Recent technology developments have made possible the creation of several commercial devices and a selected number of development platforms for the inclusion of haptics (the sense of touch) in virtual environments (VE). This thesis sought to investigate and develop a better understanding of whether or not haptics or sound substitutions improved manipulation performance or usability in VE applications. Twenty-four volunteers (12 males and 12 females) participated in a 2 (haptics) x 2 (sound) x 2 (gender) mixed factorial experiment in which they completed a VE manipulation task involving the assembly and disassembly of 5 interconnecting parts. Performance for the manipulation task was measured through completion time and the number of collisions made, as well as subjective measures of usability. Results indicated that completion times were slower and collision counts were higher for males with the addition of haptics (ptime = 0.03; pcollisions<0.05), while females exhibited a smaller increase in collision counts and no increase in completion time with the addition of haptics. Nonetheless, there were improved usability attributes when haptics were incorporated, more specifically, an increased sense of realism, perceived helpfulness and perceived utility in a design task (p<0.05 for all). Sound was found to be an effective substitute for haptics in most measures taken while the combination of sound and haptics versus either alone, did not demonstrate any signs of improving performance or any usability attributes. It is therefore recommended that sound substitution be used in VE manipulation tasks where the extra haptic information is desired, and minimizing completion time or collisions are the overall goal. Finally, for the utility of the feedback towards a design task, users ranked haptics as being more useful than sound, but ranked the combination of sound and haptics as being the best feedback condition (p<0.05). Further research is required to determine whether this belief is consistent with objective measures. / Master of Science

Horizontal curves on roadways are the site of numerous crashes and motorist deaths each year. Traditional methods to warn drivers of curve hazards, including static roadside signs, are sometimes ineffective at influencing driver behavior for reasons such as driver acclimation to inconsistency in posted advisory speeds. In-vehicle curve warning devices (CWDs) may be an effective alternative for reducing the number of collisions at curves. Multi-modality displays have elicited positive driver results and should be further explored. The objective of this study was to determine the most effective curve warning system using on-road performance and subjective evaluation. Two top-performing warning stimulus presentations, as determined by a recent simulator study, were tested at the Virginia Smart Road closed test highway. Both warnings exhibited auditory (speech) and visual (Heads Down Display) stimuli, however one included a throttle pushback haptic stimulus and the other did not. No on-road studies of this type of haptic stimulus, nor of CWDs, have been published to date. Forty-eight individuals, 24 age 18-25 years and 24 age >60 years, participated in the study. A 2 (Age) x 3 (Stimulus Presentation) between-subjects design was used to examine participant performance and ratings for the first "surprise" experience with the stimulus while driving on the Smart Road, and a 2x3 mixed factors design examined stimulus as a repeated measure. Participant braking reaction times, speed, and subjective evaluations were compared between stimulus presentations as well as driver age. Throttle reaction times and brake reaction times were significantly quicker, and curve entry speed significantly closer to an advisory speed for participants receiving a warning presentation than those without a warning presentation at alpha=0.05. No statistical differences between objective measures were found between the stimulus presentation with the haptic and the stimulus presentation without the haptic stimulus. Age was a significant main effect as older drivers reached more appropriate curve entry speeds than younger drivers. Driver risk-taking style was significantly related to age and to curve entry speed. During an interview, participants demonstrated higher comprehension when presented with the stimulus lacking the haptic component, and ranked this presentation higher, though ratings gathered from questionnaires were not significantly different between the two stimulus presentations. Driver comments were examined using a content analysis technique organized by design guideline topics. Discussion was presented in terms of four main research questions and recommendations toward CWD design guidelines were developed based on the objective and subjective results of this study. In addition, this research developed a foundation for further on-road testing of CWDs and other multi-modal in-vehicle warning systems. / Master of Science

Yes / Online retailers are increasingly using augmented reality (AR) and virtual reality (VR) technologies to solve mental and physical intangibility issues in a product evaluation. Moreover, the technologies are easily available and accessible to consumers via their smartphones. The authors conducted three experiments to examine consumer responses to technology interfaces (AR/VR and mobile apps) for hedonic and utilitarian products. The results show that AR is easier to use (vs. app), and users find AR more responsive when buying a hedonic (vs. utilitarian) product. Touch interface users are likely to have a more satisfying experience and greater recommendation intentions, as compared to AR, for buying utilitarian products. In contrast, a multisensory environment (AR) results in a better user experience for purchasing a hedonic product. Moreover, multisensory technologies lead to higher visual appeal, emotional appeal, and purchase intentions. The research contributes to the literature on computer-mediated interactions in a multisensory environment and proposes actionable recommendations to online marketers.

