Programming of time-to-peak force for brief isometric force pulses: Effects on reaction time

Abstract

According to the parallel force unit model (PFUM) the programming of an isometric force pulse requires the specification of the number of force units and force unit duration. The programming of a force pulse with minimal time-to-peak force is an exception, however, as force unit duration is limited by the minimal possible value, which should be easier to adjust than larger force unit durations. Therefore, the duration of the programming process should be shorter for these force pulses and hence should result in shorter reaction time (RT). Four experiments assessed this prediction using a response precueing procedure. In each experiment the participants produced isometric flexions with their left or right index finger, and time-to-peak force was manipulated within a block. The results are consistent with the predictions of PFUM. The results, however, are at variance with alternative accounts which assume that RT depends primarily on response duration or rate of force production.

Acknowledgments

Part of this work was described in a doctoral dissertation in psychology submitted by the author to the University of Tübingen. I thank Eva Kühlwein, Kai-Markus Müller, and Steffi Plenio for their assistance in collecting the data and Jeff Miller for the loan of his statistics program “MrF”. I appreciated the very helpful comments of Hartmut Leuthold, Jeff Miller, Gerhard Rinkenauer, Rolf Ulrich, and two anonymous reviewers on earlier drafts of the manuscript.

Notes

¹Clearly, a force pulse characteristic like rate of force production cannot influence RT directly as the past does not depend on the future. However, RT can be influenced by the duration of programming processes that involve the specification of response parameters controlling response characteristics (Rosenbaum, 1980, 1983; see also Falkenberg & Newell, 1980). In particular, the specification of response parameter(s) that control rate of force production may be completed earlier when the required rate of force production of the to-be-executed force pulse is relatively high. In the following, the terminology of “an influence of a response characteristic on RT”, is only used to enhance readability.

² A similar result was reported in a choice RT study of Masaki, Wild-Wall, Sangals, and Sommer (2004). In this study participants had to produce force pulses by extensions of their left and right index fingers, and TTP (100 vs. 300 ms) was manipulated across blocks. Mean RT for force pulses with shorter TTP was around 30 ms shorter than that for force pulses with longer TTP. However, rate of force production and peak force were not reported in this study.

³ A pre-analysis of the data revealed no systematic effects of the within-subject factor response hand (left vs. right) in any of the experiments. Therefore, this factor was excluded from the reported analyses, and all data in the table and figures were averaged across left and right responses.

⁴ One reviewer suggested this alternative account.

⁵ An alternative explanation for the especially small RT advantage for force pulses with minimal TTP in the full precue condition is that participants had different utilization strategies in the full and partial precue conditions, respectively. Specifically, they could have made more of an effort to prepare their responses in the full precue condition as they were aware that this will largely shorten RT. There is evidence, however, that different utilization strategies in full and partial precue conditions do not have a strong influence on response preparation within the response precueing paradigm (Sangals, Sommer, & Leuthold, 2002).