Introducing a new haptic illusion to increase the perceived resolution of tactile displays

Tactile high-resolution displays gained importance during the last decade due to their wide range of application areas. To maximize the throughput of information developers can be tempted to mount as many tactile actuators (tactors) as possible on a haptic device, thereby risking to overexert the user's sense of touch, and to critically decrease its usability. Studies therefore explore ways of increasing the perceived resolution of tactile displays by exploiting haptic illusions. We demonstrate a new spatiotemporal haptic illusion that has not been described in literature yet. We conducted an experiment, in which we manipulated the vibration intensity of two successive tactor activations, the direction of consecutive tactor activations (up, down) and inter-tactor distance (40, 20, or zero mm). Fourteen naive participants judged whether the second tactor activation was above or below the first activation. Our results suggest that varying the sequence of activations with different intensities leads to an error of localization. High intensity activations followed by low intensity activations resulted in an illusory downward movement, and vice versa. The haptic intensity-movement illusion provides a promising possibility to enhance the information conveyed in tactile displays, without increasing the tactor density at the cost of the product's usability, comfort and ergonomy.