A Real-time Synthesizer of Naturalistic Congruent Audio-Haptic Textures

International audienceThis demo paper presents a multi-modal device able to generate real-time audio-haptic signal as response to the users' motion and produce naturalistic sensation. The device consists in a touch screen with haptic feedback based on ultrasonic friction modulation and a sound synthesizer. The device will help investigate audio-haptic interaction. In particular the system is built to allow for an exploration of di↵erent strategy of mapping audio and haptic signal to explore the limits of congruence. Such interactions could be the key to more informative and user-friendly touchscreens for Human-Machine-Interfaces

Perception of a tactile transient during the pressing phase, by rapid adhesion reduction

En appuyant sur un bouton, nous attendons un retour tactile, qui atteste que la volonté d'activation a été prise en compte. Ce retour est absent des écrans tactiles, ayant pour conséquence de sur-solliciter le canal visuel. Nous montrons que par l'action de la lévitation ultrasonore il est possible de redonner aux dalles de verre inertes, la tangibilité qui leur manque. Pour cela c'est le frottement qui est piloté, donnant lors de l'exploration latérale une gamme riche de modulations. La perception du clic se réalise sans mouvement latéral lorsque l'on réduit brutalement le frottement au cours de l'appui. L’adhésion à la surface permet au doigt de se charger en énergie, sous forme de contraintes de contact par la cohésion de la peau avec la surface. Les contraintes s'accumulent du centre du contact initial, vers l'extérieur de la peau du doigt, qui se déroule, au fur et à mesure de l'appui sur la surface. A l'activation ultrasonore, le contact avec la surface est libéré, permettant au doigt de rechercher une nouvelle position d'équilibre de la peau. Une relaxation s'opère, générant un mouvement dans le plan du contact, venant activer les différents mécanorécepteurs, interprété comme un bouton virtuel tangible. L'utilisation de l'impédance mécanique de l'interface de contact, a permis de montrer que l'énergie absorbée et réfléchie était un bon indicateur de la tenue du phénomène de décollement du doigt, relié à la perception d'un clic. La compréhension de la perception d’infimes mouvements de relaxation de la peau, viendra apporter une lecture nouvelle des phénomènes induits par modulation du frottement.By pressing a button, we wait for a tactile feedback, which certifies that the will to activate has been taken into account. This tactile feedback is absent from touch screens, resulting in over-stressing the visual channel.We show that by the action of ultrasonic levitation it is possible to give back to inert glass slabs the tangibility that they lack. For this it is the friction which is controlled, giving during the lateral exploration a rich range of modulations. The click is perceived without lateral movement when the friction is abruptly reduced during the pressure. Adhesion to the surface allows the finger to take on energy, in the form of contact stresses by the cohesion of the skin with the surface. The stresses accumulate from the center of the initial contact, towards the outside of the skin of the finger, which unwinds as the pressure is applied to the surface. Upon ultrasound activation, contact with the surface is released, allowing the finger to seek a new position of equilibrium in the skin. A relaxation takes place, generating a movement in the contact plane, activating the different mechanoreceptors, interpreted as a tangible virtual button.The use of the contact interfaccial mechanical impedance ,made it possible to show that the absorbed and reflected energy was a good indicator of the behavior of the phenomenon of detachment of the finger, linked to the perception of a click. Understanding the perception of minute skin relaxation movements will provide a new understanding of the phenomena induced by friction modulation

Rapid change of friction causes the illusion of touching a receding surface

Shortly after touching an object, humans can tactually gauge the frictional resistance of a surface. The knowledge of surface friction is paramount to tactile perception and the motor control of grasp. While potent correlations between friction and participants' perceptual response have been found, the causal link between the friction of the surface, its evolution and its perceptual experience has yet to be demonstrated. Here, we leverage new experimental apparatus able to modify friction in real time, to show that participants can perceive sudden changes in friction when they are pressing on a surface. Surprisingly, only a reduction of the friction coefficient leads to a robust perception. High-speed imaging data indicate that the sensation is caused by a release of a latent elastic strain over a 20 ms timeframe after the activation of the friction-reduction device. This rapid change of frictional properties during initial contact is interpreted as a normal displacement of the surface, which paves the way for haptic surfaces that can produce illusions of interacting with mechanical buttons. </p

