Evaluating the Effect of Stimulus Duration on Vibrotactile Cue Localizability With a Tactile Sleeve

Haptiknit: Distributed stiffness knitting for wearable haptics

Haptic devices typically rely on rigid actuators and bulky power supply systems, limiting wearability. Soft materials improve comfort, but careful distribution of stiffness is required to ground actuation forces and enable load transfer to the skin. We present Haptiknit, an approach in which soft, wearable, knit textiles with embedded pneumatic actuators enable programmable haptic display. By integrating pneumatic actuators within high- and low-stiffness machine-knit layers, each actuator can transmit 40 newtons in force with a bandwidth of 14.5 hertz. We demonstrate the concept with an adjustable sleeve for the forearm coupled to an untethered pneumatic control system that conveys a diverse array of social touch signals. We assessed the sleeve's performance for discriminative and affective touch in a three-part user study and compared our results with those of prior electromagnetically actuated approaches. Haptiknit improves touch localization compared with vibrotactile stimulation and communicates social touch cues with fewer actuators than pneumatic textiles that do not invoke distributed stiffness. The Haptiknit sleeve resulted in similar recognition of social touch gestures compared to a voice-coil array but represented a more portable and comfortable form factor.

Investigating the Effects of Intensity and Frequency on Vibrotactile Spatial Acuity

Vibrotactile devices are commonly used in applications for sensory substitution or to provide feedback in virtual reality. An important aspect of vibrotactile perception is spatial acuity, which determines the resolutions of vibrotactile displays on the skin. However, the complex vibration characteristics of vibrotactile actuators make it challenging for researchers to reference and compare previous study results. This is because the effects of typical characteristics, such as intensity and frequency, are not well understood. In this study, we investigated the effects of intensity and frequency on vibrotactile spatial acuity. Using Linear Resonant Actuators (LRAs), we conducted relative point localization experiments to measure spatial acuity under different conditions. In the first experiment, we found that intensity had a significant effect on spatial acuity, with higher intensity leading to better acuity. In the second experiment, using a carefully designed intensity calibration procedure, we did not find a significant effect of frequency on spatial acuity. These findings provide a better understanding of vibrotactile spatial acuity, allow for comparisons to previous research, and provide insights into the design of future tactile devices.

Comparing the Perceived Intensity of Vibrotacitle Cues Scaled Based on Inherent Dynamic Range

Wearable devices increasingly incorporate vibrotactile feedback notifications to users, which are limited by the frequency-dependent response characteristics of the low-cost actuators that they employ. To increase the range and type of information that can be conveyed to users via vibration feedback, it is crucial to understand user perception of vibration cue intensity across the narrow range of frequencies that these actuators operate. In this paper, we quantify user perception of vibration cues conveyed via a linear resonant actuator embedded in a bracelet interface using two psychophysical experiments. We also experimentally determine the frequency response characteristics of the wearable device. We then compare user perceived intensity of vibration cues delivered by the bracelet when the cues undergo frequency-specific amplitude modulation based on user perception compared to modulation based on the experimental or manufacturer-reported characterization of the actuator dynamic response. For applications in which designers rely on user perception of cue amplitudes across frequencies to be equivalent, it is recommended that a perceptual calibration experiment be conducted to determine appropriate modulation factors. For applications in which only relative perceived amplitudes are important, basing amplitude modulation factors on manufacturer data or experimentally determined dynamic response characteristics of the wearable device should be sufficient.

Mechanofluidic Instability-Driven Wearable Textile Vibrotactor

Vibration is a widely used mode of haptic communication, as vibrotactile cues provide salient haptic notifications to users and are easily integrated into wearable or handheld devices. Fluidic textile-based devices offer an appealing platform for the incorporation of vibrotactile haptic feedback, as they can be integrated into clothing and other conforming and compliant wearables. Fluidically driven vibrotactile feedback has primarily relied on valves to regulate actuating frequencies in wearable devices. The mechanical bandwidth of such valves limits the range of frequencies that can be achieved, particularly in attempting to reach the higher frequencies realized with electromechanical vibration actuators ( 100 Hz). In this paper, we introduce a soft vibrotactile wearable device constructed entirely of textiles and capable of rendering vibration frequencies between 183 and 233 Hz with amplitudes ranging from 23 to 114 g. We describe our methods of design and fabrication and the mechanism of vibration, which is realized by controlling inlet pressure and harnessing a mechanofluidic instability. Our design allows for controllable vibrotactile feedback that is comparable in frequency and greater in amplitude relative to state-of-the-art electromechanical actuators while offering the compliance and conformity of fully soft wearable devices.

Anisotropic distortion in the perceived direction of motion on the arm

Skin covers the entire body, and its thickness and distribution of mechanoreceptors vary markedly across body parts. It has been shown that the brain is not able to fully compensate for such anisotropy, and as a result, the representational space of touch differs depending on which parts the stimulus is applied to. Here, by contrasting the hand and arm, we investigated the difference in perceived motion. Using a large-area braille display, we were able to present precisely controlled touchable motion stimuli with randomizing stimulus trajectories and varying the size. We found a new perceptual illusion in which the motion direction of stimuli perceived on the arm is rotated regionally, or even flipped. In particular, obliquely moving stimuli that move toward the distal radial are perceived as move toward the proximal radial, and stimuli that move toward the proximal ulnar are perceived as move toward the distal ulnar. This illusion was not observed on the palm, regardless of compensation for the stimulus size. Current study adds a clear example of how presenting the same motion stimuli to different body parts results in a different perception, emphasizing that the perceived tactile space is not uniform and needs to be examined in detail.