Common Ground in Production 1 DRAFT : DO NOT CITE WITHOUT PERMISSION . Running head : COMMON GROUND IN PRODUCTION Common Ground in Production : Effects of Mutual Knowledge on Word Duration

A key issue in models of lexical production is whether a model of hearer knowledge influences speakers’ productions. In this study we investigate whether the durational shortening of repeated words is a consequence of mutual knowledge, or if it is a byproduct of speaker internal processes. In a study of spontaneously produced narrations, in Experiment 1 we demonstrated that repeated words are shorter than their first mentions. In Experiment 2, we found that words are shortened more in the presence of a repeated hearer compared to a new hearer. Results from Experiment 3 demonstrate that shortening continues across narrations for repeated hearers, but is blocked by new hearers. These results indicate that a speaker’s model of hearer knowledge affects production. Common Ground in Production 3 Common Ground in Production: Effects of Mutual Knowledge on Word Duration Speakers commonly change the way they speak in order to conform to their interlocutors and other aspects of the speech context. These effects are pervasive and obvious; speakers raise their pitch when speaking with babies, code-switch only with appropriate interlocutors, and only use pronouns with referents that are accessible to others in the speech context. As noted by Clark and Wilkes-Gibbs (1986), in order for language to be a communicative process, there must be some sort of shared knowledge and experience between interlocutors. The knowledge that is shared between interlocutors is often referred to as common ground, "the background, the context, for everything the participants both do and say" (Clark, 1994, p. 990). While common ground is information that both speaker and hearer share, mutual knowledge is what the speaker, or hearer, knows (or assumes) about what her conversation partner knows (see Cark & Marshall, 1981). For example, if two people are talking, let us call them Cynthia and Jason, and Jason says to Cynthia “I was walking along today and the neighbors dog bit me,” then at this point the neighbors dog is considered as part of the common ground between the speaker and hearer. In the next utterance, Jason continues, “It came right at me. ” Jason presumably uses the pronoun it to refer to the dog because he knows, or has reasonable ground to assume, that Cynthia shares mutual knowledge concerning the referent of the pronoun. The intuitive notion that interlocutors rely on mutual knowledge in conversation is the foundation upon which many linguistic theories have been built. In fact, discourse pragmatic theories are largely grounded in the belief that speakers choose sentence types and forms of referring expressions based on assumptions concerning the hearer’s knowledge: Common Ground in Production 4 If a speaker assumes, prior to uttering an intonation unit, that a concept is already active in the hearer’s mind, he will verbalize that concept in an attenuated manner, giving it weak stress and probably pronominalizing it. (Chafe, 1987, p.48). Because communication is a collaborative process, it is easy to assume that mutual knowledge is a factor in language processing. But to what extent do interlocutors make use of mutual knowledge during language processing? The debate over the use of mutual knowledge in processing concerns both the comprehension system and the production system. In this study we are concerned with common ground and the production system. Intuitively, it seems that both hearer design and speaker internal factors influence the shape and production of utterances. In this study we report on a psycholinguistic study that is designed to address whether durational shortening is influenced by hearer knowledge. We use a methodology that has been demonstrated to be sensitive to speaker internal sources of reduction. Previous research in this area has provided evidence for contributions of speaker based processes, but has not excluded contributions from the speaker’s assumptions of hearer knowledge. Similarly, research demonstrating that assumptions of hearer knowledge shape productions has not excluded possible contributions from speaker internal processes. We review evidence for hearer-based models and speaker-based models of production in the following section. Finally, we report the results of three experiments designed to address the role of mutual knowledge in production. Mutual Knowledge and Production Human language production is the result of the collaboration and interaction of many layers of linguistic processes. A production begins with a thought, or a concept that the speaker wished to convey. From the initial concept, lexical items have to be chosen, syntactic structure is Common Ground in Production 5 constructed, phonological processes are consulted and then fed through the articulatory system, finally resulting in a speech stream (see Bock & Levelt, 1994; Garret, 1975; Levelt, 1989; among others). Traditionally, knowledge