Motor programming of response force and movement direction ROLF ULRICH, a HARTMUT LEUTHOLD, b and WERNER SOMMER b a University of Wuppertal, Germany b Humboldt University, Berlin, Germany Abstract Effects of movement advance information were assessed on the prestimulus amplitude of the lateralized readiness potential ~ LRP!, on the contingent negative variation ~CNV!, and on reaction time ~ RT!. In a precuing paradigm with movement parameters hand, direction, and force, partial precues provided advance information about either hand alone, hand plus force, or hand plus direction, and the full precue specified all response parameters. The full precue produced the shortest RTs and the largest CNV amplitude, precuing hand and force or hand and movement direction produced somewhat slower RTs and a somewhat smaller CNV amplitude, and precuing only hand yielded slowest RTs and the smallest CNV amplitude. In contrast, the LRP amplitude was largest for the full precue and was the same for the re- maining precues. The CNV appears to index the central assembling of a motor program, and the LRP represents the implementation of the program at more peripheral levels. Descriptors: Motor programming, LRP, CNV, Readiness potential, Reaction time, Response force The introduction of event-related brain potentials ~ ERPs! in the study of movement preparation has provided new approaches and insights into what had previously been an exclusively behavioral field. The most successful approach in cognitive psychology to analyze the nature of movement preparation employs the precuing technique developed by Rosenbaum ~1980, 1983!. This technique is a variant of a choice reaction time ~ RT! task, in which each of the possible responses is associated with a single imperative stim- ulus. Before the onset of the stimulus, a precue conveys informa- tion about certain movement parameters. Usually, RT decreases with the amount of advance information provided. From the rela- tion between advance information and the corresponding RT sav- ing, cognitive psychologists hoped to learn more about motoric preparation and the nature of motor programs ~e.g., Rosenbaum, 1980!. However, this approach was criticized by Goodman and Kelso ~1980! who argued that the RT saving observed with this technique does not reflect a genuine motor effect but rather the facilitation of response selection at a premotoric level. The debate on whether the RT saving reflects a genuine motoric effect could not be settled with the traditional behavioral RT measure because the motoric portion of RT is not directly observable. In resolving this controversy, a new measure, the lateralized readiness potential ~ LRP!, has recently been used ~ Leuthold, Som- mer, & Ulrich, 1996!; there is strong evidence that the LRP pro- vides a specific index to trace the time course of motor activation ~cf. Coles, Gratton, & Donchin, 1988; De Jong, Wierda, Mulder, & Mulder, 1988; Miller & Hackley, 1992!. Experiments employing LRP often involve a two-choice RT task in which a precue informs the participant about the responding hand and a subsequent im- perative stimulus tells the participant that the response should now be made. During the interval between the precue and the impera- tive stimulus, the motor readiness potential exhibits greater nega- tivity over the motor cortex contralateral to the responding hand, suggesting that this asymmetry reflects preparation of a specified motor action ~e.g., Kutas & Donchin, 1980!. Similar results have been found when the precue merely indicates which hand is more likely to have to respond ~Gratton et al., 1990!. Therefore, the asymmetry of the readiness potential captured by the LRP qualifies as an index for the preparation of specific motor acts. Thus, by examining how precue information affects the waveform and the timing of the LRP, the mechanisms underlying response prepara- tion may be inferred. The purpose of this present study was to extend this approach. We investigated whether the amplitude of the prestimulus LRP increases systematically with the amount of ad- vance information, as some hypotheses on motor preparation in precuing studies propose. Ulrich, Moore, and Osman ~1993, 1994! suggested two hypoth- eses about the prestimulus LRP: abstract versus muscle-specific motor preparation. They employed a precue that prespecified ei- ther the left or the right index finger but not its movement direction ~flexion or extension!. Although, participants did not know the movement direction of the prespecified index finger before the appearance of the imperative stimulus, the advance information conveyed by the precue was sufficient to elicit a clear prestimulus This research was supported by the Deutsche Forschungsgemeinschaft ~S0 17706-2! to Werner Sommer and Rolf Ulrich. We greatly appreciate the helpful comments of three anonymous re- viewers on a previous version of this paper. Address reprint requests to: Rolf Ulrich, General Psychology I, Uni- versity of Wuppertal, 42097 Wuppertal, Germany. E-mail: ulrich@uni- wuppertal.de. Psychophysiology, 35 ~1998!, 721–728. Cambridge University Press. Printed in the USA. Copyright © 1998 Society for Psychophysiological Research 721