Enhancing a Lexicon of Polarity Shifters through the Supervised Classification of Shifting Directions

Abstract

The sentiment polarity of an expression (whether it is perceived as positive, negative or neutral) can be influenced by a number of phenomena, foremost among them negation. Apart from closed-class negation words like ``no'', ``not'' or ``without'', negation can also be caused by so-called polarity shifters. These are content words, such as verbs, nouns or adjectives, that shift polarities in their opposite direction, e.g. ``abandoned'' in ``abandoned hope'' or ``alleviate'' in ``alleviate pain''. Many polarity shifters can affect both positive and negative polar expressions, shifting them towards the opposing polarity. However, other shifters are restricted to a single shifting direction. ``Recoup'' shifts negative to positive in ``recoup your losses'', but does not affect the positive polarity of ``fortune'' in ``recoup a fortune''. Existing polarity shifter lexica only specify whether a word can, in general, cause shifting, but they do not specify when this is limited to one shifting direction. To address this issue we introduce a supervised classifier that determines the shifting direction of shifters. This classifier uses both resource-driven features, such as WordNet relations, and data-driven features like in-context polarity conflicts. Using this classifier we enhance the largest available polarity shifter lexicon.

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