On the relationship between mouse operating force and display design
Kentaro Kotani 1, Ken Horii1and Yutaka Kitamura 2
1 Department of Industrial Engineering, Kansai University Suita, Osaka
564-8680, Japan
2 Faculty of Informatics, Kansai University
Takatsuki, Osaka
569-1095, Japan
ABSTRACT
This study, using a mouse equipped with a force sensitive resistor, examined the relationship between mouse operating force and fundamental design characteristics associate with display conditions such as target size and approaching angles.
KEYWORDS
Mouse, Display design, Force sensitive resistors.
INTRODUCTION
A mouse is now an integral part in almost all computer tasks due to the great popularity of PC-based software. Consequently, epidemiological study on the use of a mouse is indispensable in identifying the risk factors of physical disorders caused by using the pointing device. However, recent researches on mouse use focus chiefly on usability issue and only a few researches deal with mouse use empirically in terms of physical and epidemiological aspects (Dowell and Gscheidle, 1997). Apparently, obtaining knowledge of such aspects must contribute to the improvement of the display design in determining an ergonomically risk-free size of buttons to click on and in arranging icons that ensures less stressful mouse movements. The objective of this study is to obtain empirical data on the operating force applied to the mouse in relation to the characteristics of such display layouts as target areas and approaching angles to the target.
METHODS
A 5 mm-diameter force-sensitive resistor (FSR) was housed on the top of the microswitch inside the mouse for the measurement of operating force. The voltage signals were transmitted to a programmable A/D converter, controlled by a PC. Prior to the experiment, a calibration testing was conducted and the regression equation with R2of 0.999 was obtained for the relationship between FSR voltage and the force applied to the mouse.
Independent variables used in the study were four approaching angles(0 (horizontal), 30, 60, 90 (vertical) degrees), three target sizes(10_10mm, 20_20mm, 30_30mm) and two testing sessions. A total of five subjects were chosen from the population of the engineering majors, who have used a mouse more than one year on a daily basis. The target size and the approaching angle were chosen as factors to examine the relationship between the mouse operating force and Fitts'-Law-based pointing characteristics demonstrated by Card et al.(1978). The occurrences of wrist and forearm motions in mouse operation throughout the experimental assignment were monitored to compare and discuss effects of varied approaching angles.
The experimental paradigm consisted of a practice session (approximately 15 minutes) and two testing sessions. Each testing session consisted of 12 trials, which
were fully-crossed combined with independent variables of the approaching angle and the target size. The order of trials was randomized in the session.
RESULTS
The grand average of mouse operating force was 146gf, which was twice that of the minimum mouse operating force (75grams, catalog data). The ANOVA showed a significant main effect on the mouse operating force for target size (F(2,8)=11.64, p < .01), whereas the other effects, including the effect of subject, were not significant. Some of interaction items were also significant: 2-factor interaction of subject with session (approximate F(28,20)=9.61, p < .05) and 4-factor interaction of subject, session, target size and approaching angle (F(24,1080) = 7.92, p < .01). Indices of difficulty (IDs) were calculated from the target sizes and linear distance between targets. The smallest force (137gf) was found in the conditions with the highest ID (= 4.04). With respect to the target size, when the target area was small, the mouse operating force was accordingly small. However, as the target size increased, higher mouse operating force (approximately six percent increase) was observed.
DISCUSSION
The relationship between mouse operating force and the ID was, puzzlingly contradictory to the general anticipation. Before this experiment, the largest mouse operating force was anticipated to be observed with the highest ID. The highest mouse operating force was, in fact, observed in the task with the largest target, i.e., the lowest ID. Therefore, the results implied that the task difficulty did not directly reflect the mouse operating force. It should be noted, however, that the subjects' comments were contrastive to the results: they felt they pressed much harder when they had to click the smallest target. Currently, we hypothesized that the total amount of muscle contraction employed in pointing mouse may be related to the IDs, that is, some amount of muscle contraction was used for pointing the mouse by flexing the index finger, and the rest of the force was merely used for developing the muscle tension prompted by the task requirement. The hypothesis will be enhanced by the further study including the measurements of surface EMGs during the task and dragging force.
REFERENCES
Card, S.K., English, W.K. and Burr, B.J. (1978). Evaluation of mouse, rate-controlled
isometric joystick, step keys, and text keys for text selection on a CRT.
Ergonomics, 21(8):601-603.
Dowell, W.R. and Gscheidle, G.M. (1997). The effect of mouse location on seated
posture. In G. Salvendy, M.J. Smith, & R.J. Koubek, (eds)Advances in Human
Factors/Ergonomics, 21A Design of Computing Systems: Cognitive
Considerations, Elsevier, 607-610.
