Susan E. Brennan

GROUNDING IN COMMUNICATION

GROUNDING It takes two people working together to play a duet, shake hands, play chess, waltz, teach, or make love. To succeed, the two of them have to coordinate both the content and process of what they are doing. Alan and Barbara, on the piano, must come to play the same Mozart duet. This is coordination of content. They must also synchronize their entrances and exits, coordinate how loudly to play forte and pianissimo, and otherwise adjust to each others tempo and dynamics. This is coordination of process. They cannot even begin to coordinate on content without assuming a vast amount of shared information or common ground-that is, mutual knowledge, mutual beliefs, and mutual assumptions And to coordinate on process, they need to update their common ground moment by moment. All collective actions are built on common ground and its accumulation. We thank many colleagues for discussion of the issues we take up here.

Conceptual pacts and lexical choice in conversation.

When people in conversation refer repeatedly to the same object, they come to use the same terms. This phenomenon, called lexical entrainment, has several possible explanations. Ahistorical accounts appeal only to the informativeness and availability of terms and to the current salience of the objects features. Historical accounts appeal in addition to the recency and frequency of past references and to partner-specific conceptualizations of the object that people achieve interactively. Evidence from 3 experiments favors a historical account and suggests that when speakers refer to an object, they are proposing a conceptualization of it, a proposal their addresses may or may not agree to. Once they do establish a shared conceptualization, a conceptual pact, they appeal to it in later references even when they could use simpler references. Over time, speakers simplify conceptual pacts and, when necessary, abandon them for new conceptualizations.

A CENTERING APPROACH TO PRONOUNS

In this paper we present a formalization of the centering approach to modeling attentional structure in discourse and use it as the basis for an algorithm to track discourse context and bind pronouns. As described in [GJW86], the process of centering attention on entities in the discourse gives rise to the intersentential transitional states of continuing, retaining and shifting. We propose an extension to these states which handles some additional cases of multiple ambiguous pronouns. The algorithm has been implemented in an HPSG natural language system which serves as the interface to a database query application.

Identification and ratings of caricatures: Implications for mental representations of faces

Abstract S. Brennan (1985, Leonardo , 18 , 170–178) has developed a computer-implemented caricature generator based on a holistic theory of caricature. A face is represented by 37 lines, based on a fixed set of 169 points. Caricatures are produced by exaggerating all metric differences between a face and a norm. Anticaricatures can be created by reducing all the differences between a face and a norm. Caricatures of familiar faces were identified more quickly than veridical line drawings, which were identified more quickly than anticaricatures. There was no difference in identification accuracy for the three types of representation. The best likeness was considered to be a caricature. We discuss the implications of these results for how faces are mentally represented. The results are consistent with a holistic theory of encoding in which distinctive aspects of a face are represented by comparison with a norm. We suggest that this theory may be appropriate for classes of visual stimuli, other than faces, whose members share a configuration definable by a fixed set of points.

When conceptual pacts are broken: Partner-specific effects on the comprehension of referring expressions

Abstract When two people in conversation refer repeatedly to objects, they typically converge on the same (or similar) referring expressions. The repeated use of expressions by people in the same conversation has been called lexical entrainment. Lexical entrainment may emerge from the precedent of associating objects with expressions (and the perspectives they encode), or else from achieving conceptual pacts , or temporary, flexible agreements to view an object in a particular way (in which case the precedent is encoded as specific to a particular partner). We had people interact with a confederate speaker, entraining on shared perspectives (e.g., “the shiny cylinder”) during repeated references to objects. Then either the original speaker or a new speaker used either the original expression or a new one (“the silver pipe”) to refer to the previously discussed object. Upon hearing the original expressions, addressees looked at and then touched the target objects equally quickly regardless of speaker. However, with new expressions, there was partner-specific interference: addressees were slower to look at the object when the new expression was uttered by the original speaker than when the new expression was uttered by the new speaker. This suggests that the representations in memory from which entrainment emerges do encode a partner-specific cue, leading addressees to expect that a speaker should continue to use an entrained-upon expression unless a contrast in meaning is implicated. There appears to be no such interference when a new partner uses a new expression.

