ergonomic comparison of slanted and vertical computer mouse designs

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http://pro.sagepub.com/ Ergonomics Society Annual Meeting Proceedings of the Human Factors and http://pro.sagepub.com/content/54/6/561 The online version of this article can be found at: DOI: 10.1177/154193121005400604 2010 54: 561 Proceedings of the Human Factors and Ergonomics Society Annual Meeting Alan Hedge, David Feathers and Kimberly Rollings Ergonomic Comparison of Slanted and Vertical Computer Mouse Designs Published by: http://www.sagepublications.com On behalf of: Human Factors and Ergonomics Society can be found at: Proceedings of the Human Factors and Ergonomics Society Annual Meeting Additional services and information for http://pro.sagepub.com/cgi/alerts Email Alerts: http://pro.sagepub.com/subscriptions Subscriptions: http://www.sagepub.com/journalsReprints.nav Reprints: http://www.sagepub.com/journalsPermissions.nav Permissions: http://pro.sagepub.com/content/54/6/561.refs.html Citations: What is This? - Sep 1, 2010 Version of Record >> at TEXAS SOUTHERN UNIVERSITY on December 7, 2014 pro.sagepub.com Downloaded from at TEXAS SOUTHERN UNIVERSITY on December 7, 2014 pro.sagepub.com Downloaded from

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Page 1: Ergonomic Comparison of Slanted and Vertical Computer Mouse Designs

http://pro.sagepub.com/Ergonomics Society Annual Meeting

Proceedings of the Human Factors and

http://pro.sagepub.com/content/54/6/561The online version of this article can be found at:

 DOI: 10.1177/154193121005400604

2010 54: 561Proceedings of the Human Factors and Ergonomics Society Annual MeetingAlan Hedge, David Feathers and Kimberly Rollings

Ergonomic Comparison of Slanted and Vertical Computer Mouse Designs  

Published by:

http://www.sagepublications.com

On behalf of: 

  Human Factors and Ergonomics Society

can be found at:Proceedings of the Human Factors and Ergonomics Society Annual MeetingAdditional services and information for    

  http://pro.sagepub.com/cgi/alertsEmail Alerts:

 

http://pro.sagepub.com/subscriptionsSubscriptions:  

http://www.sagepub.com/journalsReprints.navReprints:  

http://www.sagepub.com/journalsPermissions.navPermissions:  

http://pro.sagepub.com/content/54/6/561.refs.htmlCitations:  

What is This? 

- Sep 1, 2010Version of Record >>

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Page 2: Ergonomic Comparison of Slanted and Vertical Computer Mouse Designs

ERGONOMIC COMPARISON OF SLANTED AND VERTICAL COMPUTER MOUSE DESIGNS

Alan Hedge, David Feathers, Kimberly Rollings

Department of Design and Environmental Analysis, Cornell University, Ithaca NY 14853, U.S.A.

ABSTRACT

The effect of using five different optical mice on cursor positioning task performance and on wrist posture was investigated. The 5 mouse designs included 1 conventional mouse, 2 angled mice and 2 vertical mice. Results showed that performance was significantly different for the 5 mice for the cursor point-and-click tasks and cursor dragging tasks. Task performance was slowest for the traditional mouse and fastest for the vertical mice. Wrist extension was lowest for the slanted mouse designs and highest for the vertical mice. The results show that performance and posture were affected in opposite ways by these different mouse designs, and that the design features that promote good performance may compromise good wrist posture and vice versa. Overall, an adjustable-size slanted mouse design may offer the best combination of neutral posture and performance.

INTRODUCTION Recent studies have investigated alternative mouse designs with respect to musculoskeletal exposure, comfort, positional training, and measures of productivity (e.g. Aarås et al., 2001; Gustafsson and Hagberg, 2003; Chang et al., 2007; Houwink et al., 2009; Lee et al., 2008; Odell and Johnson, 2007). Trends in alternative mouse design acknowledge that there may be musculoskeletal risks and comfort issues associated with mouse use. Statically, a more “neutral” wrist has been found to reduce self-reported hand/wrist pain (Aarås et al., 2001). Task performance effects of alternative mouse designs have been studied through assessments of movement time, movement distance, and summative Fitts' law tasks (e.g. Aarås et al., 2001; Po et al., 2005; Scarlett et al., 2005). Static and dynamic movements involving the computer mouse have been studied as positional (stationary) and dynamic (Lee et al., 2008). Lee et al. (2008) further described a dynamic mouse movement taxonomy that included moving the mouse (non-clicking or dragging), which involves primarily extrinsic hand muscles, and activating (left click, right click, scrolling), which involves a combination of intrinsic and extrinsic hand muscles. Interaction with a computer mouse places musculoskeletal demands on the upper extremity that are responsive to individual anthropometry (Hedge, et al., 1999), and relative positioning of the mouse (Dennerlein et al., 2006). Gender has also been explored for mouse use (Chang, 2006; Lee et al., 2008) Males were found to lift their mouse more and extend their fingers more than females (Lee et al., 2008) but these data were not normalized for anthropometry, mousing intensity, and psychosocial factors. The risk factors for carpal tunnel syndrome in relation to mousing tasks include the force, repetition, and awkwardness of posture (e.g. Fagarasanu and Kumar, 2003). Changes in carpal tunnel pressure in response to

