Modulation of Ultrasonic Stimulation Parameters towards Evoking Fine Tactile Sensations

An increasing number of recent studies prove that the low-intensity focused ultrasound stimulation (LIFUS) is a promising neuromodulation technique. Its feasibility of eliciting multiple fine tactile sensations, as well as the modulatory effect of ultrasonic stimulation parameters have not been investigated by far. Therefore, in this work, we enrolled eight healthy volunteers to participate into two sets of psychophysical experiment, wherein the ultrasonic stimuli were delivered onto their index fingertips under varying pulse repetition frequency (PRF) and acoustic intensity (AI). Our results showed that ultrasonic stimuli at lower PRF and lower AI were perceived more sensitively in term of Just Noticeable Difference (JND) and Weber fractions (WF) in experiment 1. In experiment 2, six types of fine tactile sensation, including tickling, vibrating, buzzing, pressure, petting, electrical, plus no sensation, could be distinguished under 18 different PRF-AI combinations. Lower PRFs tended to induce rhythmic tap-like sensations, while higher PRFs tended to evoke electrical-like sensations. A synergistic effect of PRF and AI on modulating fine tactile sensations was observed as well. These findings may shed light on modulation of ultrasonic stimulation parameters, and facilitate the application of LIFUS into various human-machine interaction settings.