Progress in Neural Network Based Statistical Language Modeling

Abstract

Statistical Language Modeling (LM) is one of the central steps in many Natural Language Processing (NLP) tasks including Automatic Speech recognition (ASR), Statistical Machine Translation (SMT) , Sentence completion, Automatic Text Generation to name a few. Good Quality Language Model has been one of the key success factors for many commercial NLP applications. Since past three decades diverse research communities like psychology, neuroscience, data compression, machine translation, speech recognition, linguistics etc, have advanced research in the field of Language Modeling. First we understand the mathematical background of LM problem. Further we review various Neural Network based LM techniques in the order they were developed. We also review recent developments in Recurrent Neural Network (RNN) Based Language Models. Early LM research in ASR gave rise to commercially successful class of LMs called as N-gram LMs. These class of models were purely statistical based and lacked in utilising the linguistic information present in the text itself. With the advancement in the computing power, availability of humongous and rich sources of textual data Neural Network based LM paved their way into the arena. These techniques proved significant, since they mapped word tokens into a continuous space than treating them as discrete. As NNLM performance was proved to be comparable to existing state of the art N-gram LMs researchers also successfully used Deep Neural Network to LM. Researchers soon realised that the inherent sequential nature of textual input make LM problem a good Candidate for use of Recurrent Neural Network (RNN) architecture. Today RNN is the choice of Neural Architecture to solve LM by most practitioners. This chapter sheds light on variants of Neural Network Based LMs.