Authors: David Schroeder, Fedor Korsakov, Carissa Mai-Ping Knipe, Lauren Thorson, Arin M. Ellingson, David Nuckley, John Carlis, Daniel F. Keefe
Abstract: In biomechanics studies, researchers collect, via experiments or simulations, datasets with hundreds or thousands of trials, each describing the same type of motion (e.g., a neck flexion-extension exercise) but under different conditions (e.g., different patients, different disease states, pre- and post-treatment). Analyzing similarities and differences across all of the motions in these collections is a major challenge. Visualizing a single trial at a time does not work, and the typical alternative to juxtaposing multiple trials in a single visual display leads to complex, difficult-to-interpret visualizations. We address this problem via a new strategy that organizes the analysis around motion trends rather than trials. This new strategy is significant because it matches the cognitive approach that scientists would like to take when analyzing motion collections. We introduce several technical innovations required to make trend- centric motion visualization possible. The first is an algorithm for detecting trends in a motion collection via time-dependent clustering. The second is a 2D graphical technique for visualizing all the trends in a motion collection, including how trends come and go over time. The third is a 3D graphical technique for visualizing the biomechanics of the set of motions within each trend using a median 3D motion and a visual variance indicator. These innovations are combined to create an interactive exploratory visualization tool, which we designed through an iterative process in collaboration with both domain scientists and a traditionally-trained graphic designer. We report on insights generated during this design process and demonstrate the toolâ€™s effectiveness via: (1) a validation study with synthetic data, and (2) feedback from expert musculoskeletal biomechanics researchers who used the tool to analyze the effects of disc degeneration on human spinal kinematics.