Learning "What" and "Where": An Interpretable Neural Encoding Model

Haibao Wang, Lijie Huang, Changde Du, Huiguang He

Abstract: Neural encoding modeling aims to reveal how brain processes perceived information by establishing a quantitative relationship between stimuli and evoked brain activities. In the field of visual neuroscience, many studies have been dedicated to building the neural encoding model for primary visual cortex and demonstrate that the population receptive field (pRF) models can be used to explain how neurons in primary visual cortex work. However, these models rely on either the inflexible prior assumptions imposed on the spatial characteristics of pRF or the clumsy parameter estimation methods which requiring too much manual adjustment. Suffering from these issues, current methods yield dissatisfactory performance on mimicking brain activity. In this paper, we address the problems under a novel "what and where" neural encoding framework. Basing on deep neural network (DNN) and the separability of the spatial ("where") and visual feature ("what") dimensions, the proposed method is not only powerful in extracting nonlinear features from images, but also rich in interpretability. Owing to two forms of regularization: sparsity and smoothness, receptive fields are estimated automatically for each voxel without prior assumptions on shape, which gets rid of the shortcomings of previous methods. Extensive empirical evaluations on publicly available fMRI dataset show that the proposed method has superior performance gains over several existing methods.