In the visuomotor mental rotation (VMR) paradigm, participants execute a center-out reaching movement to a location that deviates from a visual cue by a predetermined instruction angle. Previous work has demonstrated a linear increase in reaction time (RT) as a function of the amplitude of the instruction angle (Georgopoulos and Massey in Exp Brain Res 65:361-370, 1987). In contrast, we recently reported a RT advantage for an instruction angle of 180° relative to a 90° angle (Neely and Heath in Neurosci Lett 463:194-198, 2009). It is possible, however, that perceptual expertise with the cardinal axes, which are perceptually familiar reference frames, influenced the results of our previous investigation. To address this issue, we employed a VMR paradigm identical to that of our previous work, with the exception that the stimulus array was shifted 45° from the horizontal and vertical meridians. Our results demonstrated that RTs were fastest and least variable when the instruction angle was 0°, followed by 180°, which in turn, was faster than 90°. Such findings establish that the RT advantage for the 180° instruction angle is not influenced by perceptual expertise with the cardinal axes. Moreover, the present results provide convergent evidence that RT is not determined by the angle of rotation; instead, they indicate that response latencies reflect computational differences in the complexity of response remapping.
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