This thesis research is concerned with the exploration, design, and validation of novel haptic technologies and signals that feel natural and meaningful in a calm and pleasant way. Our ultimate goal is to expand the possibilities of human-machine interaction by developing a single tactile display and a set of signals through a systematic design approach. It is generally a challenge to evoke a broad range of emotions with vibrotactile stimulation, especially at low signal intensities. During the first part of this thesis research, three types of prototypes were developed and explored using novel haptic technologies. The first was a circular array braille display consisting of eight small six-pin braille modules. The forty-eight pins were arranged in a circular shape to deliver circular tactile information such as time and direction. The second was a braille stick consisting of sixteen six-pin braille modules arranged in a row. The entire display could be easily grasped in the hand so that tactile information can be easily accessible. The third was a 3-by-3 electroactive polymer actuator array driven at high voltages that gives a subtle “tapping” feel on the skin. However, each of the three prototypes suffered from a limited range of expression and was not pursued further.<br> After the initial prototyping efforts, a 2-by-2 vibrotactile display, the palmScape, was conceived and developed. Custom-designed stimulation patterns based on natural phenomena that feel calm and pleasant were designed and implemented with the palmScape. We use text labels to set the context for the vibrotactile icons that attempt to capture and expresses natural metaphors through variations in signal amplitude, frequency, duration, rhythm, modulation, spatial extent, as well as slow movements. Fourteen participants evaluated twenty vibrotactile icons by rating the perceived valence and arousal levels. The twenty stimuli included sixteen custom-designed vibrotactile icons from this thesis research and four reference patterns from two published studies. The results show that our custom-designed patterns were rated at higher valence levels than the corresponding reference signals at similar arousal ratings. Five of the sixteen vibrotactile icons from this research occupied the fourth quadrant of the valence-arousal space that corresponds to calm and pleasant signals. These findings support the validity of the palmScape display and our signal design approach for achieving a calm and pleasant experience and the possibility of reaching a broader range of expressiveness with vibrotactile signals.<br> Future studies will continue with the design of signals that can express a broader range of metaphors and emotions through the palmScape, and build an emotional evaluation database that can be combined with other modalities. Our work can be further expanded to support an immersive experience with naturalistic-feeling vibrotactile effects and broaden the expressiveness of human-computer interfaces in media consumption, gaming, and other communicative application domains.

Qu’ils soient voyageurs occasionnels ou réguliers, les piétons se déplaçant en environnement urbain et en transport en commun ont à faire face à la complexité du réseau de transport des grandes villes. Les aides au déplacement sont nombreuses et variées. Elles peuvent être fixes (par exemple, panneaux de signalisation) ou mobiles (par exemple, applications sur smartphone). Ces aides utilisent principalement la modalité sensorielle visuelle, déjà fortement sollicitée lors d’un déplacement urbain. Une alternative intéressante serait d’utiliser l’haptique (sens du toucher). En effet, cette modalité permet de transmettre au porteur d’un dispositif haptique des informations de déplacement et de navigation, en attirant discrètement son attention par des messages délivrés tactilement.S’inscrivant dans une démarche d’ergonomie prospective, cette thèse vise à étudier l’apport de la modalité haptique comme soutien à l’activité de déplacement piéton urbain. L’objectif appliqué est la conception d’un dispositif haptique d’aide au déplacement innovant, efficace et accepté par les utilisateurs futurs. Ce projet de conception s’est déroulé dans le cadre du projet ANR Tictact, mené par le CEA-LIST de 2011 à 2014. L’utilisation de la modalité haptique étant posée comme un parti pris initial, l’objectif du projet était de déterminer la forme que devrait prendre l’assistance aux usagers et la technologie de l’outil d’aide.Pour répondre à ce défi, nous avons mis en œuvre trois études successives. La première visait à comprendre les activités cognitives élémentaires mobilisées pour consulter les supports d’informations nécessaires à la navigation