Effective Levels of Haptic Signal Complexity for Texture Rendering Across Diverse Displays

Our ability to assess and discriminate a vast variety of surface textures relies on densely packed mechanoreceptors embedded in our fingertips, which are exquisitely attuned to both temporal and spatial changes in skin deformation. Texture perception is critical for our ability to identify and evaluate the quality and material of every surface we touch, and dynamic changes in texture can also serve as an intuitive way to haptically communicate information such as finger location or changing dial settings. This range of utility suggests diverse and realistic texture rendering is an important modality to consider for any haptic display. Yet what exactly constitutes “diverse and realistic enough,” balancing ability to render a wide breadth of realistic textures using a given haptic display while maintaining efficient signal representation and accommodating actuator limitations?<br/>My recent research focuses on texture rendering for a diverse set of displays, from friction-modulated touchscreens to wearable vibrotactile rings and watches. These devices differ broadly in site of actuation, actuator bandwidth, and concurrent visual displays, but all rely on a vibration applied to the hand during movement as the primary method of texture rendering. We explored various methods of designing new vibration patterns, such as increasing the amount of spectral content or scaling different aspects of the vibration as a function of finger speed.<br/>The impact of these texture design choices were evaluated via psychophysical ratings of both perceived haptic texture differences and similarity to real textures. Results indicate that for higher frequency vibrations, people can differentiate only a very limited amount of spectral complexity, and are also increasingly less sensitive to speed-dependent shifts in frequency. This suggests the set of fine texture sensations achievable via applied vibration alone can be composed using a manageably small set of design parameters and rendered with a few narrow bandwidth actuators.