The development of skill: The coefficient of variation as an index of skill acquisition

Previous research has found that extensive practice usually leads to faster more stable reaction times (RTs). The goal of this study was to distinguish practice effects which are due to a speed-up (where reduced RTs and correspondingly reduced variability in RT indicate that the task is being performed faster but in the same way), from practice effects due to increased automaticity (where faster RTs and reduced RT variability indicate a restructuring of task components). Subjects performed a memory search task in which 2000 trials were in a consistent mapping (CM) condition and 2000 were in a varied mapping (VM) condition. VM training has been shown to improve speed of performance but not to increase automatization. CM training on the other hand has been shown to improve performance, beyond considerations of speed alone, by automatizing performance. In the present study it was found that the coefficient of variation ((CV) the standard deviation divided by mean RT) was significantly reduced after CM but not after VM practice, showing that the CV may be a useful index of changes, other than speed, in the organization and execution of processes underlying a skilled action. The results were interpreted in terms of how practice contributes to the acquisition of performance skill.