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1. Haptic and Audio Interaction Design

   https://doi.org/10.1007/978-3-031-15019-7_5  

   Jones, Lynette A. ; Ho, Hsin-Ni ( August 2022 , Haptic and Audio Interaction Design)

   Saitis, C. ; Farkhatdinov, I ; Papetti, S. (Ed.)

   There are fundamental differences between the tactile and thermal sensory systems that must be accommodated when designing multisensory cutaneous displays for use in virtual or teleoperated robotic environments. In this review we highlight the marked temporal and spatial differences between the senses of cold and warmth as revealed in psychophysical experiments. Cold and warmth are distinct senses with marked differences in the time taken to respond to stimulation and in their temporal filtering processes. Such variations must be taken into account when time-varying profiles of thermal stimulation are delivered to the skin concurrent with tactile stimulation since the resulting sensations will not be perceived on the same time scale. Although it is often reported that the thermal senses are markedly inferior to the sense of touch with respect to their spatial acuity, it is also clear that there is considerable variability across the body in the accuracy with which thermal stimuli can be localized. The distal to proximal gradient in thermal acuity suggests that locations other than the palmar surface of the hand are better suited for displaying thermal cues, in contrast to the situation for tactile inputs. As was noted for temporal processes, there are differences between localizing warmth and cold stimuli, with localization being superior for cold. These properties provide benchmarks that can be used in designing thermal and multisensory displays. 

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2. Determination of the thermal-tactile simultaneity window for multisensory cutaneous displays

   T. Jodai ; M. Terao ; Jones, L.A. ; Ho, H-N. ( January 2023 , IEEE World Haptics Conference)

   Multisensory cutaneous displays have been developed to enhance the realism of objects touched in virtual environments. However, when stimuli are presented concurrently, tactile stimuli can mask thermal perception and so both these modalities may not be available to convey information to the user. In this study, we aim to determine the simultaneity window using the Simultaneity Judgment Task. A device was created that could present both tactile and thermal stimuli to the thenar eminence of the participant’s left hand with various stimulus onset asynchronies (SOA). The experimental results indicated that the simultaneity window width was 639 ms ranging from -561 ms to 78 ms. The point of subjective simultaneity (PSS) was at -242 ms, indicating that participants perceived simultaneity best when the thermal stimulus preceded the tactile stimulus by 242 ms. These findings have implications for the design of stimulus presentation in multisensory cutaneous displays. 

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3. Unsupervised Learning and Adaptive Classification of Neuromorphic Tactile Encoding of Textures

   https://doi.org/10.1109/BIOCAS.2018.8584702  

   Iskarous, Mark M. ; Nguyen, Harrison H. ; Osborn, Luke E. ; Betthauser, Joseph L. ; Thakor, Nitish V. ( October 2018 , Proceedings of IEEE Biomedical Circuits and Systems)

   null (Ed.)

   In this work, we investigated the classification of texture by neuromorphic tactile encoding and an unsupervised learning method. Additionally, we developed an adaptive classification algorithm to detect and characterize the presence of new texture data. The neuromorphic tactile encoding of textures from a multilayer tactile sensor was based on the physical structure and afferent spike signaling of human glabrous skin mechanoreceptors. We explored different neuromorphic spike pattern metrics and dimensionality reduction techniques in order to maximize classification accuracy while improving computational efficiency. Using a dataset composed of 3 textures, we showed that unsupervised learning of the neuromorphic tactile encoding data had high classification accuracy (mean=86.46%, sd=5 .44%). Moreover, the adaptive classification algorithm was successful at determining that there were 3 underlying textures in the training dataset. In this work, tactile information is transformed into neuromorphic spiking activity that can be used as a stimulation pattern to elicit texture sensation for prosthesis users. Furthermore, we provide the basis for identifying new textures adaptively which can be used to actively modify stimulation patterns to improve texture discrimination for the user. 

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4. A wireless haptic interface for programmable patterns of touch across large areas of the skin

   https://doi.org/10.1038/s41928-022-00765-3  

   Jung, Yei Hwan ; Yoo, Jae-Young ; Vázquez-Guardado, Abraham ; Kim, Jae-Hwan ; Kim, Jin-Tae ; Luan, Haiwen ; Park, Minsu ; Lim, Jaeman ; Shin, Hee-Sup ; Su, Chun-Ju ; et al ( June 2022 , Nature Electronics)

   Haptic interfaces can be used to add sensations of touch to virtual and augmented reality experiences. Soft, flexible devices that deliver spatiotemporal patterns of touch across the body, potentially with full-body coverage, are of particular interest for a range of applications in medicine, sports and gaming. Here we report a wireless haptic interface of this type, with the ability to display vibro-tactile patterns across large areas of the skin in single units or through a wirelessly coordinated collection of them. The lightweight and flexible designs of these systems incorporate arrays of vibro-haptic actuators at a density of 0.73 actuators per square centimetre, which exceeds the two-point discrimination threshold for mechanical sensation on the skin across nearly all the regions of the body except the hands and face. A range of vibrant sensations and information content can be passed to mechanoreceptors in the skin via time-dependent patterns and amplitudes of actuation controlled through the pressure-sensitive touchscreens of smart devices, in real-time with negligible latency. We show that this technology can be used to convey navigation instructions, to translate musical tracks into tactile patterns and to support sensory replacement feedback for the control of robotic prosthetics. 

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5. Mechanotransduction events at the physiological site of touch detection

   https://doi.org/10.7554/eLife.84179  

   Ziolkowski, Luke H ; Gracheva, Elena O ; Bagriantsev, Sviatoslav N ( January 2023 , eLife)

   Afferents of peripheral mechanoreceptors innervate the skin of vertebrates, where they detect physical touch via mechanically gated ion channels (mechanotransducers). While the afferent terminal is generally understood to be the primary site of mechanotransduction, the functional properties of mechanically activated (MA) ionic current generated by mechanotransducers at this location remain obscure. Until now, direct evidence of MA current and mechanically induced action potentials in the mechanoreceptor terminal has not been obtained. Here, we report patch-clamp recordings from the afferent terminal innervating Grandry (Meissner) corpuscles in the bill skin of a tactile specialist duck. We show that mechanical stimulation evokes MA current in the afferent with fast kinetics of activation and inactivation during the dynamic phases of the mechanical stimulus. These responses trigger rapidly adapting firing in the afferent detected at the terminal and in the afferent fiber outside of the corpuscle. Our findings elucidate the initial electrogenic events of touch detection in the mechanoreceptor nerve terminal. 

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