piétonne. Pour cela, nous avons analysé le comportement d’un piéton effectuant un trajet urbain (en métro et à pied). Les résultats nous ont permis de spécifier les fonctions d’aide que devrait remplir un futur dispositif d’aide au déplacement. Complétées par une revue de la littérature sur les interfaces haptiques et leur utilisation pour l’aide au déplacement, ces résultats nous ont conduits à déterminer les fonctions éligibles à la modalité haptique. La seconde étude visait à concevoir l’interaction haptique avec le dispositif d’aide, en deux étapes : élaborer le concept d’interface et concevoir le langage d’interaction. Une démarche de conception participative a été mise en œuvre, étayée par l’utilisation d’un prototype et de méthodes créatives. Cette démarche a abouti à : (i) identifier un message informationnel approprié à chaque fonction de déplacement ; (ii) traduire ce message (par analogie) en métaphore ; (iii) transformer chaque métaphore en motifs vibratoires délivrés par un bracelet haptique. La troisième étude visait à évaluer le dispositif haptique (bracelet couplé à un Smartphone) en environnement réel. Une analyse d’activité de déplacement urbain a été menée, comparant un groupe disposant de notre prototype haptique d’aide à un groupe sans prototype. Les résultats confirment la potentialité de la modalité haptique pour améliorer les performances de déplacement et notamment une allure de déplacement plus fluide et une diminution du temps de consultation d’un support d’information. Notre étude ouvre des perspectives pour l’utilisation de la modalité haptique dans diverses interfaces mobiles (par exemple une smartwatch). / Whether they are occasional or regular travellers, the pedestrians travelling in an urban environment and using public transportation have to face the complexity of the transportation network of large cities. The travelling aids are numerous and varied. They can be stationary or mobile (for example, applications on smartphones). These aids rely mainly on the visual sensory modality, already heavily requested during urban travel. An interesting alternative would be to use haptics (sense of touch). Indeed, this modality enables to convey travel and navigational information to the owner of a haptic device, by drawing discreetly his attention with tactile messages. Joining an approach of prospective ergonomics, this thesis aims to study the contribution of the haptic modality as a support for the activity of urban pedestrian travel. The applied objective is the design of a haptic device as an innovative travel aid, effective and accepted by the future users. This design project took place within the framework of the ANR project Tictact, led by the CEA-LIST from 2011 till 2014. The use of the haptic modality being put as an initial bias, the objective of the project was to determine the form that the assistance and the technology of the travel aid should take.To tackle this challenge, we conducted three successive studies. The first one, aimed at understanding the elementary cognitive activities mobilized when consulting information necessary to the pedestrian navigation. For that purpose, we analysed the behaviour of a pedestrian undertaking an urban travel (in the subway and on foot). The results allowed us to specify the functions that a future device assisting in the travel should include. Completed by a review of the literature on haptic interfaces and their use for assisting travel, these results led us to determine the eligible functions of the haptic modality.The second study aimed at designing the haptic interaction with the haptic interface, in two stages: first develop the concept of the interface and second design the interaction language. An approach of participative design was implemented, supported by the use of a device prototype and creative methods. This approach succeeded in: i) identifying an informative message suitable for each function of the travel; ii) translating this message (using an analogy) into a metaphor; and iii) transforming every metaphor into vibrotactile patterns delivered by a haptic wristband.The third study aimed at evaluating the haptic device (a wristband coupled with a Smartphone) in a real environment. An analysis of the activity of urban travel was conducted, comparing a group having a prototype of our haptic assistant to a group without such prototype. The results confirm the potentiality of the haptic modality to improve the travel performance in particular to enable a more fluid speed of travel and a decrease in the consultation time of an information medium. Our study opens up perspectives for the use of the haptic modality in diverse mobile interfaces (for example a smartwatch).

