Social-sparsity brain decoders: faster spatial sparsity
  Spatially-sparse predictors are good models for brain decoding: they give accurate predictions and their weight maps are interpretable as they focus on a small number of regions. However, the state of the art, based on total variation or graph-net, is computationally costly. Here we introduce sparsity in the local neighborhood of each voxel with social-sparsity, a structured shrinkage operator. We find that, on brain imaging classification problems, social-sparsity performs almost as well as total-variation models and better than graph-net, for a fraction of the computational cost. It also very clearly outlines predictive regions. We give details of the model and the algorithm. 
Ga\"el Varoquaux (PARIETAL, NEUROSPIN), Matthieu Kowalski (PARIETAL,   L2S), Bertrand Thirion (NEUROSPIN, PARIETAL)
stat.ML cs.CV q-bio.NC