It Sounds Cool: Exploring Sonification of Mid-Air Haptic Textures Exploration on Texture Judgments, Body Perception, and Motor Behaviour.

Ultrasonic mid-air haptic technology allows for the perceptual rendering of textured surfaces onto the user's hand. Unlike real textured surfaces, however, mid-air haptic feedback lacks implicit multisensory cues needed to reliably infer a texture's attributes (e.g., its roughness). In this paper, we combined mid-air haptic textures with congruent sound feedback to investigate how sonification could influence people's (1) explicit judgment of the texture attributes, (2) explicit sensations of their own hand, and (3) implicit motor behavior during haptic exploration. Our results showed that audio cues (presented solely or combined with haptics) influenced participants' judgment of the texture attributes (roughness, hardness, moisture and viscosity), produced some hand sensations (the feeling of having a hand smoother, softer, looser, more flexible, colder, wetter and more natural), and changed participants' speed (moving faster or slower) while exploring the texture. We then conducted a principal component analysis to better understand and visualize the found results and conclude with a short discussion on how audio-haptic associations can be used to create embodied experiences in emerging application scenarios in the metaverse.

"I See Where This is Going": A Psychophysical Study of Directional Mid-Air Haptics and Apparent Tactile Motion.

Mid-air haptic technology can render a plethora of tactile sensations including points, lines, shapes, and textures. To do so, one requires increasingly complex haptic displays. Meanwhile, tactile illusions have had widespread success in the development of contact and wearable haptic displays. In this article, we exploit the apparent tactile motion illusion to display mid-air haptic directional lines; a prerequisite for the rendering of shapes and icons. We present two pilot studies and a psychophysical study that contrasts a dynamic tactile pointer (DTP) to an apparent tactile pointer (ATP) in terms of direction recognition. To that end, we identify optimal duration and direction parameters for both DTP and ATP mid-air haptic lines and discuss the implications of our findings with respect to haptic feedback design, and device complexity.

UltraButton: A Minimalist Touchless Multimodal Haptic Button.

We present UltraButton a minimalist touchless button including haptic, audio and visual feedback costing only $200. While current mid-air haptic devices can be too bulky and expensive (around $2 k) to be integrated into simple mid-air interfaces such as point and select, we show how a clever arrangement of 83 ultrasound transducers and a new modulation algorithm can produce compelling mid-air haptic feedback and parametric audio at a minimal cost. To validate our prototype, we compared its haptic output to a commercially-available mid-air haptic device through force balance measurements and user perceived strength ratings and found no significant differences. With the addition of 20 RGB LEDs, a proximity sensor and other off-the-shelf electronics, we then propose a complete solution for a simple multimodal touchless button interface. We tested this interface in a second experiment that investigated user gestures and their dependence on system parameters such as the haptic and visual activation times and heights above the device. Finally, we discuss new interactions and applications scenarios for UltraButtons.

"I Can Feel It Coming in the Hairs Tonight": Characterising Mid-Air Haptics on the Hairy Parts of the Skin.

Ultrasound mid-air haptics has received much attention from both academic and industrial groups, however, such investigations have almost exclusively focused on the tactile stimulation of glabrous (hairless) skin of our hands. Meanwhile, the non-glabrous (hairy) part of the skin covers the largest area of our body, yet remains largely untouched and unexplored by this haptic technology. 1) We study acoustic streaming and the 2) acoustic radiation force associated with a mid-air haptic stimulus. 3) We characterise the perceived strength, temperature, and definition of the stimulus through a user study. 4) Finally, in a second user study we explore the possibility of conveying affective (pleasant) touch. These objective and subjective experiments provide the first deep understanding of how mid-air haptics can affect tactile perception through stimulating the hairy skin. To that end, we discuss how researchers and haptic designers can leverage mid-air haptic technology to vary the perceived touch intensity, temperature, and deliver affective touch.

Corrigendum: May I Smell Your Attention: Exploration of Smell and Sound for Visuospatial Attention in Virtual Reality.

[This corrects the article DOI: 10.3389/fpsyg.2021.671470.].

May I Smell Your Attention: Exploration of Smell and Sound for Visuospatial Attention in Virtual Reality.

