PROCEEDINGS of the HUMAN FACTORS and ERGONOMICS SOCIETY 56th ANNUAL MEETING - 2012 1104 Are there Differences in Force Exposures and Typing Productivity between Touchscreen and Conventional Keyboard? Jeong Ho Kim 1, Lovenoor Aulck 2, Michael C Bartha 3, Christy A Harper 3, and Peter W Johnson 1 1 Department of Environmental and Occupational Health Sciences 2 Department of Bioengineering University of Washington, Seattle, WA 3 Hewlett-Packard Company, Houston, TX As the use of tablets is becoming increasingly prevalent, it is important to understand how using a touchscreen (virtual) keyboard affects typing forces, productivity and. Thus, the objective of this study was to investigate whether there were differences in typing forces, typing productivity and users dis between virtual and conventional keyboards. A total of 19 subjects (10 males and 9 females) typed for 10 minutes on a virtual keyboard and two conventional keyboards. The results showed that virtual keyboard use resulted in lower typing forces (p < 0.0001), lower typing performance (p < 0.0001), and higher subjective dis at the hand/wrist and the neck/shoulder (p < 0.0001). The results indicate that using a virtual keyboard may not cause any detrimental effect on physical exposures, but may increase musculoskeletal dis on the upper extremities and neck/shoulder regions; therefore, appropriate interventions should be considered for the prolonged use of a virtual keyboard. Copyright 2012 by Human Factors and Ergonomics Society, Inc. All rights reserved. DOI 10.1177/1071181312561240 INTRODUCTION Previous studies have shown that computer keyboard use may be associated with musculoskeletal disorders (MSDs) in the upper extremities (Chang, Johnson, Katz, Eisen, & Dennerlein, 2009; Gerr, Monteilh, & Marcus, 2006). Repetitive finger movements (Lin, Liang, Lin, & Hwang, 2004) and applied finger forces (Rempel, Tittiranonda, Burastero, Hudes, & So, 1999) are thought to be potential risk factors behind these MSDs. Previous experimental studies have shown that the keyboard s key activation force, force-displacement characteristics, and tactile feedback affect typing forces (Armstrong, Foulke, Martin, Gerson, & Rempel, 1994; Martin, Armstrong, Foulke, Natarajan, Klinenberg, Serina, & Rempel, 1996; Rempel, Serina, Klinenberg, Martin, Armstrong, Foulke, & Natarajan, 1997). Increased typing forces due to inadequate activation force force-displacement, and tactile feedback increased muscle activity levels (Martin, et al., 1996; Rempel, et al., 1997), and users dis (Rempel, et al., 1999). As tablets have become increasingly prevalent, touchscreen (virtual) keyboards have replaced traditional computer input devices such as the keyboard and mouse. Because virtual keyboards have interfaces and forcedisplacement characteristics that differ from their conventional counterparts, typing exposures and risks for MSDs when using a virtual keyboard may also differ. Since most conventional keyboards have the same fixed activation force (between 0.5 and 0.8 N per ISO 9241-410; 2008), most users can rest their fingers on the keyboard keys without any accidental key activation. However, because a virtual keyboard is activated by physical contacts (zero activation force and travel distance), users must elevate their fingers and hands over the keyboard to avoid accidental key activation. This may cause static muscle loading in the finger extensor, wrist extensor and shoulder muscles. Furthermore, as applied typing forces on a keyboard are influenced by key activation force (Armstrong, et al., 1994; Martin, et al., 1996; Rempel, et al., 1997), there may be differences in applied typing forces between a virtual and conventional keyboard. Due to the substantial differences in keyboard characteristics, the possibility exists that typing exposures and user dis may be different between the keyboards. Thus, it would be important to understand how the use of a virtual keyboard may affect physical exposures and/or risks for MSDs. There have been some studies on tablet usability (Ozok, Benson, Chakraborty, & Norcio, 2008) and the effect of touchscreen use on muscle activity and subjective dis (Shin & Zhu, 2011). Shin and Zhu (2011) found that the use of a virtual interface increased user dis and muscle activity at the neck and shoulder. However, there is a lack of research into
