Human Motor Transfer Is Determined by the Scaling of Size and Accuracy of Movement

ABSTRACT

A transfer of training design was used to examine the role of the Index of Difficulty (ID) on transfer of learning in a sequential Fitts's law task. Specifically, the role of the ratio between the accuracy and size of movement (ID) in transfer was examined. Transfer of skilled movement is better when both the size and accuracy of movement are changed by the same factor (ID is constant) than when only size or accuracy is changed. The authors infer that the size–accuracy ratio is capturing the control strategies employed during practice and thus promotes efficient transfer. Furthermore, efficient transfer is not dependent on maintaining relative timing invariance and thus the authors provide further evidence that relative timing is not an essential feature of movement control.

Keywords:

• Fitts's law
• generalized motor program
• transfer of motor learning

ACKNOWLEDGMENTS

Portions of this research were presented in 2005 Annual Meetings of the Society for Mathematical Psychology and 2006 VSS Annual Meeting. This research was supported in part by grants from Purdue Research Foundation and the Air Force Office of Scientific Research. The authors wish to thank the Envision Center at Purdue University for its support.

Notes

1. In a number of cases the 81st trial contained an error and so the time of this trial was not used. In such cases, we took the time of the first trial after transfer where the participant makes no error. The mean error rate of the 81st trial was 39% in the transfer to dr condition and 26% in the transfer to DR condition. The difference in error rate between two groups was significant, t(190) = 2.00, p = .046. There was no significant difference between the conditions within a group.

2. We used principal component analysis (PCA), rather than regression analysis, to find the best-fitting line. PCA minimizes the sum of squared distances of the data points from the line measured in the direction orthogonal to the line, whereas the regression analysis minimizes the sum of squared distances measured in the direction of the dependent (predicted) variable. A regression line is used to make predictions, whereas the direction of the principal component is used to characterize the factor common in two or more variables. It seems quite clear that the analysis of relative timing is related to PCA more than to regression. In fact, PCA is a more conservative test in the sense that regression analysis leads to the rejection of the relative timing more often.