Mechanical and psychophysical studies of surface wave propagation during vibrotactile stimulation

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 50-51).Vibrotactile displays are based on mechanical stimulation delivered using an array of motors to communicate with the user. The way in which the display's motors are spaced and positioned on the body can have a significant impact on the effectiveness of communication, especially for tactile displays used to convey spatial information. The objective of the present research was to determine how the surface waves induced by vibrotactile stimulation of the skin varied as a function of the site on the body where the motors were mounted, and how these waves influenced the ability to localize vibrotactile stimulation. Three locations on the body were selected for study: the palm, the forearm, and the thigh. A flexible printed circuit board containing 3-axis micro-accelerometers was fabricated to measure the amplitude and frequency of surface waves produced by a vibrating motor at each body site. Results of these experiments showed significant differences in the frequency and amplitude of vibration on the glabrous skin on the palm as compared to the hairy skin on the arm and thigh. The palm had the highest frequency and lowest amplitude surface waves, and the forearm and thigh were very similar with lower frequency higher amplitude surface waves. No anisotropies were found from surface wave measurements. Most wave attenuation occurred within the first 8 mm from the motor, but there were still detectable amplitudes at a distance of 24 mm from the motor, which suggests that motor spacing should be at least 24 mm for this type of motor when used for precise spatial localization. A series of psychophysical experiments was conducted using a three-by-three array of motors in which the ability of subjects to localize the point of stimulation in an array was determined at each of the three body locations. The results from these experiments indicated that the palm had the highest localization accuracy (81% correct) as compared to the forearm and thigh which had similar localization accuracies (49% correct on forearm, 45% correct on thigh). Accuracy on the palm and forearm improved when the motor spacing increased from 8 mm to 16 mm, but increased spacing did not improve accuracy on the thigh. The results also showed that subjects were more able to identify the column of activation as opposed to the row of activation, which suggests a higher spatial acuity along the mediallateral as opposed to proximal-distal axis. The localization experiments indicate that glabrous skin is better suited for precise spatial localization than hairy skin, and that precise spatial localization requires an inter-motor spacing of more than 16 mm at these sites.by Katherine O. Sofia.S.M

A tactile communication system for navigation

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (leaves 42-43).A vibrotactile display for use in navigation has been designed and evaluated. The arm and the torso, which offer relatively large and flat surface areas, were chosen as locations for the displays. The ability of subjects to identify patterns of vibrotactile stimulation on the arm and torso was tested in a series of experiments using the vibrotactile displays. A variety of patterns of stimulation was evaluated to determine which was most effective, and the efficacy of two types of motors (pancake and cylindrical) was compared. The arm display was tested with sedentary subjects in the laboratory, and the torso display was tested both in the laboratory with sedentary subjects and outdoors with active subjects. The results indicated that identification of the vibrotactile patterns was superior on the torso as compared to the forearm, with subjects achieving 99-100% accuracy with seven of the eight patterns presented. The torso display was equally effective for both sedentary and active subjects.by Erin M. Piateski.S.M

