Research on visual sensory function combines behavioral measures and electrophysiology in humans as a meaningful approach to identify alterations of the sensory pathways in neurological disorders. However, transiently elicited visual evoked responses are not very reliable measures. Hundreds of repetitions are required to achieve a proper signal-to-noise ratio. Furthermore, sensory evoked responses often interfere with electrophysiological signatures of higher-level function. In some clinical populations, such as Parkinson's disease, electrical background activity is increased and sensory responses might appear embedded in broadband noise.

In this thesis, we developed a new visual stimulation principle that allows robust measurement of visual responses in non-invasive human EEG, by exploiting aspects of the anatomy of the primary visual area. After a first study describing the basic principle and verifying its ability to improve reliability, this principle was applied in a second study to estimate electrophysiological and perceptual signatures of visual contextual interactions in humans (i.e., visual surround suppression phenomenon), and to quantify temporal profiles linked to the spatial aspects of this phenomenon. In a third study, we examined such visual contextual interactions in patients with Parkinson's disease (PD), a neurological disorder in which perceptual deficits and delayed visual sensory responses have been previously identified. We found a profile of higher suppression by stimulus context, steeper adaptation of visual responses over time, and an abnormally greater background noise level in PD subjects. These findings extend our understanding of previously reported visual function abnormalities in Parkinson's disease. Last, we designed a visual paradigm that allows to simultaneously track electrophysiological responses of each cortical processing stage (i.e., sensory, integration and motor preparation) in a continuous monitoring task, in order to examine the link between sensory signals that feed further stages of cortical integration up to the motor level in PD.

Paradigm design for the assessment of visual abnormalities and sensory to motor transformation processes must be thoughtfully made. The paradigms developed in this thesis have proved to elicit robust visual responses, and can be successfully applied in healthy and neurologically impaired populations, providing innovative tools for basic research and clinical neuroscience.