Can mental rotation occur before the dual-task bottleneck?

The effect of character disorientation on mirror-normal judgments was found to be partially attenuated with increasing task overlap with a preceding tone-frequency discrimination judgment. These results suggest that orientation-sensitive processing, used to prepare disoriented stimuli for mirror-normal discrimination, can be initiated and proceed in parallel with mental activities required for a tone-frequency discrimination task. The attenuation indicates that at least some of the orientation effect on mirror-normal discriminations has its locus prior to the dual-task processing bottleneck. The possibility that the partial attenuation of the orientation effect was due to attenuation of the effect of orientation on character identification, but not on the mental rotation required for mirror-normal judgments, was examined and rejected.