Visuomotor mental rotation: reaction time is not a function of the angle of rotation.

The goal of the present investigation was to determine whether the anti-pointing task (i.e., pointing to a location 180 degrees from a visual cue [M. Heath, A. Maraj, A. Gradkowski, G. Binsted, Anti-pointing is mediated by a perceptual bias of target location in left and right visual space, Exp. Brain Res. 192 (2009) 275-286]) and a 90 degrees -rotated-pointing task are supported by a similar cognitive strategy. Previous work evaluating visuomotor mental rotation (MR) has reported a monotonic increase in reaction time (RT) as a function of the angle of rotation [A.P. Georgopoulos, G. Pellizzer, The mental and the neural: psychological and neural studies mental rotation and memory scanning, Neuropsychologia 33 (1995) 1531-1547]. Interestingly, however, anti-pointing movements have not been evaluated in concert with intermediary angles of rotation. We therefore examined RT for center-out pointing movements in four tasks: pro-pointing (PRO), anti-pointing (ANTI), and 90 degrees clockwise (CW90) and counter-clockwise (CCW90) pointing. We found that response latencies for PRO responses were faster than ANTI responses, which in turn were faster than CW90 and CCW90 responses. These findings counter the notion that the angle of rotation influences the speed of visuomotor MR. Instead, we posit that visuomotor MR is supported by a serial process requiring the suppression of a stimulus-driven response followed by voluntary response generation. Further, we suggest that preparation of the voluntary response is cognitively less demanding for the ANTI task because the sensorimotor transformations underlying such an action are completed within the same plane as the stimulus-driven response. In contrast, the cognitive demands associated with CW90 and CCW90 are more complex because the action requires the transformation of response parameters in a movement plane orthogonal to the original - and suppressed - stimulus-driven response.