Simon effect in the rat: a new model for studying the neural bases of the dual-route architecture.

In humans, the Simon effect refers to the fact that choice reaction time (RT) is shorter when the stimulus corresponds spatially to the response than when it does not, albeit the location of the stimulus is irrelevant to the task. This effect has motivated innumerable empirical and theoretical studies and is considered to reflect elementary cognitive processes. We report an experiment demonstrating that rats also display a Simon effect, the dynamics of which--as assessed by factorial manipulations and RT distribution analyses--partly corresponds to those of the effect studied in human participants. The present results are consistent with the ideas that in rats, like in humans, (i) the information conveyed by the stimulus is processed via two parallel routes, one controlled and relatively slow, and one fast and automatic (dual-route architecture) and (ii) the dual-route processing is finished before the start of motor processes. The correspondence between these findings and those reported in humans open new perspectives for neurophysiological investigations of the dual-route architecture in an animal model routinely studied in neuroscience research.