PROCEEDINGS of the HUMAN FACTORS and ERGONOMICS SOCIETY 56th ANNUAL MEETING - 2012 1105 how a virtual keyboard may influence typing force exposures and typing performance. By comparing virtual and conventional keyboards, the present study investigated the effect of virtual keyboard use on typing forces, productivity, and subjective dis on the upper extremities and neck/ /shoulder. Based on previous research, it was hypothesized thatt applied typing forces as well as user dis differ between a virtual keyboard and conventional keyboards. METHODS Subjects A total of 19 subjectss (10 male and 9 female) were recruited to participate in the study through e-mail solicitations. All subjects were experienced touch typists with no history of upper extremity musculoskeletal disorders and 17 participants were right hand dominant. The average age and typing speed for all subjects was 24.3 (SD 6.4) and 62. 7 words per minute (SD 9.8), respectively. Their average years of computer use were 14.1 years (SD 5.5). The experimental protocol was approved by the Human Subjects Committee of the University of Washingtonn and all subjects gave their written consent prior to their participation in the study. counterbalanced to minimize any potential confoundingg due to keyboard testing order. Before starting the typing task, the chair, table, and monitor were adjusted to each subject s anthropometry in accordance with ANSI/HFES 100-2007. During the typing sessions, typing forces were also measured by placing the devices on a force platformm (Figure 1). The force platform consisted of a 36 cm x 188 cm x 0.64 cm (14.17 in x 7.09 in x 0.25 in) aluminumm platee mounted to a six-degree of freedom force/torque load cell (Mini40E, ATI Inc., USA) which allowedd detection of forces and torques in three dimensions. The devices were placed on the force platform such that the H key of each keyboard aligned with the center of the broadest face of the force platform. Only forces appliedd by typists that were orthogonal to the face of the keyboard (z-axis)) were analyzed. A polyoxymethylene frame was constructed to surround the force plate both too offset the height of the force platform (thereby creating a flat work surface) and to allow for subjects to rest their hands without applying forces to either the device beingg tested or the force platform. Experiment design During the repeated-measures laboratory experiment, participants typed for two five-minutee sessions on each of three keyboards used in the experiment: a detachable keyboard with 4. 0 mm of key travel (SK-8115, Dell Inc., USA), a laptop with a keyboard with 1.6 mm of key travel (Envy14, Hewlettt Packard Inc., USA), and a laptop with a dual touch screen interface with 0 mm of key travel (Iconia, Acer Inc., Taiwan). The 1.6 and 4.0 mm keyboard had roughly the same activation force, approximately 0.6 N. During the typing sessions, typing speed and accuracy were measured by a software program (Mavis Beacon Teaches Typing Platinum - 25th Anniversary Edition, Broderbund Software Inc., USA). After typing on each keyboard, subjective and preference ratings were collected using a 7-point Likert scale questionnaire, a modification of the ISO keyboard questionnaire (ISO9241-410; 2008). A 5-minute break was given between each keyboard to minimize residual fatigue effects of the previous condition. The order in which the keyboards were used was randomized and Figure 1. Experiment setup. A LabVIEW program (Ver 2009, National Instruments, USA) was used to record force data at a rate of 500 Hz. The force platform was zeroed prior to eachh typing task. Mean and peak forces, keystroke duration, and keystroke time-tension product (KTTP) were calculated for each individual keystroke. The KTTP was
