Investigation of icon design and touchable area for effective smart phone controls

As the full-touch screen is being implemented in more smart phones, controllability of touch icons need to be considered. Previous research focused on recommendations for absolute key size. However, the size of tactual input on touch interface is not precisely equal to the icon size. This study aims to determine the suitable touchable area to improve touch accuracy. In addition, there was an investigation into the effect of layout (3 × 4, 4 × 5, 5 × 6, and 6 × 8) and icon ratio (0.5, 0.7, and 0.9). To achieve these goals, 40 participants performed a set of serial tasks on the smart phone. Results revealed that the layout and icon ratio were statistically significant on the user response: input offset, hit rate, task completion time, and preference. The 3 × 4 and 4 × 5 layouts were shown to have better performance. The icon ratio of 0.9 was shown to have greater preference. Furthermore, the hit rate (proportion of correct input) of touchable area was estimated through the bivariate normal distribution of input offset. The hit rate could vary, depending on the size of touchable area, which is a rectangle that yields a specific hit rate. A derivation procedure of the touchable area was proposed to guarantee the desirable hit rate. Meanwhile, the locations of the central region indicated a pattern of vertical touch and showed better performance. The users felt more difficulty when approaching the edge of the frame. The results of this study could be used in the design of touch interfaces for mobile devices.