Songil Lee

Grasp and index finger reach zone during one-handed smartphone rear interaction: effects of task type, phone width and hand length

Abstract Recently, some smartphones have introduced index finger interaction functions on the rear surface. The current study investigated the effects of task type, phone width, and hand length on grasp, index finger reach zone, discomfort, and muscle activation during such interaction. We considered five interaction tasks (neutral, comfortable, maximum, vertical, and horizontal strokes), two device widths (60 and 90 mm) and three hand lengths. Horizontal (vertical) strokes deviated from the horizontal axis in the range from −10.8° to −13.5° (81.6–88.4°). Maximum strokes appeared to be excessive as these caused 43.8% greater discomfort than did neutral strokes. The 90-mm width also appeared to be excessive as it resulted in 12.3% increased discomfort relative to the 60-mm width. The small-hand group reported 11.9–18.2% higher discomfort ratings, and the percent maximum voluntary exertion of their flexor digitorum superficialis muscle, pertaining to index finger flexion, was also 6.4% higher. These findings should be considered to make smartphone rear interaction more comfortable. Practitioner Summary: Among neutral, comfortable, maximum, horizontal, and vertical index finger strokes on smartphone rear surfaces, maximum vs. neutral strokes caused 43.8% greater discomfort. Horizontal (vertical) strokes deviated from the horizontal (vertical) axis. Discomfort increased by 12.3% with 90-mm- vs. 60-mm-wide devices. Rear interaction regions of five commercialised smartphones should be lowered 20 to 30 mm for more comfortable rear interaction.

Effects of Display Curvature and Task Duration on Proofreading Task Performance, Visual Fatigue, Visual Discomfort, and Display Satisfaction:

With more curved display products in the market and more exposure to such products, it is necessary to examine the effects of display curvature and task duration from the ergonomics perspective. The current study examined the effects of these two factors on visual performance, visual fatigue, visual discomfort, and display satisfaction during proofreading tasks. We incorporated five display curvatures (600R, 1140R, 2000R, 4000R, and flat) and five task durations (0, 15, 30, 45, and 60 min). Each of 50 individuals completed a 1-hr proofreading task at one of five display curvature conditions. The horizontal viewing distance was fixed at 600mm. Proofreading performance (speed and error rate), subjective visual fatigue [on ECQ (Eye Complaint Questionnaire)], physiological visual fatigue [CFF (Critical Fusion Frequency), blink duration, and blink frequency], visual discomfort (on VAS), and display satisfaction (on VAS) were measured. The highest mean proofreading speed was at 600R. The mean proofreading speed and error rate increased by 15.5% and 22.3%, respectively, over the 1-h task. The mean ECQ score and visual discomfort increased by 188.6% and 107.2% during 45 and 60 min of the task, respectively. The mean CFF and display satisfaction decreased by 0.49Hz and 11.2% during 15 and 15-45 min of the task. A polynomial regression model for subjective visual fatigue was developed (adjusted R2 = 0.6). These findings can be used when determining ergonomic display curvatures and predicting visual fatigue.

