Limits on the application of additive factors logic: Violations of stage robustness suggest a dual-process architecture to explain flanker effects on target processing

Investigated the applicability of additive factors logic to flanker effects (i. e., single or multi-element stimuli composed of a target flanked by elements with no response-relevant information) on target processing, in 3 reaction time (RT) experiments. 32 college students were exposed to 3 factors: Flanker presence, target size (TS), and stimulus-response compatibility (SRC). In Exp 2, the nature of the flankers was changed, and in Exp 3, incongruent stimulus arrays were added to the stimulus set. Results show that the effects of TS and SRC on RT were additive when the target was flanked by stimuli containing no information response-relevant. This additivity changed to a superadditive interaction when flankers signaled the same response as the target: The effect of SRC was larger when targets were small rather than large. The relation between TS and SRC was subadditive when flankers signaled the response opposite to that designated by the target.