Past research has indicated that motor imagery, or imagined movement, follows Fitts' law similarly to physical movement. Additionally, motor imagery has been shown to improve real motor performance in multiple contexts, showcasing a remarkable connection with real motion. The current study examines how the subject of motor imagery, imagining oneself, another person, or an object, impacts this faithfulness to real movement, specifically in following Fitts' law. Participants viewed 2D photos of a virtual environment with an "X", a humanoid, or a disc facing a gate at 6 distances and 4 widths for 24 combinations. Each combination was repeated twice randomly for 48 trials per condition, and conditions were presented in random order for a total of 144 trials. Results indicate that object-imagery does trigger motor imagery and follow Fitts' law, in contrast to prior research. However, further analysis showed that the function produced in the object condition was significantly different from both self and other, while self and other were not significantly different from one another. This was due to a higher index of performance value in the object condition, implying that participants assigned the object different abilities than the two human-centered conditions. These results indicate a difference related to biological, or perhaps human, motion, and future studies should further explore the impact of the subject and characteristics of the subject on motor imagery. Understanding these intricacies is crucial to refine and understand the benefits of motor imagery seen in multiple motor performance contexts.

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Muscle weakness is one of the major causes of post-stroke disability. Stroke rehabilitation programs now often incorporate the same type of resistance training that is used for healthy subjects; however, the training effects induced from these training strategies are often limited for stroke patients. An important resistance training principle is that an optimal level of stress is exerted on the neuromuscular system, both during concentric (shortening) and eccentric (lengthening) contractions. One potential problem for post-stroke patients might be difficulties achieving sufficient levels of stress on the neuromuscular system. This problem may be associated with altered muscular function after stroke. In healthy subjects, maximum strength during eccentric contractions is higher than during concentric contractions. In individuals with stroke, this difference in strength is often increased. Moreover, it has also been shown that individuals with stroke exhibit alteration with respect to how the strength varies throughout the range of motion. For example, healthy subjects exhibit a joint specific torque-angle relationship that normally is the same irrespective of contraction mode and contraction velocity. In contrast, individuals with stroke exhibit an overall change of the torque-angle relationship. This change, as described in the literature, consists of a more pronounced strength loss at short muscle length. In individuals with stroke, torque-angle relationships are only partially investigated and so far these relationships have not been analysed using testing protocols that include eccentric, isometric, and concentric modes of contraction.   This thesis investigates the torque-angle relationship of elbow flexors in subjects with stroke during all three modes of contractions – isometric, concentric, and eccentric ­– and the relative loading throughout the range of movement during a resistance exercise. In addition, this thesis studies possible central nervous system mechanisms involved in the control of muscle activation during eccentric and concentric contractions.   The torque-angle relationship during maximum voluntary elbow flexion was examined in stroke subjects (n=11), age-matched healthy subjects (n=11), and young subjects (n=11) during different contraction modes and velocities. In stroke subjects, maximum torque as well as the torque angle relationship was better preserved during eccentric contractions compared to concentric contractions. Furthermore, the relative loading during a resistance exercise at an intensity of 10RM (repetition maximum) was examined. Relative loading throughout the concentric phase of the resistance exercise, expressed as percentage of concentric torque, was found to be similar in all groups. However, relative loading during the eccentric contraction phase, expressed as the percentage of eccentric isokinetic torque, was significantly lower for the stroke group. In addition, when related to isometric maximum