The optimization of conversational coherence




Black, Alexander Kenneth

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Coherence and incoherence in conversation refer to the relationship between adjacent parts of the conversation (e.g., between one statement and the next, or between one topic and the next). A clear, relevant connection is called coherent; the absence of an obvious connection is incoherent. Coherence and incoherence are therefore central to any analysis of discourse, but, despite many existing theories of coherence and incoherence, there is little empirical knowledge of these phenomena. This dissertation continues the study of coherence began in my master's thesis. In it I propose three axioms to describe the structure of coherence throughout conversations: I. Both coherence and incoherence are necessary for conversation to occur. II. Conversations optimize coherence both globally and locally. III. Coherence is optimized at several different, hierarchical levels of conversation. Because there is already evidence that coherence is maximized at a global level (Black, 1986/1988), I chose to test whether coherence is optimized at a local level. Specifically, local optimization of sequential coherence relations would consist of a series of alternations between coherence and incoherence. I also sought to test this hypothesis at several different levels of conversation (statement, topic, and macrotopic). In order to test the hypothesis, it was necessary to develop a method for segmenting conversations into statements, topics, and macrotopics and a method for measuring the degree of coherence between these segments. Using the guidelines developed, two judges were able to segment conversations at all three levels with high reliability. Similarly, other sets of raters used a magnitude estimation procedure to scale the degree of coherence between units at each of these levels and again achieved high reliability. It was also necessary to develop a time-series analytic technique for verifying the predicted series of alternations in short sequences of data, because existing methods are not applicable to small Ns. The new statistic is based on the geometric properties of a particular data set: it compares the obtained sum of the interior angles facing toward the mean of the data series with the sum of the interior angles facing the mean of all other permutations of these data points. Three getting-acquainted conversations were obtained; these yielded 325 statements (the spoken equivalent of a sentence). After segmentation, coherence scaling, and application of the optimization statistic, there was moderate support for the hypothesis of local optimization. Three quarters of the topics contained sequences of propositions with a sum of interior angles that was smaller than the sum of half of the alternative permutations. At the macrotopic level, however, the hypothesis was not supported. The contributions of this dissertation are (1) an explicit, parsimonious, discourse-based theory of coherence; (2) objective methods for measuring and studying coherence; and (3) a new time-series statistic; and (4) encouraging but not yet convincing evidence for the theory.



Cohesion (Linguistics), Conversation, Discourse analysis