Determining ergonomic forms for rollable display devices

Following commercialization of curved displays, foldable and rollable displays are under development. The rollable display should be unrolled first using a pulling motion to access the screen. The corresponding pulling force acting on the lateral grip (bezel) areas of the device should be higher than the spring force typically used for retracting the screen. The objective of the current study was to examine the effects of hand length and device thickness on the required lateral grip area sizes of the rollable display device and the grip comfort for the screen unrolling motion, and to ultimately determine the ergonomic bezel width and device thickness associated with high grip comfort. Thirty young individuals with the mean (SD) age of 22.1 (2.2) years participated in this study. All participants were recruited from a university population, right-handed, and healthy without any musculoskeletal diseases on their upper limbs. This study was a 3 (Hand length) × 3 (Device thickness) mixed factorial design. Hand length (HandS/M/L; between-subjects factor) consisted of HandS (short hand length; ≤162.5 mm, 10th percentile), HandM (medium hand length; 174.6–177.3 mm, 45th–55th percentile), and HandL (large hand length; ≥189.4 mm, 90th percentile). Device thickness (DeviceThin/Medium/Thick; within-subjects factor) consisted of DeviceThin (2 mm thick), DeviceMedium (6 mm thick), and DeviceThick (10 mm thick). Each of three rollable display device prototypes was comprised of Acrylonitrile Butadiene Styrene plastic panels, a roll of paper screen (to show a default screen), a roller, and a spring (to roll the screen). The thickness of the right side of the device was manipulated, whereas that of the left side was fixed at 10 mm to house the three parts described above (a rollable screen, a roller, and a spring). When fully unrolled, the sizes of each prototype and the screen were 140H × 300W × 2.5R (mm) and 130H × 260W (mm), respectively. The prototype was equally split into two sides, with each grip part (bezel) 20 mm wide. A 1 mm-interval grid image (130H × 20W (mm)) was attached to each bezel to measure the bezel area involved in gripping. The initial pulling force for unrolling the screen was 2.5N. A desk (150 × 60 × 73 cm) and a height-adjustable chair were used. First, participants unrolled and rolled the prototypes freely for five min to familiarize themselves with how to use the prototypes. A randomly assigned prototype was evaluated three times as follows. Each seated participant repeated unrolling and rolling motions with the assigned prototype until they found the most comfortable grip. While the screen was fully unrolled using the most comfortable grip, each grip area was photographed from four different directions. Then, each individual rated the grip comfort of each hand on a 100mm Visual Analogue Scale (0: Very uncomfortable, 100: Very comfortable). A paper-and-pencil method was used for comfort ratings. The entire procedure to evaluate the three prototypes required about 30 min per participant. Regardless of hand length, the width of the grip area from the device side edge was up to 20 mm. The mean (SD) height of the grip areas for HandS/M/L was 108.8 (3.1), 116.8 (2.5), 124.2 (2.3), respectively. Regardless of hand length, the lower end of the grip area reached the bottom of the device, while the upper end moved more upward with hand lengths. The thinner the device was, the smaller the difference in the grip areas was across the three hand-length groups. In addition, grip comfort increased with device thickness. When gripping a thinner object, the grip posture becomes more deviated from a relaxed hand posture to make more flexions of the thumb and fingers. The simple linear regression model for the left-hand grip comfort on the right-hand grip comfort was constructed (R2 = 0.68 and p-values <0.001): Y(left-hand grip comfort)=23.1+0.74×X(right-hand grip comfort) This regression model indicates that the two grip comfort ratings were positively correlated. In addition, the right-hand grip comfort ratings were lower than the left-hand grip comfort ratings. The mean (SD) comfort ratings for the left and right hands were 75.1 (19.2) and 78.6 (17.3), respectively, with p-value for a paired t-test < 0.001. Thus, device thickness appears to be an important design dimension that influences the grip comfort associated with screen unrolling. There are some limitations in the current study. First, the initial pulling force required for screen unrolling was fixed at 2.5N. The screen unrolling motion involves external rotation of the shoulders. To the authors’ knowledge, no study has investigated an ergonomic force range for this motion. Second, some measurement errors may have been involved in manually identifying the grip area based on the photographs. Using touch sensors would provide more accurate and faster measurements. Finally, it is necessary to analyze the grip areas more in detail. The current study investigated the effects of hand length and device thickness on the grip area and the grip comfort of each hand for rollable display devices. The findings suggested that regardless of hand length, the side bezel of a rollable display device should be at least 20 mm wide and the device should be sufficiently thick (preferably 10 mm thick) to ensure high grip comfort. These findings will be useful when designing ergonomic rollable display devices with high grip comfort.

Determining Ergonomic Smartphone Forms With High Grip Comfort and Attractive Design

Objective: The authors aimed to identify ergonomic smartphone forms by investigating the effects of hand length, four major smartphone dimensions (height, width, thickness, and edge roundness), and smartphone mass on grip comfort and design attractiveness. Background: Despite their potential effect on grip comfort and design attractiveness, the dimensions specified above have never been simultaneously considered in a study investigating smartphone gripping. Method: Seventy-two young individuals participated in a three-stage study. Stage 1 determined the ranges of the four smartphone dimensions suitable for grip comfort and identified the strengths of their influences. Stage 2 investigated the effects of width and thickness (determined to have the greatest influence) on grip comfort and design attractiveness. Mock-ups of varying masses were fabricated using the dimensions determined during the first two stages to investigate the effect of mass on grip comfort and design attractiveness in Stage 3. Results: Phone width was found to significantly influence grip comfort and design attractiveness, and the dimensions of 140 × 65 (or 70) × 8 × 2.5 mm (height × width × thickness × edge roundness) provided high grip comfort and design attractiveness. The selected dimensions were fit with a mass of 122 g, with masses in the range of 106–137 g being comparable. Conclusion: The findings of this study contribute to ergonomic smartphone design developments by specifying dimensions and mass that provide high grip comfort and design attractiveness. Application: The dimensions and mass determined in this study should be considered for improving smartphone design grip comfort and attractiveness.

Rear interaction zones of 140 smartphone models vs. ergonomic recommendation

Rear interaction is a new interaction method adopted by many recent smartphone models. This study compared the rear interaction zones of 140 smartphone models with Lee et al. (2016)’s recommendation, and examined the effects of smartphone width and height on the location of rear interaction zone. The mean center (X, Y) of the rear interaction zones of these smartphone models was (0.5, 111.6), while the center of the recommended zone was (11.5, 94.5). The mean (SD) distance (D) between the center of rear interaction zone of each model and the recommended center was 21.0 (4.8). The significant interaction effect of width × height on the location of the rear interaction zone indicated that larger models had higher rear interaction zones. Using the K-Means clustering method, the smartphone models were divided into three groups – Small (PS), Medium (PM), and Large (PL). The XY ranges of the rear interaction zones were (-6–16, 78–132) for PS, (-7–16, 99–134) for PM, and (-6–6, 91–140) for PL. The mean center of each smartphone group’s interaction zones was deviated from the center of the recommended zone by 18.4mm for PS, 22.7mm for PM, and 24.7mm for PL. Only seven out of the 140 models provided a rear interaction zone that was partially overlapped with the recommended zone. It is recommended to lower the rear interaction zones provided by the current smartphone models regardless of their size in order to enhance hand comfort during rear interactions.