Abstract How do conversations change when two partners use different media of communication, one speaking and the other typing? The principle of least collaborative effort (Clark & Wilkes-Gibbs, 1986) as applied to the contrasting costs of speaking and typing (Clark & Brennan, 1991) makes a clear prediction: Speakers communicating with typists should take on more of the communicative load because they expend less effort to produce utterances. To test this prediction, we had two partners complete a referential communication task using either the same or different medium of communication (speaking or typing). Results followed the prediction. Two speakers produced many more words than two typists, but finished faster. When speakers were paired with typists, they produced more of the content; they also took on more of the load by asking the typists questions that allowed brief answers. Two speakers lessened their loads by exploiting precision timing in interrupting and responding to each other. Speakers paired with typists could not, and that added to their load and completion time. Is Timing Everything? Grounding Costs in Speech and Typing MICHELLE GUMBRECHT & HERBERT H. CLARK, Stanford University Introduction In conversation, speakers adjust their workload to benefit both themselves and their addressees. They do so, it is claimed, according to a principle of least collaborative effort (Clark & Wilkes-Gibbs, 1986). People also change their communicative strategies based on certain costs of the medium (Clark & Brennan, 1991). The cost of producing a sentence, for example, is much greater in typing than in speaking. There are also contrasting costs in formulating sentences; making repairs; changing speakers; dealing with asynchronies; and dealing with delays. Most of these costs are far greater in typing than in speaking (e.g. Fussell et al., 2004; Newlands, Anderson, & Mullin, 2003; Cohen, 1984; Ford, Chapanis, & Weeks, 1979). In most previous studies, the two partners used the same medium to communicate, so the costs for the two of them were equal. However, suppose one person speaks to another person with a motor speech disorder who must type to communicate. How do the two of them adapt to a situation in which the costs are unequal? Will they change the way they communicate? In our study, we addressed these questions by comparing speech-typing pairs with speech-only and typing-only pairs. Acknowledgments We thank Teenie Matlock and the members of the Stanford Language User Group (SLUGS) for helpful feedback. We also thank Aurélie Beaumel, Roma Shah, and Olivia Tam for assistance in running participants and data coding. References Clark, H. H., & Brennan, S. E. (1991). Grounding in communication. In L. B. Resnick, J. Levine, & S. D. Teasley (Eds.), Perspectives on socially shared cognition (pp ). Washington, DC: APA. Clark, H.H., & Wilkes-Gibbs, D. (1986). Referring as a collaborative process. Cognition, 22, Cohen, P.R. (1984). The pragmatics of referring and the modality of communication. Computational Linguistics, 10, Ford, W.R., Chapanis, A., & Weeks, G.D. (1979). Self-limited and unlimited word usage during problem solving in two telecommunication modes. Journal of Psycholinguistic Research, 8, Fussell, S. R., Kiesler, S., Setlock, L. D., Scupelli, P., & Weisband, S. (2004). Effects of Instant Messaging on the management of multiple project trajectories. CHI 2004 (pp ). NY: ACM Press. Newlands, A., Anderson, A.H., & Mullin, J. (2003). Adapting communicative strategies to computer-mediated communication: An analysis of task performance and dialogue structure. Applied Cognitive Psychology, 17, Children saw chimeras from eight different stimulus sets, and heard four referred to with perceptually counter-intuitive labels and four with the phrase “this one,” as illustrated below: Summary: As expected, typing-only partners took significantly longer to complete the task than pairs in the other three conditions. Typing takes much more time and effort than speaking. Summary: As predicted, speakers (regardless of their role) took on more of the communicative load when paired with typists than with other speakers. Results Procedure: Pairs of students (labeled director and matcher) worked on a tangram matching task. In each of six trials, a director communicated freely with a matcher about a set of ten tangrams, who was to place the tangrams in the instructed order. The two partners communicated with either the same or different media (speech or typing) in separate rooms. Speakers wore microphones, and we used iChat to enable either one- or two-way audio through the computers. Typists used MSN Messenger. Director’s display. Matcher’s display. Design: Method Participants: Sixty-four university students (34 men and 30 women, M = 19 years). Summary: Management questions were those questions in the conversations that did not include information about tangram descriptions, e.g. “Ok, you got it?” With two speakers or two typists, the directors did most of the managing. But as predicted, in the mixed pairs, the management role was taken over by the speaker. It takes effort to do this management, so speakers took over that role. Summary: Content questions were those questions in the conversations that were about the content of the tangrams, e.g. “It’s standing on one foot, right?” In all conditions, content questions were asked more often by matchers than by directors. It was the matchers themselves who recognized what they had not understood. Conclusions As predicted, people immediately adapted to the relative costs of the medium of communication. In speech-typing pairs, speakers took on more of the effort, regardless of their role as director or matcher. For example, when matchers could speak, they took over more than one-third of the directors’ load when the director could only type. Speaking directors contributed 92% of the total words when paired with typing matchers, whereas typing directors contributed only 56% of the total words when paired with speaking matchers. The content of the conversation itself changed with the medium of communication. Usually it is the director who manages these conversations, asking management questions to check on the matcher’s current state of understanding. But when only one of the partners could speak, that partner took over the management role, whether he or she was the director or the matcher. Managing takes effort, and speakers could afford that effort. Likewise, it is usually the matcher who asks the content questions. When matchers spoke to directors who were typing, they especially made use of content questions that yielded brief answers (e.g. yes/no questions). In summary, these findings support the principle of least collaborative effort when there are gross differences in effort (or cost) between the two partners.