2014 IEEE International Conference on Systems, Man, and Cybernetics October 5-8, 2014, San Diego, CA, USA
Effect of Touchscreen and Input Device Softness on Task Performance and Subjective Evaluation Kyung-mi Chung
Min-Gyu Kim
Dong-Hee Shin*
Department of Interaction Science Sungkyunkwan University Seoul, South Korea
[email protected]
Department of Industrial Design Eindhoven University of Technology Eindhoven, The Netherlands
[email protected]
Department of Interaction Science Sungkyunkwan University Seoul, South Korea
[email protected]
Abstract—The purpose of this study was to investigate the relationships between the softness of two mobile touchscreens and three direct input devices on user’s task performance and subjective evaluation for tapping tasks. In the within-subjects design, 44 participants were asked to perform tasks as quickly and accurately as possible across the six combinations. After completing tasks in each condition, they filled out a questionnaire to evaluate the perceived pleasantness and degree of elasticity. The result showed a main effect of different touchscreen types on the task performance and degree of elasticity while different input device types showed a main effect on all three dependent variables. An interaction effect of two independent variables on the degree of elasticity was found. Along with the result, the practical implications of these findings are also discussed.
I.
I NTRODUCTION
To enable users to experience a pleasant touch when using their touch-based mobile devices, product designers and developers have considered sensory feedback types and material properties including texture and hardness [1], [2] for the devices as important determinants in the design process. As direct-touch mobile devices like smartphones, tablet PCs, and handheld game consoles are commonly used, users have thought of touch-based interaction as the natural process of handling their own devices with a stylus or fingers. Nevertheless, users can experience a lack of tactile feedback when pressing the virtual and graphical buttons displayed on the hard-surfaced touchscreen. To experience high-fidelity tactile sensations and let the users feel what they are actually doing, much effort is being devoted to develop new display technologies, such as Senseg TixelTM and Tactus Intelligent SurfaceTM, as recently highlighted at the international Consumer Electronics Show. In addition, users have also tried to choose and attach different types of screen protective films, such as glossy or matt films, on the surface of their devices, thereby protecting from scratches and conferring a high-quality texture inexpensively. To meet these needs, 3MTM released soft and matt Mobile Shield protectors made of a shape memorizing material, polyurethane with excellent flexibility and resiliency. It is easy to bring the film to its original shape even if the surface is touched with a rigid probe. Besides the display technology, it is important to focus on the interactions that involve the sense of touch with direct input devices. Despite differing styles, most stylus pens are designed to improve task performance, not to provide rich tactual experience. This is because the relationships with
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touchscreen displays and different input devices have not been carefully taken into account in the user experience design process. People tend to have a preference for soft, light-weighted or elastic materials, with the important factors for pleasant feeling ranked in descending order as the degree of softness, degree of elasticity, temperature, and texture [3]. In this research, we focused on the degree of softness to the touchscreen surface and pen-shaped input devices including the finger as a performance baseline. The importance of tactile sensation cannot be overemphasized, since touch feelings that can affect users’ emotions enable them to perceive the product’s usefulness and usability [4]. In this respect, the findings of this study can contribute to helping designers and developers to understand the underlying human factors of direct touch-based interaction and to design haptic products with pleasant tactile feeling. II.
M ETHODS
The study had a 2 (touchscreen : elastic surface vs. glass surface) × 3 (direct input device : fingertip vs. stylus with acrylic tip vs. stylus with rubber tip) within-subjects factorial design. The experiment consisted of two sessions for all participants: a warm-up session with the pre-survey (7 minutes) and a main session with the tests for 6 conditions (10 trials for each condition) and post-survey (30 minutes). A. Participants Forty-four undergraduate and graduate students (24 males, 20 females) from Sungkyunkwan University in South Korea, aged from 19 to 28 years (M = 23.25, SD = 2.08) participated. B. Apparatus and Materials The experiment was conducted using two Samsung Galaxy S3 smartphones with a 4.8 inch display. To manipulate the degree of surface softness, an elastic sheet was attached to one of them, but not to the other smartphone. The elastic sheet consisted of 0.1 mm thick silicon film and 0.5 mm thick urethane film. The upper surface of the urethane film was covered with the thin silicon film to provide participants with apparently elastic touch feeling. As direct input devices, we a capacitive stylus (OZAKI O! Tool stylus R) and Adonit Jot Pro 1, whose tips are made of soft rubber material and hard acrylic material, respectively.
