Perceptual and Motor Space Representation: An Event‐Related Potential Study

The purpose of this experiment was to study the brain potentials generated during spatial tasks related to the “schema corporel” (a mental map of sensory‐motor relationships). Seven right‐handed subjects performed a choice reaction‐time task (Experiment 1), in which the spatial position of a visual stimulus (right or left of a fixation point) was varied independently of the spatial position of the response (right or left hand). The subjects also made self‐paced extensions and flexions of the right and left index fingers (Experiment 2). Experiments 1 and 2 were performed with the hands both crossed and uncrossed. Spatio‐temporal maps showed that the P300 component elicited by the choice RT situation in Experiment 1 was largest ipsilateral to the hand involved in the response, whether or not the hands were crossed. The later part of the pre‐movement potentials during Experiment 2 and the motor potential were significantly larger contralateral to the moving hand under all conditions. Thus this pattern of lateralization can be attributed to the superimposition of a bilateral P300 wave on the asymmetrical motor potential. This suggests that distinct neuronal populations are involved in the generation of these two components. P300 latency and RT reflected the spatial conflict: both were longer when the stimulus and response were on opposite sides than when they were on the same side, even when the hands were crossed. However, the average P300 latency was not increased when the hands were crossed, whereas the average RT was substantially increased. Since the additional time required for programming the movement in the crossed hand situation had no effect on P300 generation, we infer that the P300 does not index this motor programming. However, P300 does reflect the stimulus‐response spatial matching, since its latency was delayed by spatial conflict.