Latencies of event related potentials as a tool for studying motor processing organization

The aim of this experiment was to better define the relative organization of motor processing using both behavioral measures and ERPs. Using the additive factors method, three motor variables; (1) stimulus-response (S-R) compatibility, (2) movement extent, and (3) time uncertainty, were all manipulated in a visuo-bimanual, four-choice, pointing task. As expected, all three variables significantly lengthened RT without interaction. All three motor variables also affected ERP latencies. Both P300 and N200 latencies were lengthened by greater movement extent. Moreover, N200 and P300 latencies were differentially affected by S-R compatibility and time uncertainty. Finally, both RT-minus-N200 and RT-minus-P300 were significantly lengthened by S-R incompatibility and greater time uncertainty whereas movement extent had no effect. In sum, ERP results did not support the assumptions of the classical serial model but rather of a contingent-parallel model. Furthermore, the ERP data can be used to infer the relative order of the different stages in this model.