Le interfacce aptiche, ovvero le tecnologie che trasmettono delle sensazioni tattili digitalizzate, si stanno diffondendo in vari contesti sociali come telerobotica, comunicazione mobile, arte, videogiochi e cinema. Queste tecnologie stanno permettendo agli ingegneri di realizzare qualcosa mai fatto prima: la digitalizzazione del tatto (che ora può quindi essere registrato e mediatizzato). L’obbiettivo di questa tesi è di decostruire il tatto digitalizzato come un artefatto tecnologico socialmente costruito, il quale sta prendendo forma in un sistema di pratiche interrelate performate da attori in campi disparati della conoscenza. Questi attori si muovono all’interno e attorno ad una comunità di ingegneri apticisti. Adottando un approccio ispirato alla grounded theory, sono stati raccolti dati qualitativi attraverso interviste presso un campo etnografico multi-situato composto da laboratori europei e conferenze internazionali, in cui la conoscenza riguardo il tatto è collettivamente creata e condivisa. Due framework teorico-metodologici sono stati presi in considerazione: la tradizione dei Science and Technology Studies (STS) è stata scelta come principale guida metodologica; in seguito, l’intreccio tra pratiche sociali e tecnologie è stato approfondito attraverso una prospettiva practice-based tipica della cosiddetta ‘practice theory’. Al fine di cogliere il processo in corso di costruzione sociale e flessibilità che caratterizzano il tatto digitalizzato, lo studio si è concentrato sull'assenza di standardizzazione che caratterizza gli aspetti sia hardware che software di questa tecnologia emergente. Inoltre, è stata prestata attenzione alla distinzione controversa e scivolosa tra feedback tattile simbolico e realistico usata nel gergo degli apticisti. Infine, sono stati analizzati i diversi significati, o potenzialità d'uso, che gli intervistati attribuiscono a questa tecnologia. Questi significati si collegano a specifici immaginari sociotecnici geograficamente situati, ad ampi discorsi sociali riguardo l’innovazione tecnologica, e a diverse visioni riguardo le pratiche che possono beneficiare dell’implementazione di queste interfacce. / Devices that provide tactile feedback, called haptic interfaces, are spreading in various contexts such as tele-robotics, prosthetics, videogames, mobile communication, and arts. These technologies are allowing engineers to accomplish something never done before: the digitization of touch (which can now be stored and mediatized). This dissertation aims to deconstruct the digitized touch as a socially constructed technological product, emerging from a system of interrelated practices enacted by actors performing in disparate fields which revolve around the community of haptics engineers. Using a grounded-theory inspired approach, qualitative data were collected through interviews in a multi-sited ethnographic field consisting in European laboratories and international conferences, where knowledge about touch is collectively created and shared. Two theoretical-methodological frameworks have been taken into consideration: the tradition of Science and Technology Studies (STS) has been chosen as the main methodological guide; moreover, the interlacements between social practices and technology have been deepened through the adoption of a practice-based perspective proposed by different approaches in social sciences gathered under the umbrella term ‘practice theory’. In order to grasp the ongoing process of social construction and flexibility that characterize digitized touch, the study focused on the absence of standardization involving both hardware and software aspects of this emerging technology. Furthermore, attention has been paid to the controversial and slippery distinction between ‘symbolic’ and ‘realistic’ tactile feedback which is used in engineers’ jargon. Finally, the different meanings or potentialities of use, which respondents attributed to this technology, have been analysed. These meanings are connected to geographically located socio-technical imaginaries, to broad social discourses about technological innovation, and to different visions regarding the practices that can benefit from the implementation of these interfaces.

