Interference effects in the Stroop and Simon paradigms.

The possibility that Stroop and Simon effects reflect the same cognitive processes was tested in 3 experiments with 62 adult Ss. The words LEFT and RIGHT were shown left and right of screen center. Similar levels of interference were found for a Simon task (keypress to meaning of word) and a spatial Stroop task (name its location). A reverse Simon task (keypress to word location) showed minimal interference from the irrelevant word, but in a reverse spatial Stroop task (read the word aloud) interference from the irrelevant location was sizable. This poses difficulty for translational accounts of Stroop interference. Presenting LEFT and RIGHT laterally balanced by a color-name foil yielded a Simon effect inconsistent with an orienting response hypothesis. With bilateral stimuli in a reverse Simon task, interference was marked, supporting an integrative account of Stroop and Simon effects in terms of cognitive activation and the salience of irrelevant stimuli.