A spatial analogue of a dissonance mainpulation was used to test the claim that the mere acquisition of incongruent data produces cognitive reorganization. Undergraduates ranked distances among 13 campus landmaks before and after detouring around an imaginary barrier on embedding new landmarks in their mental maps. Scaling procedures revealed that barrier detours generated structural distortions of existing cognitive maps whereas landmark substitutions did not. The detour transformation produced systematic biases in subjects' postmanipulation maps; the substitution transformation was completely nonreactive. It is concluded that mental acts which create momentary distortions of cognitive structure can permanently reshape one's internal representations. (26pp.)