Preparation for action, motor programs, and the brain

Leuthold, H.
Department of Psychology, University of Glasgow, Scotland, UK

The mental processes underlying action preparation are not directly observable. To infer the hidden mechanisms underlying action preparation, psychologists and neuroscientists have been using the response precuing technique. The present paper reviews movement-related brain potential (MRP) correlates of action preparation and its consequences on information processing in the response precuing paradigm. Two aspects of action preparation are considered: (1) The covert processes going on during the preparatory interval before the imperative response signal and (2) the chronometric effects of such preparation on the processes following the imperative response signal. Firstly, MRPs provide access to at least some of the action preparation processes going on during the preparatory period. Precuing effects in MRPs are by and large consistent with a dual-process model of motor preparation that incorporates abstract and effector-specific programming levels. Accordingly, higher-level motor areas perform abstract programming, whereas effector-specific processes implement motor acts through activation at a lower level muscle-specific level. In this model specification processes of both higher and lower programming levels appear to benefit from advance information and also when temporal uncertainty is reduced. However, motor programming at the muscle-specific level is subject to specific boundary conditions. Secondly, using a chronopsychophysiological approach that combines measurement of reaction time and of the onset of the lateralized readiness potential (LRP), preparation has been found to shorten both premotoric and motoric processing time, depending on the specific movement parameters involved. Implications for current models of action preparation are discussed.