of the production system has come through the study of different types of speech errors (Cutler, 1982; Dell, 1984; Raymond, 2000; Stemberger, 1983; Shattuck-Hufnagel, 1979). More recently, researchers have begun to tap into the production system by investigating the effects of external factors on production, including aspects of common ground and mutual information. Studies concerning common ground and the production system generally fall into two categories. The first involves aspects of mutual knowledge that are involved in offline processes such as initial utterance design. Included in this category are the pragmatic factors that influence lexical selection (such as the choice to pronominalize or use a full referring expression). The second area of research is concerned with whether mutual knowledge is involved in fast, automatic processes such as articulation. Common Ground and Initial Design There have been a number of studies that demonstrate that hearer knowledge (defined as the speaker’s assumptions of what the hearer knows) is a major factor in audience design (Clark & Brennan, 1991; Chafe, 1976; Gerrig et al., 2001; Gundel et al., 1993; Nadig & Sedivy, 2001; Prince, 1981). For example, in a corpus study of forms of referring expressions, Gundel et al. (1993) illustrated that the form of a referring expression that a speaker chooses is directly correlated with the assumptions speakers make concerning the cognitive status of the referring expressions in the mind of the hearer. In a study of the use of the use of prenominal adjectives (e.g., the big cup), Sedivy (2002) found that adult speakers only use scalar and material adjectives in the presence of a contrast set Common Ground in Production 6 (where both a big and small cup were in the speaking environment). Nadig and Sedivy (2001) found that children as young as 5 or 6 are also sensitive to common ground in their productions. They found that children were more likely to use a scalar adjective when describing an object to a confederate when the confederate had access to a contrast set, but not when the contrast set was blocked from view of the confederate, even though the children still had access to the contrast set. These results demonstrate that children’s utterance design is influenced by information perceived to be common ground. There is evidence that speakers rely on more than mutual knowledge for lexical choice in conversations. Brennan and Clark (1996) argue that speakers and hearers engage in conceptual pacts in conversations. In a task where speakers had to give instructions to hearers on how to match cards with pictures of objects on them, they found that speakers propose a conceptualization of an object, which is then accepted or denied by the hearer. Once a conceptualization is agreed upon, both interlocutors tend to use that term for that object (the result of a process called lexical entrainment). Moreover, they found that the conceptualization pact is partner specific; the same speaker is more likely to refer to the pictured objects with the same lexical item when they are giving instructions to the same partner. Once they switch partners, they change their lexical choice based on the conceptualization pact they make with the new partner. There have been a number of studies, however, that find that mutual knowledge is not a factor in initial utterance design. For example, Brown & Dell (1987) (see also Dell & Brown, 1991) conducted a series of experiments in which they tested if mutual knowledge between speakers and hearers played a role in the explicit mention of atypical ins truments. Participants were asked to retell a story that they read. They found that participants were more likely to use t Common Ground in Production 7 atypical instruments than typical ones in their re-telling of the story (e.g., ice pick over knife). However, they found that the speaker’s belief about the listener’s knowledge of the instrument, as determined by the presence or absence of a picture of the scene, had little impact on whether the instrument was mentioned. They claim that the mechanisms behind what seems to be listener adaptation are “automatic products of the production system” (Dell & Brown, 1991, p.107). Consistent with Dell and Brown (1991), Horton and Keysar (1996) also found that speakers do not take common ground into consideration during the initial stages of utterance planning. In an investigation of adjective use, they found that when under a time constraint, speakers do not use adjectives, like “the big ball,” even when a contrast set was available to hearers. Horton and Keysar concluded that common ground does not play a primary role in utterance design, but that speakers do fall back on it during the monitoring and adjustment phase of production, which happens later in the production process (see Levelt, 1983). Articulation and Mutual Knowledge As with the debate concerning initial design, there is evidence for and against the notion that mutual knowledge is a factor in the fast, automatic processes that are involve