Causal networks versus goal hierarchies in summarizing text∗

Abstract

The importance of a statement in a story was investigated, contrasting two alternative approaches to story understanding: hierarchical vs. causal. The importance of a statement was operationalized in terms of the statement's being included in a summary. Goal‐statements across versions of a story were varied in their hierarchical level. In addition, the causal‐chain status and the number of direct causal connections for goal and other statements were identified. The effects of these three properties on inclusion of statements in summaries were studied. A goal‐statement's change from a superordi‐nate to a subordinate level decreased its probability of being included in a summary only if this shift was accompanied by a change in its causal role. When the number of causal connections and the causal‐chain status were held constant, the hierarchical level had no effect. When the number of causal connections increased, the likelihood of summarization for both goal and other statements increased. Similarly, causal‐chain statements were included more often than statements that were not in the chain. The data suggest that the importance of a statement in a structure is the result of causal reasoning during comprehension.