The focus of my PhD was into the mechanisms of visual categorization. Mre specifically, we investigated how physical features (such as amplitude spectrum and spatial frequency) and top-down processes (the categorization task that the participants perform) interact and modulate the visual ERPs. We found ERP correlates of categorical representation for animal and inanimate object categories, as well as early, task- related top-down modulation of the visual ERPs. These results indicate that top-down factors can modulate visual processing both at the level of lower-level physical features and at the level of category representations. The results are discussed in terms of shape- and/or category-selective representations and brain areas in the ventral visual pathway, and they are interpreted within the framework of flexible evidence accumulation processes.