The Role of Task Manipulations on the Invariant Phasing Characteristics of a Generalized Motor Program (Relative Timing).

Four experiments are reported that investigate the role of relative timing as an invariant characteristic of the generalized motor program. Based upon the concept of a generalized motor program, relative time as an invariant characteristic, should remain constant when variant features of a movement are manipulated. In the present series of experiments, a practice and transfer paradigm was used to investigate the influence of required parameter modifications on the relative timing characteristics during the transfer performance of a practiced three-component movement response. Following 150 training trials (100 trials on Day 1 and 50 trials on Day 2), subjects (n = 12) were randomly assigned to 1 of 10 transfer conditions that manipulated the variant features of the training task. Fifty transfer trials were performed that differed from the training task in terms of the geometric, dimension, direction or muscle selection characteristics. Results based on group analysis of variance and individual linear regression, indicated that for all parameter characteristic manipulations, relative timing patterns during transfer performance deviated significantly from those established during training trials. These results are in contradiction with previous studies which have supported the idea that timing structure remains invariant across changes in muscle selection and event duration. However, since the absolute magnitude of the relative timing proportion changes were so small, typically from .5 to 2%, a modification in the current definition of relative timing invariance is suggested rather than an abandonment of the construct as a generalized motor program feature