Haptic Information Access Using Touchscreen Devices: Design Guidelines for Accurate Perception of Angular Magnitude and Line Orientation

The overarching goal of our research program is to address the long-standing issue of non-visual graphical accessibility for blind and visually-impaired (BVI) people through development of a robust, low-cost solution. This paper contributes to our research agenda aimed at studying key usability parameters governing accurate rendering and perception of haptically-accessed graphical materials via commercial touchscreen-based smart devices, such as smart phones and tablets. The current work builds on the findings from our earlier studies by empirically investigating the minimum angular magnitude that must be maintained for accurate detection and angular judgment of oriented vibrotactile lines. To assess the minimum perceivable angular magnitude (i.e., cord length) between oriented lines, a psychophysically-motivated usability experiment was conducted that compared accuracy in oriented line detection across four angles (2°, 5°, 9°, and 22°) and two radiuses (1-in. and 2-in.). Results revealed that a minimum 4 mm cord length (which corresponds to 5° at a 1-in. radius and 2° at a 2-in. radius) must be maintained between oriented lines for supporting accurate haptic perception via vibrotactile cuing. Findings provide foundational guidelines for converting/rendering oriented lines on touchscreen devices for supporting haptic information access based on vibrotactile stimuli.