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 the following: The natural range of pressure used in drawing and writing is concentrated in the 0.82N 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 6 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 6 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 modeled as a logarithmic function of pressure control precision ratio σ. Taken together, the current work provides a systematic body of empirical knowledge as basis for future research and design of digital pen applications.

Publications

Yin, J., Ren, X. and Zhai (2009). Pen Pressure Control in Trajectory-based Interaction, to appear in Behaviour & Information Technology, Taylor & Francis.    

This research presents seven experiments to determine the optimal size of a box for the input of handwriting characters on PDAs. The experiments involve consideration of boxes for different kinds of characters, different sizes and shapes (square and rectangular), the learning effect, and the age differences of users. The results are assessed in terms of high performance factors (e.g., high character recognition rates, minimal stroke protrusions outside the character box) and subjective ratings (e.g., ease of writing and minimum degree of fatigue). The results show that the optimal size of character boxes for the input of alphanumeric characters is 1.20 x 1.44 cm (rectangular), and for Kanji mixed with Kana characters and Hiragana & Katakana characters the optimal size is 1.44 x 1.44 cm (square). We believe that knowledge of the optimal size of a character input box will be useful for the design of the user interfaces of PDAs.

Publications

Ren, X. 2006. The Optimal Size of Text Entry Boxes on PDAs. In Proceedings of CHI-SA 2006 , ACM Press. pp.31-40.  PDF  

Ren, X. and Zhou, X. (2009). The Optimal Size of Handwriting Character Input Boxes on PDAs, to appear in Int. J. Human-Computer Interaction, Lawrence Erlbaum Associates. 

   

This paper investigates the age factor on the usability of pens when using PDAs. Older users and child users were asked to perform the experiments in which they conducted pointing and steering tasks on a PDA using various sizes of pen. Six combinations of pen length, width and pen-tip width were compared in the test. Five pen-lengths (7, 9, 11, 13, 15 cm), three pen-tip widths (0.5, 1.0 and 1.5mm) and the two pen widths (4 and 7mm) were compared. The results show that the most suitable pen dimensions for older users are 11-15cm for length, 1.0-1.5mm for tip width, and 7.0mm for pen width; and for child users the length is 7-13cm, tip width is 1.0-1.5mm, and 4.0mm is the optimum pen width.

Publications

Ren, X., Fukutoku, F. 2006. Usability of the Stylus Pen and Age, to appear in Proceedings of APCHI2006: 6th Asia Pacific Conference on Computer Human Interaction. 10 pages, Springer.  PDF