voluntary contraction, the loading for the stroke group was significantly lower than for the control groups during both the concentric and eccentric contraction phases. Functional magnetic resonance imaging was used to examine differences between recruited brain regions during the concentric and the eccentric phase of imagined maximum resistance exercise of the elbow flexors (motor imagery) in young healthy subjects (n=18) and in a selected sample of individuals with stroke (n=4). The motor and premotor cortex was less activated during imagined maximum eccentric contractions compared to imagined maximum concentric contraction of elbow flexors. Moreover, BA44 in the ventrolateral prefrontal cortex, a brain area that has been shown to be involved in inhibitory control of motor activity, was additionally recruited during eccentric compared to concentric conditions. This pattern was evident only on the contralesional (the intact hemisphere) in some of the stroke subjects. On the ipsilesional hemisphere, the recruitment in ventrolateral prefrontal cortex was similar for both modes of contractions.    Compared to healthy subjects, the stroke subjects exhibited altered muscular function comprising a specific reduction of torque producing capacity and deviant torque-angle relationship during concentric contractions. Therefore, the relative training load during the resistance exercise at a training intensity of 10RM was lower for subjects with stroke. Furthermore, neuroimaging data indicates that the ventrolateral prefrontal cortex may be involved in a mechanism that modulates cortical motor drive differently depending on mode of the contractions. This might partly be responsible for why it is impossible to fully activate a muscle during eccentric contractions. Moreover, among individuals with stroke, a disturbance of this system could also lie behind the lack of contraction mode-specific modulation of muscle activation that has been found in this population. The altered neuromuscular function evident after a stroke means that stroke victims may find it difficult to supply a sufficient level of stress during traditional resistance exercises to promote adaptation by the neuromuscular system. This insufficiency may partially explain why the increase in strength, in response to conventional resistance training, often has been found to be low among subjects with stroke. / Muskelsvaghet är en av orsakerna till funktionshinder efter stroke. I rehabiliteringsprogram för personer som drabbats av stroke förekommer det numera att styrketräning används i syfte att öka muskelstyrkan. Effekten av styrketräning har dock ofta visat sig vara begränsad. En viktig styrketräningsprincip är att muskulaturen belastas tillräckligt nära maximal styrka under både koncentriska kontraktioner (när man lyfter en vikt) och excentriska kontraktioner (när man kontrollerat sänker en vikt). Ett potentiellt problem skulle kunna vara att personer med stroke inte belastas optimalt under träning på grund av förändrad muskelfunktion. Efter stroke är muskelfunktionen ofta förändrad såtillvida att styrkenedsättningen är mer uttalad under koncentriska kontraktioner. Därutöver har man funnit att styrkenedsättningen är mest uttalad när muskeln är i sitt mest förkortade läge. Detta fenomen har dock inte studerats för alla tre kontraktionstyper, det vill säga excentriska, koncentriska och isometriska kontraktioner, hos personer med stroke.   Denna avhandling undersöker sambandet mellan styrka och ledvinkel över armbågsleden hos personer med stroke under alla tre kontraktionstyper – excentrisk, koncentrisk och isometrisk, samt relativ belastning genom rörelsebanan under en styrketräningsövning. Därutöver undersöker denna avhandling också hjärnans aktiveringsmönster under excentriska och koncentriska kontraktioner.   Sambandet mellan styrka och ledvinkel undersöktes hos personer med stroke (n = 11), åldersmatchade (n = 11) och unga försökspersoner (n = 11). Jämfört med kontrollgrupperna var maximal styrka för personer med stroke mest nedsatt, samt även den oproportionerligt stora styrkenedsättningen vid kort muskelängd som mest uttalad, under koncentriska kontraktioner. Denna avvikelse var minst uttalad vid excentriska kontraktioner. Vidare studerades hur hög belastningen på muskulaturen var i jämförelse med muskelns maximala styrka under en styrketräningsliknande övning för armbågsflexorer vid en träningsintensitet på 10RM. Den uppmätta belastningen under den koncentriska fasen av styrketräningsövningen, uttryckt som procent av den genomsnittliga koncentriska styrkan, var densamma för alla grupperna. Under den excentriska fasen av övningen var dock belastningen, uttryckt som procent av den maximala excentriska styrkan, signifikant lägre för personer med stroke. Träningsbelastningen utgjorde också en lägre andel av den maximala isometriska styrkan för personer med stroke, både under den koncentriska och under den excentriska fasen.   