Mental rotation interferes with response preparation.

Reaction times (RTs) and lateralized readiness potentials (LRPs) were studied to find out whether response preparation begins after mental rotation finishes, as assumed by discrete-stage models. Stimuli were disoriented normal or mirror-image characters, with character name determining which hand would respond. In Experiment 1, the normal/mirror-image information determined whether the response was to be executed (go) or withheld (no-go), and LRPs indicated that responses were weakly prepared before the end of mental rotation. Mental rotation was not required in Experiment 2, and significantly more response preparation was observed. In Experiment 3, probe RT trials embedded in the mental rotation task indicated that hand information is available to the response preparation process during rotation. Apparently, some response preparation occurs before mental rotation finishes, but rotation interferes with response preparation.