Characteristics of pressure-based input for mobile devices

Abstract

We conducted a series of user studies to understand and clarify the fundamental characteristics of pressure in user interfaces for mobile devices. We seek to provide insight to clarify a longstanding discussion on mapping functions for pressure input. Previous literature is conflicted about the correct transfer function to optimize user performance. Our study results suggest that the discrepancy can be explained by different signal conditioning circuitry and with improved signal conditioning the user-performed precision relationship is linear. We also explore the effects of hand pose when applying pressure to a mobile device from the front, the back, or simultaneously from both sides in a pinching movement. Our results indicate that grasping type input outperforms single-sided input and is competitive with pressure input against solid surfaces. Finally we provide an initial exploration of non-visual multimodal feedback, motivated by the desire for eyes-free use of mobile devices. The findings suggest that non-visual pressure input can be executed without degradation in selection time but suffers from accuracy problems.

Side pressure for bidirectional navigation on small devices

“…Third, these studies are in accordance with earlier ones about pen pressure [15,16], that highlighted the importance of feedback mechanisms for efficient pressure control [24]. Finally, twosided (grasping type) pressure input is preferable to singlesided (pointing type) in a mobile context [20]. The design of the SidePress hardware prototype and the associated software was informed by these experimental findings.…”

“…Another example is the tablet prototype presented in [22]: a pressure sensor is attached to the front bezel held with the dominant hand. As most previous work that investigated pressure as an input channel [20,24], they considered a single pressure sensor, which limits the range of tasks users can achieve with it. Indeed, a pressure sensor is typically unidirectional and has a rest position.…”

“…Like GraspZoom [13] and [23], SidePress uses two-sided (grasping type) pressure input, which is preferable to single-sided (pointing type) pressure input in a mobile context [20]. However, unlike GraspZoom, we overcome occlusion problems by squeezing the device along its y-axis rather than pinching it along its z-axis.…”

“…This issue was discussed in [20], that recommends a linear mapping function for pressure input. In order to linearize pressure input, we used an op-amp based current-to-voltage converter circuit [20]. With this circuit, sensor output increases linearly with applied pressure.…”

Novel Modalities for Bimanual Scrolling on Tablet Devices

“…The interaction techniques were implemented on a Viewsonic Viewpad 10" touchscreen tablet running custom software on Windows 7. A Griffin Technologies PowerMate Dial, with an extended radius (using the lid from a jar of fruit so that it could be easily reached at the side of the tablet), was used for the dial conditions and a single Force Sensing Resistor connected through a SAMH Engineering SK7-ExtGPI01 input/output module (which handled A-D conversion and sensor linerisation [21]) was used for pressure sensing (See Figure 2). Users applied pressure by performing a pinch gesture with the thumb and forefinger of their NDH on the lefthand bezel of the device.…”