A photograph typically depicts an aspect of the real world, such as an outdoor landscape, a portrait, or an event. The task of creating abstract digital representations of images has received a great deal of attention in the computer vision literature because it is rarely useful to work directly with the raw pixel data. The challenge of working with raw pixel data is that small changes in lighting can result in different digital images, which is not typically useful for downstream tasks such as object detection. One approach to representing an image is automatically extracting and quantising visual features to create a bag-of-terms vector. The bag-of-terms vector helps overcome the problems with raw pixel data but this unstructured representation discards potentially useful information about the spatial and semantic relationships between the parts of the image. The central argument of this thesis is that capturing and encoding the relationships between parts of an image will improve the performance of extrinsic tasks, such as image description or search. We explore this claim in the restricted domain of images representing events, such as riding a bicycle or using a computer. The first major contribution of this thesis is the Visual Dependency Representation: a novel structured representation that captures the prominent region–region relationships in an image. The key idea is that images depicting the same events are likely to have similar spatial relationships between the regions contributing to the event. This representation is inspired by dependency syntax for natural language, which directly captures the relationships between the words in a sentence. We also contribute a data set of images annotated with multiple human-written descriptions, labelled image regions, and gold-standard Visual Dependency Representations, and explain how the gold-standard representations can be constructed by trained human annotators. The second major contribution of this thesis is an approach to automatically predicting Visual Dependency Representations using a graph-based statistical dependency parser. A dependency parser is typically used in Natural Language Processing to automatically predict the dependency structure of a sentence. In this thesis we use a dependency parser to predict the Visual Dependency Representation of an image because we are working with a discrete image representation – that of image regions. Our approach can exploit features from the region annotations and the description to predict the relationships between objects in an image. In a series of experiments using gold-standard region annotations, we report significant improvements in labelled and unlabelled directed attachment accuracy over a baseline that assumes there are no relationships between objects in an image. Finally, we find significant improvements in two extrinsic tasks when we represent images as Visual Dependency Representations predicted from gold-standard region annotations. In an image description task, we show significant improvements in automatic evaluation measures and human judgements compared to state-of-the-art models that use either external text corpora or region proximity to guide the generation process. In the query-by-example image retrieval task, we show a significant improvement in Mean Average Precision and the precision of the top 10 images compared to a bag-of-terms approach. We also perform a correlation analysis of human judgements against automatic evaluation measures for the image description task. The automatic measures are standard measures adopted from the machine translation and summarization literature. The main finding of the analysis is that unigram BLEU is less correlated with human judgements than Smoothed BLEU, Meteor, or skip-bigram ROUGE.

Le syndrome d’Ehlers-Danlos (SED) est un groupe mixte de maladies héréditaires dont la caractéristique commune est une altération d’origine génétique du tissu conjonctif. Sa forme hypermobile (SEDh) se caractérise par une hypermobilité articulaire généralisée, associée à une hyperélasticité cutanée, générant toutes deux un déficit somesthésique. Or, le système somesthésique est, avec les systèmes visuel et vestibulaire, crucialement impliqué dans le fonctionnement du système sensorimoteur. Ce travail de thèse visait donc à comprendre comment le déficit somesthésique propre au SEDh modifie les mécanismes perceptifs et sensorimoteurs sous-tendant le contrôle postural. L’appréhension de ces mécanismes s’est articulée autour de deux types d’approches : l’une indirecte, au travers de l’étude des mécanismes sensoriels sous-tendant la perception de la verticale, et l’autre directe, au travers d’analyses posturographiques approfondies.Le premier objectif de travail visait à déterminer comment le déficit somesthésique affecte l’utilisation des cadres de référence spatiale (allocentré, égocentré et géocentré) pour la perception de la verticale visuelle. Pour ce faire, nous avons conduit deux études évaluant respectivement la perception de la verticale avec ou sans indices visuels (test de la baguette et du cadre, RFT ; test de verticale visuelle subjective, VVS). Ces deux études ont montré que le déficit somesthésique diminuait la contribution du référentiel égocentré (axe corporel) à la perception de la verticale. En réponse, les patients présentent