Evaluation of mapping functions for one-handed flick operations on a mobile device

Abstract

As the number of full-touch screen mobile devices has increased, the importance of screen movement methods become critical, especially for scrolling. “Flick” is one of the most preferred alternatives of screen movement methods for “scrolling”. To improve the usability of “flick”, this study examined the user characteristics for flicking and attempted to evaluate various mapping functions for flick which consider the user characteristics. The mapping functions were established by combing the “shapes” and the “reference point” which was determined by the maximum control velocity of flick (Vc_max) for each user and the initial movement velocity of screen (Vim_max). For this study, a total number of 30 participants who were right-handed were recruited, and they were in their twenties and thirties. For examining the user characteristics, the maximum velocities of “flick” operated toward 8 directions from the center of the screen were collected and analyzed. The mapping functions which were customized for each participant were then evaluated by measuring the task completion time (performance) and the ease of use (satisfaction). The shapes of mapping function include four types: the LINEAR, the QUADRATIC, the LOG, and the LOGISTIC. The Vim_maxs of mapping function include three types: 1500 pixels/s, 3000 pixels/s, and 4500 pixels/s. As a result of analyzing the user characteristics, it was found that the hand size (thehand length and the thumb length) affects the speed of flick

the Vc of male is faster than that of female because the hand size of male is larger than that of female. The biomechanical features of hand also affect the speed of flick for each direction

flicks in the vertical movement are faster than those in the horizontal movement, and east than west. By evaluating twelve mapping functions, it is found that the LINEAR with 3000 pixels/s, the QUADRATIC with 3000 pixels/s, and the QUADRATIC with 4500 pixels/ are recommended for flick. However, since this study regulate the environment such as the one-handed thumb use, one dimensional movement, and the grip posture, the results of this study cannot be directly applied to the real products. In addition, there would be various ways to establish mapping functions and lots of user characteristics to be considered. Therefore, if more user characteristics such as age, handedness, and the strength of hand, are considered, the best mapping function could be developed. Nevertheless, this study is meaningful in that it highlights the necessity of mapping functions considering the user characteristics, and suggests some specifications for the appropriate mapping functions.