computer mouse design have been studied (Keir et al., 1999). New medical imaging techniques have elucidated the impact of non-neutral wrist postures on carpal tunnel morphology, especially in wrist extension which is widely regarded as the riskiest postural deviation of the wrist when using an input device (Bower et al., 2006; Mogk and Keir, 2007). The ANSI/HFES 100 standard specifies a wrist extension of <30° as desirable for performance (ANSI/HFES, 2007). Other work has suggested that a maximum of 15° may be a reasonable threshold for acceptable wrist extension and ulnar deviation for input devices for health (Hedge et al., 1999). Numerous alternative mouse designs exist and many describe themselves as “ergonomic”, but to be “ergonomic” a product must facilitate performance and minimize injury risks. A recent trend in “ergonomic” mouse design has been to present the product as a slanted design or even a vertical design and to use an optical mechanism rather than a ball potentiometer which potentially facilitates performance by offering less resistance to movement, but less is known about the postural effects of these designs. In this study five current optical mouse designs were selected and the effects of these designs on performance and posture were evaluated.

METHODS Participants Twenty-four right-handed, healthy students (12 males, 12 females) from Cornell University, familiar with computer mouse use, voluntarily participated. All participants, between 18-35 years of age, were compensated with $25 for their time and provided signed consent forms. Experimental procedures were approved by Cornell University’s Institutional Review Board for Human Participants.

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Materials Right-hand wrist posture was measured using a twin axis electrogoniometer (Biometrics Ltd., model SG65 with DataLink DLK 800 Base and RS485 data transfer cable) recording at 50Hz. Five optical computer mice were selected for the study. To eliminate any potential bias from the manufacturer’s name, any identification information was covered and each mouse was randomly assigned a solid shape name as follows:

Triangle: a conventional mouse design (HP, model M875U)

Pronated hand

Circle: An ergonomic mouse design with 4 different right-hand sizes (Contour Design, models CMO-BLK-S-R;M-R; L-R;XL-R)

Sloped, semi-pronated hand

Rectangle: Microsoft Natural Wireless Laser Mouse (Microsoft, model 1083)

Mid- pronate, supinate hand

Square: Evoluent Vertical Mouse 3 rev 2 (Evoluent LLC, model VM3R2-RSB)

Mid- pronate, supinate hand

Diamond: Switch Mouse (HumanScale, model SMUSB). This is an adjustable length mouse design.

Sloped, semi-pronated hand

Table 1. The 5 optical mice used in the experiment. Two laptop PC’s (Dell Latitude D600 and Dell Latitude D620) were used. One PC presented the performance task, and the other PC simultaneously recorded wrist posture data. To standardize the extent of mouse movements all tasks were performed on a horizontal circular mousing platform (26cm diameter: ~10 inches diameter) that was attached to a negative tilt keyboard tray (HumanScale 5G). The tray was attached to the undersurface of an electric, height adjustable table (Workrite with Linak

