A fresh perspective on dissecting action into discrete submotions.

The hypothesis that reaching motions are constructed from discrete components has been explored since the earliest scientific investigations of human movement, although composition specifics have been contentious. We reinspect this process by analyzing the underlying motor intent (rather than actual motion) using our recently-developed intent determination technique. First, synthetic data analysis was used to determine our accuracy in detecting submotion events. Next, we evaluated this on healthy reaching movements and overcame the problem of indistinguishably blended submotions by exposing subjects to strong, abruptly changing forces, which lead to clear corrections identifiable using direction-based clustering. We were able to accurately recover submotion parameters and identify patterns in submotion count, peak kinetic energy, and peak-to-peak duration. These values were all exponentially distributed, which implies that selection of submotions may follow simple rules. This provides a novel opportunity to investigate human motor action using the tools of statistics.