Gap Detection in Pairs of Ultrasound Mid-air Vibrotactile Stimuli

Abstract

Ultrasound mid-air haptic (UMH) devices are a novel tool for haptic feedback, capable of providing localized vibrotactile stimuli to users at a distance. UMH applications largely rely on generating tactile shape outlines on the users’ skin. Here, we investigate how to achieve sensations of continuity or gaps within such 2D curves by studying the perception of pairs of amplitude-modulated (AM) focused ultrasound stimuli. On the one hand, we aim to investigate perceptual effects which may arise from providing simultaneous UMH stimuli. On the other, we wish to provide perception-based rendering guidelines for generating continuous or discontinuous sensations of tactile shapes. Finally, we hope to contribute towards a measure of the perceptually achievable resolution of UMH interfaces. We performed a user study to identify how far apart two focal points need to be in order to elicit a perceptual experience of two distinct stimuli separated by a gap. Mean gap detection thresholds were found at 32.3mm spacing between focal points, but a high within- and between-subject variability was observed. Pairs spaced below 15mm were consistently (>95%) perceived as a single stimulus, while pairs spaced 45mm apart were consistently (84%) perceived as two separate stimuli. To investigate the observed variability, we resort to acoustic simulations of the resulting pressure fields. These show a non-linear evolution of actual peak pressure spacing as a function of nominal focal point spacing. Beyond an initial threshold in spacing (between 15mm and 18mm), which we believe to be related to the perceived size of a focal point, the probability of detecting a gap between focal points appears to linearly increase with spacing. Our work highlights physical interactions and perceptual effects to consider when designing or investigating the perception of UMH shapes.

An Interactive Tool for Simulating Mid-Air Ultrasound Tactons on the Skin

“…We selected 𝑓 𝐴𝑀 = 0 Hz to test pure STM rendering (𝑃𝑢𝑟𝑒𝑆𝑇 𝑀) and 𝑓 𝐴𝑀 > 60 Hz, as the power lines in our country introduces a constant 60 Hz measurement noise. We also used four combinations of size and drawing speed as (𝑑 in 𝑚𝑚, 𝑣 in 𝑚/𝑠): (0, 0), (10,6), (20,12), (30,18). We chose (0 𝑚𝑚, 0 𝑚/𝑠) to test pure AM rendering (𝑃𝑢𝑟𝑒𝐴𝑀), and maintained the same ratio of 𝑣 𝑑 for the other three combinations to have the same drawing frequency at 191 Hz.…”

“…Thus, the physical simulations of the mid-air ultrasound Tacton can help understand its perception and reduce the Tacton design cost. Prior literature proposes physical simulations for the ultrasound vibrations and their measurement data, for example, AM or STM of a focal point [2,3] and gap detection thresholds between two static focal points [2,10]. Yet, as the existing simulations typically simulate one parameter or one rendering technique, more research is needed on interactive simulation tools for testing the interaction of temporal and spatiotemporal parameters in complex ultrasound Tactons and the combination of rendering techniques.…”

Survey on Hand-Based Haptic Interaction for Virtual Reality

“…Perquin et al [129] studied the discrimination of motion direction and evidenced the directional bias for dynamic STM patterns. Howard et al [130] investigated the perception of continuity or gaps between neighboring AM focal focused ultrasound stimuli.…”

An Exploration of Just Noticeable Differences in Mid-Air Haptics

“…For instance, Martinez et al [12] studied various methods of rendering 3D shapes by emphasizing salient features, and especially object corners. Howard et al [13], [14] studied the recognition of local shapes and the gap detection thresholds between nearby mid-air haptic point stimuli. Hasegawa et al [15] studied the detection threshold curve for different mid-air haptic stimuli.…”