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Abstract

Body sway—the subtle, low frequency movement of the human body measured during quiet-standing—has long been used as a tool to help diagnose a range of medical conditions. It can be measured in a number of ways, including force platforms, sway magnetometry and marker or marker-less motion capture. In the current work—by analogy—we examined whether “iPad sway” could be used as an indirect measure of performance in a simple interactive task. We asked participants to stand and play a simple iPad game that involved tracking and controlling multiple objects using the touch screen. In addition to measuring variations in task performance as a function of set size and object speed, we also used the iPad’s built-in accelerometer to record changes in applied force along three axes. Analysis of this force data revealed both task relevant and task irrelevant components. The former relating directly to task demands—particularly touching the screen—and the latter reflecting idiosyncratic posture and movement patterns that can be used to uniquely identify individual users.