mechanism). The height of the mouse platform was set to a comfortable working height by each participant. Participants sat in an ergonomic chair (Freedom Chair, HumanScale). Performance was measured as movement times using the Generalized Fitts’ Law Model Builder software (GFLMB V. 1.1C; Sourkoreff & MacKenzie,1986). This software presents tasks comparable to those described as relevant mouse performance measures in ISO 9241-9 (ISO, 2000). Starting from a central location, two movement target amplitudes were selected (80mm and 160 mm: 3.15” and 6.30” respectively), with targets presented in random order at 0°, 45°, 90°, 135°, 180°, 225°, 270° and 315° with 0° as the vertical 12 noon position. Each target was presented 4 times in each location and all sequences were randomized for each participant. Targets were only presented one at a time and they disappeared after acquisition. Two tasks were used. The cursor point-and-click task required participants to click on a central cross hair and then to move the cursor to an empty circular target (9.8m mm diameter, 0.39 inches diameter) and click on this target. The cursor dragging task required that participants drag the central cross hair and drop this onto the circular target. Procedure The Contour and Switch mice were sized per manufacturer’s instructions for each participant. An electrogoniometer was attached to the dorsal side of the right hand and forearm placed on a flat surface using double-sided medical tape. A twin axis electrogoniometer, base and subject units, and software were used to register right wrist flexion/extension and radial/ulnar deviation. The reference or zero position was set with the pronated forearm, wrist, and hand held at a neutral position with the palm facing down on the flat work surface. The two vertical mice were intended to be held with the ulnar side of the hand and wrist facing the work surface and in this position the “left click” button, located under the index finger, could be activated by a horizontal press of the finger towards the mouse. These vertical mice could be moved with hand and wrist movements. The two other mice (Contour and Switch) positioned the hand mid-pronate/supinate and horizontal mouse movement could also engage more use of the arm to reduce wrist extension. Participants first practiced five repetitions of each of the multipoint standard Fitts’ cursor point-and-click and dragging tasks using the HP mouse. Software speed settings were adjusted to the same level for all mice. The order of presentation of the mice was balanced and randomly assigned to participants, but the cursor point-and-click task was always completed before the dragging task for each mouse. A stopwatch was used to record the rest time between the cursor point-and-click and dragging tasks, and while surveys were being completed (60 seconds, minimum).

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Data Analysis All survey, measurement, GFLMB and electro-goniometer data were entered into spreadsheets (MS Excel 2007). The first and last 20 seconds of electrogoniometer data was omitted to eliminate any extraneous movements related to starting or stopping the tasks. All data subsequently were analyzed using repeated-measures analysis of variance with a multivariate statistical package (SPSSv18).

RESULTS

Cursor Point-and-Click Task: Performance Summary For the performance data that were gathered there was a significant difference in the movement times between the 5 mice for the cursor point-and-click task (F4,12284=75.641, p<0.001). The movement times were slower for the HP and Switch mice and faster for the Contour, Evoluent, and MS Vertical mice. Figure 1 shows the mean movement times for each mouse for the 80 mm and 160 mm movement amplitudes (note the profile is almost identical for each movement distance) for the point-and-click task.

Figure 1. The mean movement times for each amplitude Fitts’ cursor point-and-click task for each of the 5 mice. Cursor Point-and-click: Wrist posture Analysis of the overall wrist postural impact of each of the 5 mice showed that for the cursor point-and-click task there was a significant difference (F1,22= 13.272, p<0.001) in overall wrist extension (F/E) between men (23.8°) and women (34.1°). For the point-and-click task the mean wrist extension angles varied among the mouse designs (F4,88= 30.958, p<0.001). However, there was no significant interaction of gender and mouse design for wrist extension for the point-and-click tasks. For ulnar/radial deviation (U/R) for the point-and-click task there was no significant effect of gender but there was a significant difference among the mice (F4,88= 6.709, p<0.001). Figure 2 shows that the average wrist extension was highest, exceeding 30° wrist extension for the cursor point-and-click task, for the Evoluent and MS Vertical mice and lowest for the Switch mouse, where the hand was semi-pronated.

Figure 2. The average wrist postures for the cursor point-and-click task for each of the 5 mice. The wrist extension data was grouped into 4 ranges of angles (<10°, 10.1-15°, 15.1-20°, >20°) and the percentages of wrist extension movements in each range were compared for the mice for the cursor point-and-click task (Figures 3). The results shows that apart from the Switch mouse, the vast majority of wrist extension movements were greater than 20° for each of the other 4 mice.

Figure 3. The percentages of wrist extension postures for the point-and-click task for each of the 5 mice. Dragging Task: Performance Summary For the performance data there was a significant difference in the movement times between the 5 mice for the cursor dragging task (F4,12284=28.011, p<0.001 where movement times were faster for the Evoluent, and MS Vertical mice than for the other 3 designs. Figure 4 shows the mean movement times for each mouse and also for the 80 mm and 160 mm movement amplitudes (note the profile is almost identical for each movement distance) for the dragging task. Comparison of the movement times for the cursor point-and-click and dragging tasks showed a significant effect of task (F1,3070 = 54.750, p<0.001), with the cursor point-and-click task taking ~50 msec longer than the dragging task on average.

