Based on Shannon’s theorem for information processing, Fitts’ law allows the estimation of required times for rapid movements between a starting point and a target area. Fitts introduced the index of difficulty (ID) as a characteristic measure for such movements. The ID is defined as: ID = log2 (2 A / W). The term A describes the amplitude of the movement, or the distance between starting point, and target area, and the term W, the width of the target area. The movement time MT is linearly dependent on the ID. It is: MT = a + b ID. The coefficients a and b are both regression coefficients. The coefficient [a] defines the intercept for ID=0 and the coefficient b the steepness of the relationship.
Published in Chapter:
Assessing Human Mobile Computing Performance by Fitts' Law
Thomas Alexander (FGAN - Research Institute for Communication, Information Processing, and Ergonomics, Germany), Christopher Schlick (RWTH Aachen University, Germany), Alexander Sievert (German Sport University Cologne, Germany), and Dieter Leyk (German Sport University Cologne, Germany, and Central Institute of the Federal Armed Forces Medical Services Koblenz, Germany)
Copyright: © 2008
|Pages: 17
DOI: 10.4018/978-1-59904-871-0.ch049
Abstract
This chapter describes the interdependence between locomotion while walking and human input performance in mobile Human-Computer-Interaction (HCI). For the analysis of the interdependence, appropriate performance measures, for example, subjective workload ratings or error rate, have to be applied. The way in which Fitts’ law can enhance the analysis is explained. In an experiment with n=18 participants, the general indices of performance (bits per second) were measured while standing and walking with constant speed (2, 3.5, 5 km/h). Results show a significant increase of the error rate and a significant decrease of the index of performance for increased walking speed. Subsequent regression analyses allow quantitative estimation of these effects. The results show a division of the interdependence in two parts, based on the difficulty of the input task; they define threshold values for accuracy of user input. These values can be applied for the implementation and design of future Graphical User Interfaces (GUI) for mobile devices.