The effects of intensity and irrelevant location of a tactile stimulation in a choice reaction time task.

Simon and his colleagues have demonstrated that the location of a stimulus in the sensory field, even if it is irrelevant for the task, may critically affect reaction time. This so-called 'Simon effect' is a general phenomenon that encompasses all sensory modalities. The experiment reported here showed that the tactile version of the Simon effect was additive on reaction time with the respective effects of stimulus intensity and of the within-hand/between-hand composition of the repertoire of fingers devoted to the task. In light of recent theoretical developments, the present data suggest that the locus of the Simon effect is stimulus identification, a perceptual stage which follows stimulus encoding and precedes stimulus-response translation.