Exploration strategies for tactile graphics displayed by electrovibration on a touchscreen

Abstract

Advancements in surface haptics technology have given rise to the development of interactive applications displaying tactile content on touch surfaces such as images, signs, diagrams, plots, charts, graphs, maps, net-works, and tables. In those applications, users manually explore the touch surface to interact with the tactile data using some intuitive strategies. The user's exploration strategy, tactile data's complexity, and tactile rendering method all affect the user's haptic perception, which plays a critical role in designing and prototyping of those applications. In this study, we conducted experiments with human participants to investigate the recognition rate and time of five tactile shapes (i.e., triangle, square, pentagon, hexagon, and octagon) rendered by electro-vibration on a touchscreen using three different methods (electrovibration was active inside, on the edges, or outside the shapes), and displayed in prototypical orientations and non-prototypical orientations (i.e., 15 degrees CW and CCW to the prototypical orientation). The results showed that the correct recognition rate of the shapes was higher when the haptically active area (area where electrovibration was on) was larger. However, as the number of edges was increased, the recognition time increased and the recognition rate dropped significantly, arriving to a value slightly higher than the chance rate of 20% for non-prototypical octagon. Moreover, the recognition time for inside rendering condition was significantly shorter compared to edge and outside rendering conditions, and edge rendering condition led to the longest recognition time. We also recorded the participants' finger movements on the touchscreen to examine their haptic exploration strategies. Based on our temporal analysis, we classified six exploration strategies adopted by participants to identify the shapes, which were different for the prototypical and non-prototypical shapes. Moreover, our spatial analysis revealed that the participants first used global scanning to extract the coarse features of the displayed shapes, and then they applied local scanning to identify finer details, but needed another global scan for final confirmation in the case of non-prototypical shapes, possibly due to the current limitations of electrovibration technology in displaying tactile stimuli to a user. We observed that it was highly difficult to follow the edges of shapes and recognize shapes with more than five edges under electrovibration when a single finger was used for exploration.