This thesis describes a series of experiments in human observers using neurophysiological and behavioural approaches to investigate the effects of varying haptic stimuli, attentional demand and age on motor control and perception during haptic sensing (i.e., using the hand to seek sensory information by touch). In Experiments I-IV, transcranial magnetic stimulation (TMS) was used to explore changes in corticomotor excitability when participants were actively engaged in haptic sensing tasks. These studies showed that corticospinal excitability, as reflected in motor evoked potential (MEP) amplitude, was greatly enhanced when participants were engaged in different forms of haptic sensing. Interestingly, this extra corticomotor facilitation was absent when participants performed finger movements without haptic sensing or when attention was diverted away from haptic input by a concurrent cognitive task (Exp I). This provided strong evidence that the observed corticomotor facilitation was likely central in origin and related to haptic attention. Neuroimaging has shown activation of the parieto-frontal network likely subserves this aspect of haptic perception. Further, this haptic-specific corticomotor facilitation was finely modulated depending on whether participants focused attention on identifying material (texture) as opposed to geometric properties of scanned surfaces (Exp II). With regards to aging effects, haptic-related corticomotor facilitation was associated with higher recognition accuracy in seniors (Exp III). In line with this, seniors exhibited similar levels of haptic-related corticomotor facilitation to young adults when task demands were adjusted for age (Exp IV). Interestingly, both young and senior adults also showed substantial corticomotor facilitation in the ‘resting’ hand when the ipsilateral hand was engaged in haptic sensing (Exp IV). Simply touching the stimulus without being required to identify its properties (no attentional task demands) produced no extra corticomotor facilitation in either hand or age group, attesting again to the specificity of the effects with regards to haptic attention. In Experiments V-VI, the ability to recognise 2-D letters by touch was investigated using kinematic and psychophysical measures. In Experiment V, we characterized how age affected contact forces deployed at the fingertip. This investigation showed that older adults exhibited lower normal force and increased letter-to-letter variability in normal force when compared to young adults. This difference in contact force likely contributed to longer contact times and lower recognition accuracy in older adults, suggesting a central contribution to age-related declines in haptic perception. Consistent with this interpretation, Experiment VI showed that haptic letter recognition in older adults was characterized not only by lower recognition accuracy but also by substantial increases in response times and specific patterns of confusion between letters. All in all, these investigations highlight the critical interaction of central factors such as attentional demand with aging effects on motor and perceptual aspects of haptic sensing. Of particular significance is the clear demonstration that corticomotor excitability is greatly enhanced when a haptic sensing component (i.e., attending to specific haptic features) is added to simple finger movements performed at minimal voluntary effort levels (typically <15 % of the maximal effort). These observations underline the therapeutic potential of active sensory training strategies based on haptic sensing tasks for the re-education of motor and perceptual deficits in hand function (e.g., subsequent to a stroke). The importance of adjusting attentional demands and stimuli is highlighted, particularly with regards to special considerations in the aging population.

With the continuous development in computer and communications technology the use of computer aided design in design processes is becoming more commonplace. A wide range of virtual prototyping technologies are currently in development, some of which are commercially viable for use within a product design process. These virtual prototyping technologies range from graphics tablets to haptic devices. With the compression of design cycles the feasibility of using these technologies for product evaluation is becoming an ever more important consideration. This thesis begins by presenting the findings of a comprehensive literature review defining product design with a focus on product evaluation and a discussion of current virtual prototyping technologies. From the literature review it was clear that user involvement in the product evaluation process is critical. The literature review was followed by a series of interconnected studies starting with an investigation into design consultancies' access and use of prototyping technologies and their evaluation methods. Although design consultancies are already using photo-realistic renderings, animations and sometimes 3600 view CAD models for their virtual product evaluations, current virtual prototyping hardware and software is often unsatisfactory for their needs. Some emergent technologies such as haptic interfaces are currently not commonly used in industry. This study was followed by an investigation into users' psychological acceptance and physiological discomfort when using a variety of virtual prototyping tools for product evaluation compared with using physical prototypes, ranging from on-screen photo-realistic renderings to 3D 3600 view models developed using a range of design software. The third study then went on to explore the feasibility of using these virtual prototyping tools and the effect on product preference when compared to using physical prototypes. The forth study looked at the designer's requirements for current and future virtual prototyping tools, design tools and evaluation methods. In the final chapters of the thesis the relative strengths and weaknesses of these technologies were re-evaluated and a definitive set of user requirements based on the documentary evidence of the previous studies was produced. This was followed by the development of a speculative series of scenarios for the next generation of virtual prototyping technologies ranging from improvements to existing technologies through to blue sky concepts. These scenarios were then evaluated by designers and consumers to produce documentary evidence and recommendations for preferred and suitable combinations of virtual prototyping technologies. Such hardware and software will require a user interface that is intuitive, simple, easy to use and suitable for both the designers who create the virtual prototypes and the consumers who evaluate them.