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C. Degree of Elasticity
Fig. 1. Stylus pens with two different hard and soft tips, touchscreen with elastic sheet, installed mobile application for performaing task
As can be seen in Fig. 1, the Android app Yellow 25 was used to performing tasks. The tiles with a number on them from 1 to 25 were jumbled together on the screen. The object of the game was to touch the numbers in order until all numbers were dimmed. Unless the numbers were touched in order, further progress did not occur and the game would not end. The game could save the time to three decimal places. III.
R ESULTS
A. Task Performance There was a significant main effect for the softness of touchscreen, F (1, 43) = 15.193, p < .05, such that the elastic surface condition (M = 14.309, SE = .280) led to more outstanding task performance than the glass surface condition (M = 14.509, SE = .291). There was also a main effect for the softness of input devices, F (2, 86) = 15.423, p < .001, such that the fingertips (M = 14.173, SE = .303) and the rubbertipped stylus (M = 14.240, SE = .267) conditions led to more significantly outstanding task performance than the acrylictipped stylus condition (M = 14.814, SE = .302). The fingertips as the input device led to the fastest task performance when the surface texture of touchscreen is soft (M = 14.054, SE = .287). The stylus with the acrylic tip led to the slowest task performance when the surface texture of touchscreen was hard (M = 14.890, SE = .295). B. Perceived Pleasantness The analysis of perceived pleasantness revealed a main effect for the direct input device factor, F (2, 86) = 60.573, p < .001. According to the pairwise comparisons of input devices, the difference among three conditions was significant. Among all comparisons, pressing the touchscreen via the stylus with the soft tip (M = 3.875, SE = .120) was perceived as more pleasant than with the hard tip (M = 2.307, SE = .117) and the fingertips (M = 3.273, SE = .113). The interaction between the associations with the softness of touchscreen and different input devices was significant, F (2, 86) = 3.104, p = .05. Pressing the elastic-surfaced touchscreen via the rubber-tipped stylus (M = 3.886, SE = .146) was considered as the most pleasant touch, while the glass-surfaced touchscreen via the acrylic-tipped stylus (M = 2.159, SE = .145) was considered as the most unpleasant touch.
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All effects were statistically significant: the main effect for the softness of output display (F (1, 43) = 4.619, p < .05), the main effect for the softness of input devices (F (2, 86) = 52.354, p < .001), and the interaction effect of two factors (F (2, 86) = 3.894, p < .05). Pairwise comparisons of the two displays indicated that the elastic display condition (M = 2.932, SE = .104) was significantly higher than the glass display condition (M = 2.667, SE = .113). In comparisons of three input devices, the rubber-tipped stylus condition (M = 3.659, SE = .144) led to the highest degree of elasticity, followed by the fingertip (M = 2.761, SE = .125) and the rubber-tipped stylus (M = 1.977, SE = .121) conditions. With the combination of the glass touchscreen, the rubber-tipped stylus led to the highest degree of elasticity (M = 3.705, SE = .186), and the acrylic-tipped stylus led to the lowest degree of elasticity (M = 1.818, SE = .157). IV.
C ONCLUSION
This study was designed to provide designers with the practical findings to design the pleasant haptic experience of mobile phones and their accessories. The main finding was that the combination leading to the outstanding task performance did not guarantee the high level of pleasantness. Given that the combination of the glass display and fingers was the control condition, the combination of elastic display and fingers was the fastest task performance, followed by the combination of elastic display and rubber-tipped pen. In terms of evaluating perceived pleasantness, the combination of elastic display and rubber-tipped pen was rated as the highest satisfaction, followed by the combination of glass display and rubber-tipped pen. The two combinations of the perceived pleasantness were higher than that of the control condition. However, the task performance of the glass display with rubber-tipped pen was worse than that of the control condition as a performance baseline. Thus, it will be desirable to use the rubber-tipped stylus with the elastic surfaced touchscreen for tapping tasks because this combination is the most recommendable to satisfy both user’s task performance and subjective satisfaction. ACKNOWLEDGMENT This study was supported by the Brain Korea 21 Plus Project of the Korean Ministry of Education via the National Research Foundation (10Z20130000013). *Corresponding author R EFERENCES [1]
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