The modularity of visual working memory revisited
How does the human brain support visual working memory (WM)? Which processes occur in parallel, and which are serial? We addressed these questions with a series of behavioural and functional imaging studies. Using a dual task paradigm we showed that the manipulation of spatial and colour information can be performed in parallel. Functional magnetic resonance imaging (fMRI) revealed that information-specific modules in dorsal premotor and ventrolateral prefrontal cortex support these processes. How the activity of these modules is integrated for dual task processing is subject of ongoing research. Serial processing seems to govern the sequence of encoding, maintenance/manipulation and retrieval in classical working memory paradigms. A finer-grained temporal analysis of the processes during memory retrieval was possible through a combination of fMRI with event-related potentials. We finally sought to disentangle the relationship between memory and attentional processes at the encoding stage. We designed a paradigm with orthogonal manipulation of attentional and memory demand and showed that WM encoding is limited by an attentional bottleneck localized in visual and left precentral regions. These results suggest that the interplay between the visual brain and the frontal lobes represents a key neural locus of the attention-based constraints of our mental representation of the visual world.