Neuron sparseness versus connection sparseness in deep neural network for large vocabulary speech recognition

Exploiting sparseness in deep neural networks is an important method for reducing the computational cost. In this paper, we study neuron sparseness in deep neural networks for acoustic modeling. For the feed-forward stage, we only activate neurons whose input values are larger than a given threshold, and set the outputs of inactive nodes to zero. Thus, only a few nonzero outputs are fed to the next layer. Using this method, the output vector of each hidden layer becomes very sparse, so that the computational cost of the feed-forward algorithm can be reduced by adopting sparse matrix operations. The proposed method is evaluated in both small and large vocabulary speech recognition tasks, and results demonstrate that we can reduce the nonzero outputs to fewer than 20% of the total number of hidden nodes, without sacrificing speech recognition performance.