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Call number: LD2668 .T4 1962 E92

Call number: LD2668 .T4 1955 J66 / Master of Science

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Background: A lot of previous research have studied the correlation between bilateral jumps with performance in change of direction (COD) even though COD occurs unilateral. Only a few researches have studied the relationship between COD and unilateral jumps but the results are conflicting. Neither of these have studied the correlation between COD, measured with the Zigzag agility test, and both unilateral horizontal jumps (UHJ) and unilateral lateral jumps (ULJ) among young soccer players.  Aim: The aim was to study the magnitude of the correlation between UHJ and the Zigzag agility test and between ULJ and the Zigzag agility test among young male soccer players.  Method: Thirty young male soccer players between 17-19 years were tested in a Zigzag agility test and two different jumps (UHJ and ULJ). The time of the Zigzag agility test was measured in seconds and the length of the two jumps in meters. Everything were tested during one test session. Pearson correlation coefficient was used to calculate the relationships between UHJ, ULJ and the Zigzag agility test. Following guidelines were used to determine the magnitude of the correlation: r below -0.29 for a small correlation, r= -0.30 to -0.49 for a medium correlation and r -0.50 to -1.0 for a strong correlation.    Results: Small correlation were found between UHJ and the Zigzag agility test (r= -0.028) and as well as between ULJ the Zigzag agility test (r= -0.27). The mean value (SD±) was 6.41s (0.18) for the Zigzag agility test, 1.87m (0.15) for UHJ and 1.65m (0.13) for ULJ.  Conclusion: The findings of this study showed that both UHJ and ULJ had small correlations with the Zigzag agility test as a measurement of COD performance, with a slightly higher correlation for the ULJ. This means that unilateral jumps and COD performance probably are two different skills and should be trained in different ways. Not much research has been done in this area and the results concerning the correlation between COD and unilateral jumps are still mixed. More research is needed to declare the relationship with unilateral jumps and COD performance. Interesting for the further research would also be to involve other factors such as running technique and straight sprinting to determine the importance of each factor.

How does the brain convert sensory information into abstract representations that can support complex behaviours? The rodent head-direction (HD) system, whose cell ensembles represent head direction in the horizontal plane, is a striking example of a “cognitive” representation without a direct sensory correlate. It can be updated by sensory inputs fromdifferentmodalities, yet persists in the absence of external input. Together with cells tuned for place, the HD system is thought to be fundamental for navigation and spatial information processing. However, relatively few studies have sought to characterise the connection between the HD system and spatial behaviour directly, and their overall outcome has been inconclusive. In the experiments that make up the first part of this thesis, we approach this issue by isolating the self-motion component of the HDsystem. We developed an (angular) path integration task in which we show that rats rely on their internal sense of direction to return to a trial-unique starting location, allowing us to investigate the contribution of the HD system to this behaviour without influences from uncontrolled external cues. Using this path integration task, we show that rats with bilateral lesions of the lateral mammillary nuclei (LMN) are significantly impaired compared to sham-operated controls. Lesions of the LMN, which contains HDcells, are known to abolish directional firing in downstream HD areas, suggesting that impairment on the task is due to loss of HD activity. We also recorded HD cell activity as rats are performing the path integration task, and found the HD representation to correlate with the rats’ choice of return journey. Thus, we provide both causal and correlational experimental evidence for a critical role of the HD system in path integration. For the second part of this thesis, we implemented a computational model of how the HD system is updated by head movements during path integration, providing a novel explanation for HD cells’ ability to anticipate the animal’s head direction. The model predicts that such anticipatory time intervals (ATIs) should depend on the frequency spectrum of the rats’ head movements. In direct comparison with experimental recording data, we show that the model can explain up to 80% of the experimentally observed variance, where none was explained by previous models. We also consider the effects of propagating the HD signal through multiple layers, identifying several potential sources of anticipation and lag. In summary, this thesis provides behavioural, lesion, and unit-recording evidence that during path integration, rats use a directional signal provided by the head direction system. The neural mechanisms responsible for the generation and maintenance of this signal are explored computationally. The finding that ATIs depend on the statistics of head movements has methodological implications and constrains models of the HD system.

L'objectif de cette thèse est l'estimation de la pose de la tête humaine à partir d'imagesmonoculaires. Le but est d'avoir un retour d'information de l'utilisateur sur l'orientationde son regard, et ce, de manière non-intrusive. Ce domaine de recherche est très actifcompte tenu de l'évolution des interfaces de communication entre l'homme et la machine,d'autant plus que plusieurs défis sont toujours ouverts. Notamment, la robustesse dusystème, son invariabilité à l'identité des personnes et à l'illumination ainsi que la qualitédu matériel de capture requis.L'approche que nous avons proposée est basée sur la symétrie bilatérale du visage.Nous utilisons des caractéristiques extraites de la symétrie pour estimer la pose de latête par le biais de l'apprentissage. Les caractéristiques utilisées sont géométriques maisextraites de manière globale à partir de toute la texture du visage, sans que des pointsou des contours spécifiques ne soient requis.Ces caractéristiques ont été validées expérimentalement à l'aide de bases d'images etde vidéos publiques dédiées à l'estimation de la pose de la tête. L'apprentissage superviséainsi que la régression sont utilisés pour construire des modèles de poses. Ces modèles ontété testés sur des séquences vidéo indépendantes des bases utilisées pour l'apprentissage.L'erreur d'estimation a été calculée et les résultats sont supérieurs ou équivalents à l'étatde l'art. / The aim of this thesis is to estimate the pose of a human head frommonocular images. The goal is to have a feedback from the user on the direction of hisgaze, and this is done in a non-intrusive manner. This area of research is very activegiven the evolution of the communication interfaces between a human and a machine,especially as many challenges are still there. In particular, the robustness of the system,its invariance to the identity of individuals and enlightenment.The approach we propose is based on the bilateral symmetry of the face. We usefeatures extracted from the symmetry to estimate head pose through learning. Thefeatures used are geometric but extracted holistically from the whole texture of the face,without the need for specifc points or contours.These features have been experimentally validated by means of publicly availabledatabases of images and videos dedicated to head pose estimation. Supervised learningand regression have been used to build models of poses. These models have been testedon video sequences different from the bases used for learning. The estimation error hasbeen calculated and the results are superior or equivalent to the state of the art.