Learning to Shift the Polarity of Words for Sentiment Classification Daisuke Ikeda author Hiroya Takamura author Lev-Arie Ratinov author Manabu Okumura author 2008 text Proceedings of the Third International Joint Conference on Natural Language Processing: Volume-I conference publication ikeda-etal-2008-learning https://aclanthology.org/I08-1039/ 2008