Les deux fonctions principales de la main sont la manipulation d’objet et l’exploration tactile. La détection du glissement, rapportée par les mécanorécepteurs de la peau glabre, est essentielle pour l’exécution de ces deux fonctions. Durant la manipulation d’objet, la détection rapide du micro-glissement (incipient slip) amène la main à augmenter la force de pince pour éviter que l’objet ne tombe. À l’opposé, le glissement est un aspect essentiel à l’exploration tactile puisqu’il favorise une plus grande acuité tactile. Pour ces deux actions, les forces normale et tangentielle exercées sur la peau permettent de décrire le glissement mais également ce qui arrive juste avant qu’il y ait glissement. Toutefois, on ignore comment ces forces contrôlées par le sujet pourraient être encodées au niveau cortical. C’est pourquoi nous avons enregistré l’activité unitaire des neurones du cortex somatosensoriel primaire (S1) durant l’exécution de deux tâches haptiques chez les primates. Dans la première tâche, deux singes devaient saisir une pastille de métal fixe et y exercer des forces de cisaillement sans glissement dans une de quatre directions orthogonales. Des 144 neurones enregistrés, 111 (77%) étaient modulés à la direction de la force de cisaillement. L’ensemble de ces vecteurs préférés s’étendait dans toutes les directions avec un arc variant de 50° à 170°. Plus de 21 de ces neurones (19%) étaient également modulés à l’intensité de la force de cisaillement. Bien que 66 neurones (59%) montraient clairement une réponse à adaptation lente et 45 autres (41%) une réponse à adaptation rapide, cette classification ne semblait pas expliquer la modulation à l’intensité et à la direction de la force de cisaillement. Ces résultats montrent que les neurones de S1 encodent simultanément la direction et l’intensité des forces même en l’absence de glissement. Dans la seconde tâche, deux singes ont parcouru différentes surfaces avec le bout des doigts à la recherche d’une cible tactile, sans feedback visuel. Durant l’exploration, les singes, comme les humains, contrôlaient les forces et la vitesse de leurs doigts dans une plage de valeurs réduite. Les surfaces à haut coefficient de friction offraient une plus grande résistance tangentielle à la peau et amenaient les singes à alléger la force de contact, normale à la peau. Par conséquent, la somme scalaire des composantes normale et tangentielle demeurait constante entre les surfaces. Ces observations démontrent que les singes contrôlent les forces normale et tangentielle qu’ils appliquent durant l’exploration tactile. Celles-ci sont également ajustées selon les propriétés de surfaces telles que la texture et la friction. Des 230 neurones enregistrés durant la tâche d’exploration tactile, 96 (42%) ont montré une fréquence de décharge instantanée reliée aux forces exercées par les doigts sur la surface. De ces neurones, 52 (54%) étaient modulés avec la force normale ou la force tangentielle bien que l’autre composante orthogonale avait peu ou pas d’influence sur la fréquence de décharge. Une autre sous-population de 44 (46%) neurones répondait au ratio entre la force normale et la force tangentielle indépendamment de l’intensité. Plus précisément, 29 (30%) neurones augmentaient et 15 (16%) autres diminuaient leur fréquence de décharge en relation avec ce ratio. Par ailleurs, environ la moitié de tous les neurones (112) étaient significativement modulés à la direction de la force tangentielle. De ces neurones, 59 (53%) répondaient à la fois à la direction et à l’intensité des forces. L’exploration de trois ou quatre différentes surfaces a permis d’évaluer l’impact du coefficient de friction sur la modulation de 102 neurones de S1. En fait, 17 (17%) neurones ont montré une augmentation de leur fréquence de décharge avec l’augmentation du coefficient de friction alors que 8 (8%) autres ont montré le comportement inverse. Par contre, 37 (36%) neurones présentaient une décharge maximale sur une surface en particulier, sans relation linéaire avec le coefficient de friction des surfaces. La classification d’adaptation rapide ou lente des neurones de S1 n’a pu être mise en relation avec la modulation aux forces et à la friction. Ces résultats montrent que la fréquence de décharge des neurones de S1 encode l’intensité des forces normale et tangentielle, le ratio entre les deux composantes et la direction du mouvement. Ces résultats montrent que le comportement d’une importante sous-population des neurones de S1 est déterminé par les forces normale et tangentielle sur la peau. La modulation aux forces présentée ici fait le pont entre les travaux évaluant les propriétés de surfaces telles que la rugosité et les études touchant à la manipulation d’objets. Ce système de référence s’applique en présence ou en absence de glissement entre la peau et la surface. Nos résultats quant à la modulation des neurones à adaptation rapide ou lente nous amènent à suggérer que cette classification