Non-Topical Coherence in Social Talk: A Call for Dialogue Model Enrichment (2020)

Abstract: Current models of dialogue mainly focus on utterances within a topically coherent discourse segment, rather than new-topic utterances (NTUs), which begin a new topic not correlating with the content of prior discourse. As a result, these models may sufficiently account for discourse context of task-oriented but not social conversations. We conduct a pilot annotation study of NTUs as a first step towards a model capable of rationalizing conversational coherence in social talk. We start with the naturally occurring social dialogues in the Disco-SPICE corpus, annotated with discourse relations in the Penn Discourse Treebank and Cognitive approach to Coherence Relations frameworks. We first annotate content-based coherence relations that are not available in Disco-SPICE, and then heuristically identify NTUs, which lack a coherence relation to prior discourse. Based on the interaction between NTUs and their discourse context, we construct a classification for NTUs that actually convey certain non-topical coherence in social talk. This classification introduces new sequence-based social intents that traditional taxonomies of speech acts do not capture. The new findings advocates the development of a Bayesian game-theoretic model for social talk.

## introduction and background social talk or casual conversation, one of the most popular instances of spontaneous discourse, is commonly defined as the speech event type in which "all participants have the same role: to be "equals;" no purposes are pre-established; and the range of possible topics is open-ended, although conventionally constrained" @xcite . even though we do not establish any purposes in terms of information exchange or practical tasks, we do share certain social goal from the back of our mind when deciding to engage in a casual conversation. this work rests upon the assumption that casual conversations can be modeled as goal-directed rational interactions, similar to task-oriented conversations, and therefore both of these types demonstrate grice's cooperative principle, i.e. conversational moves are constrained by "a common purpose or set of purposes, or at least a mutually accepted direction" which "may be fixed from the start" or "evolve during the exchange", "may be fairly definite" or "so indefinite as to leave very considerable latitude to the participant" @xcite . a similar assumption is made in @xcite 's discourse structure framework as it affirms the primary role of speakers' intentions in "explaining discourse structure, defining discourse coherence, and providing a coherent conceptualization of the term "discourse" itself." we adopt the following terminology from @xcite : in terms of theoretical models, asher and lascarides (2003)'s segmented discourse representation theory attributes conversational coherence to the existence of rhetorical relations between utterances, while @xcite and @xcite propose that a conversational move is coherent if it is relevant to the question under discussion. computational models such as belief-desire-intention (allen, 1995, chapter 17) and information state update @xcite assume coherence to be a natural property of dialogues within a specific task domain. these models, both theoretical and computational, may adequately account for discourse dynamics of taskoriented conversations, where adjacent utterances tend to share a lot of linguistic material and speakers' intents are drawn from a narrow set of taskrelated goals. however, without any enrichment, they are not capable of handling the complexity of conversational coherence in social talk in which both speaker goals and utterances are less con-strained. specifically, all of these models treat ntus as incoherent conversational moves. this work, therefore, seeks to identify the constraints on new topics in casual conversations as a first step towards a model which is capable of rationalizing ntus and accounting for conversational coherence in social talk. the main contributions of this paper are as follows. we introduce ntus as a novel research object that is capable of advancing our understanding of the interactive and rational aspects of social talk. we propose an annotation strategy for exploring ntus in naturally occurring dialogues. a pilot annotation study of ntus in a significant amount of spoken conversation text led us to amend the available taxonomies of speech acts with new sequence-based social intents that shed light on non-topical coherence in social talk. these new findings feed into a framework for the bayesian game-theoretic models that are capable of predicting the emergence of the newly identified intents and accounting for conversational coherence in social talk. ## methodology overview before studying the interaction between ntus and their discourse context, we need to locate them in instances of social talk. @xcite handles a similar task by annotating every turn-constructional unit (tcu) in casual conversations with two topicrelated variables: to improve the reliability and rigor of ntu detection, we approach the task reversely: we first annotate content-based coherence relations between utterances and then identify ntus as those utterances that bear no coherence relation to the content of prior discourse. this approach shares certain features with the integration of new utterances in free dialogues presented in @xcite : if a new utterance is not covered by the current conversational topic, the hearer can expand the current topic to cover it, or connect its topic with the current topic using a semantic relation from a predefined set. this similarity reflects the following view of discourse coherence: "[a discourse is] coherent just in case (a) every proposition (and question and request) that's introduced in the discourse is rhetorically connected to another bit of information in the discourse, resulting in a 'single' connected structure for the whole discourse; and (b) all anaphoric expressions can be resolved"; and therefore, "[a] discourse is incoherent whenever there's a proposition introduced in the discourse which doesn't seem to be connected to any of the other bits of the discourse in any meaningful way." @xcite . the main difference between @xcite 's model of topic shift and our work is that the former allows the total shift relation, the succeeding topic of which is totally new, only when all of the preceding topics have been exhausted and closed, while we do not impose any constraints on the nature of dtcs. we assume that interlocutors are coherent in naturally occurring conversations (wherein incoherent moves need convincing evidence). analyzing the coherence of a conversation, we put ourselves in