HaptiCase: Back-of-Device Tactile Landmarks for Eyes-Free Absolute Indirect Touch

Using a smartphone for touch input to control apps and games mirrored to a distant screen is difficult, as the user cannot see where she is touching while looking at the distant display. We present HaptiCase, an interaction technique that provides back-of-device tactile landmarks that the user senses with her fingers to estimate the location of her finger in relation to the touchscreen. By pinching the thumb resting above the touch-screen to a finger at the back, the finger position is transferred to the front as the thumb touches the screen. In a study, we compared touch performance of different landmark layouts with a regular landmark-free mobile device. Using a land-mark design of dots on a 3×5 grid significantly improves eyes-free tapping accuracy and allows targets to be as small as 17.5 mm—a 14 % reduction in target size—to cover 99% of all touches. When users can look at the touchscreen, land-marks have no significant effect on performance. HaptiCase is low-cost, requires no electronics, and works with unmodi-fied software. Author Keywords Eyes-free touch; back-of-device interaction; tactile feedbac