Funktionell magnetresonanstomografi (fMRI) användes för att undersöka hjärnans aktiveringsmönster hos unga försökspersoner (n = 18) och hos individer med stroke (n = 4) när de föreställde sig att de utförde maximal styrketräning för armbågsflexorer (motor imagery). Resultatet visade att primära motorbarken och premotoriska barken var mindre aktiverade när unga friska försökspersonerna föreställde sig utföra maximala excentriska, jämfört med maximala koncentriska kontraktioner. Dessutom var en region i ventrolaterala prefrontala barken, som i tidigare studier visat sig vara inblandat i reglering och hämning av muskelaktivering, mer aktiverade under föreställda excentriska kontraktioner. Detta aktiveringsmönster i den prefrontala barken återfanns dock endast i den icke skadade hjärnhalvan hos personer med stroke.   Jämfört med kontrollgrupperna uppvisade försökspersonerna med stroke en förändrad muskelfunktion som bestod av en specifik nedsättning av styrkan under koncentriska kontraktioner samt också ett mer avvikande samband mellan styrka och ledvinkel under koncentriska kontraktioner. Den relativa belastningen under utförandet av en styrketräningsövning med en intensitet på 10RM var på grund av dessa avvikelser lägre för försökspersoner med stroke. Hjärnavbildnings-studierna indikerade att ventrolaterala prefrontala barken verkar vara involverat i ett kortikalt moduleringssystem som reglerar muskel-aktivering olika beroende på kontraktionstyp under maximala kontraktioner. Detta skulle kunna vara en underliggande mekanism bakom den hittills obesvarade frågan varför det är omöjligt att aktivera muskulaturen maximalt under excentriska kontraktioner. En störning av detta moduleringssystem hos personer med stroke verkar också kunna ligga bakom den förändrade regleringen av muskelaktivering som visat sig förekomma hos personer med stroke. Neuromuskulär funktion efter stroke är förändrad i flera avseenden vilket verkar medföra att muskulaturen inte belastas optimalt under konventionell styrketräning. Detta kan vara en delförklaring till varför styrkeökningen som svar på träning ofta är liten hos personer med stroke.

Imagética motora é um processo mental que produz modulações na amplitude dos sinas de eletroencefalogramas em progresso. Os padrões presentes nestas modulações podem ser usados para classificar este processo mental, mas a identificação destes padrões não é uma tarefa trivial, porque eles estão presentes em bandas de frequências que são específicas para cada pessoa. Neste trabalho, apresenta-se um novo método para selecionar as bandas de frequência específicas para cada pessoa baseado na arquitetura do método Filter Bank Common Spatial Pattern. Para selecionar as bandas de frequência mais relevantes para cada pessoa, o método proposto aplica uma busca exaustiva para encontrar o melhor subconjunto de bandas de frequência contendo os padrões mais discriminativos dentro de um espaço de busca restrito a um tamanho fixo para este subconjunto. Esse tamanho é determinado usando validação cruzada e o método Sequential Forward Floating Selection. O método proposto foi avaliado usando a base de dados pública 2b da BCI Competition IV, mostrando melhores resultados do que todos os métodos também avaliados nessa base de dados. / Motor imagery is a mental process that when performed, produces modulations in the amplitude of ongoing electroencephalogram signals. These modulations happen following a series of patterns that can be used to classify this mental process, but the detection of those patterns is not a trivial task, because they occur in frequency bands that are specific for each person. In this work, we present a method to select these subject-specific frequency bands based on the arquitecture of the Filter Bank Common Spatial Pattern approach. To select the most relevant frequency bands for each person, our method uses an exhaustive search to find the best subset of frequency bands containing the most discriminative patterns, but with one restriction, the search space is restricted to find a subset with a fixed number of frequency bands. The number is determined using cross-validation and the Sequential Forward Floating Selection method. We demonstrate that, using the data set 2b of the BCI Competition IV, our method is more accurate than current methods evaluated on the same data set.

