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 two-dimensional curves by studying the perception of pairs of amplitude-modulated focused ultrasound stimuli. On the one hand, we aim to investigate perceptual effects that may arise from providing simultaneous UMH stimuli. On the other hand, we wish to provide perception-based rendering guidelines for generating continuous or discontinuous sensations of tactile shapes. Finally, we hope to contribute toward 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 to elicit a perceptual experience of two distinct stimuli separated by a gap. Mean gap detection thresholds were found at 32.3-mm spacing between focal points, but a high within- and between-subject variability was observed. Pairs spaced below 15 mm were consistently (>95%) perceived as a single stimulus, while pairs spaced 45 mm 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 15 and 18 mm), 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.

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Temporal binding refers to a systemic bias in the perceived time interval between two related events, most frequently voluntary motor actions and a subsequent sensory effect. An inevitable component of most instrumental motor actions is tactile feedback. Yet, the role of tactile feedback within this phenomenon remains largely unexplored. Here, we used local anesthesia of the index finger to temporarily inhibit incoming sensory input from the finger itself, while participants performed an interval-estimation task in which they estimated the delay between a voluntary motor action (button press) and a second sensory event (click sound). Results were compared to a control condition with intact sensation. While clear binding was present in both conditions, the effect was significantly enhanced when tactile feedback was temporarily removed via local anesthesia. The results are discussed in light of current debates surrounding the underlying mechanisms and function of this temporal bias.

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Voice is a rich modality for conveying emotions, however emotional prosody production can be situationally or medically impaired. Since thermal displays have been shown to evoke emotions, we explore how thermal stimulation can augment perception of neutrally-spoken voice messages with affect. We designed ThermalWear, a wearable on-chest thermal display, then tested in a controlled study (N=12) the effects of fabric, thermal intensity, and direction of change. Thereafter, we synthesized 12 neutrally-spoken voice messages, validated (N=7) them, then tested (N=12) if thermal stimuli can augment their perception with affect. We found warm and cool stimuli (a) can be perceived on the chest, and quickly without fabric (4.7-5s) (b) do not incur discomfort (c) generally increase arousal of voice messages and (d) increase / decrease message valence, respectively. We discuss how thermal displays can augment voice perception, which can enhance voice assistants and support individuals with emotional prosody impairments.

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This study concerns the perceived roughness of 3D printed material samples (print process: fused deposition modelling, or FDM), generated across changes in print speed, build angle, and layer height. Physical sample surface roughness parameters Ra and Rq were first obtained via optical scanning. Next, using a custom-designed apparatus, surface roughness perception was assessed via a psychophysical procedure that identified the just noticeable difference in roughness through the sense of touch alone. By comparing both data sets, this study concludes that for FDM-printed materials, objective surface roughness parameters (Ra, Rq) cannot adequately predict users’ haptic experience. This finding is of importance for all 3D printing applications where equally perceptible roughness is desired. As a whole, the study highlights the role of 3D printing as a new tool for the science of haptics and as a means for generating new material qualities by design.

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This design paper describes the development of custom built interface between a force-replicating virtual reality (VR) haptic interface glove, and a user. The ability to convey haptic information – both kinematic and tactile – is a critical barrier in creating comprehensive simulations. Haptic interface gloves can convey haptic information, but often the haptic “signal” is diluted by sensory “noise,” miscuing the user’s brain. Our goal is to convey compelling interactions – such as grasping, squeezing, and pressing – with virtual objects by improving one such haptic interface glove, the SenseGlove, through a redesign of the user-glove interface, soft glove. The redesign revolves around three critical design factors – comfort, realism, and performance – and three critical design areas – thimble/fingertip, palm, and haptic feedback. This paper introduces the redesign method and compares the two designs with a quantitative user study. The benefit of the improved soft glove can be shown by a significant improvement of the design factors, quantified through QUESI, NASA-TLX, and comfort questionnaires.

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It is known that the duration of a short stimulus affects the perceived intensity of both visual, auditory, and, vibrotactile events, but it is still unclear whether such a relationship also exists for mid-air ultrasonic inputs to the hand. Here we investigate this issue and show how the perceived intensity of focused ultrasonic stimulations of the palm is indeed systematically related to stimulus duration - a relationship that is, however, independent of modulation frequency. This is an important finding for the overall goal of providing perceptually stronger inputs and enlarging the repertoire of realistic mid-air haptic experiences. @en

This paper describes the development of custom built interface between a force-replicating Virtual Reality (VR) haptic glove, and a user. The ability to convey haptic information - both kinesthetic and tactile - is a critical barrier in creating comprehensive simulations. Haptic interface gloves can convey haptic information, but often the haptic signal is diluted by sensory noise, miscuing the users brain. Our goal is to convey compelling interactions with virtual objects, such as grasping, squeezing, and pressing by improving one such haptic interface glove - the Sense Glove - through a redesign of the user-glove interface - Soft Glove. The redesign revolves around three critical design factors - comfort, realism, and performance - and three critical design areas - thimble/fingertip, palm, and haptic feedback. This paper introduces the redesign method and compares the two designs with a quantitative user study. The benefit of the Improved Soft Glove can be shown by a significant improvement of the design factors.

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Recent studies, [1, 2], suggest that the mechanics of fingertip-object interactions can provide insight into the functional link between the hand, the brain, and our haptic perception of the world. When two convex objects, a finger′푓′and a surface′푠′, come into Hertzian contact, the respective elastic moduli퐸&, and 퐸', the radii of curvature, 푅&and 푅', the pressing force,푓, the deflection, 푑, and the size of the contact area, 푎, of these bodies are interrelated. If we assume that the finger and the surface are incompressible, and that the finger is a homogeneous, isotropic sphere, (its behaviour does not deviate much from that theory [3]), then it can be shown that 퐸'and 푅'play interchangeable roles in the relationship that link 푎to 푓. If 푎is an adequate representation of the mechanical state of the finger, then two behavioural hypotheses follow, namely:There exists perceptual metamers of compliance, i.e, physically distinct stimuli give rise to the same perception becauseRsandEsare confounds.An object's surface curvature and compliance are increasingly confused with increasedEs.Our findings suggest that, indeed, the interaction between a fingertip and a convex surface produces a perceptual outcome equivalent to decreasing 퐸', while the interaction between the fingertip and a concave surface creates a perceptual estimate of surface compliance equivalent to an increase in 퐸'. A low or high 퐸'both yield a metameric response, however, as predicted, for low 퐸', the effect diminishes significantly. These results, for the first time, provide evidence of a tactile perceptual metamer that can be predicted basic mechanics. The implications of this finding for perceiving and rendering object properties are discussed with respect to the functional link between the hand, brain and environment. @en