Adjustment and readjustment of the relative timing of a motor pattern

Summary The hypothesis of a generalized motor program with relative timing as an invariant characteristic is contrasted with a continuity hypothesis. According to this hypothesis, temporal characteristics are determined by the same parameters of a generalized motor program as spatial characteristics are; different temporal patterns are assumed to be associated with different costs. In two experiments uniarticular arm movements with different relative timing were studied. Three results were obtained that support the continuity hypothesis. (1) Reproductions exhibited asymmetric biases, that is, reproductions of one target pattern were biased toward the other, but not vice versa. (2) Readjustment to a new target pattern that had a correlation of almost zero with the practice pattern was not immediate, as found by Heuer and Schmidt (1988), who used more similar patterns. This suggests that readjustment of a temporal pattern depends on the similarity between the old and the new patterns. (3) Readjustment to another target pattern that had been practiced before was immediate for similar patterns, but not immediate for dissimilar patterns. The effects of the similarity of different temporal patterns on readjustment are not consistent with the view that each temporal pattern is governed by its own generalized motor program.