Whereas every effort was made to equate the stimulus categories with regard to their physical properties (graphic dimensions, overall perceived brightness), it should nonetheless be obvious that words and faces inherently differ in their spatial frequency composition and complexity. However, we would expect these physical differences between stimulus categories to primarily affect early, exogenous ERP components (P1, N1). Although these differences may complicate task comparisons, they seem of subordinate importance compared to their intended and more obvious distinctions (i.e., linguistic vs. face processing). Furthermore, within each stimulus category, any late old/new effects are well-controlled for physical properties.
