Brain Activities during 3-D Structure Perception from 2-D Motion as Assessed by Combined MEG/fMRI Techniques

Recent neuroimaging studies suggest the involvement of the parieto-occipital, the intraparietal, and the ventral inferior-temporal regions in the 3-D object perception from 2-D retinal motion (3D-SFM: 3-D structure-from-motion), however, the neural dynamics underlying the 3D-SFM is not fully understood. Here, we used both the neuromagnetic (MEG) and the hemodynamic (fMRI) measurements to visualize the spatiotemporal brain dynamics during 3-D SFM. The coherence of the random-dot motion stimuli was parametrically controlled, which made us possible to infer the changes of the brain activities between the different 3-D object perception conditions. The results of the fMRI analysis were used to impose plausible constraints on the MEG inverse calculation using the 'weighted' minimum-norm approach to improve spatial resolution of the spatiotemporal activity estimates. The inferior-temporal, the parieto-occipital, and the intraparietal regions showed increased neural activity in the highly coherent motion conditions in which subjects perceived robust 3-D object structure at different latencies. The results indicate that these regions play an important role in the perception of 3-D object structure from retinal motion. These results are in agreement with the previous fMRI studies and add further insight into the temporal dynamics of the neural activities in the multiple brain regions along both the dorsal and the ventral visual processing streams during 3D-SFM.