Pen pressure control in trajectory-based interaction

Abstract

This study presents a series of three experiments that evaluate human capabilities and limitations in using pen-tip pressure as an additional channel of control information in carrying out trajectory tasks such as drawing, writing and gesturing on computer screen. The first experiment measured the natural range of force used in regular drawing and writing tasks. The second experiment tested human performance of maintaining pen-tip pressure at different levels with and without a visual display of the pen pressure. The third experiment, using the steering law paradigm, studied path steering performance as a function of the steering law index of difficulty, steering path type (linear and circular) and pressure precision tolerance interval. The main conclusions of our investigation are as follows. The natural range of pressure used in drawing and writing is concentrated in the 0.82N (SI force unit Newton (N) is used in this article) to 3.16N region. The resting force of the pen tip on the screen is between 0.78N and 1.58N. Pressure near or below the resting force is markedly more difficult to control. Visual feedback improves pressure-modulated trajectory tasks. Up to six layers of pressure can be controlled in steering tasks, but the error rate changed from 4.9% for one layer of pressure to 35% for six layers. The steering law holds for pressure steering tasks, which enables systematic prediction of successful steering time for a given path's length, width and pressure precision criterion. The steering time can also be modelled as a logarithmic function of pressure control precision ratio . Taken together, the current work provides a systematic body of empirical knowledge as basis for future research and design of digital pen applications. © 2010 Taylor & Francis.