Doctor of Philosophy

dissertationCarpal tunnel syndrome (CTS) is the number one cause of disability at work in the United States. Loss of time at work and worker's compensation expenditure caused by CTS is more than that caused by any other condition. However, workplace surveillance is likely to help in detecting CTS at a stage that is treatable at a significantly lower cost. Vibrotactile threshold (VT) testing can be used for this purpose. The VT is the smallest displacement applied (as a sinusoid) to a finger innervated by the median nerve that can be detected by the patient. Vibrotactile threshold evaluation can be a versatile tool for applications involving haptics interfaces, for evaluating peripheral neuropathies, and for studying the effects of chemotherapy induced neuropathies. This dissertation presents the prototype design of a vibrotactile threshold evaluator for the workplace (VTEW), which is portable, and configurable in terms of the probe diameter (1-6 mm), surround diameter (8-10 mm), applied frequency (1-250 Hz), angle of probe (0-1200), and displacement of probe (1-1500 ?m) and is operated with a customizable LabView interface. The VTEW also incorporates a special mount for the probe stimulus to test the subjects in at least two distinctive postures of the hand. Subjects were tested using an existing validated device, Vibrotactile Threshold Tester (VTT) and VTEW. Subjects were tested at 50 Hz with VTT and VTEW for validation. The effect of flexion on VT was observed by testing the subjects on VTEW at 50 Hz with their dominant hand in neutral posture and again with their dominant hand in provocative flexion. Use of low frequency for testing in VT studies is uncommon due to hardware constraints. However, low frequency studies could be potentially useful for investigating the effects of chemotherapy on the perception of pain. Thus, subjects were also tested at 4 Hz using VTEW to obtain preliminary data. Finally, an age regression model was developed to correct for the changes occurring in VT with age

Measuring relative vibrotactile spatial acuity: effects of tactor type, anchor points and tactile anisotropy

Publisher's version (útgefin grein)Vibrotactile displays can compensate for the loss of sensory function of people with permanent or temporary deficiencies in vision, hearing, or balance, and can augment the immersive experience in virtual environments for entertainment, or professional training. This wide range of potential applications highlights the need for research on the basic psychophysics of mechanisms underlying human vibrotactile perception. One key consideration when designing tactile displays is determining the minimal possible spacing between tactile motors (tactors), by empirically assessing the maximal throughput of the skin, or, in other words, vibrotactile spatial acuity. Notably, such estimates may vary by tactor type. We assessed vibrotactile spatial acuity in the lower thoracic region for three different tactor types, each mounted in a 4 × 4 array with center-to-center inter-tactor distances of 25 mm, 20 mm, and 10 mm. Seventeen participants performed a relative three-alternative forced-choice point localization task with successive tactor activation for both vertical and horizontal stimulus presentation. The results demonstrate that specific tactor characteristics (frequency, acceleration, contact area) significantly affect spatial acuity measurements, highlighting that the results of spatial acuity measurements may only apply to the specific tactors tested. Furthermore, our results reveal an anisotropy in vibrotactile perception, with higher spatial acuity for horizontal than for vertical stimulus presentation. The findings allow better understanding of vibrotactile spatial acuity and can be used for formulating guidelines for the design of tactile displays, such as regarding inter-tactor spacing, choice of tactor type, and direction of stimulus presentation.The research leading to these results has received funding from the European Union’s Horizon 2020 Research and Innovation Program under Grant agreement No 643636 “Sound of Vision”.Peer Reviewe

