In 4 experiments, the authors investigated the reversal of spatial congruency effects when participants concurrently practiced incompatible mapping rules (J. G. Marble & R. W. Proctor, 2000). The authors observed an effect of an explicit spatially incompatible mapping rule on the way numerical information was associated with spatial responses. The authors also observed an effect of an incompatible numerical mapping rule (if smaller than 5, press right; if larger than 5, press left) on the Simon effect. This effect was observed only when both tasks used the same effectors. The results point to a shared spatial representation for explicit spatial information (locations) and implicit spatial information (numbers).