Recognizing complex negation on twitter

After the Great East Japan Earthquake in 2011, an abundance of false rumors were disseminated on Twitter that actually hindered rescue activities. This work presents a method for recognizing the negation of predicates on Twitter to find Japanese tweets that refute false rumors. We assume that the predicate "occur" is negated in the sentence "The guy who tweeted that a nuclear explosion occurred has watched too many SF movies." The challenge is in the treatment of such complex negation. We have to recognize a wide range of complex negation expressions such as "it is theoretically impossible that..." and "The guy who... watched too many SF movies." We tackle this problem using a combination of a supervised classifier and clusters of n-grams derived from large un-Annotated corpora. The n-gram clusters give us a gain of about 22% in F-score for complex negations.