The Effects of Mobility on Mobile Input

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto. fi Author Joanna Bergström-Lehtovirta Name of the doctoral dissertation The Effects of Mobility on Mobile Input Publisher School of Science Unit Department of Information and Computer Science Series Aalto University publication series DOCTORAL DISSERTATIONS 120/2014 Field of research Computer and Information Science Manuscript submitted 10 June 2014 Date of the defence 30 August 2014 Permission to publish granted (date) 8 August 2014 Language English Monograph Article dissertation (summary + original articles) Abstract Mobile interfaces are designed for interaction while the user is on the move across mobile contexts. Walking, handling a wallet, visually attending to the environment, and even simply carrying a mobile device, however, can have a negative effect on mobile human–computer interaction (HCI). Understanding the negative effects of mobility is important because potential exists for overcoming them via good interface design. Previous work has shown that mobility decreases input performance with a mobile interface. However, the causes of declines in performance often remain unclear and, with them, possible avenues for compensation. I argue that systematic variation of physical constraints emerging from mobile conditions in controlled experiments can reveal considerable effects of mobility on mobile input. Among these physical constraints are competing allocations of hand function, body movement, and various sensory modalities. The thesis contributes to mobile HCI research by examining the effects of four causes of physical constraints in mobility: 1) gripping of the device, 2) walking, 3) manipulation of external objects, and 4) sensory feedback. The research includes four studies, isolating one constraint each in controlled experiments. In the first two, the levels of grip position and walking speed are varied systematically, for modeling of their effects on mobile input. The other two vary the presence of external objects and sensory feedback. The findings highlight the constraints' negative effect on manual input performance. However, all of the studies also reveal unaffected sensory or motor resources of the user. Across the four studies, the following findings were made. First, a model for the functional area of the thumb predicts the reachable interface elements on a mobile touchscreen as a function of grip, hand size, and screen size. Secondly, a function describing the tradeoff between walking speed and input performance demonstrates that while walking hampers input performance, users can adjust to an optimal walking speed for mobile interaction. Thirdly, interface design is shown to significantly affect input performance when the user simultaneously manipulates external objects or when sensory feedback is limited. This work calls for mobile HCI research to consider the operationalization of mobile conditions in controlled experiments that can extend knowledge of the effects of mobility on interaction. It also invites exploitation of the empirical results and the proposed methods and models in practice for interface evaluation and design.Mobile interfaces are designed for interaction while the user is on the move across mobile contexts. Walking, handling a wallet, visually attending to the environment, and even simply carrying a mobile device, however, can have a negative effect on mobile human–computer interaction (HCI). Understanding the negative effects of mobility is important because potential exists for overcoming them via good interface design. Previous work has shown that mobility decreases input performance with a mobile interface. However, the causes of declines in performance often remain unclear and, with them, possible avenues for compensation. I argue that systematic variation of physical constraints emerging from mobile conditions in controlled experiments can reveal considerable effects of mobility on mobile input. Among these physical constraints are competing allocations of hand function, body movement, and various sensory modalities. The thesis contributes to mobile HCI research by examining the effects of four causes of physical constraints in mobility: 1) gripping of the device, 2) walking, 3) manipulation of external objects, and 4) sensory feedback. The research includes four studies, isolating one constraint each in controlled experiments. In the first two, the levels of grip position and walking speed are varied systematically, for modeling of their effects on mobile input. The other two vary the presence of external objects and sensory feedback. The findings highlight the constraints' negative effect on manual input performance. However, all of the studies also reveal unaffected sensory or motor resources of the user. Across the four studies, the following findings were made. First, a model for the functional area of the thumb predicts the reachable interface elements on a mobile touchscreen as a function of grip, hand size, and screen size. Secondly, a function describing the tradeoff between walking speed and input performance demonstrates that while walking hampers input performance, users can adjust to an optimal walking speed for mobile interaction. Thirdly, interface design is shown to significantly affect input performance when the user simultaneously manipulates external objects or when sensory feedback is limited. This work calls for mobile HCI research to consider the operationalization of mobile conditions in controlled experiments that can extend knowledge of the effects of mobility on interaction. It also invites exploitation of the empirical results and the proposed methods and models in practice for interface evaluation and design.