Playing the Telephone Game: Determining the Hierarchical Structure of Perspective and Speech Expressions

Playing the Telephone Game: Determining the Hierarchical Structure of Perspective and Speech Expressions Eric Breck and Claire Cardie Department of Computer Science Cornell University Ithaca, NY 14853 USA ebreck,cardie@cs.cornell.edu Abstract News articles report on facts, events, and opin- ions with the intent of conveying the truth. However, the facts, events, and opinions appear- ing in the text are often known only second- or third-hand, and as any child who has played “telephone” knows, this relaying of facts often garbles the original message. Properly under- standing the information filtering structures that govern the interpretation of these facts, then, is critical to appropriately analyzing them. In this work, we present a learning approach that cor- rectly determines the hierarchical structure of information filtering expressions 78.30% of the time. 1 Introduction Newswire text has long been a primary target for natural language processing (NLP) techniques such as information extraction, summarization, and ques- tion answering (e.g. MUC (1998); NIS (2003); DUC (2003)). However, newswire does not offer direct access to facts, events, and opinions; rather, journalists report what they have experienced, and report on the experiences of others. That is, facts, events, and opinions are filtered by the point of view of the writer and other sources. Unfortu- nately, this filtering of information through multiple sources (and multiple points of view) complicates the natural language interpretation process because the reader (human or machine) must take into ac- count the biases introduced by this indirection. It is important for understanding both newswire and narrative text (Wiebe, 1994), therefore, to appropri- ately recognize expressions of point of view, and to associate them with their direct and indirect sources. This paper introduces two kinds of expression that can filter information. First, we define a per- spective expression to be the minimal span of text that denotes the presence of an explicit opinion, evaluation, emotion, speculation, belief, sentiment, etc.1 Private state is the general term typically used 1Note that implicit expressions of perspective, i.e. Wiebe et to refer to these mental and emotional states that cannot be directly observed or verified (Quirk et al., 1985). Further, we define the source of a perspec- tive expression to be the experiencer of that private state, that is, the person or entity whose opinion or emotion is being conveyed in the text. Second, speech expressions simply convey the words of an- other individual – and by the choice of words, the reporter filters the original source’s intent. Consider for example, the following sentences (in which per- spective expressions are denoted in bold, speech ex- pressions are underlined, and sources are denoted in italics): 1. Charlie was angry at Alice’s claim that Bob was unhappy. 2. Philip Clapp, president of the National Environ- ment Trust, sums up well the general thrust of the reaction of environmental movements: “There is no reason at all to believe that the polluters are sud- denly going to become reasonable.” Perspective expressions in Sentence 1 describe the emotions or opinion of three sources: Charlie’s anger, Bob’s unhappiness, …

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