30 D.Reirter.I.D.Moore/of Memory and Longuage 76 (2014)29-46 relate prim ing at levels of syntactic,but also lexical choices.A qua sna ly s lar co Hypotheses e t tron unction dialogue partners that develop coherent situation models. second adds a functional perspective by showing a correla- ehakw chan tion system bet articipants.They found that speak thougbtiido5otcsiammchariguoo veloped a common on Lebiere.19 )prim d However.the full causal cascade from lower-level prim ing to high-level alignment has not yet been observed.Spe communication by priming suggested by the IAM could Forinstance syntactic representations may be temporarily tics held in working memo and so me ng is syntactic struct this in and coherence of when speaker 0 yto prefer 861Gd gdhis9cireorhavingheardannte iations cuto cluste as well use it( We hypothe Bernolet. than in sponta tion.Regardle term priming effects and whethe n the Man Task em adaptation in situations where they s is derived fron the IAM's core and task s cult to manipulate in naturalistic human-human dialogue ver we expect observable variation in adaptation from the e]from the car tely vield r een ask suc e the caravans est this prediction in Experiments -4.e nclud struction (hesha that both syntactic and lexical alig e one an oval s pe)m The spontanous syntactic choice adaptation.Adaptation denotesan inreased amount pf rather than p lausible alternatives to describe an oval after a few seconds long-tern shaped path.This example of repetition reflects not only adaptation is adaptation that is enhanced by repeatedalignment. In this paper, we correlate priming at levels of sentence structure (syntax) and word choice, the prob￾lem-solving objective of the dialogue, and success. Hypotheses Humans align their linguistic choices at several repre￾sentational levels. At a low level, phonetic reductions occur in jointly understood words (Bard et al., 2000). An example of adaptation at a higher level of representation involves dialogue partners that develop coherent situation models, as in Garrod and Anderson’s (1987) Maze Game study. The task was designed to elicit a coordinated communica￾tion system between participants. They found that speak￾ers tended to make the same semantic and pragmatic choices as in the utterances they had just heard. As the games proceeded, participants developed a common description scheme for positions in the maze. However, the full causal cascade from lower-level prim￾ing to high-level alignment has not yet been observed. Spe￾cifically, the hypothesized correlation between the two, and ultimately successful communication, has eluded empirical verification. In this paper, we focus on implicit linguistic decisions: the basic mechanics of communication implemented in syntactic structure, as opposed to the high-level strategies speakers use to describe aspects of a task, or the more explicitly controlled lexical choices. Syntactic priming occurs when speakers show a tendency to prefer one phrase structure over an available alternative shortly after having used this structure or having heard an interlocutor use it (Bock, 1986). Verbatim, lexical repetition is known to increase the strength of priming (Gries, 2005; Hartsuiker, Bernolet, Schoonbaert, Speybroeck, & Vanderelst, 2008; Pickering & Branigan, 1998). This lexical boost is a crucial effect for the IAM, as it shows propagation of alignment from lower to higher levels of representation. Thus far, there is only limited evidence for the occur￾rence of structural adaptation outside of carefully con￾trolled laboratory settings. As we will see, speakers also adapt in situated, realistic dialogue. For example, consider this excerpt from the Map Task corpus (Anderson et al., 1991; McKelvie, 1998), a dataset that we will use exten￾sively in this study. One speaker (g) is giving directions for another one (f) to follow on a map: f: from the mill wheel and up to the abandoned cottage to the right like a tick shape it’d be s– [the shape of a tick] from the g: no g: [the shape of a] [like an oval shape] from the car￾avan park you start just above the caravans Here, g first sets out to repeat the latest syntactic con￾struction (the shape of an oval), but proceeds to use an alternative one (like an oval shape) in its repair, mirroring his interlocutor’s first syntactic choice (like a tick shape). The spontaneous syntactic choice is a direct repetition, but would be ungrammatical if completed (the shape of a oval). Both of g’s expressions reflect structural repetitions rather than plausible alternatives to describe an oval￾shaped path. This example of repetition reflects not only syntactic, but also lexical choices. A quantitative model of priming should cover such cases, but also repetitions that occur outside of lexically or semantically similar contexts. In our study, we are concerned with implicit (syntactic) effects. We therefore measure priming of syntactic phrase-structure rules, whereby word-by-word repetition (topicality effects, parroting) is explicitly excluded. We examine the IAM from a functional perspective, and derive two groups of testable hypotheses. The first exam￾ines syntactic priming in task-oriented dialogue, while the second adds a functional perspective by showing a correla￾tion between adaptation and task success. Our first hypothesis concerns the mechanisms of prim￾ing. Syntactic priming is claimed to be a mechanistic effect, though this does not necessarily mean that it is automatic and agnostic to contextual influence. According to some cognitive architectures (Anderson & Lebiere, 1998), prim￾ing effects are the result of working memory activity. From a functional and rationalist point of view, the enhancement of communication by priming suggested by the IAM could have led to an architectural configuration where the demands of the dialogue situation drive syntactic priming. For instance, syntactic representations may be temporarily associated with semantic ones. Topics determine seman￾tics held in working memory, and so, meaning is typically clustered rather than randomly mixed. In line with this, theories of dialogue have suggested clustering of topics, and coherence of topic structure (Grosz, Joshi, & Weinstein, 1995; Grosz & Sidner, 1986). Given any syntac￾tic-semantic associations, syntactic structure may tend to cluster as well. We hypothesize that there is a tendency for dialogue partners to repeat syntactic structure within brief time windows, and that they do more so in task-oriented dia￾logue than in spontaneous conversation. Regardless of the underlying mechanisms, the IAM seems incompatible with the inverse hypothesis: less priming in task-oriented dialogue. In the first set of experiments (1–2), we look at short￾term priming effects and whether speakers implicitly use increased short-term adaptation in situations where they may benefit from it. The second hypothesis is derived from the IAM’s core idea connecting low-level priming to high-level mutual understanding and task success. Adaptation itself is diffi- cult to manipulate in naturalistic human–human dialogue. However, we expect observable variation in adaptation levels. The IAM predicts that task-oriented dialogues that exhibit more syntactic adaptation between the interac￾tion partners will ultimately yield more task success. We test this prediction in Experiments 3–4. We conclude with an experiment that uses machine learning techniques to demonstrate that both syntactic and lexical alignment can be exploited to predict task success (Experiment 5). We will refer to several different variants of syntactic adaptation. Adaptation denotes an increased amount of re-use of decisions compared to expected repetition occur￾ring by chance. Short-term priming is short-lived adapta￾tion, which disappears after a few seconds. Long-term adaptation is adaptation that is enhanced by repeated 30 D. Reitter, J.D. Moore / Journal of Memory and Language 76 (2014) 29–46