The posterior semantic asymmetry (PSA): specific to written not auditory semantic word processing

The present study replicates the finding of a posterior semantic asymmetry (PSA; Koppehele-Gossel et al., Brain Lang 157-158:35-43, 2016), a lateralized event-related potential (ERP) suggested to reflect semantic activation from visually presented single words. This ERP negativity, derived from the subtraction of right-side from left-side scalp activity, again peaked around 300 ms at temporoparietal electrodes and was more pronounced in a semantic task, compared to both a silent naming task and a passive viewing task. With analogous tasks, no comparable negativity was found for auditorily presented words. This suggests that the PSA specifically reflects visual-verbal semantic activation. For auditory words, a later variation with the demands on semantic processing was observed for a left-lateralized late positive potential (500-800 ms), which, however, showed a remarkably similar topography as the PSA. Thus, while semantic processing of visual and auditory words converges on left temporoparietal brain areas, the exact patterns of brain electrical activation in terms of time course and polarity are different.