Unsupervised Feature Learning Improves Prediction of Human Brain Activity in Response to Natural Images

Encoding and decoding in functional magnetic resonance imaging has recently emerged as an area of research to noninvasively characterize the relationship between stimulus features and human brain activity. To overcome the challenge of formalizing what stimulus features should modulate single voxel responses, we introduce a general approach for making directly testable predictions of single voxel responses to statistically adapted representations of ecologically valid stimuli. These representations are learned from unlabeled data without supervision. Our approach is validated using a parsimonious computational model of (i) how early visual cortical representations are adapted to statistical regularities in natural images and (ii) how populations of these representations are pooled by single voxels. This computational model is used to predict single voxel responses to natural images and identify natural images from stimulus-evoked multiple voxel responses. We show that statistically adapted low-level sparse and invariant representations of natural images better span the space of early visual cortical representations and can be more effectively exploited in stimulus identification than hand-designed Gabor wavelets. Our results demonstrate the potential of our approach to better probe unknown cortical representations.Author Summary: An important but difficult problem in contemporary cognitive neuroscience is to find what stimulus features best drive responses in the human brain. The conventional approach to solve this problem is to use descriptive encoding models that predict responses to stimulus features that are known a priori. In this study, we introduce an alternative to this approach that is independent of a priori knowledge. Instead, we use a normative encoding model that predicts responses to stimulus features that are learned from unlabeled data. We show that this normative encoding model learns sparse, topographic and invariant stimulus features from tens of thousands of grayscale natural image patches without supervision, and reproduces the population behavior of simple and complex cells. We find that these stimulus features significantly better drive blood-oxygen-level dependent hemodynamic responses in early visual areas than Gabor wavelets–the fundamental building blocks of the conventional approach. Our approach will improve our understanding of how sensory information is represented beyond early visual areas since it can theoretically find what stimulus features best drive responses in other sensory areas.