Elektrophysiologische und bildgebende Untersuchungen zum Einfluss visueller Aufmerksamkeit auf die Objektwahrnehmung des Menschen

Attention is essential component of visual perception. The present thesis contains experimental results of several studies investigating the influence of selective attention mechanisms on visual perception using electrophysiological and functional neuroimaging recordings in humans. Feature-based attention represents the focusing of visual perception towards a specific feature attribute (e.g. blue ) and facilitates its processing throughout the visual field. Two studies provide evidence that feature-based attention comprises two distinct mechanisms acting in a global manner. While the attribute-specific process enables the discrimination of feature attributes ( blue ) within the behaviorally relevant dimension, the dimension-specific process was shown to be likewise acting in a global way enhancing the processing of non-target attributes assigned to the relevant dimension ( color ). Differences in event-related potentials (ERPs) were found both for the processing of color- and motion-defined objects. The dimension of color can further be subdivided into categories providing the categorical perception of color. The third study investigated neural correlates of categorical color perception using functional magnetic resonance imaging (fMRI). The results show a faster/more accurate discrimination of colors assigned to different categories (e.g. blue and green ) than to the same category (e.g. blue1 and blue2 ). FMRI analysis revealed correlates of color category effects in language related brain regions as well as the primary visual cortex. While performing a visual attention task, temporal expectation can be very useful in order to optimize behavior. Preliminary results of an additional study show that the stimulus structure itself can also be a critical factor. Both behavioral and ERP data were strongly influenced by different probability distributions and illustrate the impact of temporal expectation on the experimental design of a spatial-cueing task.