Contextually Guided Convolutional Neural Networks for Learning Most Transferable Representations
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Deep Convolutional Neural Networks (CNNs), trained extensively on very large labeled datasets, learn to recognize inferentially powerful features in their input patterns and represent efficiently their objective content. Such objectivity of their internal representations enables deep CNNs to readily transfer and successfully apply these representations to new classification tasks. Deep CNNs develop their internal representations through a challenging process of error backpropagation-based supervised training. In contrast, deep neural networks of the cerebral cortex develop their even more powerful internal representations in an unsupervised process, apparently guided at a local level by contextual information. Implementing such local contextual guidance principles in a single-layer CNN architecture, we propose an efficient algorithm for developing broad-purpose representations (i.e., representations transferable to new tasks without additional training) in shallow CNNs trained on limited-size datasets. A contextually guided CNN (CG-CNN) is trained on groups of neighboring image patches picked at random image locations in the dataset. Such neighboring patches are likely to have a common context and therefore are treated for the purposes of training as belonging to the same class. Across multiple iterations of such training on different context-sharing groups of image patches, CNN features that are optimized in one iteration are then transferred to the next iteration for further optimization, etc. In this process, CNN features acquire higher pluripotency, or inferential utility for any arbitrary classification task, which we quantify as a transfer utility. In our application to natural images, we find that CG-CNN features show the same, if not higher, transfer utility and classification accuracy as comparable transferable features in the first CNN layer of the well-known deep networks.
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