., 23, 293–305]. We argue instead that the differences between the results of Heil et al. [Heil, M., Rolke, B., Pecchinenda, A., 2004. Automatic semantic activation is no myth: semantic context effects on the N400 in the Letter-Search task in the absence of response time effects. Psychol. Sci., 15 (12), 852–857] and Marí-Beffa et al. [Marí-Beffa, P., Valdés, B., Cullen, D.J.D., Catena, A., Houghton, G., 2005. ERP analyses of task effects on semantic processing from words. Cogn. Brain Res., 23, 293–305] are largely due to differences in experimental method and procedure, rather than to the technique used for the ERP analysis.