Investigating the Recognition of Local Shapes Using Mid-air Ultrasound Haptics

Abstract

Mid-air haptics technologies are able to convey haptic sensations without any direct contact between the user and the haptic interface. One representative example of this technology is ultrasound haptics, which uses ultrasonic phased arrays to deliver haptic sensations. Research on ultrasound haptics is only in its beginnings, and the literature still lacks principled perception studies in this domain. This paper presents a series of human subject experiments investigating important perceptual aspects related to the rendering of 2D shapes by an ultrasound haptic interface (the Ultrahaptics STRATOS platform). We carried out four user studies aiming at evaluating (i) the absolute detection threshold for a static focal point rendered via amplitude modulation, (ii) the absolute detection and identification thresholds for line patterns rendered via spatiotemporal modulation, (iii) the ability to discriminate different line orientations, and (iv) the ability to perceive virtual bumps and holes. These results shed light on the rendering capabilities and limitations of this novel technology for 2D shapes.

Discriminating Between Intensities and Velocities of Mid-Air Haptic Patterns

“…Using our estimated Weber fraction, one could decrease the reference MAH velocity by 10 levels and still remain in this range. Similarly, previous studies reported a perceptual threshold for MAH intensities around 30% of the maximum output pressure [10,20]. Using our estimated Weber fraction, one could decrease the reference intensity by 9 levels and still remain above this threshold.…”

Mid-Air Haptic Rendering of 2D Geometric Shapes With a Dynamic Tactile Pointer

“…It was also noted that a dial like sensation was more accurately recognised than a static shape. Howard et al [5], studied the ability of people to discriminate line orientation using mid-air haptics. 83% of participants did not express a preference of line orientation in their subjective reports, and this finding was reflected in the indifferent identification scores too.…”

“…Modulating the focus points, such that it matches the resonant frequency of the cutaneous mechanoreceptors found in humans (∼5 Hz to 400 Hz) [2], causes a localised tactile sensation to be perceived by the user. With the use of multipoint and spatiotemporal modulation techniques, it is possible to create more advanced tactile sensations such as lines, circles, and even 3D geometric shapes [3], [4], [5], [6], [7].…”

Can Stiffness Sensations Be Rendered in Virtual Reality Using Mid-air Ultrasound Haptic Technologies?

“…Frier et al [3] have investigated the trade-off between pattern repetition rate in STM and perceived intensity. A study on human's detection of focal points and basic shapes rendered via focused ultrasound stimuli can be found in [4].…”

“…Arrays of ultrasonic transducers can produce phase-shifted acoustic waves which constructively interfere at points in space called focal points and destructively interfere elsewhere, conveying haptic sensations by varying acoustic radiation pressure on the skin. Focused ultrasounds have been already employed in several applications of Virtual Reality (VR) [4,5,9,10]. However, despite the recent popularity of mid-air ultrasound technologies, to the best of our knowledge, no study has analyzed if and to what extent ultrasound haptic arrays can provide effective stiffness sensations.…”