Charakteristische Nutzereigenschaften und ihr Einfluss auf die Bedienung von Notebook-Eingabegeräten : eine arbeitspsychologische Evaluation von Touchpad und Trackpoint

摘要

The aim of this thesis was a work-psychological evaluation of notebook-input devices, touchpad and trackpoint, in the framework of human-computer interaction. The focus of the studies conducted was on effects of differential user characteristics on the usability of notebook input devices. Additionally, essential variables of human-computer interaction were under survey, e.g., specific aspects of hardware design or input task. The research was based on fundamental psychological concept and theories (e.g., Fitts, 1954; Heuer, 1983; Meyer et al., 1988). Thus, the more practical approach of the past was offered a theoretical framework. First, an objective and standardized test was developed (cp., DIN EN ISO 9241-9, 2000) as well as a survey for the assessment of musculoskeletal discomfort (Sutter & Ziefle, 2003a). Second, the evaluation of both input devices was undertaken with motor performance measures, and ratings of preference and discomfort. The results show distinct differences between the usability of touchpad and trackpoint. The touchpad (easier spatial transformation) was used more efficient compared to the trackpoint (more difficult spatial transformation). Responsible for the performance discrepancy is the spatial transformation: Cursor movements are optimised when executed with the touchpad. Performance decreased because of an inefficient cursor adjustment and -control with the trackpoint. In the meaning of the anticipation of action effects (e.g., James, 1890), the manipulation of the trackpoint follows in fact psychomotor laws. Nevertheless, beyond motor factors further cognitive aspects have to be addressed for an alternative behaviour model. Expertise, age and musculoskeletal discomfort were found to be critical user characteristics. They all have a strong impact on the handling of notebook input devices. It was found that the efficiency of the input device usage increased through practice and high expertise. Moreover, age, and the resulting increase and decrease of psychomotor skills over lifespan respectively, is an important factor for the usability of notebook input devices. Performance of children (11 years of age) and middle-aged adults (50 years) differed distinctly from the “best case”, young adult users (20 years). Both age groups performed less efficient, but they compensated very well the developmental lack by practice and experience. The repetitive usage of notebook input devices, and the appearance and impact of musculoskeletal discomfort was under study. Even young and healthy users show to have an increase of discomfort in finger and hand after several hours of exposure. This was found for both input devices likewise. The focussing of discomfort on finger and hand must be discussed in relation to repetitive strain injuries and their development. Musculoskeletal impaired users reported specific discomfort locations compared to healthy users. Users, who formerly suffered from RSI but were free of symptoms for several years, felt strong discomfort when exposed to input devices (cp., Sorgatz, 2002). The manipulation of both notebook input devices was heavily limited, e.g. work and rest periods were by 3 times higher compared to healthy users. The analyses of human-computer interaction revealed a variety of optimisation options, independently from user characteristics. The usage is best for input devices with easy spatial transformation (touchpad) in combination with a high cursor speed. Input devices with more difficult transformations (trackpoint) will profit from low cursor speed. This will gain a better cursor adjustment and – control. The analysis of work organisation showed that human-computer interaction was remarkably improved by button use strategy (two-handed), task type (point-click task) and task difficulty (large and close targets). This was found for both input devices. In general, the touchpad was found to be an effective and multi-purpose applicable input device. Its usability is only marginally affected by the user characteristics investigated. In contrast to the trackpoint the usage of the touchpad is recommended thoroughly for all user groups under survey.