When interacting with technology, attention is mainly driven by audiovisual and increasingly haptic stimulation. Olfactory stimuli are widely neglected, although the sense of smell influences many of our daily life choices, affects our behavior, and can catch and direct our attention. In this study, we investigated the effect of smell and sound on visuospatial attention in a virtual environment. We implemented the Bells Test, an established neuropsychological test to assess attentional and visuospatial disorders, in virtual reality (VR). We conducted an experiment with 24 participants comparing the performance of users under three experimental conditions (smell, sound, and smell and sound). The results show that multisensory stimuli play a key role in driving the attention of the participants and highlight asymmetries in directing spatial attention. We discuss the relevance of the results within and beyond human-computer interaction (HCI), particularly with regard to the opportunity of using VR for rehabilitation and assessment procedures for patients with spatial attention deficits.

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

An important challenge that affects ultrasonic mid-air haptics, in contrast to physical touch, is that we lose certain exploratory procedures such as contour following. This makes the task of perceiving geometric properties and shape identification more difficult. Meanwhile, the growing interest in mid-air haptics and their application to various new areas requires an improved understanding of how we perceive specific haptic stimuli, such as icons and control dials in mid-air. We address this challenge by investigating static and dynamic methods of displaying 2D geometric shapes in mid-air. We display a circle, a square, and a triangle, in either a static or dynamic condition, using ultrasonic mid-air haptics. In the static condition, the shapes are presented as a full outline in mid-air, while in the dynamic condition, a tactile pointer is moved around the perimeter of the shapes. We measure participants' accuracy and confidence of identifying shapes in two controlled experiments ( n1 = 34, n2 = 25). Results reveal that in the dynamic condition people recognise shapes significantly more accurately, and with higher confidence. We also find that representing polygons as a set of individually drawn haptic strokes, with a short pause at the corners, drastically enhances shape recognition accuracy. Our research supports the design of mid-air haptic user interfaces in application scenarios such as in-car interactions or assistive technology in education.

Creating an Illusion of Movement between the Hands Using Mid-Air Touch.

Apparent tactile motion has been shown to occur on many contiguous parts of the body, such as the fingers, forearms, and back. More recently, the illusion has also been elicited on non-contiguous parts of the body, such as between one hand and the other, either when the hands are interconnected or not interconnected by an object (e.g., when holding a tablet or not). Here, we explore the reproducibility of the intermanual tactile illusion of movement between two free hands by employing mid-air tactile stimulation. We investigate the optimal parameters to generate a continuous and smooth motion using two arrays of ultrasound speakers and two stimulation techniques (i.e., static versus dynamic focal point). In the first experiment, we investigate the occurrence of the illusion when using a static focal point, and we define a perceptive model. In the second experiment, we examine the illusion using a dynamic focal point, defining a second perceptive model. Finally, we discuss the differences between the two techniques.

Cerebellar and Motor Cortical Transcranial Stimulation Decrease Levodopa-Induced Dyskinesias in Parkinson's Disease.

Transcranial direct current stimulation (tDCS) is a non-invasive technique for inducing prolonged functional changes in the human cerebral cortex. This simple and safe neurostimulation technique for modulating motor functions in Parkinson's disease could extend treatment option for patients with movement disorders. We assessed whether tDCS applied daily over the cerebellum (cerebellar tDCS) and motor cortex (M1-tDCS) improves motor and cognitive symptoms and levodopa-induced dyskinesias in patients with Parkinson's disease (PD). Nine patients (aged 60-85 years; four women; Hoehn & Yahr scale score 2-3) diagnosed as having idiopathic PD were recruited. To evaluate how tDCS (cerebellar tDCS or M1-tDCS) affects motor and cognitive function in PD, we delivered bilateral anodal (2 mA, 20 min, five consecutive days) and sham tDCS, in random order, in three separate experimental sessions held at least 1 month apart. In each session, as outcome variables, patients underwent the Unified Parkinson's Disease Rating Scale (UPDRS III and IV) and cognitive testing before treatment (baseline), when treatment ended on day 5 (T1), 1 week later (T2), and then 4 weeks later (T3), at the same time each day. After patients received anodal cerebellar tDCS and M1-tDCS for five days, the UPDRS IV (dyskinesias section) improved (p < 0.001). Conversely, sham tDCS, cerebellar tDCS, and M1-tDCS left the other variables studied unchanged (p > 0.05). Despite the small sample size, our preliminary results show that anodal tDCS applied for five consecutive days over the motor cortical areas and cerebellum improves parkinsonian patients' levodopa-induced dyskinesias.