Yon Visell’s research while affiliated with University of California, Santa Barbara and other places

Tactile displays that lend tangible form to digital content could profoundly transform how we interact with computers, much like visual displays have driven successive revolutions in computing over the past 60 years. However, creating tactile displays with the actuation speeds, dynamic ranges, and resolutions that are required for perceptual fidelity has proved challenging. Here, we present a tactile display that directly converts projected light into visible tactile patterns using an energetically passive, photomechanical surface populated with arrays of millimeter-scale optotactile pixels. The pixels transduce incident light into mechanical displacements through rapid, light-stimulated thermal gas expansion, yielding displacements of up to 1 millimeter and response times of 2 to 100 milliseconds. Our use of projected light for power transmission and addressing enables these displays to be scaled in size and resolution at sustainable cost and complexity. We demonstrate devices with up to 1,511 independently addressable pixels. Perceptual studies confirm the capacity of the display to accurately reproduce tactile patterns in location, timing, frequency, and structure. This research establishes a foundation for practical, versatile high-resolution tactile displays driven by light.

Tactile feedback is essential for upper-limb prostheses functionality and embodiment, yet its practical implementation presents challenges. Users must adapt to non-physiological signals, increasing cognitive load. However, some prosthetic devices transmit tactile information through socket vibrations, even to untrained individuals. Our experiments validated this observation, demonstrating a user's surprising ability to identify contacted fingers with a purely passive, cosmetic hand. Further experiments with advanced soft articulated hands revealed decreased performance in tactile information relayed by socket vibrations as hand complexity increased. To understand the underlying mechanisms, we conducted numerical and mechanical vibration tests on four prostheses of varying complexity. Additionally, a machine-learning classifier identified the contacted finger based on measured socket signals. Quantitative results confirmed that rigid hands facilitated contact discrimination, achieving 83% accuracy in distinguishing index finger contacts from others. While human discrimination decreased with advanced hands, machine learning surpassed human performance. These findings suggest that rigid prostheses provide natural vibration transmission, potentially reducing the need for tactile feedback devices, which advanced hands may require. Nonetheless, the possibility of machine learning algorithms outperforming human discrimination indicates potential to enhance socket vibrations through active sensing and actuation, bridging the gap in vibration-transmitted tactile discrimination between rigid and advanced hands.

When the hand touches a surface, the ensuing contact elicits skin oscillations that travel throughout the hand, driving responses in numerous exquisitely sensitive Pacinian corpuscle neurons (PCs). Although the tuning properties of individual PCs are well-documented, they have been characterized using stimuli applied adjacent to the receptor location. Such experiments are insensitive to the modulating influence of biomechanical filtering, which can significantly alter skin oscillations as they travel through the hand's soft tissues. Here, we used an integrated approach combining vibrometry imaging and computer simulation to characterize the effects of biomechanical filtering on evoked spiking activity in whole-hand PC populations. We observed complex distance- and frequency-dependent patterns of biomechanical transmission arising from the interplay of tissue mechanics and hand morphology. This source of modulation altered the response properties and spike timing of PCs, diversifying evoked activity in whole-hand PC populations. Together, these effects enhanced information encoding efficiency. These findings suggest that the biomechanics of the hand furnishes a pre-neuronal mechanism that facilitates efficient tactile processing.

The importance of interpersonal touch for social well-being is widely recognized, and haptic technology offers a promising avenue for augmenting these interactions. We presented smart bracelets that use vibrotactile feedback to augment social interactions, such as handshakes, by transmitting vibrations between two people. This work conducts mechanical and perceptual experiments to investigate key factors affecting the delivery of interpersonal vibrotactile feedback via bracelets. Our results show that low-frequency vibrations elicited through tangential actuation are efficiently transmitted from the wrist to the hand, with amplitude varying based on distance, frequency, and actuation direction. We also found that vibrations transmitted to different locations on the hand can be felt by a second person, with perceptual intensity correlated with oscillation magnitude at the touched location. Additionally, we demonstrate how wrist-interfaced devices can elicit spatial vibration patterns throughout the hand surface, which can be manipulated by the frequency and direction of actuation at the wrist. Our experiments provide important insights into the human factors associated with interpersonal vibrotactile feedback and have significant implications for the design of technologies that promote social well-being.

Soft robotics is attractive for wearable applications that require conformal interactions with the human body. Soft wearable robotic garments hold promise for supplying dynamic compression or massage therapies to improve lymphatic and blood circulation. In this paper, we present a wearable robot capable of supplying dynamic compression and massage therapy via peristaltic motion of finger-sized, soft, fluidic actuators. We show that this peristaltic wearable robot can supply dynamic compression pressures exceeding 22 kPa at frequencies of 14 Hz or more, meeting requirements for compression and massage therapy. A large variety of software-programmable compression wave patterns can be generated by varying frequency, amplitude, phase delay, and duration parameters. We finally demonstrate the utility of this peristaltic wearable robot for compression therapy, showing fluid transport in a laboratory model of the upper limb. We theoretically and empirically identify driving regimes that optimize fluid transport. These findings show the potential of such a wearable robot for the treatment of several health disorders associated with lymphatic and blood circulation, such as lymphedema and blood clots.

Emerging surface haptic technologies can display localized haptic feedback anywhere on a touch surface by focusing mechanical waves generated via sparse arrays of actuators. However, rendering complex haptic scenes with such displays is challenging due to the infinite number of physical degrees of freedom intrinsic to such continuum mechanical systems. Here, we present computational focusing methods for rendering dynamic tactile sources. They can be applied to a variety of surface haptic devices and media, including those that exploit flexural waves in thin plates and solid waves in elastic media. We describe an efficient rendering technique based on time-reversal of waves emitted from a moving source, and motion path discretization. We combine these with intensity regularization methods that reduce focusing artifacts, improve power output, and increase dynamic range. We demonstrate the utility of this approach in experiments with a surface display that uses elastic wave focusing to render dynamic sources, achieving millimeter-scale resolution in experiments. Results of a behavioral experiment show that participants could readily feel and interpret rendered source motion, attaining 99% accuracy across a wide range of motion speeds.

Emerging holographic haptic interfaces focus ultrasound in air to enable their users to touch, feel, and manipulate three-dimensional virtual objects. However, current holographic haptic systems furnish tactile sensations that are diffuse and faint, with apparent spatial resolutions that are far coarser than would be theoretically predicted from acoustic focusing. Here, we show how the effective spatial resolution and dynamic range of holographic haptic displays are determined by ultrasound-driven elastic wave transport in soft tissues. Using time-resolved optical imaging and numerical simulations, we show that ultrasound-based holographic displays excite shear shock wave patterns in the skin. The spatial dimensions of these wave patterns can exceed nominal focal dimensions by more than an order of magnitude. Analyses of data from behavioral and vibrometry experiments indicate that shock formation diminishes perceptual acuity. For holographic haptic displays to attain their potential, techniques for circumventing shock wave artifacts, or for exploiting these phenomena, are needed.