HapticHead - Augmenting Reality via Tactile Cues

Information overload is increasingly becoming a challenge in today's world. Humans have only a limited amount of attention to allocate between sensory channels and tend to miss or misjudge critical sensory information when multiple activities are going on at the same time. For example, people may miss the sound of an approaching car when walking across the street while looking at their smartphones. Some sensory channels may also be impaired due to congenital or acquired conditions. Among sensory channels, touch is often experienced as obtrusive, especially when it occurs unexpectedly. Since tactile actuators can simulate touch, targeted tactile stimuli can provide users of virtual reality and augmented reality environments with important information for navigation, guidance, alerts, and notifications. In this dissertation, a tactile user interface around the head is presented to relieve or replace a potentially impaired visual channel, called \emph{HapticHead}. It is a high-resolution, omnidirectional, vibrotactile display that presents general, 3D directional, and distance information through dynamic tactile patterns. The head is well suited for tactile feedback because it is sensitive to mechanical stimuli and provides a large spherical surface area that enables the display of precise 3D information and allows the user to intuitively rotate the head in the direction of a stimulus based on natural mapping. Basic research on tactile perception on the head and studies on various use cases of head-based tactile feedback are presented in this thesis. Several investigations and user studies have been conducted on (a) the funneling illusion and localization accuracy of tactile stimuli around the head, (b) the ability of people to discriminate between different tactile patterns on the head, (c) approaches to designing tactile patterns for complex arrays of actuators, (d) increasing the immersion and presence level of virtual reality applications, and (e) assisting people with visual impairments in guidance and micro-navigation. In summary, tactile feedback around the head was found to be highly valuable as an additional information channel in various application scenarios. Most notable is the navigation of visually impaired individuals through a micro-navigation obstacle course, which is an order of magnitude more accurate than the previous state-of-the-art, which used a tactile belt as a feedback modality. The HapticHead tactile user interface's ability to safely navigate people with visual impairments around obstacles and on stairs with a mean deviation from the optimal path of less than 6~cm may ultimately improve the quality of life for many people with visual impairments.Die Informationsüberlastung wird in der heutigen Welt zunehmend zu einer Herausforderung. Der Mensch hat nur eine begrenzte Menge an Aufmerksamkeit, die er zwischen den Sinneskanälen aufteilen kann, und neigt dazu, kritische Sinnesinformationen zu verpassen oder falsch einzuschätzen, wenn mehrere Aktivitäten gleichzeitig ablaufen. Zum Beispiel können Menschen das Geräusch eines herannahenden Autos überhören, wenn sie über die Straße gehen und dabei auf ihr Smartphone schauen. Einige Sinneskanäle können auch aufgrund von angeborenen oder erworbenen Erkrankungen beeinträchtigt sein. Unter den Sinneskanälen wird Berührung oft als aufdringlich empfunden, besonders wenn sie unerwartet auftritt. Da taktile Aktoren Berührungen simulieren können, können gezielte taktile Reize den Benutzern von Virtual- und Augmented Reality Anwendungen wichtige Informationen für die Navigation, Führung, Warnungen und Benachrichtigungen liefern. In dieser Dissertation wird eine taktile Benutzeroberfläche um den Kopf herum präsentiert, um einen möglicherweise beeinträchtigten visuellen Kanal zu entlasten oder zu ersetzen, genannt \emph{HapticHead}. Es handelt sich um ein hochauflösendes, omnidirektionales, vibrotaktiles Display, das allgemeine, 3D-Richtungs- und Entfernungsinformationen durch dynamische taktile Muster darstellt. Der Kopf eignet sich gut für taktiles Feedback, da er empfindlich auf mechanische Reize reagiert und eine große sphärische Oberfläche bietet, die die Darstellung präziser 3D-Informationen ermöglicht und es dem Benutzer erlaubt, den Kopf aufgrund der natürlichen Zuordnung intuitiv in die Richtung eines Reizes zu drehen. Grundlagenforschung zur taktilen Wahrnehmung am Kopf und Studien zu verschiedenen Anwendungsfällen von kopfbasiertem taktilem Feedback werden in dieser Arbeit vorgestellt. Mehrere Untersuchungen und Nutzerstudien wurden durchgeführt zu (a) der Funneling Illusion und der Lokalisierungsgenauigkeit von taktilen Reizen am Kopf, (b) der Fähigkeit von Menschen, zwischen verschiedenen taktilen Mustern am Kopf zu unterscheiden, (c) Ansätzen zur Gestaltung taktiler Muster für komplexe Arrays von Aktoren, (d) der Erhöhung des Immersions- und Präsenzgrades von Virtual-Reality-Anwendungen und (e) der Unterstützung von Menschen mit Sehbehinderungen bei der Führung und Mikronavigation. Zusammenfassend wurde festgestellt, dass taktiles Feedback um den Kopf herum als zusätzlicher Informationskanal in verschiedenen Anwendungsszenarien sehr wertvoll ist. Am interessantesten ist die Navigation von sehbehinderten Personen durch einen Mikronavigations-Hindernisparcours, welche um eine Größenordnung präziser ist als der bisherige Stand der Technik, der einen taktilen Gürtel als Feedback-Modalität verwendete. Die Fähigkeit der taktilen Benutzerschnittstelle HapticHead, Menschen mit Sehbehinderungen mit einer mittleren Abweichung vom optimalen Pfad von weniger als 6~cm sicher um Hindernisse und auf Treppen zu navigieren, kann letztendlich die Lebensqualität vieler Menschen mit Sehbehinderungen verbessern

