Integration processes of oculomotor memory in the normal and pathological brain

Vision is an extremely important sense, and the eye movements that allow us to make use of it involve neural pathways across most major areas of our brain. The wide distribution of these pathways has made the study of eye movements a valuable window into the inner workings of our brains. In this thesis, we investigate the eye movements of healthy and pathological participants, first to validate and challenge a current theoretical and computational model of these movements, then to further our understanding of complex disorders that can affect the brain. In particular, we first investigate model-driven predictions by presenting participants with noisy visual information, in the form of a moving target having a Gaussian distribution of luminosity, and with variable levels of prior information about target motion. Through this, we validate a prediction of our reference model by showing reliability-weighted integration of visual and memory inputs in the control of eye movements. Then, we expand our investigation to pathological participants presenting one of two disorders thought to compromise brain areas involved in this process: either a developmental disorder that affects visual processing, amblyopia, or a degenerative disorder affecting the control of behavior and speech, fronto-temporal dementia. Using healthy participants as a reference, we discuss their performance in eye-movements tasks, highlight specific deficits, then draw parallels with the brain areas involved and our reference model.(FSA - Sciences de l'ingénieur) -- UCL, 201

Frontotemporal dementia patients exhibit deficits in predictive saccades.

Prediction and time estimation are all but required for motor function in everyday life. In the context of eye movements, for instance, they allow predictive saccades and eye re-acceleration in anticipation of a target re-appearance. While the neural pathways involved are not fully understood, it is known that the frontal lobe plays an important role. As such, neurological disorders that affect it, such as frontotemporal (FTD) dementia, are likely to induce deficits in such movements. In this work, we study the performances of frontotemporal dementia patients in an oculomotor task designed to elicit predictive saccades at different rates, and compare them to young and older adults. Clear deficits in the production of predictive saccades were found in patients, in particular when the time between saccades was short (~500 ms). Furthermore, one asymptomatic C9ORF72 mutation bearer showed patterns of oculomotor behavior similar to FTD patients. He exhibited FTD symptoms within 3 years post-measure, suggesting that an impairment of oculomotor function could be an early clinical sign. Taken together, these results argue in favor of a role of the frontal lobe in predictive movements timing over short timescales, and suggest that predictive saccades in FTD patients warrant further investigation to fully assess their potential as a diagnostic aid

Integration of past and current visual information during eye movements in amblyopia

Combination of signals based on their reliability is an increasingly popular model for sensorimotor processing. However, how reliability is estimated, or how such estimation is affected by prolonged exposure to noisy inputs, is still unknown. In this study, we compare patients with unilateral functional amblyopia with control subjects tracking either a reliable target, or a blurry, unreliable target, in a task of repeated, sustained smooth pursuit. We provide evidence for a lower weight of visual information during smooth pursuit in amblyopic and control subjects tracking a blurry target, with no significant difference of prior information weight. In contrast, we found no evidence of lower visual information weight in the catch-up saccades of amblyopic subjects. We conclude that oculomotor performance in unilateral amblyopia mostly lays within the continuum between our control groups, without significant differences in the relative weights of prior and visual information. However, smooth pursuit exhibits additional deficits that might result from abnormal visual development