David L Lee

University of California, San Francisco, San Francisco, CA, United States

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Publications (4)4.94 Total impact

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    ABSTRACT: The design and selection of 3D modeled hand gestures for human-computer interaction should follow principles of natural language combined with the need to optimize gesture contrast and recognition. The selection should also consider the discomfort and fatigue associated with distinct hand postures and motions, especially for common commands. Sign language interpreters have extensive and unique experience forming hand gestures and many suffer from hand pain while gesturing. Professional sign language interpreters (N=24) rated discomfort for hand gestures associated with 47 characters and words and 33 hand postures. Clear associations of discomfort with hand postures were identified. In a nominal logistic regression model, high discomfort was associated with gestures requiring a flexed wrist, discordant adjacent fingers, or extended fingers. These and other findings should be considered in the design of hand gestures to optimize the relationship between human cognitive and physical processes and computer gesture recognition systems for human-computer input.
    International Journal of Human-Computer Studies 01/2014; · 1.42 Impact Factor
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    ABSTRACT: In this study, we evaluated the effects of key spacing on a conventional computer keyboard on typing speed, percentage error, usability, and forearm muscle activity and wrist posture. International standards that specify the spacing between keys on a keyboard have been guided primarily by design convention because few studies have evaluated the effects of key spacing on productivity, usability, and biomechanical factors. Experienced male typists (N = 37) with large fingers (middle finger length > or = 8.7 cm or finger breadth of > or = 2.3 cm) typed on five keyboards that differed only in horizontal and vertical key spacing (19 x 19 mm, 18 x 19 mm, 17 x 19 mm, 16 x 19 mm, and 17 x 17 mm) while typing speed, percentage error, fatigue, preference, extensor carpi ulnaris and flexor carpi ulnaris muscle activity, and wrist extension and ulnar deviation were recorded. Productivity and usability ratings were significantly worse for the keyboard with spacing of 16 x 19 mm compared with the other keyboards. Differences on these measures between the other keyboards were not significant. Muscle activity tended to increase in the left forearm and decrease in the right with decreasing horizontal key spacing. There was also a trend for left wrist extension to increase and left ulnar deviation to decrease with decreasing horizontal key spacing. Reducing vertical key spacing from 19 to 17 mm had no significant effect on productivity or usability ratings. The study findings support key spacing on a computer keyboard between 17 and 19 mm in both vertical and horizontal directions. These findings may influence keyboard standards and the design of keyboards.
    Human Factors The Journal of the Human Factors and Ergonomics Society 06/2013; 55(3):557-66. · 1.18 Impact Factor
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    ABSTRACT: /st> The design of periodontal curette handles may cause or aggravate arm pain in dental practitioners. The authors conducted a four-month randomized controlled trial to evaluate the effects of curette handle diameter and weight on arm pain among dental hygienists and dentists. /st> One hundred ten dental hygienists and dentists who performed scaling, root planing or dental prophylaxis procedures participated in this study. The authors assessed right wrist/hand, elbow/forearm and shoulder pain levels weekly. They randomized participants to receive either a set of light (14 grams) periodontal curettes with a large diameter (11 millimeters) or a set of heavy (34 g) periodontal curettes with a narrow diameter (8 mm). The authors compared changes in mean pain scores across the study period between intervention groups by using general linear models and controlling for covariates. /st> The improvement in pain scores across the three body regions was greater for participants who used the lighter, wider-diameter curettes. In the final adjusted model, the differences were statistically significant only for the shoulder region (P = .02). /st> The study results show that dental instrument design has an effect on upper-extremity pain in dental practitioners. Using a lighter instrument with a wider diameter may be an easy and cost-effective intervention to reduce or prevent upper-extremity pain associated with dental hygiene procedures. Clinical implications To prevent or reduce arm pain, practitioners should consider using lightweight instruments with large diameters when performing scaling and root planing procedures.
    Journal of the American Dental Association (1939) 10/2012; 143(10):1105-13. · 1.82 Impact Factor
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    ABSTRACT: Pipetting involves static upper arm positions with the pipette held away from the body for sustained periods of time, putting increased musculoskeletal load on the shoulder and upper back. This study explores the effect of using two alternative arm supports while pipetting on muscle loading in the shoulder/neck region. 15 experienced pipette users participated in this study. In a repeated-measures design, participants performed simulated pipetting in a laboratory setting under three arm support conditions: (1) a gel pad on the work surface, (2) a freely-moving counter-balanced forearm support, and (3) no support (control). Surface electromyography (EMG) of the anterior deltoid and upper trapezius muscles were recorded, as well as productivity and subjective usability. Both arm support conditions resulted in significantly lower mean muscle activity of the anterior deltoid and upper trapezius muscles (p<0.001) and significantly higher subjective comfort ratings (p<0.001) compared to the control condition. The freely moving forearm support resulted in significantly lower peak muscle activity in the anterior deltoid compared to the control condition (p<0.001). Productivity was not affected by the arm supports. These findings suggest that arm support may be beneficial in reducing muscle loading and improving comfort in the shoulder and upper back during pipetting. Future studies are needed to measure the impact of these arm supports in the workplace.
    Work 01/2011; 39(2):195-200. · 0.52 Impact Factor