High-Frequency Gripping Area for One-Handed Smartphone Rear Interactions

Abstract: Recent years of cell phone development have proposed ways to extend the interaction with mobile devices by equipping the device with a touch-sensitive rear for back-of-device (BoD) interaction. Although previous work [1] provided a classification of hand-hold/grip styles, a detailed understanding of the location of high-frequency touch areas at the back of the cell phone and the position of different fingers is missing. Knowledge of this information is necessary to develop ergonomically based interaction techniques on the back of the device. In addition, the location of high-frequency gripping areas needs to be taken into account when designing the location and size of the heating elements of a cell phone, and such areas should be avoided as much as possible to achieve a better user experience. The purpose of this study is to investigate the distribution of high-frequency gripping areas in the portrait view (one-handed vertical screen scenarios) for BoD interaction of a cell phone. We conducted an experiment to collect the rear area of the phone held by one hand in the natural settings. The rear and surrounding bezel area of the phone is partitioned in 10*10mm squares, with a total of 8*16 grids. 60 human subjects (normal smartphone users recruited by demographic segments) participated in this study. Their hand-hold/grip behaviors data were recorded by simulating their natural usage of the testing device with using an ink-based handprint technique. Then, through image recognition, filter the grid of the rear and surrounding bezel area of the phone, where handprints area account for more than 40% of the grid area. The final processing of the experiment yields a high-frequency grip area map and its corresponding grip posture which indicates how the user hold the smartphone and their BoD interaction. The whole grip area can be divided into three major parts: purlicue area (space between the forefinger and thumb), index finger area, and three fingers (middle, ring, and pinky) area. The results show that in the purlicue area and three-finger area, the grip frequency is normally distributed, and the location and size of the specific areas where the users' grip frequency reaches 90% and 95% in these two areas are obtained. The high-frequency grasping area identified in this study could provide references to design BoD interaction and improve the touch experience on the rear of such devices. In addition, the research results can lay the foundation for exploring the thermal tactile experience of mobile devices, provide a theoretical basis for the PCB layout design of heating components in mobile phones, and guide the system optimization of mobile phone cooling systems.Reference:[1]Choi, Y., Jung, H., Park, J., & You, H. (2017, September). Analysis of grip posture for ergonomic smartphone interface design. In Proceedings of the Human Factors and Ergonomics Society Annual Meeting (Vol. 61, No. 1, pp. 1058-1061). Sage CA: Los Angeles, CA: SAGE Publications.

Keywords: High-Frequency Gripping Area, Back-of-Device, Grip Posture

DOI: 10.54941/ahfe1004814

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