PROCEEDINGS of the HUMAN FACTORS and ERGONOMICS SOCIETY 56th ANNUAL MEETING - 2012 1106 the integrated area under a keystroke and had units of Newton-milliseconds (Figure 1). Data analysis The statistical analysis was conducted in JMP (Version 9; SAS Institute Inc., USA). A mixed model with restricted maximum likelihood estimation (REML) was used to determine if any keyboard-based differences existed in terms of typing forces and typing performances. Any statistical significance was followed by the Tukey-Kramer method to determine differences between groups. The Friedman test and post-hoc multiple comparisons in R (R 2.13.2, Development Core Team) were used to determine the effect of keyboards on subjective, typing performance, and preference. All data are presented as mean and standard error; significance was noted when Type I error was less than 0.1 or 0.05. RESULTS The results showed that there were significant differences in peak and mean keystroke forces (p < 0.0001), keystroke durations (p < 0.0001), and KTTP (p < 0.0001) between the keyboards (Table 1). The 0 mm (virtual) keyboard had significantly lower peak force than the other keyboards whereas the 4.0 mm travel keyboard had higher peak forces compared to the other keyboards. The mean keystroke force on the virtual keyboard was lower than the other keyboards (p < 0.0001) while there were no differences in the mean keystroke forces (p = 0.61) between 1.6 and 4.0 mm travel keyboards. Similarly, the virtual keyboard had shorter keystroke durations compared to the other keyboards (p < 0.0001) while no differences in keystroke duration were found between 1.6 and 4.0 mm travel keyboards (p = 0.43). Table 1 Mean (± SE) typing forces compared across the three keyboards [n = 19]. Across rows, different letters indicate significant difference. Peak Force (N) Mean Force (N) Keystroke Duration (ms) KTTP (N-ms) Keyboard 1.15 a (±0.10) 0.76 a 38.63 a (±4.02) 36.30 b (±6.90) 2.15 b (±0.10) 1.12 b 110.36 b (±4.00) 132.86 b (±6.84) 2.38 c (±0.07) 1.14 b 104.22 b (±3.99) 130.79 b (±5.75) Table 2. Mean (± SE) typing speed in word per minute and percent accuracy compared across the three keyboards [n = 19]. Across rows, different letters indicate significant difference. Typing Speed (WPM) Typing Accuracy (%) Key Travel 24.3 a 84.4 a 63.4 b 95.4 b 62.7 b 95.2 b As shown in Table 2, there were significant differences in typing speed and accuracy between the virtual keyboard and the conventional keyboards (p < 0.0001). Typing speed on the virtual keyboard was approximately 60% slower compared to the other keyboards (p < 0.0001) while there was no difference in terms of typing speed (p = 0.97) between 1.6 and 4.0 mm travel keyboard. Accuracy on the virtual keyboard was 84.5% while the accuracy on the 1.6 and 4.0 mm travel keyboards was 95% on average (p < 0.0001). Table 3. Mean (± SE) of subjective and preference ratings [n=19]. Across rows, different letters indicate significant difference. Hand/Wrist Arm/Shoulder Easy-to-use Typing accuracy Typing speed Activation force Adjustment speed Preference Keyboard 2.9 a (1.72) 3.4 a (1.74) 1.7 a (1.28) 1.5 a (1.02) 1.7 a (1.29) 2.4 a (1.57) 2.4 a (1.38) 1.6 a (1.11) 5.5 b (1.17) 2.1 b (1.20) 5.7 b (0.89) 5.2 b (1.07) (0.93) 4.1 b (1.75) (1.11) (1.05) 5.2 b (1.01) 5.1 b (0.88) 5.9 b (0.74) 6.1 c (0.88) 5.7 c (0.67) 4.6 b (0.84) 6.1 b (0.78) 5.5 b (0.96) 0.0005 Subjective dis, productivity and preference ratings showed that the virtual keyboard consistently received the worst (least preferable) ratings whereas the only differences between the 1.6 and 4.0 mm travel keyboards were for subjective typing accuracy and speed (Table 3). The 1.6 mm travel keyboard received the lowest dis ratings while 4.0 mm travel keyboard had the highest subjective productivity and usability ratings in terms of subjective user perceptions of accuracy, speed, easy-to-use, and the time to adjust to the keyboard (p < 0.0001). Similarly, the perceived activation force on the virtual keyboard was substantially lower than the other keyboards (p <
