Visuomotor mental rotation: reaction time is determined by the complexity of the sensorimotor transformations mediating the response.

In the visuomotor mental rotation (VMR) task, participants point to a location that deviates from a visual target by a predetermined angle. A seminal investigation of the VMR task reported a linear increase in reaction time (RT) as a function of increasing angle, for 5°, 10°, 15°, 35°, 70°, 105°, and 140° (Georgopoulos and Massey, 1987). This finding led to the development of the mental rotation model (MRM) and the assertion that response preparation is mediated via the imagined rotation of a movement vector. To determine if the MRM can be extrapolated to perceptually familiar angles (e.g., 90° and 180°) within a range of equally spaced angles, we evaluated two independent sets of angles: 5°, 10°, 15°, 35°, 70°, 105°, and 140° (experiment one) and 30°, 60°, 90°, 120°, 150°, 180°, and 210° (experiment two). Consistent with the MRM, experiment one revealed a linear increase in RT as a function of increasing angle; however, a non-linear relation was revealed for experiment two. RTs were fastest for 180°, followed by 30°, 90°, 60°, 150°, 210°, and 120°. Such results demonstrate that response preparation was not uniquely mediated via a mental rotation process. Instead, the present work provides evidence of a temporally demanding and cognitively mediated response substitution process, wherein the computational demands of response preparation are determined by the complexity of the sensorimotor transformations mediating the response.