Imagética motora é um processo mental que produz modulações na amplitude dos sinas de eletroencefalogramas em progresso. Os padrões presentes nestas modulações podem ser usados para classificar este processo mental, mas a identificação destes padrões não é uma tarefa trivial, porque eles estão presentes em bandas de frequências que são específicas para cada pessoa. Neste trabalho, apresenta-se um novo método para selecionar as bandas de frequência específicas para cada pessoa baseado na arquitetura do método Filter Bank Common Spatial Pattern. Para selecionar as bandas de frequência mais relevantes para cada pessoa, o método proposto aplica uma busca exaustiva para encontrar o melhor subconjunto de bandas de frequência contendo os padrões mais discriminativos dentro de um espaço de busca restrito a um tamanho fixo para este subconjunto. Esse tamanho é determinado usando validação cruzada e o método Sequential Forward Floating Selection. O método proposto foi avaliado usando a base de dados pública 2b da BCI Competition IV, mostrando melhores resultados do que todos os métodos também avaliados nessa base de dados. / Motor imagery is a mental process that when performed, produces modulations in the amplitude of ongoing electroencephalogram signals. These modulations happen following a series of patterns that can be used to classify this mental process, but the detection of those patterns is not a trivial task, because they occur in frequency bands that are specific for each person. In this work, we present a method to select these subject-specific frequency bands based on the arquitecture of the Filter Bank Common Spatial Pattern approach. To select the most relevant frequency bands for each person, our method uses an exhaustive search to find the best subset of frequency bands containing the most discriminative patterns, but with one restriction, the search space is restricted to find a subset with a fixed number of frequency bands. The number is determined using cross-validation and the Sequential Forward Floating Selection method. We demonstrate that, using the data set 2b of the BCI Competition IV, our method is more accurate than current methods evaluated on the same data set.

Developmental Coordination Disorder (DCD) is characterised by impairments to motor control and learning, the cause of which remains unclear. Recently, researchers have used cognitive neuroscientific approaches to explore the basis of poor coordination in children, with one hypothesis suggesting that an internal modelling deficit (IMD) is one of the underlying causes of DCD. The aim of this thesis was to further test the IMD hypothesis using a motor imagery paradigm - the mental rotation of hands. Versions of this task were used in all studies to assess motor imagery ability, with an additional whole-body task used in Studies 2 and 3. Further, an alphanumeric rotation task was used in Studies 1 and 2 to assess visual imagery ability. Studies 1 and 2 provided varying levels of support for the IMD hypothesis. In Study 1, only a subgroup of DCD children performed differently from other children in the study on the hand tasks, but tighter task constraints in Study 2 led to overall group differences between DCD and controls in terms of accuracy. The DCD group were also significantly less accurate than controls in the whole-body task, but there were no group differences in either Study 1 or 2 on the visual imagery task. Interestingly, in Study 2, there was an indication that children with severe levels of motor impairment were less accurate than children with less severe motor impairment, suggesting that motor impairment level could play a role in the severity of motor imagery deficits. Study 3 was designed to explore the impact of motor impairment severity on motor imagery ability further. The results confirmed that children with severe DCD had greater motor imagery impairment than children with mild DCD - children with severe DCD performed less accurately than both controls and those with mild DCD in the hand task with instructions and the controls in the whole-body task. Further, those children with mild DCD were able to respond somewhat to motor imagery instructions, whereas those with severe DCD were not. This study provided support to the IMD hypothesis, though the deficit was shown to be dependent on a number of factors. Chapter 5 presents a reasoned account of these various findings and their implications are discussed. It is concluded that motor imagery deficits are evident in many children with DCD, but more so in children with severe motor impairment. A general imagery deficit was ruled out based on the findings of Studies 1 and 2 which showed that visual imagery processes appear intact in children with DCD. Taken together with previous imagery and IMD studies, and related research on feedforward control in DCD, it is concluded that the deficits in motor imagery observed in this thesis are consistent with the hypothesis that an IMD is one likely causal factor in the disorder, particularly in more severe DCD. The observation of differing response patterns between children with mild and severe forms of DCD has important implications for developing a theory of DCD and for remediation.