PROCEEDINGS of the HUMAN FACTORS and ERGONOMICS SOCIETY 56th ANNUAL MEETING - 2012 1107 0.0001) whereas there were no differences in the perceived force between 1.6 and 4.0 mm travel keyboards. DISCUSSION The present study tested the hypothesis that differences exist between virtual and conventional keyboards in terms of typing forces, productivity, subjective and preference. This study found that the virtual keyboard had lower typing forces but was also less preferred than the other keyboards, given its significantly lower productivity and higher subjective dis ratings. Typing forces are known to be positively correlated with key activation forces (Radwin and Ruffalo 1999, Rempel et al. 1999, Radwin and Jeng 1997, Armstrong et al. 1994, Lee et al. 2009). That is, higher activation forces typically leads to higher typing forces applied to the keyboard. The activation force of 1.6 and 4.0 mm travel keyboard were both approximately 0.6 N whereas a virtual keyboard had no activation force threshold. This substantial difference in activation force was likely the reason for the keyboardrelated differences in typing forces. Typing productivity, as measured by the software program, was consistent with the corresponding subjective measures. Both the objective and subjective typing speed and accuracy on the virtual keyboard were lower while the 4.0 mm keyboard had the highest typing speed and accuracy (Tables 1 and 2). The keyboardbased differences in the typing productivity may be due to participant s familiarity with the keyboards. All the participants stated that they regularly use either a desktop computer (n=10) with a standard keyboard or a laptop computer (n=9), thus making them more familiar with the conventional keyboards than with the virtual keyboard. The unfamiliarity may have made it more difficult for the participants to adjust to and use the virtual device. Moreover, the typing speed on the virtual keyboard tested in this study is likely slower than on tablets due to the dual viewing demands created by the laptop. Hence, the slower typing on the virtual keyboard is likely the result of subjects having to view the laptop screen and then switch to viewing the virtual keyboard keys when they typed. Subjective dis ratings of the hand, wrist, arm and shoulder showed that the virtual keyboard was the most unable while there were no differences between the conventional keyboards (Table 3). Participants could not rest their fingers and hands on the virtual keyboard due to the minimal activation force of the device. This may have resulted in prolonged static muscle loading on the upper extremity extensor, shoulder, and neck muscles whilst using the virtual keyboard, consequently resulting in increased user dis. This finding is consistent with a previous study (Shin & Zhu, 2011). The prolonged muscle loading is a risk factor for musculoskeletal disorders (Chang et al. 2007, Ijmker et al. 2007, Jensen et al. 2002); thus, using a virtual keyboard may pose an increased risk for musculoskeletal dis and/or injuries. In conclusion, this study demonstrated that there were differences between a virtual keyboard and conventional keyboards in terms of typing forces, productivity, and subjective dis. The lower typing forces may imply that using a virtual keyboard may not be detrimental in terms of physical exposures (e.g. force). However, the virtual keyboard showed a substantial reduction on typing performance, as compared to the other keyboards. Furthermore, users dis on the upper extremity and neck/shoulder regions was higher on the virtual keyboards than the other keyboards. Given higher dis and detriment in typing productivity, ergonomic interventions should be proposed for using a virtual keyboard on a regular basis to prevent its possible adverse health effects. ACKNOWLEDGEMENTS This research was supported by a research grant from the Washington State Medical Aid and Accident Fund and the Ergonomic Research and Development Group within Hewlett-Packard. Authors would also like to thank Ornwipa Thamsuwan from the University of Washington for her support with the EMG data processing and all of the participants in this study. REFERENCES Armstrong, T. J., Foulke, J. A., Martin, B. J., Gerson, J., & Rempel, D. M. (1994). Investigation of applied forces in alphanumeric keyboard work. American Industrial Hygiene Association Journal, 55(1), 30-35. Chang, C. H., Johnson, P. W., Katz, J. N., Eisen, E. A., & Dennerlein, J. T. (2009). Typing keystroke duration changed after submaximal isometric finger exercises. European Journal of Applied Physiology, 105(1), 93-101. Gerr, F., Monteilh, C. P., & Marcus, M. (2006). Keyboard use and musculoskeletal outcomes among computer users. Journal of Occupational Rehabilitation, 16(3), 265-277.
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