Somatic ABC's: A Theoretical Framework for Designing, Developing and Evaluating the Building Blocks of Touch-Based Information Delivery

abstract: Situations of sensory overload are steadily becoming more frequent as the ubiquity of technology approaches reality--particularly with the advent of socio-communicative smartphone applications, and pervasive, high speed wireless networks. Although the ease of accessing information has improved our communication effectiveness and efficiency, our visual and auditory modalities--those modalities that today's computerized devices and displays largely engage--have become overloaded, creating possibilities for distractions, delays and high cognitive load; which in turn can lead to a loss of situational awareness, increasing chances for life threatening situations such as texting while driving. Surprisingly, alternative modalities for information delivery have seen little exploration. Touch, in particular, is a promising candidate given that it is our largest sensory organ with impressive spatial and temporal acuity. Although some approaches have been proposed for touch-based information delivery, they are not without limitations including high learning curves, limited applicability and/or limited expression. This is largely due to the lack of a versatile, comprehensive design theory--specifically, a theory that addresses the design of touch-based building blocks for expandable, efficient, rich and robust touch languages that are easy to learn and use. Moreover, beyond design, there is a lack of implementation and evaluation theories for such languages. To overcome these limitations, a unified, theoretical framework, inspired by natural, spoken language, is proposed called Somatic ABC's for Articulating (designing), Building (developing) and Confirming (evaluating) touch-based languages. To evaluate the usefulness of Somatic ABC's, its design, implementation and evaluation theories were applied to create communication languages for two very unique application areas: audio described movies and motor learning. These applications were chosen as they presented opportunities for complementing communication by offloading information, typically conveyed visually and/or aurally, to the skin. For both studies, it was found that Somatic ABC's aided the design, development and evaluation of rich somatic languages with distinct and natural communication units.Dissertation/ThesisPh.D. Computer Science 201