The human brain is unquestionably the most complex organ of the body as it controls and processes its movement and senses. A healthy brain is able to generate responses to the signals it receives, and transmit messages to the body. Some neural disorders can impair the communication between the brain and the body preventing the transmission of these messages. Brain Computer Interfaces (BCIs) are devices that hold immense potential to assist patients with such disorders by analyzing brain signals, translating and classifying various brain responses, and relaying them to external devices and potentially back to the body. Classifying motor imagery brain signals where the signals are obtained based on imagined movement of the limbs is a major, yet very challenging, step in developing Brain Computer Interfaces (BCIs). Of primary importance is to use less data and computationally efficient algorithms to support real-time BCI. To this end, in this thesis we explore and develop algorithms that exploit the sparse characteristics of EEGs to classify these signals. Different feature vectors are extracted from EEG trials recorded by electrodes placed on the scalp. In this thesis, features from a small spatial region are approximated by a sparse linear combination of few atoms from a multi-class dictionary constructed from the features of the EEG training signals for each class. This is used to classify the signals based on the pattern of their sparse representation using a minimum-residual decision rule. We first attempt to use all the available electrodes to verify the effectiveness of the proposed methods. To support real time BCI, the electrodes are reduced to those near the sensorimotor cortex which are believed to be crucial for motor preparation and imagination. In a second approach, we try to incorporate the effect of spatial correlation across the neighboring electrodes near the sensorimotor cortex. To this end, instead of considering one feature vector at a time, we use a collection of feature vectors simultaneously to find the joint sparse representation of these vectors. Although we were not able to see much improvement with respect to the first approach, we envision that such improvements could be achieved using more refined models that can be subject of future works. The performance of the proposed approaches is evaluated using different features, including wavelet coefficients, energy of the signals in different frequency sub-bands, and also entropy of the signals. The results obtained from real data demonstrate that the combination of energy and entropy features enable efficient classification of motor imagery EEG trials related to hand and foot movements. This underscores the relevance of the energies and their distribution in different frequency sub-bands for classifying movement-specific EEG patterns in agreement with the existence of different levels within the alpha band. The proposed approach is also shown to outperform the state-of-the-art algorithm that uses feature vectors obtained from energies of multiple spatial projections.

Brain-computer interfaces are an emerging technology that could provide channels for communication and control to severely disabled people suffering from locked-in syndrome. It has been found that motor imagery can be detected and classified from EEG signals. The motivation of the present work was to compare several algorithms for motor imagery classification in EEG signals as well as to test several novel algorithms. The algorithms tested included the popular method of common spatial patterns (CSP) spatial filtering followed by linear discriminant analysis (LDA) classification of log-variance features (CSP+LDA). A second set of algorithms used classification based on concepts from Riemannian geometry. The basic idea of these methods is that sample spatial covariance matrices (SCMs) of EEG epochs belong to the Riemannian manifold of symmetric positive-definite (SPD) matrices and that the tangent space at any SPD matrix on the manifold is a finite-dimensional Euclidean space. Riemannian classification methods tested included minimum distance to Riemannian mean (MDRM), tangent space LDA (TSLDA), and Fisher geodesic filtering followed by MDRM classification (FGDA). The novel algorithms aimed to combine the CSP method with the Riemannian geometry methods. CSP spatial filtering was performed prior to sample SCM calculation and subsequent classification using Riemannian methods. The novel algorithms were found to improve classification accuracy as well as reduce the computational costs of Riemannian classification methods for binary, synchronous classification on BCI competition IV dataset 2a. / Master of Science

It is still controversial whether mental practice – the internal rehearsal of movements to improve later performance – relies on processes engaged during physical motor performance and, if so, which processes these are. This series of experiments investigates this question. It utilizes a framework of ideomotor action planning theories, and tests whether mental practice may specifically draw upon planning- rather than execution-related motor processes, specifically those processes that “bind” intended action features to action plans. Experiments 1 to 4 utilize a classical stimulus response compatibility paradigm. Participants mentally practiced complex rhythms with either feet or hands while using the same or different body parts to respond to unrelated sounds. In contrast to previous work on stimulus response compatibility, we indeed found that responses were impaired – rather than facilitated – for those body parts that were concurrently used in mental practice. This result was found when participants mentally trained to memorize the rhythms (Experiment 1), to