une plus grande dépendance au champ visuel et s’appuient donc préférentiellement sur le référentiel allocentré. Le second axe de travail visait à identifier les stratégies sensorielles adoptées par ces patients, et à évaluer les répercussions de celles-ci sur les mécanismes de régulation posturale. Ces questions ont été investiguées au moyen d’évaluations posturographiques approfondies, utilisant à la fois des paradigmes de perturbation sensorielle et de double tâche, ainsi que des analyses linéaires et non-linéaires. Nous avons ainsi observé que le déficit somesthésique des patients altérait la contribution de la proprioception musculaire aux mécanismes en charge de la régulation automatique de l’équilibre postural. Ces modifications dans la régulation posturale se répercutent par une augmentation du monitoring actif des oscillations posturales par le système nerveux central. En retour, les patients SEDh développent une visuodépendance, et mettent en place des stratégies adaptatives basées sur une rigidification des mécanismes correctifs à long terme. Enfin, deux études pilotes ont été conduites afin de tester l’effet de stratégies de remédiation proprioceptive, à savoir les orthèses somesthésiques et la reprogrammation sensorimotrice, sur le contrôle postural de ces patients. Chacune de ces prises en charge semble exercer un effet bénéfique sur leur contrôle postural, qui se traduit par une augmentation de la stabilité posturale lors du port des orthèses somesthésiques, et une amélioration de l’efficacité du contrôle postural suite à la reprogrammation sensorimotrice. Néanmoins, les résultats indiquent également que l’effet immédiat opéré par les dispositifs orthétiques de suppléance somesthésique est limité puisqu’il ne permet pas de diminuer la visuodépendance des patients. Cet effet est, en revanche, induit par l’action de la reprogrammation sensorimotrice, qui, par le renforcement du système proprioceptif, libère les patients SEDh de leur visuodépendance. Ainsi, ces observations nous ont permis de caractériser les spécificités de la régulation posturale chez les patients SEDh, et, de façon préliminaire, d’observer la façon dont celles-ci évoluent en réponse à des prises en charge spécifiquement orientées sur la remédiation sensorielle. / Ehlers-Danlos syndrome (EDS) is the clinical manifestation of hereditary connective tissue disorders, comprising several clinical forms. The EDS hypermobility type (EDSh) is characterized by generalized joint hypermobility and variable skin hyperextensibility, which both generate somatosensory impairment. Somatosensory system is, together with visual and vestibular systems, crucially involved in sensorimotor system functioning. The aim of this work was to understand the impact of impaired proprioception on perceptive and sensorimotor mechanisms underlying postural control in EDSh patients. Evaluation of postural control was structured around two approaches. The first one was indirect, and evaluated the sensory mechanism underlying vertical perception. The second one was direct, and used detailed stabilometric analyses to investigate postural control.The first objective of this work was to evaluate how somatosensory impairment affects the contribution of spatial frame of reference (allocentric, egocentric, and geocentric) to visual vertical perception. Two types of tests were conducted to assess the vertical perception with and without visual information (Rod and Frame Test, RFT; Subjective visual vertical, SVV). These two studies showed that somatosensory impairment reduces the contribution of egocentric frame of reference (body axis) to vertical perception. In response, patients increase their visual field dependence, and thus, use preferentially allocentric frame of reference. The second axis aimed to identify sensory strategies adopted by these patients and their repercussion on postural regulation mechanisms. To investigate this question, a thorough postural assessment was conducted, using sensory perturbation and dual-task paradigm, and linear and non-linear analyses. We observed that somatosensory impairment impacts muscular proprioceptive contribution to automatic regulation mechanism involved in postural control. These modifications in postural regulation induce an increase of active monitoring of postural sway. In response, EDSh patients develop a visual dependence, and produce adaptive strategies based on stiffening of corrective mechanisms acting in long term. Finally, two pilot studies were conducted to test the impact of proprioceptive remediation, somatosensory orthoses and sensorimotor rehabilitation program, on postural control of these patients. Both of these two therapeutic solutions seem to induce a beneficial effect on postural control. This effect is reflected by an improvement of postural stability when patients wore somatosensory orthoses, and an enhancement of postural efficiency in response to sensorimotor rehabilitation. However, results also indicate that the immediate effect induced by orthotic device of somatosensory substitution is limited, because it did not help to decrease visual dependency. Hence, these observations allowed us to identify the postural regulation specificities in EDSh patients, and, in a preliminary way, to observe how they change in response to therapeutic solutions based on sensory remediation.