Designing Distinguishable Mid-Air Ultrasound Tactons with Temporal Parameters

TL;DR

This work addresses the lack of guidelines for distinguishing mid-air ultrasound Tactons by systematically exploring temporal parameters through five studies (n=72). It combines a JND study for AM frequency with four Tacton sets derived from mechanical vibrotactile literature, using pairwise similarity judgments and nMDS to map perceptual spaces and compare ultrasound to mechanical Tactons via Spearman correlations (all reported as $\rho$ values). The results identify envelope frequency $f_e \leq 5$ Hz, rhythm, and total duration as key drivers of perceptual dissimilarity, with strong cross-modal correspondence (mean $\rho$ across studies ranging roughly from 0.61 to 0.89) and notable differences in how certain parameters influence spectral vs temporal cues. The authors derive six design guidelines for parameter-based and metaphor-based ultrasound Tactons and discuss implications for design tools and future perceptual modeling, enabling more distinguishable contactless haptic feedback in applications such as public displays and VR.

Abstract

Mid-air ultrasound technology offers new design opportunities for contactless tactile patterns (i.e., Tactons) in user applications. Yet, few guidelines exist for making ultrasound Tactons easy to distinguish for users. In this paper, we investigated the distinguishability of temporal parameters of ultrasound Tactons in five studies (n=72 participants). Study 1 established the discrimination thresholds for amplitude-modulated (AM) frequencies. In Studies 2-5, we investigated distinguishable ultrasound Tactons by creating four Tacton sets based on mechanical vibrations in the literature and collected similarity ratings for the ultrasound Tactons. We identified a subset of temporal parameters, such as rhythm and low envelope frequency, that could create distinguishable ultrasound Tactons. Also, a strong correlation (mean Spearman's $ρ$=0.75) existed between similarity ratings for ultrasound Tactons and similarities of mechanical Tactons from the literature, suggesting vibrotactile designers can transfer their knowledge to ultrasound design. We present design guidelines and future directions for creating distinguishable mid-air ultrasound Tactons.

Figures (10)

• Figure 1: An overview diagram for Studies 1--5. In Study 1, we examined the discrimination thresholds for AM frequencies of 30 Hz, 80 Hz, and 210 Hz. In Studies 2--5, we investigated the perceptual distinguishability for four sets of mid-air ultrasound Tactons that vary in their temporal parameters. We selected the four sets of mechanical Tactons from park2011perceptuallim2023canternes2008designingseifi2015vibviz to create the ultrasound Tactons.
• Figure 2: Stimuli and set up for the studies: (a) The spatiotemporal stimulation used for Studies 1--5. We maintained a radius of 10 $mm$ and a drawing speed of 12 $m/s$ with a single focal point STM, (b) Experimental setup used for Study 1, and (c) A screenshot of the GUI program used to collect user responses in Study 1. The selected response was highlighted in red. The color did not indicate the correctness of the response.
• Figure 3: Results of Study 1 on the Just Noticeable Differences (JND) for AM frequencies of ultrasonic mid-air stimuli with 12 participants. (a) An example of a study session with the reference AM frequency of 30 Hz. "I" represents an increasing series of frequencies, and "D" a decreasing series. Red, green, and blue colors denote "lower", "equal", and "greater" responses from the participant, respectively. (b) JNDs for AM frequency for each participant and average values. An asterisk (*) indicates a significant difference in JNDs. The dotted and solid lines denote the mean and median, respectively. (c) Post-hoc paired t-tests for JND values.
• Figure 4: Screenshots of the graphical user interface for the (a) training and (b) main pair-wise similarity rating sessions in Studies 2--5.
• Figure 5: Plots of the ultrasound Tactons, perceptual spaces, and distance trends for Study 2.