Multi-voxel coding in frontal, parietal and visual cortices

To cope with the complex visual world around us, we can select particular aspects of visual input by directing our attention to them. This ability is fundamental, yet the mechanism remains elusive. One influential hypothesis is that frontal and parietal brain regions exert control over the visual cortices by biasing processing in favour of relevant information (Duncan and Miller, 2002). Accordingly, the overall level of activation in visual cortical areas increases with attention (e.g. Hopfinger et al., 2000). However, it remains unclear how this overall increase leads to improved performance. Recent advances in analysis techniques for fMRI have made it possible to assess attentional processing changes in greater detail, by considering what information is carried in patterns of activity across voxels. We used fMRI to record the BOLDresponse to three novel objects. Strength of codingwas assessed by calculating the discriminability of patterns for different objects. We found that when participants directed attention towards one of two objects in a visual display, the representation of the attended object was enhanced, relative to the less attended object, in both frontoparietal and visual cortices. Our results suggest that selection of visual information is mediated by enhanced multi-voxel coding of attended information.