Generative statistical models of chord sequences play crucial roles in music processing. To capture syntactic similarities among certain chords (e.g. in C major key, between G and G7 and between F and Dm), we study hidden Markov models and probabilistic context-free grammar models with latent variables describing syntactic categories of chord symbols and their unsupervised learning techniques for inducing the latent grammar from data. Surprisingly, we find that these models often outperform conventional Markov models in predictive power, and the self-emergent categories often correspond to traditional harmonic functions. This implies the need for chord categories in harmony models from the informatics perspective.
Unsupervised learning has also been applied to adapt statistical language models for particular data. For NLP, there exist corpora of syntactic trees that are based on widely accepted linguistic theories (e.g. @cite_27 ), from which production probabilities can be obtained by supervised learning. On the other hand, studies have shown that extending the standard annotation symbols (e.g. NP) to incorporate context dependence and subcategories of words, often called symbol refinement, improves the accuracy of parsing @cite_12 . Unsupervised learning of variants of PCFG models has been successfully applied to find optimal refinement of nonterminal symbols from data @cite_23 .
@cite_27 @cite_23 @cite_12
2069699492 2129882630 2142523187 2953291403
This paper investigates supervised and unsupervised adaptation of stochastic grammars, including n-gram language models and probabilistic context-free grammars (PCFGs), to a new domain. It is shown that the commonly used approaches of count merging and model interpolation are special cases of a more general maximum a posteriori (MAP) framework, which additionally allows for alternate adaptation approaches. This paper investigates the effectiveness of different adaptation strategies, and, in particular, focuses on the need for supervision in the adaptation process. We show that n-gram models as well as PCFGs benefit from either supervised or unsupervised MAP adaptation in various tasks. For n-gram models, we compare the benefit from supervised adaptation with that of unsupervised adaptation on a speech recognition task with an adaptation sample of limited size (about 17h), and show that unsupervised adaptation can obtain 51 of the 7.7 adaptation gain obtained by supervised adaptation. We also investigate the benefit of using multiple word hypotheses (in the form of a word lattice) for unsupervised adaptation on a speech recognition task for which there was a much larger adaptation sample available. The use of word lattices for adaptation required the derivation of a generalization of the well-known Good-Turing estimate. Using this generalization, we derive a method that uses Monte Carlo sampling for building Katz backoff models. The adaptation results show that, for adaptation samples of limited size (several tens of hours), unsupervised adaptation on lattices gives a performance gain over using transcripts. The experimental results also show that with a very large adaptation sample (1050h), the benefit from transcript-based adaptation matches that of lattice-based adaptation. Finally, we show that PCFG domain adaptation using the MAP framework provides similar gains in F-measure accuracy on a parsing task as was seen in ASR accuracy improvements with n-gram adaptation. Experimental results show that unsupervised adaptation provides 37 of the 10.35 gain obtained by supervised adaptation. We present a generative distributional model for the unsupervised induction of natural language syntax which explicitly models constituent yields and contexts. Parameter search with EM produces higher quality analyses than previously exhibited by unsupervised systems, giving the best published un-supervised parsing results on the ATIS corpus. Experiments on Penn treebank sentences of comparable length show an even higher F1 of 71 on non-trivial brackets. We compare distributionally induced and actual part-of-speech tags as input data, and examine extensions to the basic model. We discuss errors made by the system, compare the system to previous models, and discuss upper bounds, lower bounds, and stability for this task. We describe a novel approach for inducing unsupervised part-of-speech taggers for languages that have no labeled training data, but have translated text in a resource-rich language. Our method does not assume any knowledge about the target language (in particular no tagging dictionary is assumed), making it applicable to a wide array of resource-poor languages. We use graph-based label propagation for cross-lingual knowledge transfer and use the projected labels as features in an unsupervised model (Berg-, 2010). Across eight European languages, our approach results in an average absolute improvement of 10.4 over a state-of-the-art baseline, and 16.7 over vanilla hidden Markov models induced with the Expectation Maximization algorithm. Unsupervised representation learning algorithms such as word2vec and ELMo improve the accuracy of many supervised NLP models, mainly because they can take advantage of large amounts of unlabeled text. However, the supervised models only learn from task-specific labeled data during the main training phase. We therefore propose Cross-View Training (CVT), a semi-supervised learning algorithm that improves the representations of a Bi-LSTM sentence encoder using a mix of labeled and unlabeled data. On labeled examples, standard supervised learning is used. On unlabeled examples, CVT teaches auxiliary prediction modules that see restricted views of the input (e.g., only part of a sentence) to match the predictions of the full model seeing the whole input. Since the auxiliary modules and the full model share intermediate representations, this in turn improves the full model. Moreover, we show that CVT is particularly effective when combined with multi-task learning. We evaluate CVT on five sequence tagging tasks, machine translation, and dependency parsing, achieving state-of-the-art results.