New Metrics for Understanding Touch by People with and without Limited Fine Motor Function

Current performance measures with touch-based systems usually focus on overall performance, such as touch accuracy and target acquisition speed. But a touch is not an atomic event; it is a process that unfolds over time, and this process can be characterized to gain insight into users’ touch behaviors. To this end, our work proposes 13 target-agnostic touch performance metrics to characterize what happens during a touch. These metrics are: touch direction, variability, drift, duration, extent, absolute/signed area change, area variability, area deviation, absolute/signed angle change, angle variability, and angle deviation. Unlike traditional touch performance measures that treat a touch as a single (x, y) coordinate, we regard a touch as a time series of ovals that occur from finger-down to finger-up. We provide a mathematical formula and intuitive description for each metric we propose. To evaluate our metrics, we run an analysis on a publicly available dataset containing touch inputs by people with and without limited fine motor function, finding our metrics helpful in characterizing different fine motor control challenges. Our metrics can be useful to designers and evaluators of touch-based systems, particularly when making touch screens accessible to all forms of touch.