This article considers tools to support remote gesture in video systems being used to complete collaborative physical tasks-tasks in which two or more individuals work together manipulating three-dimensional objects in the real world. We first discuss the process of conversational grounding during collaborative physical tasks, particularly the role of two types of gestures in the grounding process: pointing gestures, which are used to refer to task objects and locations, and rep- HUMAN-COMPUTER INTERACTION, 2004, Volume 19, pp. 273-309 Copyright © 2004 resentational gestures, which are used to represent the form of task objects and the nature of actions to be used with those objects. We then consider ways in which both pointing and representational gestures can be instantiated in systems for remote collaboration on physical tasks. We present the results of two studies that use a "surrogate" approach to remote gesture, in which images are intended to express the meaning of gestures through visible embodiments, rather than direct views of the hands. In Study 1, we compare performance with a cursor-based 274 FUSSELL ET AL.

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People's physical embodiment and presence increase their salience and importance. We predicted people would anthropomorphize an embodied humanoid robot more than a robot-like agent, and a collocated more than a remote robot. A robot or robot-like agent interviewed participants about their health. Participants were either present with the robot/agent, or interacted remotely with the robot/agent projected life-size on a screen. Participants were more engaged, disclosed less undesirable behavior, and forgot more with the robot versus the agent. They ate less and anthropomorphized most with the collocated robot. Participants interacted socially and attempted conversational grounding with the robot/agent though aware it was a machine. Basic questions remain about how people resolve the ambiguity of interacting with a humanlike nonhuman.By virtue of our shared global fate and similar DNA, we humans increasingly appreciate our similarity to nature's living things. At the same time, we want machines, animals, and plants to meet our needs. Both impulses perhaps motivate the increasing development of humanlike robots and software agents. In this article, we examine social context moderation of anthropometric interactions between people and humanlike machines. We studied whether an embodied humanlike robot would elicit stronger anthropomorphic interactions than would a software agent, and whether physical presence moderated this effect.At the outset, robots and agents differ from ordinary computer programs in that they have autonomy, interact with the environment, and initiate tasks (Franklin & Graesser, 1996). The marriage of artificial intelligence and computer science has made possible robots and agents with humanlike capabilities, such as lifelike gestures and speech. Typically, "robot" refers to a physically-embodied system whereas "agent" refers to a software system. Examples of humanlike robots are NASA's Robonaut-a humanoid that can hand tools to an astronaut (robonaut.jsc.nasa.gov/robonaut.html), Honda's Asimo, and Hiroshi Ishiguro's 169

Two pairs of studies examined effects of perspective taking in communication, using a 2-stage methodology that first obtained people's estimates of the recognizability to others of specific stimuli (public figures and everyday objects) and then examined the effects of these estimates on message formulation in a referential communication task. Ss were good at estimating stimulus identifiability but were biased in the direction of their own knowledge. The amount of information in a referring expression varied inversely with the perceived likelihood that addressees could identify the target stimulus. However, effects were less strong than anticipated. Although communicators do take others' knowledge into account, the extent to which they do so involves a trade-off with other sorts of information in the communicative situation.

We review several studies examining perspective-taking in communication. One set of studies indicates that speakers exploit the common ground they share with their addressees in creating referring expressions and that such perspective-taking improves the listener's comprehension. A second set of studies examines an element of the perspective-taking process itself: the accuracy of people's assessments of others' knowledge. We find that such estimates are both fairly accurate and biased in the direction of the perceiver's own knowledge. However, the extent of their influence on message formulation depends on the availability of feedback. We conclude that perspective-taking in communication combines prior theories about what others know with information drawn from such conversational resources as verbal and nonverbal feedback. an expert.3 Thus, for utterances to conform to the maxim of quantity, speakers must be able to assess what their addressees do and do not 1. We will use "knowledge" as a shorthand that includes beliefs, suppositions, inferences, and the like.2. To facilitate exposition, "speaker" will be used to refer to the initiator of a message, and "listener" or "addressee," the intended recipient, regardless of the modality of communication (oral, written, electronic, etc.).3. Consider, for example, a surgeon who, in the midst of an operation, said to a surgical nurse, "Hand me a hemostat that's the pointy thing that looks like a barber's scissors except that the blades are flat and clamp together." Under normal circumstances, the utterance would be understood as more than a simple request for an instrument. PERSPECTIVE-TAKING IN COMMUNICATION 9 THE PERSPECTIVE-TAKING PROCESSRecently we have begun to look more closely at some of the elements that enter into communicators' prior hypotheses about their addressee's background knowledge. Although many conceptualizations of the communication process assume that speakers and listeners can and do take each other's background knowledge and perspective into account (e.g., Clark & Marshall, 1981;Krauss, 1987;Rommetveit, 1974;Volosinov, 1986), there has been remarkably little discussion of the process by which this might be accomplished. We will describe briefly some of the issues involved and then discuss some research that addresses these issues. Our focus will be on the coordination of knowl edge, but similar problems arise when one considers attitudes, beliefs, points of view, and other sorts of perspectival coordination on which communication rests.