découle de la manière que la peau est stimulée. Nous discuterons aussi de la possibilité que l’activité des neurones de S1 puisse inclure une composante motrice durant ces tâches sensorimotrices. Finalement, un nouveau cadre de référence tridimensionnel sera proposé pour décrire et rassembler, dans un même continuum, les différentes modulations aux forces normale et tangentielle observées dans S1 durant l’exploration tactile. / The two most important functions of the hand are object manipulation and tactile exploration. The detection of slip provided by specialized mechanoreceptors in the glabrous skin is essential for the execution of both these functions. During object manipulation, the early detection of incipient slip leads to a grip force increase in order to prevent dropping an object. Slip is also an important aspect of tactile exploration because it greatly increases the acuity of touch perception. In both actions, normal and tangential forces on the skin can describe slip itself but also what occurs just before slip. However, little is known about how these self-generated forces are encoded at the cortical level. To better understand this encoding, we recorded from single neurons in primary somatosensory cortex (S1) as monkeys executed two haptic tasks. In the first task, two monkeys grasped a stationary metal tab with a key grip and exerted shear forces, without slip, in one of four orthogonal directions. Of 144 recorded neurons, 111 (77%) had activity modulated with shear force directions. These preferred shear force vectors were distributed in every direction with tuning arcs varying from 50° to 170°. Also, more than 21 (19%) of these neurons had a firing rate correlated with shear force magnitude. Even if 66 (59%) modulated neurons showed clear slowly adapting response and 45 (41%) other neurons a rapidly adapting response, this classification failed to explain the modulation to force direction and magnitude. These results show that S1 neurons encode force direction and magnitude simultaneously even in the absence of slip. In the second task, two monkeys scanned different surfaces with the fingertips in search of a tactile target without visual feedback. During the exploration, the monkeys, like humans, carefully controlled the finger forces and speeds. High friction surfaces offered greater tangential shear force resistance to the skin that was associated with decrease of the normal contact forces. Furthermore, the scalar sum of the normal and tangential forces remained constant. These observations demonstrate that monkeys control the applied normal and tangential finger forces within a narrow range which is adjusted according to surface properties such as texture and friction. Of the 230 recorded neurons during tactile exploration, 96 (42%) showed instantaneous frequency changes in relation to finger forces. Of these, 52 (54%) were correlated with either the normal or tangential force magnitude with little or no influence from the other orthogonal force component. Another subset of 44 neurons (46%) responded to the ratio between normal and tangential forces regardless of magnitude. Namely, 29 neurons (30%) increased and 15 (16%) others decreased their discharge frequency related to this ratio, which corresponds to the coefficient of friction. Tangential force direction significantly modulated about half the recorded neurons (112). Of these, 59 (53%) responded to both direction and force magnitude. Of the 102 neurons recorded during exploration of three or more surfaces, 17 (17%) showed increased firing rate with increased surface friction and 8 (8%) presented the opposite behavior. However, 37 (36%) neurons seemed to discharge optimally for one of the surfaces without any linear relation to the surfaces’ coefficient of friction. The classification of rapidly and slowly adaptation for neuronal responses in S1 could not be associated with the modulation to forces or direction. These results show that the firing rates of S1 neurons reflect the tangential and normal force magnitude, the ratio of the two forces and the direction of finger movement. These results show that the activity of a significant subpopulation of S1 neurons is represented by normal and tangential forces on the skin. This force modulation uses a frame of reference that can be applied with or without slip. This aspect provides a link between investigations of the cortical representation of surface properties and studies on object manipulation. Our results regarding the distinction between rapidly and slowly adapting neurons leads us to suggest that this difference is a consequence of the manner in which the skin was stimulated. A potential motor component in the modulation of S1 neurons during these sensorimotor tasks is also discussed. Finally, a novel three-dimensional reference frame is proposed to describe, as a single continuum, the different modulations to forces observed in S1 during tactile exploration.

