Ultrasound haptic devices can create parametric audio as well as contactless haptic feedback. In a paper at the 2021 ACM International Conference on Multimodal Interaction, I investigated if multimodal output from these devices can influence the perception of haptic feedback. I used a magnitude estimation experiment to evaluate perceived roughness of an ultrasound haptic pattern.
We rendered a circular haptic pattern using a focal point moving at one of three frequencies (a): 50, 70, 90 Hz. This was accompanied by a parametric audio effect (b): noise, tone, or none. Participants moved their hand back and forth across the haptic pattern then rated how rough it felt.
Results suggest that white noise audio from the haptics device increased perceived roughness and pure tones did not, and that lower rendering frequencies may increase perceived roughness.
Scatterplot showing the mean roughness estimates with 95% confidence intervals. X-axis shows rendering frequency with three levels: 50 Hz, 70 Hz, 90 Hz. Y-axis shows normalised roughness estimates on a scale from 0 to 1. The two key trends in the figure are that roughness estimates are higher for the white noise audio condition, and higher for the 50 Hz rendering frequency.
Our results show that multimodal output has the potential to expand the range of sensations that can be presented by an ultrasound haptic device, paving the way to richer mid-air haptic interfaces.
Enhancing Ultrasound Haptics with Parametric Audio Effects E. Freeman. In Proceedings of 23rd ACM International Conference on Multimodal Interaction – ICMI ’21, 692-696. 2021.
@inproceedings{ICMI2021AudioHaptic,
author = {Freeman, Euan},
booktitle = {{Proceedings of 23rd ACM International Conference on Multimodal Interaction - ICMI '21}},
title = {{Enhancing Ultrasound Haptics with Parametric Audio Effects}},
year = {2021},
publisher = {ACM},
pages = {692--696},
doi = {10.1145/3462244.3479951},
url = {http://euanfreeman.co.uk/enhancing-ultrasound-haptics-with-parametric-audio-effects/},
pdf = {http://research.euanfreeman.co.uk/papers/ICMI_2021_AudioHaptic.pdf},
data = {https://zenodo.org/record/5144878},
}
Acknowledgements
This research has received funding from the 🇪🇺 European Union’s Horizon 2020 research and innovation programme under grant agreement #737087. This work was completed as part of the Levitate project.
Ultrasound haptic patterns can be rendered by continuously moving an ultrasonic focal point. It is not known how this focal point motion affects haptic perception. In a paper at the 2021 ACM International Conference on Multimodal Interaction, we describe two psychophysical experiments investigating the perception of an ultrasound haptic focal point moving along a circular path.
Mid-air haptic patterns can be created by rapidly moving ultrasonic focal points, e.g., along a circular path. In this work, we investigated how such motion is perceived.
Our first experiment finds that a sensation of motion is perceived at speeds up to 17 revolutions per second (17 Hz rendering frequency), similar to the so-called ‘flutter’ sensation associated with low frequency vibrations and movements.
Plot showing the mean threshold render frequencies with 95% confidence intervals. The x-axis shows circle diameter, from 4 to 7 centimetres. The y-axis shows focal point render frequency, from 0 to 18 revolutions per second. The plot shows a mean of approximately 17 revolutions per second for all circle sizes.
Our second experiment found a mostly linear relationship between movement speed and perceived intensity up to this speed.
Plot showing mean intensity estimates for both sized circles with 95% confidence intervals. The x-axis shows rendering frequency, from 5 to 19 revolutions per second. The y-axis shows normalised intensity estimates, from 0 to 1. Plot shows that magnitude estimates increase with frequency, and there are higher magnitude estimates for the larger circle.
Haptic circles are widely used in ultrasound haptic interfaces: e.g., for spherical virtual objects or to give feedback about mid-air gestures. Our results can inform the design of ultrasound haptic interfaces, so that designers can create or avoid the sensation of tactile motion. Motion may be desirable for dynamic feedback: e.g., using below the 17 revolutions per second threshold to create moving patterns to indicate changing values or to accompany animated visual icons. Conversely, designers may wish to emphasise the contiguous outline of a virtual shape by rendering significantly above 17 revolutions per second. Since perceived intensity scales with circle size and rendering frequency, our results can also be used to create perceptually similar haptic objects: i.e., balancing size and frequency to yield similar intensity.
Perception of Ultrasound Haptic Focal Point Motion E. Freeman and G. Wilson. In Proceedings of 23rd ACM International Conference on Multimodal Interaction – ICMI ’21, 697-701. 2021.
@inproceedings{ICMI2021Motion,
author = {Freeman, Euan and Wilson, Graham},
booktitle = {{Proceedings of 23rd ACM International Conference on Multimodal Interaction - ICMI '21}},
title = {{Perception of Ultrasound Haptic Focal Point Motion}},
year = {2021},
publisher = {ACM},
pages = {697--701},
doi = {10.1145/3462244.3479950},
url = {http://euanfreeman.co.uk/perception-of-ultrasound-haptic-focal-point-motion/},
pdf = {http://research.euanfreeman.co.uk/papers/ICMI_2021_Motion.pdf},
data = {https://zenodo.org/record/5142587},
}
Acknowledgements
This research has received funding from the 🇪🇺 European Union’s Horizon 2020 research and innovation programme under grant agreement #737087. This work was completed as part of the Levitate project.