merely improve their performance (Experiment 3), when mental practice and execution directly followed one another and when separated by a different task (Experiment 4). These data link mental practice not to execution but planning related motor processes that are involved in binding intended action features to intended action plans. Experiment 5 and 6 then extend these results to imitation learning. Participants were instructed to learn the rhythms by observing somebody else, while again making unrelated responses with their hand and feet. While previous work on stimulus response compatibility focussed on testing automatic imitation processes, here imitation was therefore goal directed. We found, as in the previous experiments, that responses with the same body parts as used in the observed rhythms were impaired, suggesting that goal-directed imitation might rely on the same planning-related motor processes as the mental practice of action (Experiment 5). Importantly, these effects were only found as long as participants observed the actions with VI the purpose of imitating them later (i.e. formed action plans), but not when they merely tried to memorize the rhythms for later recognition (Experiment 6). The previous experiments suggest that mental practice and observation learning draw upon body-part specific planning processes. Ideomotor theories suggest, however, that action plans can be relatively abstract, and represented in terms of higher-level goals (i.e. the sequence of left and right button presses independent of the body part used). Experiment 7 and 8 therefore tested whether rhythms learned through mental practice or observation learning could be transferred to other body parts. As expected, we found a relatively high amount of potential transfer when rhythms were mentally practiced with one body part, and then had to be transferred to another body part (Experiment 7). However, this only held when participants learned the rhythms based on an abstract rhythm description, as in Experiments 1 to 4. If participants learned the same rhythms during action observation, any benefits were only obtained when the rhythms later had to be executed with the same (rather than a different) body part. Together, the present data suggest that mental practice does not rely on execution related-motor processes, and points to an involvement of planning related motor processes instead. We argue that such a planning-based account of mental practice is more compatible with the available evidence from body neuroscientific and behavioral studies, and allows one to resolve several debates. Moreover, it allows one to conceptualize goal-directed imitation in a similar manner as mental practice.

Quel rôle joue la gravité dans les représentations internes de l'action ? Au-delà des contraintes d'équilibre, le vecteur gravitaire influence-t-il l'action de façon globale, jusqu'à la perception des mouvements de nos semblables ? Ces questions ont été celles qui ont guidé mes travaux de thèse. L'originalité de notre approche a été de placer l'exécution et la perception de l'action dans un « continuum fonctionnel » s'articulant autour des représentations internes de l'action. Pour ce faire, l'outil de choix qui est commun aux trois expériences de cette thèse est la microgravité (0G). Les expériences de cette thèse ont montré que les représentations internes de l'action se nourrissaient des informations graviceptives pour se construire et s'adapter constamment. Cependant, dans certaines conditions telle que la 0G à court terme, apparaît un ordre de priorité. En effet, le SNC est capable de mettre en place des solutions immédiates et efficaces pour l'exécution, comme en témoigne la repondération sensorielle rapide qui s'opère en 0G dans une tâche d'orientation posturale. Cependant, un temps de latence est observé dans la recalibration des modèles internes sur la base des afférences sensorielles fortement perturbées. C'est ce que nous avons montré grâce à un protocole d'imagerie motrice, mettant en évidence une perte de l'isochronie entre les mouvements exécutés et imaginés en 0G. Enfin, nous avons mis en évidence, chez des sujets sans expérience aucune de microgravité, que la perception du mouvement humain est efficace même lorsque ce dernier est exécuté en apesanteur, bien que des réseaux cérébraux différents soient mis en jeux. / What is the role of gravity in the internal representations of action? Beyond the constraints of balance, does the gravity vector influence the action globally, up to the perception of our peers' movement? These issues have guided my thesis work. The originality of our approach was to place the execution and the perception of action in a "functional continuum" built around the internal representations of the action. To do this, the tool of choice, that is common to all three experiments presented here, is microgravity (0G). The experiments of this thesis showed that the internal representations of action are fed with graviceptive information to build and adapt constantly. However, under certain conditions such as short-term 0G, an order of priority appears. Indeed, the CNS is able to implement immediate and effective solutions, as we demonstrate it with the fast sensorial reweighting observed during a postural orientation task. However, a lag is observed in the recalibration of internal models based on sensory inputs severely disrupted. This is what we have shown through a protocol of motor imagery, showing a loss of isochrony between executed and imagined movements under 0G. Finally, we have demonstrated in subjects without any experience of microgravity, that the perception of human movement is effective even when it is performed in weightlessness, although different cerebral networks are involved.