Choice between finger movements of different and identical form: The effect of relative signal frequency

Summary Binary choice reaction time depends on the relationship between the alternative responses. In particular, it is longer when choice is between finger movements of either hand, which have different forms, than when choice is between movements of identical form. This effect can be interpreted in terms of conjunctive preparation. If everything common to both responses is prepared in advance of the response signal, the form of the movement can only be prepared if it is the same for both responses. An alternative interpretation is in terms of single preparation. Under this hypothesis either one or the other response is prepared completely, but in case the not prepared response is demanded by the signal the time needed to shift should be longer if the movements are of different form. Thus, an effect of the form-relation will be seen only in unprepared responses, while under the hypothesis of conjunctive preparation it should be present in prepared responses as well. To decide between both hypotheses relative signal frequency and thus the proportion of expected (and prepared) responses was varied in three experiments. It turned out that the effect of the form-relation is larger with low relative signal frequency than with high frequency. This indicates the existence of single preparation. However, single preparation appears to be incomplete. When the obtained data are extrapolated to a relative signal frequency of 1.0 an effect of the form-relation still remains.This research was supported by Deutsche Forschungsgemeinschaft (grants No. He 1187/1 and 1187/2-1)