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L'étude de la lecture s'intéresse, entre autres, aux facteurs déterminant la visibilité de lettres et les mouvements oculaires. Néanmoins, l'approche de ces mécanismes reste différente selon qu'elle concerne la vision centrale ou périphérique. Cette thèse proposait, au contraire, une approche conjointe dans le but (1) de mettre en évidence les effets des facteurs visuels limitant la reconnaissance de mots, (2) de mieux comprendre le comportement oculomoteur lors de la lecture en vision centrale et (3) d'étudier le rôle des facteurs oculomoteurs spécifiques à la lecture en vision périphérique. Trois expériences ont été menées. La première axée sur l'étude des facteurs visuels, a mis en évidence que l'effet OVP était moins important pour des mots présentés dans le champ visuel inférieur. Ce résultat pouvant s'expliquer par la géométrie de l'acuité visuelle et de l'encombrement, suggère que la lecture en périphérie est limitée par les mêmes facteurs qu'en vision centrale. La deuxième étude, concernant la stabilité de fixation durant la lecture en présence d'un scotome artificiel, a révélé que la vitesse de lecture pouvait être améliorée en présence d'une stimulation fovéale stable. Enfin, nous avons montré que les mouvements oculaires variaient selon la taille des lettres, et ce, différemment selon la position du regard par rapport au centre des mots. Ce résultat, nouveau, est vraisemblablement attribuable à l'effet de processus visuomoteurs précoces. En conclusion, l'étude conjointe de la lecture en vision centrale et périphérique est prometteuse, non seulement d'un point de vue fondamental, mais aussi pour l'aide aux patients atteints de DMLA. / Reading is a large research field, which investigates for a great part the variables influencing letter visibility and eye movements. However, its study in central and peripheral vision has been conducted in parallel and with different approaches. Our work relied, on the contrary, on a joint approach in order (1) to uncover the visual factors limiting word recognition, (2) to better determine how the eyes move during reading in central vision, and (3) to study the role of oculomotor factors that might affect reading in peripheral vision. Three experiments were conducted. The first study focused on the role of visual factors in word identification. It showed that the OVP effect is reduced for words displayed in the lower visual field. This result, which can be explained by the geometry of visual acuity andl crowding, suggests that reading in peripheral vision is limited by the same visual factors as in central vision. Then we investigated the influence of fixation stability on sentence reading using an artificial scotoma. It revealed that reading speed could be improved with a stable foveal stimulation. The third experiment re-examined the possible influence of character size on eye movements in central vision. It revealed that eye movements varied depending on letter size, and differently as a function of the location of the eye relative to the center of words. This novel finding was very likely the effect of early visuomotor processes. In conclusion, the joint study of reading in central and peripheral vision is promising, not only at a fundamental level, but also for a better understanding of retinal visual deficits, such as AMD.

Deafferented cortical visual areas exhibit topographical plasticity such that their constituent neural populations adapt to the loss of sensory input through the expansion and eventual remapping of receptive fields to new regions of space. Such representational plasticity is most compelling in the long-term (months or years) but begins within seconds of retinal deafferentation (short-term plasticity). The neural mechanism proposed to underlie topographical plasticity is one of disinhibition whereby long-range horizontal inputs are "unmasked" by a reduction in local inhibitory drive. In this dissertation, four experiments investigated the neural mechanisms of short-term visual plasticity and disinhibition in humans using a combination of psychophysics and event-related potentials (ERPs). Short-term visual plasticity was induced using a stimulus-induced analog of retinal deafferentation known as an artifical scotoma. Artificial scotomas provide a useful paradigm for the study of short-term plasticity as they induce disinhibition but are temporary and reversible. Experiment 1 measured contrast response functions from within the boundaries of an artificial scotoma and evaluated them relative to a sham control condition. Changes in the contrast response function suggest that disinhibition can be conceived of in terms of two dependent but separable processes: receptive field expansion and unrestricted neural gain. A two-process model of disinhibition is proposed. A complementary ERP study (Experiment 2) recorded visual evoked potentials elicited by probes appearing within the boundaries of an artificial scotoma. Results revealed a neural correlate of disinhibition consistent with origins in striate and extrastriate visual areas. Experiment 3 and 4 were exploratory examinations of the representation of space surrounding an artificial scotoma and revealed a neural correlate of invading activity from normal cortex. Together, the results of these four studies strengthen the understanding of the neural mechanisms that underlie short-term plasticity and provide a conceptual framework for their evaluation.