Analogous mechanisms compensate for neural delays in the sensory and the motor pathways: evidence from motor flash-lag.

Motor behaviors require animals to coordinate neural activity across different areas within their motor system. In particular, the significant processing delays within the motor system must somehow be compensated for. Internal models of the motor system, in particular the forward model, have emerged as important potential mechanisms for compensation. For motor responses directed at moving visual objects, there is, additionally, a problem of delays within the sensory pathways carrying crucial position information. The visual phenomenon known as the flash-lag effect has led to a motion-extrapolation model for compensation of sensory delays. In the flash-lag effect, observers see a flashed item colocalized with a moving item as lagging behind the moving item. Here, we explore the possibility that the internal forward model and the motion-extrapolation model are analogous mechanisms compensating for neural delays in the motor and the visual system, respectively. In total darkness, observers moved their right hand gripping a rod while a visual flash was presented at various positions in relation to the rod. When the flash was aligned with the rod, observers perceived it in a position lagging behind the instantaneous felt position of the invisible rod. These results suggest that compensation of neural delays for time-varying motor behavior parallels compensation of delays for time-varying visual stimulation.