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Figure 4. The mean movement times for 80 mm and 160 mm amplitude Fitts’ dragging task for each of the 5 mice. Wrist posture: Dragging Analysis of the overall wrist postural impact of each of the 5 different mice showed that for the dragging task there was a significant difference (F1,22= 10.536, p=0.004) in overall wrist extension between men (24.1°) and women (35.7°). For the dragging task, the mean wrist extension angles varied among the mouse designs (F4,88= 3.889, p=0.006). Again, there was no significant interaction of gender and mouse design for wrist extension for the dragging task. For ulnar/radial deviation for the dragging task there was no significant effect of gender but there was a significant difference among the mice (F4,88= 13.543, p<0.001). Figure 5 shows that the average wrist extension was highest, (exceeding 30° wrist extension) for the dragging task for the Evoluent and MS Vertical mice. Wrist extension was lowest for the Switch mouse where the hand was semi-pronated. Figure 6 summarizes percentages of wrist movements in each range and apart from the Switch mouse, the vast majority of wrist extension movements were greater than 20° for each of the other 4 mice.

Figure 5. The average wrist postures for the dragging task for each of the 5 mice.

Figure 6. The percentages of wrist extension postures for the dragging task for each of the 5 mice. Overall, for the performance data there was a significant effect main effect of Mouse (F4,12280 = 55.258, p<0.001) and a significant interaction of Mouse and Task (F4,12280 = 33.716, p<0.001). Movement times were fastest for cursor point and click than dragging for the Contour mouse, but the reverse for the other 4 mice. There were no other significant effects.

DISCUSSION Overall task performance movement times were some 15% faster for both of the vertical mice than the conventional mouse design, around 10% faster than the Switch mouse and 6% faster than the Contour mouse. Average ulnar deviation was less for the vertical mice compared to the other mice because the ulnar surface of the hand is close to the work surface with little opportunity for ulnar deviation. However, with the pronate and semi-pronate hand mouse designs the wrist can be bent into ulnar deviation to move the mouse. Even though ulnar deviation was greater for the non-vertical designs the average ulnar deviation was fairly moderate for these mice. Of more concern is the magnitude of wrist extension movements, because these were more extreme for the vertical designs. Previous research has studied some of the mice used in the present work. For the Contour mouse, Keir et al. (1999) reported that wrist extension averaged 28.2° for dragging tasks and 25.6° for point-and-click tasks, and the current results are similar with wrist extension averaging 25.8° for dragging tasks and 26.9°for point-and-click tasks. Scarlett et al. (2005) tested the Contour mouse using a Fitts’ task and found an average movement time of around 1.04 seconds (averaged for 37.5mm and 127.5mm target amplitudes) which is the similar to the 1.4 seconds in the present study averaged for 80mm and 160mm target amplitudes. Gustafsson and Hagberg (2003) compared a conventional mouse with the Evoluent mouse and reported an average wrist extension of 23° for the conventional mouse and 18° for the Evoluent mouse. These values are lower than those found in the present study, where the average wrist extension was 30.6° for

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the conventional mouse and 35.5° for the Evoluent mouse. Perhaps the difference between these findings is a function of the task; Gustafsson and Hagberg (2003) used a text editing task rather than a Fitts’ tasks. The results of the present study compare well with those reported by Odell and Johnson (2007), who also used a Fitts’ task and found that wrist extension averaged between 35.0° and 41.2° for alternative vertical mouse designs. In addition to comparing the average wrist postures we also evaluated the pattern of wrist postures by analyzing the percentages of movements that fell into each of four ranges of angular deviations from neutral for wrist extension. Previous work has suggested that wrist extension may be more problematic than ulnar deviation in the etiology of hand/wrist discomfort associated with input devices and that a maximum of 15° may be a reasonable threshold for acceptable wrist extension for using input devices (Hedge et al., 1999). Apart from the Switch mouse, this angular limit was greatly exceeded during the use of the other mice. The ANSI/HFES 100 standard specifies a more liberal wrist extension of <30° as desirable (ANSI/HFES, 2007). Using this criterion, the average percentage of wrist movements exceeding this 30° threshold for each of the mice was 69% (MS Vertical), 67.3% (Evoluent), 55.6% (HP), 41.2% (Contour), and 8.4% (Switch). In summary, the present results show that although movement times can be slightly faster with a vertical mouse design, there is a substantial increase in the percentage of wrist extension movements beyond a neutral zone of movement. The potential injury risk of high exposures to undesirable wrist extension may offset any marginal performance benefit. In balancing the effects found in this study an adjustable-size slanted mouse design may offer the best combination of neutral posture and performance.

ACKNOWLEDGEMENTS This research was supported by funds from the College of Human Ecology and the Human Factors and Ergonomics Laboratory, Cornell University.

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