Coordinating Cognition: The Costs and Benefits of Shared Gaze During Collaborative Search

Collaboration has its benefits, but coordination has its costs. We explored the potential for remotely located pairs of people to collaborate during visual search, using shared gaze and speech. Pairs of searchers wearing eyetrackers jointly performed an O-in-Qs search task alone, or in one of three collaboration conditions: shared gaze (with one searcher seeing a gaze-cursor indicating where the other was looking, and vice versa), shared-voice (by speaking to each other), and shared-gaze-plus-voice (by using both gaze-cursors and speech). Although collaborating pairs performed better than solitary searchers, search in the shared gaze condition was best of all: twice as fast and efficient as solitary search. People can successfully communicate and coordinate their searching labor using shared gaze alone. Strikingly, shared gaze search was even faster than shared-gaze-plus-voice search; speaking incurred substantial coordination costs. We conclude that shared gaze affords a highly efficient method of coordinating parallel activity in a time-critical spatial task.

Accommodating variation: Dialects, idiolects, and speech processing

Listeners are faced with enormous variation in pronunciation, yet they rarely have difficulty understanding speech. Although much research has been devoted to figuring out how listeners deal with variability, virtually none (outside of sociolinguistics) has focused on the source of the variation itself. The current experiments explore whether different kinds of variation lead to different cognitive and behavioral adjustments. Specifically, we compare adjustments to the same acoustic consequence when it is due to context-independent variation (resulting from articulatory properties unique to a speaker) versus context-conditioned variation (resulting from common articulatory properties of speakers who share a dialect). The contrasting results for these two cases show that the source of a particular acoustic-phonetic variation affects how that variation is handled by the perceptual system. We also show that changes in perceptual representations do not necessarily lead to changes in production.

First Impressions and Last Resorts How Listeners Adjust to Speaker Variability

Perceptual theories must explain how perceivers extract meaningful information from a continuously variable physical signal. In the case of speech, the puzzle is that little reliable acoustic invariance seems to exist. We tested the hypothesis that speech-perception processes recover invariants not about the signal, but rather about the source that produced the signal. Findings from two manipulations suggest that the system learns those properties of speech that result from idiosyncratic characteristics of the speaker; the same properties are not learned when they can be attributed to incidental factors. We also found evidence for how the system determines what is characteristic: In the absence of other information about the speaker, the system relies on episodic order, representing those properties present during early experience as characteristic of the speaker. This “first-impressions” bias can be overridden, however, when variation is an incidental consequence of a temporary state (a pen in the speakers mouth), rather than characteristic of the speaker.

Conversation with and through Computers

People design what they say specifically for their conversational partners, and they adapt to their partners over the course of a conversation. A comparison of keyboard conversations involving a simulated computer partner (as in a natural language interface) with those involving a human partner (as in teleconferencing) yielded striking differences and some equally striking similarities. For instance, there were significantly fewer acknowledgments in human/computer dialogue than in human/human. However, regardless of the conversational partner, people expected connectedness across conversational turns. In addition, the style of a partners response shaped what people subsequently typed. These results suggest some issues that need to be addressed before a natural language computer interface will be able to hold up its end of a conversation.

Use and acquisition of idiomatic expressions in referring by native and non‐native speakers

When referring repeatedly to an object in conversation, two people typically come to use the same expression, a phenomenon called lexical entrainment (Brennan & Clark, 1996; Garrod & Anderson, 1987). But what happens when one partner is not as linguistically skilled as the other? In three experiments, we examined how native and non‐native speakers adjust their referring expressions to each other in conversation. Twenty Asian language speakers learning English were tested before and after conversations with native English speakers in which they repeatedly matched pictures of common objects (Experiment 1). Lexical entrainment was just as common in native/non‐native pairs as in native/native pairs. People alternated director/matcher roles in the matching task: natives uttered more words than non‐natives in the same roles. In Experiment 2, 31 natives rated the pre‐ and post‐test expressions for naturalness: non‐natives’ post‐test expressions were more natural than their pre‐test expressions. In Experiment 3, ...