No description available.

No description available.

Any image can be described in terms of its statistics (i.e. quantitative parameters calculated from the image, for example RMS-contrast, the skewness of image brightness distribution, and slope constant of an average amplitude spectrum). It was previously shown that insect and vertebrate visual systems are optimised to the statistics common among natural scenes. However, the exact mechanisms of this process are still unclear and need further investigation. This thesis presents the results of examining links between some image statistics and visual responses in humans and hoverflies. It was found that while image statistics do not play the main role when hoverflies (Eristalis tenax and Episyrphus balteatus) chose what flowers to feed on, there is a link between hoverfly (Episyrphus balteatus) active behaviours and image statistics. There is a significant difference in the slope constant of the average amplitude spectrum, RMS contrast and skewness of brightness distribution between photos of areas where hoverflies were hovering or flying. These photos were also used to create a prediction model of hoverfly behaviour. After model validation, it was concluded that photos of both the ground and the surround should be used for best prediction of behaviour. The best predictor was skewness of image brightness distribution. By using a trackball setup, the optomotor response in walking hoverflies (Eristalis tenax) was found to be influenced by the slope constant of an average amplitude spectrum.  Intracellular recording showed that the higher-order neuron cSIFE (The centrifugal stationary inhibited flicker excited) in the hoverfly (Eristalis tenax) lobula plate was inhibited by a range of natural scenes and that this inhibition was strongest in a response to visual stimuli with the slope constant of an average amplitude spectrum of 1, which is the typical value for natural environments.  Based on the results of psychophysics study in human subjects it was found that sleep deprivation affects human perception of naturalistic slope constants differently for different image categories (“food” and “real world scenes”). These results help provide a better understanding of the link between visual processes and the spatial statistics of natural scenes.

Il est connu que le cannabis, par son action sur le système endocannabinoïde, affecte de multiples paramètres de la vision. Les fonctions de GPR55, un récepteur associé au système endocannabinoïde, ont moins été étudiées que celles des récepteurs cannabinoïdes les plus importants, CB1 et CB2. Nous savons cependant que GPR55 est présent dans la rétine de la souris et qu’il module la croissance et le guidage axonal des cellules ganglionnaires rétiniennes durant le développement. Le but de cette étude est d’étudier les effets de GPR55 sur la vision en utilisant un modèle de souris avec une délétion du gène Gpr55. Des électrorétinographies (ERG) plein champ scotopique et photopique ont été effectuées dans le but d’étudier le rôle du récepteur sur les fonctions rétiniennes. Nous avons trouvé que les souris Gpr55-/- ont, en ERG scotopique, une amplitude réduite de l’onde-b et des potentiels oscillatoires qui ont aussi une latence plus longue. Chez ces animaux, l’onde-a photopique a aussi une amplitude plus basse. Par la suite, pour vérifier les conséquences des déficits de fonction rétinienne sur les fonctions visuelles, le modèle de réflexe optomoteur a été utilisé sur des souris knock-out ou avec des injections systémiques d’un antagoniste et d’un agoniste de GPR55. L’absence de GPR55 retarde le développement de l’acuité visuelle, mais la délétion de Gpr55 ou l’action pharmacologique sur le récepteur ne change pas l’acuité visuelle chez les adultes. La délétion de Gpr55 et l’administration d’un antagoniste du récepteur diminuent la sensibilité au contraste. Ces observations suggèrent que GPR55 peut modifier l'activité des cônes, des cellules bipolaires et des cellules de la rétine interne avec des conséquences comportementales. / The observations on how cannabis affects multiple properties of vision have fostered the interest in the study of the functions of cannabinoid receptors CB1 and CB2 in the visual system. However, other non-classical cannabinoid receptors are thought to be involved in mediating the actions of cannabinoid ligands in the eye. One of these candidate receptors is GPR55, a receptor that modulates the growth and axonal guidance of retinal ganglion cells during development in mice. The purpose of this study was to investigate the effects of the deletion of the Gpr55 gene and the pharmacological modulation of GPR55 on retinal function and visual behavior. Full-field scotopic and photopic electroretinography (ERG) were used to functionally assess the state of the retina. Recordings obtained from Gpr55-/- mice revealed a diminution of the scotopic b-wave and the photopic a-wave responses. These animals also had reduced and delayed oscillatory potentials. The optomotor reflex method was used to evaluate the consequences of Gpr55 deletion on visual acuity and contrast sensitivity. The absence of GPR55 delayed the developmental trajectory of visual acuity in Gpr55 knockout mice without affecting the maximum visual acuity reached in adulthood. Pharmacological manipulation of GPR55 in adult wild-type mice did not alter visual acuity. Both the deletion of Gpr55 and the administration of a receptor antagonist decreased contrast sensitivity while an agonist of GPR55 increased contrast sensitivity. These observations suggest that GPR55 can modify the activity of cones, bipolar cells, and cells in the inner retina with behavioral consequences.