Thanks to functional magnetic resonance imaging (fMRI), it is possible to identify low-level cortical visual areas in vivo, on the basis of their retinotopy property. Retinotopic mapping is an essential preliminary to interpret results of many studies on visual processing. It is thus important to make sure it is robust. We have obtained retinotopic maps from acquisitions on a 3T scanner, and measured the increase of the functional signals variance induced by the use of a high magnetic eld. Our results confirm that this increase is not solely due to the increasing contribution of physiological noise, but also to an improvement of the variance related to visual stimuli. The main drawback of the EPI acquisition sequence we are using is its sensitivity to magnetic fi eld inhomogeneities, which induces geometric distortions in the images. Our analyses reveal that the distortions correction method we are using avoids signi cant cortical misallocations of the functional activations and contributes to the robustness of studies in low level visual areas. On the basis of retinotopic maps, we have set up a new representation frame for individual data, for group studies purpose. This frame allows to overcome the important functional intersubject variability of low-level visual areas, and to visualize group studies results in a uni ed coordinate system. We have estimated the robustness of this approach and we have applied it on two studies about local and global visual information processing.
