The functional locus of the lateralized readiness potential


  • Portions of this article were presented at the 42nd Annual Meeting of the Society for Psychophysiological Research, Washington, DC, October 2–6, 2002.

  • This study was supported by a fellowship of the Japan Society for the Promotion of Science to the first author. The authors would like to thank Allen Osman for valuable discussions, Kathrin Pusch for her assistance in collecting the data, and William Gehring, Toby Mordkoff, Birgit Stürmer, and one anonymous reviewer for their helpful comments on an earlier draft of this article.

Address reprint requests to: Dr. Hiroaki Masaki, School of Sport Sciences, Waseda University, 2-579-15, Mikajima, Tokorozawa, Saitama, Japan, 359-1192. E-mail:


The lateralized readiness potential (LRP) is considered to reflect motor activation and has been used extensively as a tool in elucidating cognitive processes. In the present study, we attempted to more precisely determine the origins of the LRP within the cognitive system. The response selection and motor programming stages were selectively manipulated by varying symbolic stimulus response compatibility and the time to peak force of an isometric finger extension response. Stimulus response compatibility and time to peak force affected response latency, as measured in the electromyogram, in a strictly additive fashion. The effects of the experimental manipulations on stimulus- and response-synchronized LRPs indicate that the LRP starts after the completion of response-hand selection and at the beginning of motor programming. These results allow a more rigorous interpretation of LRP findings in basic and applied research.