The Tactile Motion Aftereffect

The tactile motion aftereffect (tMAE) is a perceptual phenomenon in which illusory motion is reported following adaptation to a unidirectionally moving tactile stimulus. Unlike its visual counterpart, relatively little is known about the tMAE. For that reason, the purpose of this dissertation was to gain a better understanding of the tMAE using both psychophysical and neuroimaging techniques. In a series of five experiments the skin was adapted using a plastic cylinder with a square-wave patterned surface. Chapter 2 consists of two experiments, both of which adapted the glabrous surface of the right hand. Experiment 1 showed that the prevalence, duration, and vividness of the tMAE did not differ between the fingers (thumb excluded), palm and fingers (thumb included), and palm and fingers (thumb excluded). Thus, the divergent prevalence rates of two previous studies (Hollins & Favorov, 1994; Lerner & Craig, 1994) cannot be explained by the inclusion of the thumb in the latter study. Experiment 2 showed that as adapting speed increased from 15 to 75 rpm so did the prevalence, duration, and vividness of the tMAE. Previously it has been shown that the tMAE duration increases with adapting duration (Hollins & Favorov, 1994). Given that speed * duration = distance, increasing either adapting speed or duration also increases distance. As such, it was unclear which parameter(s) caused the observed increase in prevalence, duration, and vividness. Chapter 3 manipulated adapting duration (1, 2, and 4 min) and speed (30 and 60 rpm) in the same experiment, thereby allowing the effect of distance to be assessed in the interaction. The results showed that the prevalence, duration, and vividness of the tMAE increased with adapting speed. There was also a positive relationship between adapting duration and prevalence, but not duration or vividness, of the illusion. Distance was only a factor when it came to the tMAE duration. To gain insight into the peripheral neural basis of the tMAE, Chapter 4 measured the prevalence, duration, and vividness of the tMAE on skin areas that differ in their composition of fast adapting (FA) mechanoreceptive units, namely the right cheek, volar surface of the forearm, and glabrous surface of the hand. While there was no difference in duration or vividness between the skin surfaces tested, the tMAE was reported twice as often on the hand than the cheek and forearm, which did not differ significantly from one another. This finding suggests that the tMAE can be induced by adapting FA type I (FA I) units in the glabrous skin (hand) and the hair follicle units (cheek and forearm) and/or the FA I (cheek) and field (forearm) units in the hairy skin. Chapter 5 investigated the central neural basis of the tMAE using functional magnetic resonance imaging (fMRI). Of the areas shown to be responsive to tactile motion on the glabrous surface of the right hand, namely the contralateral (left) thalamus, postcentral gyrus (PCG), and parietal operculum, only the PCG showed evidence of the tMAE; that is, there was a sustained fMRI response following the offset of the illusion trials (cylinder rotating at 60 rpm), but not the control trials (cylinder rotating at 15 rpm), presumably reflecting illusory motion perception. Taken together, the experiments described herein expand our knowledge of the tMAE. Using a cylinder adapting apparatus, it was shown that: prevalence is the best measure of tMAE strength; the tMAE is not as robust as its visual counterpart; adapting duration and speed positively affect the prevalence of the tMAE; the tMAE is twice as prevalent on the glabrous than the hairy skin; the FAI and hair follicle units likely underlie the tMAE; the tMAE is likely caused by adapting direction selective neurons in the contralateral PCG

Reaching Performance in Heathy Individuals and Stroke Survivors Improves after Practice with Vibrotactile State Feedback

Stroke causes deficits of cognition, motor, and/or somatosensory functions. These deficits degrade the capability to perform activities of daily living (ADLs). Many research investigations have focused on mitigating the motor deficits of stroke through motor rehabilitation. However, somatosensory deficits are common and may contribute importantly to impairments in the control of functional arm movement. This dissertation advances the goal of promoting functional motor recovery after stroke by investigating the use of a vibrotactile feedback (VTF) body-machine interface (BMI). The VTF BMI is intended to improve control of the contralesional arm of stroke survivors by delivering supplemental limb-state feedback to the ipsilesional arm, where somatosensory feedback remains intact. To develop and utilize a VTF BMI, we first investigated how vibrotactile stimuli delivered on the arm are perceived and discriminated. We determined that stimuli are better perceived sequentially than those delivered simultaneously. Such stimuli can propagate up to 8 cm from the delivery site, so future applications should consider adequate spacing between stimulation sites. We applied these findings to create a multi-channel VTF interface to guide the arm in the absence of vision. In healthy people, we found that short-term practice, less than 2.5 hrs, allows for small improvements in the accuracy of horizontal planar reaching. Long-term practice, about 10 hrs, engages motor learning such that the accuracy and efficiency of reaching is improved and cognitive loading of VTF-guided reaching is reduced. During practice, participants adopted a movement strategy whereby BMI feedback changed in just one channel at a time. From this observation, we sought to develop a practice paradigm that might improve stroke survivors’ learning of VTF-guided reaching without vision. We investigated the effects of practice methods (whole practice vs part practice) in stroke survivors’ capability to make VTF-guided arm movements. Stroke survivors were able to improve the accuracy of VTF-guided reaching with practice, however there was no inherent differences between practice methods. In conclusion, practice on VTF-guided 2D reaching can be used by healthy people and stroke survivors. Future studies should investigate long-term practice in stroke survivors and their capability to use VTF BMIs to improve performance of unconstrained actions, including ADLs

A review of the physiology and psychophysics of tactile sensory response. Project 2817, report one : a progress report to Members of Group project 2817

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