A dissociation of perception and action in normal human observers: the effect of temporal-delay

Neuropsychological results support the proposal that the human visual system is organised into distinct processing pathways, one for conscious perception and one for the control of action. Here, we compare perceptual and action responses following a pre-response-delay. Experiment 1 required participants to reproduce remembered locations and found that although perceptual matches were unaffected by delays of up to 4 s, pointing responses were significantly biased after only 2 s. Experiment 2 examined whether both the transport and grasp components of a natural prehensile movement were similarly affected by delay. Both peak wrist velocities and peak grip-apertures were affected equivalently by delay, suggesting that the two components of a prehensile movement have similar temporal constraints. The results from both experiments are consistent with the general perception-action dichotomy as originally proposed by Milner and Goodale [The visual brain in action, Oxford: Oxford University Press, 1995].