Abstract : Many individuals that had a stroke have motor impairments such as timing deficits that hinder their ability to complete daily activities like getting dressed. Robotic rehabilitation is an increasingly popular therapeutic avenue in order to improve motor recovery among this population. Yet, most studies have focused on improving the spatial aspect of movement (e.g. reaching), and not the temporal one (e.g. timing). Hence, the main aim of this study was to compare two types of robotic rehabilitation on the immediate improvement of timing accuracy: haptic guidance (HG), which consists of guiding the person to make the correct movement, and thus decreasing his or her movement errors, and error amplification (EA), which consists of increasing the person’s movement errors. The secondary objective consisted of exploring whether the side of the stroke lesion had an effect on timing accuracy following HG and EA training. Thirty-four persons that had a stroke (average age 67 ± 7 years) participated in a single training session of a timing-based task (simulated pinball-like task), where they had to activate a robot at the correct moment to successfully hit targets that were presented a random on a computer screen. Participants were randomly divided into two groups, receiving either HG or EA. During the same session, a baseline phase and a retention phase were given before and after each training, and these phases were compared in order to evaluate and compare the immediate impact of HG and EA on movement timing accuracy. The results showed that HG helped improve the immediate timing accuracy (p=0.03), but not EA (p=0.45). After comparing both trainings, HG was revealed to be superior to EA at improving timing (p=0.04). Furthermore, a significant correlation was found between the side of stroke lesion and the change in timing accuracy following EA (r[subscript pb]=0.7, p=0.001), but not HG (r[subscript pb]=0.18, p=0.24). In other words, a deterioration in timing accuracy was found for participants with a lesion in the left hemisphere that had trained with EA. On the other hand, for the participants having a right-sided stroke lesion, an improvement in timing accuracy was noted following EA. In sum, it seems that HG helps improve the immediate timing accuracy for individuals that had a stroke. Still, the side of the stroke lesion seems to play a part in the participants’ response to training. This remains to be further explored, in addition to the impact of providing more training sessions in order to assess any long-term benefits of HG or EA. / Résumé : À la suite d’un accident vasculaire cérébral (AVC), plusieurs atteintes, comme un déficit de timing, sont notées, et ce, même à la phase chronique d’un AVC, ce qui nuit à l’accomplissement de tâches quotidiennes comme se vêtir. L’entrainement robotisé est un entrainement qui est de plus en plus préconisé dans le but d’améliorer la récupération motrice à la suite d’un AVC. Par contre, la plupart des études ont étudié les effets de l’entrainement robotisé sur l’amélioration de l’aspect spatial du mouvement (ex : la direction du mouvement), et non l’aspect temporel (ex : timing). L’objectif principal de ce projet était donc d’évaluer et de comparer l’impact de deux entrainements robotisés sur l’amélioration immédiate du timing soit : la réduction de l’erreur (RE), qui consiste à guider la personne à faire le mouvement désiré, et l’augmentation de l’erreur (AE), qui nuit au mouvement de la personne. L’objectif secondaire consistait à explorer s’il y avait une relation entre le côté de la lésion cérébrale et le changement dans les erreurs de timing suivant l’entrainement par RE et AE. Trente-quatre personnes atteintes d’un AVC au stade chronique (âge moyen de 67 ± 7 années) ont participé à cette étude, où ils devaient jouer à un jeu simulé de machine à boules. Les participants devaient activer une main robotisée au bon moment pour atteindre des cibles présentées aléatoirement sur un écran d’ordinateur. Les participants recevaient soit RE ou AE. Une ligne de base et une phase de rétention étaient données avant et après chaque entrainement, et elles étaient utilisées pour évaluer et comparer l’effet immédiat de RE et AE sur le timing. Les résultats ont démontré que RE permet d’améliorer les erreurs de timing (p=0,03), mais pas AE (p=0,45). De plus, la comparaison entre les deux entrainements a démontré que RE était supérieur à AE pour améliorer le timing (p=0,04). Par ailleurs, une corrélation significative a été notée entre le côté de la lésion cérébrale et le changement des erreurs de timing suivant AE (r[indice inférieur pb]=0,70; p=0,001), mais pas RE (r[indice inférieur pb]=0,18; p=0,24). En d’autres mots, une détérioration de l’exécution de la tâche de timing a été notée pour les participants ayant leur lésion cérébrale à gauche. Par contre, ceux ayant leur lésion à droite ont bénéficié de l’entrainement par AE. Bref, l’entrainement par RE peut améliorer les erreurs de timing pour les survivants d’AVC au stade chronique. Toutefois, le côté de la lésion cérébrale semble jouer un rôle important dans la réponse à l’entrainement par AE. Ceci demeure à être exploré, ainsi que l’impact d’un entrainement par RE et AE de plus longue durée pour en déterminer leurs effets à long terme.