Stimulus-response compatibility and position of the hands: nonadditive effects

An experiment was conducted using a two-choice stimulus-response compatibility task factorially combined with position of the hands. Subjects responded to a visual target word (Left or Right) by pressing on the left or the right key depending on the compatible or incompatible assignment and performed the task with the hands uncrossed or crossed. The effects of Stimulus-response compatibility and Position of hands were not additive. Moreover, no effect of compatibility occurred in the crossed-hand condition. These findings are consistent with the predictions derived from a recent hypothesis assuming that in some particular experimental conditions the presentation of the stimulus will activate two automatic responses. The two stimulus-response compatibility mappings related to these two automatic responses have been shown to be positively or negatively correlated depending on the factorial combination of Stimulus-Response Compatibility and Position of Hands. As a consequence the effects of the two factors theoretically cannot be additive. This assumption accounts for the present results.