Nomadic Input on Mobile Devices: The Influence of Touch Input Technique and Walking Speed on Performance and Offset Modeling

Abstract

In everyday life, people use their mobile phones on-the-go with different walking speeds and with different touch input techniques. Unfortunately, much of the published research in mobile interaction does not quantify the influence of these variables. In this article, we analyze the influence of walking speed, gait pattern, and input techniques on commonly used performance parameters like error rate, accuracy, and tapping speed, and we compare the results to the static condition. We examine the influence of these factors on the machine learned offset model used to correct user input, and we make design recommendations. The results show that all performance parameters degraded when the subject started to move, for all input techniques. Index finger pointing techniques demonstrated overall better performance compared to thumb-pointing techniques. The influence of gait phase on tap event likelihood and accuracy was demonstrated for all input techniques and all walking speeds. Finally, it was shown that the offset model built on static data did not perform as well as models inferred from dynamic data, which indicates the speed-specific nature of the models. Also, models identified using specific input techniques did not perform well when tested in other conditions, demonstrating the limited validity of offset models to a particular input technique. The model was therefore calibrated using data recorded with the appropriate input technique, at 75% of preferred walking speed, which is the speed to which users spontaneously slow down when they use a mobile device and which presents a trade-off between accuracy and usability. This led to an increase in accuracy compared to models built on static data. The error rate was reduced between 0.05% and 5.3% for landscape-based methods and between 5.3% and 11.9% for portrait-based methods.

Additional information

Funding

Nokia provided equipment and funding to support this research. Funding was also provided by Croatian Ministry of Science, Education and Sports, under the Grant “Biomechanics of Human Motion, Control and Rehabilitation” (023-0232006-619 165).

Notes on contributors

Josip Musić

Josip Musić ([email protected]) is a computer scientist with an interest in analysis and development of user interface input techniques in mobile setting; he is an Assistant Professor in the Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Split.

Roderick Murray-Smith

Roderick Murray-Smith ([email protected], http://www.dcs.gla.ac.uk/~rod/) is a computer scientist with interests in machine learning and mobile interaction; he is a Professor in the Inference, Dynamics and Interaction research group in the School of Computing Science, University of Glasgow.