Illusory-UMH: A Systematic Comparison of Tactile Illusions and Modulation Techniques in Ultrasonic Mid-air Haptics

Spatiotemporal modulation (STM) is the current de facto standard technique for generating continuous tactile sensations in Ultrasonic Mid-Air Haptics (UMH). However, like other techniques, it assumes a uniform sensitivity distribution across the hand. Tactile illusions, such as the funneling effect (FE) and cutaneous rabbit effect (CRE) create continuous sensations by stimulating only a few points along the shape, which could be strategically selected at highly sensitive points in the hand for stronger effects, but such effects remain unexplored in UMH. This paper investigates tactile illusions (FE, CRE) as potential alternatives for STM, comparing their ability to produce continuous and intense shapes at regions on the palm with different skin sensitivity. Our results reveal significantly superior performance for CRE, when compared to FE and STM in the tested parameter range. FE in turn provides slightly higher continuity, even across sensitivity regions, while STM provides higher intensity.