The Effects of Curvature of Edge Screen on Subjective Feelings in Smartphone Usage
Authors: Lee Yushin , Lee Joong Hee , Kim Yong Min , Lee Jihwan , Kwon Sanghyun , Sim Hyungmin , Yun Myung Hwan 
Published: September 2017

As the penetration rate of Smartphone grows high and the market gets saturated, the technological and aesthetic progress for manufacturers are heavily demanded to sustain their market share. To meet such demands, manufacturers continuously improve the design of their products. As the design of smartphone varies by manufacturers, there have been many existing researches to identify the relationships between various physical dimensions of smartphones and how users feel (Chowdhury, A., & Kanetkar, M., 2017; Lee, S., Kyung, G., Lee, J., Moon, S. K., & Park, K. J., 2016; Pereira, A., Miller, T., Huang, Y. M., Odell, D., & Rempel, D., 2013; Sung, K., Cho, J., & Freivalds, A., 2016). Recently, in accordance with the development and improvement of flexible displays, curved displays have been applied on smartphones with various curvatures. The popular one among them is the “edge screen” on smartphones, which refers to curved display implemented either on one single side or both sides. Considering that physical dimensions such as shape and size are the important features for customer satisfaction (Hwang, 2012; Ling, C., Hwang, W., and Salvendy, G., 2007), curvature of edge screen can influence on user comfort when the users carry out their tasks on their smartphones. However, such issue hasn’t been dealt in previous studies. Therefore, as a preliminary study, this study aimed to identify the relationships between curvatures of edge screens and subjective feelings in smartphone usage with various usage patterns using subjective evaluation experiment. In this laboratory study, 47 subjects assessed their subjective feelings (grip comfort, control comfort, stability, front visibility, side visibility) towards given samples with four different kinds of usage patterns. The samples were designed with a 5.5-inch flat display of 16:9 ratio (Samsung Galaxy Note 2) as a main screen along with a curved display of different radii of curvatures (R, unit: mm) on the right edge as an edge screen: 4R, 6R, 8R, and 10R. The usage patterns were defined according to which hands were used for grip and control: Grip with right hand and control with right thumb (usage pattern (a)), Grip with left hand and control with right index finger (usage pattern (b)), Grip with both hands and control with both thumbs (usage pattern (c)), and Grip with right hand without control (usage pattern (d)). The statistically significant results of one-way analysis of variance (ANOVA) and post hoc analysis (Duncan’s test) showed that the sample with 4R curvature belonged to the third homogeneous subset (in descending order) for the front visibility while it belonged to the second homogeneous subset for the control comfort in usage pattern (b) and (c). Whereas the sample with 6R curvature belonged to the second homogeneous subset for the front visibility and the second homogeneous subset for the control comfort in usage pattern (b) and (c). In case of the sample with 8R curvature, it was within the first homogeneous subset throughout all analyses conducted. Lastly, the sample with 10R curvature was within the second homogeneous subset for the grip comfort in usage pattern (d). Therefore, it is concluded that the optimal radius of curvature for edge screens is 8R. Although there were some samples evaluated better than the 8R sample in descriptive manner, however, such results were not statistically significant. This study is expected to contribute towards the design of smartphones with edge screens in terms of better subjective feeling by various usage patterns. However, this study is yet a preliminary study which is based on a subjective evaluation. In the future research, more criteria of subjective feeling are needed to be evaluated to decide more precise optimal curvature. In addition, objective evaluation method such as analysis of muscle activity, motion tracking analysis, or behavior analysis could be applied to verify the reliability and validity of the result of this study.