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Population receptive field (pRF) mapping based on functional magnetic resonance imaging (fMRI) is an ideal method for obtaining detailed retinotopic information. One particularly promising application of pRF mapping is the estimation and quantification of visual field effects, for example scotomata in patients suffering from macular dysfunction or degeneration (MD) or hemianopic defects in patients with intracranial dysfunction. However, pRF mapping performance is influenced by a number of factors including spatial and temporal resolution, distribution of dural venous sinuses and patient performance. This study addresses the ability of current pRF methodology to assess the size of simulated scotomata in healthy individuals. The data demonstrate that central scotomata down to a radius of 2.35° (4.7° diameter) visual angle can be reliably estimated in single subjects using high spatial resolution protocols and multi-channel receive array coils.

Population receptive field (pRF) mapping based on functional magnetic resonance imaging (fMRI) is an ideal method for obtaining detailed retinotopic information. One particularly promising application of pRF mapping is the estimation and quantification of visual field effects, for example scotomata in patients suffering from macular dysfunction or degeneration (MD) or hemianopic defects in patients with intracranial dysfunction. However, pRF mapping performance is influenced by a number of factors including spatial and temporal resolution, distribution of dural venous sinuses and patient performance. This study addresses the ability of current pRF methodology to assess the size of simulated scotomata in healthy individuals. The data demonstrate that central scotomata down to a radius of 2.35° (4.7° diameter) visual angle can be reliably estimated in single subjects using high spatial resolution protocols and multi-channel receive array coils.

Functional MRI enables the acquisition of a retinotopic map that relates regions of the visual field to neural populations in the visual cortex. During such a "population receptive field" (PRF) experiment, stable gaze fixation is of utmost importance in order to correctly link the presented stimulus patterns to stimulated retinal regions and the resulting Blood Oxygen Level Dependent (BOLD) response of the appropriate region within the visual cortex. A method is described that compensates for unstable gaze fixation by recording gaze position via an eyetracker and subsequently modifies the input stimulus underlying the PRF analysis according to the eyetracking measures. Here we show that PRF maps greatly improve when the method is applied to data acquired with either saccadic or smooth eye movements. We conclude that the technique presented herein is useful for studies involving subjects with unstable gaze fixation, particularly elderly patient populations.

There seems to be a tendency within the education of neuroscience and cognitive psychology to give little attention to what is not well understood. One subject that tends to get left out of education for this reason is the concept of consciousness. There have been, however, a number of studies that tried to address the question of how brain processes are related to consciousness. The main question of this thesis therefore is: what are, according to contemporary views, the cognitive and neuronal processes that are needed for, or correlated with conscious experience? Through high level cognitive theories a scientific understanding of consciousness was arrived. Based on this, lower level neural theories where developed, focusing on how neurons interact with each other, and which neurons/areas interact with each other during conscious and unconscious processing. Three important theories will be discussed to illustrate this. First, the global workspace hypothesis will be discussed which is a cognitive theory. It was developed to, for the first time after behaviourism, address questions on consciousness scientifically. It states that different forms of information are usually autonomously and unconsciously processed in different brain areas. Consciousness is however derived when brain areas share their output to a global ‘workspace’ onto which different areas are connected such as for instance memory, language and association areas. Second, the 40 Hz theory is discussed which was based on the same notions as the global workspace theory but which takes a neural point of view, and focuses on how remote brain areas communicate to form a unified conscious percept. It states that neurons in different brain areas that are involved in conscious percept, fire in synchronized oscillations in order to bind their information processing. Finally, the recurrent processing theory is considered which is also a neural theory of consciousness that is to some extend based on the notions of