conversational participants' shoes and rely on our communicative competence to identify all possible dsps that account for the relevance of each conversational move. we are interested in the cases where an identified dsp cannot be assigned to a pre-existing coherence relation. we hypothesize that the pre-existing coherence relations account for topical coherence (i.e. talk-about), but not nontopical coherence such as interactional coherence (i.e. talk-that-does) @xcite . ## annotating coherence relations we start with the casual telephone dialogues in the disco-spice corpus foot_5 @xcite , based on the spice-ireland corpus 7 (kallen and kirk, 2012), in which discourse relations -triples consisting of a discourse-level predicate and its two arguments -are annotated with the ccr @xcite and the early version of the pdtb 3.0 @xcite schemes. we ignore the ccr annotations in favour of the pdtb 3.0-based annotation because the latter covers more discourse relations in the corpus, including: we enrich disco-spice with spice-ireland's original pragmatic annotation, consisting of searlean speech acts @xcite , prosody, and quotatives among others. this information is helpful in identifying, for example, the quote content, or speech act query, i.e. asking for information, even in declarative clauses. we use the latest version of the pdtb 3.0 taxonomy of discourse relations @xcite , and annotate the instances which are not covered in the disco-spice corpus, such as: specifically, if a relation is not entity-based, it will be labeled with a sense in the pdtb 3.0 sense hierarchy. annotators are encouraged to choose the most fine-grained labels. for example, expansion.equivalence is preferred over expansion for an expansion.equivalence relation, although both are acceptable. in total, there are 53 sense labels available for explicit/implicit/altlex discourse relations. we also enrich our repertory of content-based coherence relations with additional semantic relations from iso 24617-8 and iso 24617-2, which take care of the interactive nature of dialogue: it is worth noting that the argument order of annotated coherence relations is chronological, i.e. the second argument always appears after the first argument in the conversational flow. we aim at annotating coherence relations that cover as many utterances as possible (rather than exhaustively annotating every relation), adding notes to the ones that are not very clear and therefore can be considered non-existent in the next step -ntu identification. in case of multiple relations available to the same pair of arguments, annotating just one relation is sufficient. as seen in ## identifying ntu candidates based on both inherited and newly annotated relations described in section 3, excluding those relations noted as "not very clear", which account for less than 3% of the newly annotated relations, we heuristically identified 72 candidates for ntus, each of which is: ## identifying ntus and patterns of dtcs an ntu candidate identified in section 4 is valid only if there is no a content-based coherence relation with respect to prior discourse, which can be missed or annotated as "not very clear" in section 3. to separate genuine ntus from other ntu candidates, we carry out a more detailed inspection. specifically, the following pieces of information are further annotated for each ntu candidate: the content of prior discourse. we were able to single out 38 true cases of ntus, roughly 50% of ntu candidates, which contain discourse-new topics and new focused entities. based on the annotated information about the interaction between the ntus and their discourse context, we identified the following patterns of dtcs (see detailed examples in appendix b): ## classifying ntus the patterns of dtcs identified in section 5 (except for @xcite 's true interruption and the forgotten topic, covering 7 identified instances of ntus) show that non-topical coherence, sustained or built by dtcs, is created via sequential adjustment of the distances between the active conversational topic and each interlocutor. this adjustment seems to be constrained by the relational work between the interlocutors, i.e. the social aspect of the conversations, rather than the content-based relevance. based on the interlocutors' intents, a simple version of the classification of ntus in social dialogues, covering 31 identified instances of ntus, can be proposed as below: these newly found intents, characterizing nontopical coherence in social talk, convincingly demonstrate social talk as a sophisticated form of goal-directed rational interactions rather than a random walk through loosely connected topics. this shows real promise and new perspectives for research in dialogue modeling. we hypothesize that a workable dialogue model for social talk needs to explicitly handle all of the key aspects of goaldirected rational interactions. ## toward a game-theoretic model to formally capture the interactive and rational aspects of social conditioned language use in conversation, recent work such as iterated best response @xcite , rational speech act @xcite , and social meaning game @xcite pairs @xcite 's signaling games with the bayesian approach to speaker/listener reasoning. in essence, these models formalize gricean inference by predicting: speaker behavior: the probability p s (o|h, c s ) that the speaker uses the observed linguistic value o to convey hidden meaning h in the speaker's context model c s is a function of u s (o, h, c s )), the utility of o in c s given the speaker's desire to communicate h. ## conclusion and future work in this paper, we present a pilot annotation study foot_9 as a first step towards a dialogue model which is capable of rationalizing ntus and conversational coherence in social talk. analyzing the interaction between the identified ntus and their discourse context, we discover a set of patterns of dtcs, represented by the ntus. based on these patterns, we propose a simple classification of ntus in social talk, yet introducing new sequence-based social intents that traditional taxonomies of speech acts do not capture. these intents not only adequately account for non-topical coherence in social talk but also convincingly demonstrate social talk as a sophisticated form of goal-directed rational interactions. we hypothesize that the bayesian gametheoretic framework, which explicitly models the interactive and rational aspects of social interaction, is a sensible architecture for handling social talk. next, we aim to develop an actionable bayesian game-theoretic model for social talk, focusing on decomposing its utility function. particularly, we seek to learn from social interaction work such as @xcite for designing the goal-directedness aspect of the model.