Physical and behavioral comparison of haptic touchscreens

Touchscreens equipped with friction modulation can provide rich tactile feedback to their users. To date, there are no standard metrics to properly quantify the benefit brought byhaptic feedback on touchscreen usability. The definition of such metrics is not straightforward since friction modulation technologies can be achieved by either ultrasonic waves or with electroadhesion. In addition, the output depends strongly on the user, both because of the mechanical behavior of the fingertip and personal tactile somatosensorycapabilities. We investigate here a method to evaluate and compare the performance of haptic tablets on an objective scale. The method first defines some metrics using physicalmeasurements of friction and latency. The comparison is completed with metrics based on pointing tasks performed by users. We evaluated the comparison method with two hapticdevices, one based on ultrasonic friction modulation (Tpad) and the other based on electroadhesion (Tanvas)

Physical and behavioral comparison of haptic touchscreens quality

Touchscreens equipped with friction modulation can provide rich tactile feedback to their users. To date, there are no standard metrics to properly quantify the benefit brought by haptic feedback. The definition of such metrics is not straightforward since friction modulation technologies can be achieved by either ultrasonic waves or with electroadhesion. In addition, the output depends strongly on the user, both because of the mechanical behavior of the fingertip and personal tactile somatosensory capabilities. This paper proposes a method to evaluate and compare the performance of haptic tablets on an objective scale. The method first defines multiple metrics using physical measurements of friction and latency. The comparison is completed with metrics derived from information theory and based on pointing tasks performed by users. We evaluated the comparison method with two haptic devices, one based on ultrasonic friction modulation and the other based on electroadhesion. This work paves the way toward the definitions of standard specifications for haptic tablets, to establish benchmarks and guidelines for improving surface haptic devices

Eyes-Off Your Fingers: Gradual Surface Haptic Feedback Improves Eyes-Free Touchscreen Interaction

International audienceMoving a slider to set the music volume or control the air conditioning is a familiar task that requires little attention. However, adjusting a virtual slider on a featureless touchscreen is much more demanding and can be dangerous in situations such as driving. Here, we study how a gradual tactile feedback, provided by a haptic touchscreen, can replace visual cues. As users adjust a setting with their finger, they feel a continuously changing texture, which spatial frequency correlates to the value of the setting. We demonstrate that, after training with visual and auditory feedback, users are able to adjust a setting on a haptic touchscreen without looking at the screen, thereby reducing visual distraction. Every learning strategy yielded similar performance, suggesting an amodal integration. This study shows that surface haptics can provide intuitive and precise tuning possibilities for tangible interfaces on touchscreens

Perception of Ultrasonic Switches Involves Large Discontinuity of the Mechanical Impedance

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Detection of friction-modulated textures is limited by vibrotactile sensitivity

International audienceModulation of the frictional force of a fingertip sliding over a surface-haptic device can produce compelling sensations of texture and relief. The virtual sensation is particularly apparent and feel as fixed in space if the stimulus is rigorously correlated with the displacement of the finger. While frictional textures tactually resemble their real counterparts, some exploratory conditions under which the sharpness of the texture declines exist. We postulate that this decline in sharpness is caused by the perceptual limitation of the attempt to interpret the variation in friction as an out-of-plane sinusoidal topography. To investigate these questions, we measured the detection thresholds of sinusoidal friction-modulated gratings for a wide range of spatial periods explored at two different speeds. We compared the results with the detection thresholds, reported in the literature, of real gratings and vibrotactile stimuli. We found that the detection of spatial friction-modulated textures does not follow the same trend as that of real textures but is more similar to the vibrotactile rendering, which is strongly influenced by the exploratory speed. This study provides a better understanding of the perception of friction-modulated textures and provides insight into how to design impactful stimuli on surface-haptic devices

Optimal skin impedance promotes perception of ultrasonic switches

International audienceUltrasonic friction reduction is one potential technology for bringing tangibility to flat touchscreens. We previously established that this approach can be used to create an artificial sensation of pressing a mechanical switch by varying the coefficient of friction, which depends on the force applied by the user. This sensation proves effective majority of, but a non-negligible fraction reported feeling only weak sensations or none at all. In the present study, we examined the factors possibly involved in producing a vivid perception of a stimulus by measuring the mechanical impedance of the fingertip as an index to the frictional behavior, and performing psychophysical experiments. Subjects who experienced weaker sensations were found to have a weaker susceptibility to friction modulation, which may in turn be attributable to either a larger or a smaller than average/normal impedance; whereas those with a mechanical impedance of around 55 N.s/m clearly perceived the ultrasonic switch. Measuring and factoring the users impedance in real time could therefore provide a useful means of improving the rendering of ultrasonic surface haptic devices

國民中小學教師資訊科技素養自評系統實施計畫

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