Taken more generally, it
can include any achievement of commonality between agents, including
actual beliefs about the communicated information and joint intentions
or goals for future action. Clark and Wilkes-Gibbs [Clark and Wilkes-Gibbs1986]
point out that it is often not necessary to fully ground every aspect
of the interaction, merely that the agents reach the grounding
criterion: ``The contributor and the partners mutually believe that
the partners have understood what the contributor meant to a criterion
sufficient for the current purpose.'' What this criterion may be
depends on the reasons for needing this information in common ground
and can vary with the type of information and the collaborators local
and overall goals.
Clark and Wilkes-Gibbs also consider another important principle, that least collaborative effort. Contrary to classical efficiency principles, which try to minimize effort on the receiver, or the number of repairs, Clark and Wilkes-Gibbs's principle trues to minimize the total effort of the collaborators. This means that in some cases the cost of producing a perfectly interpretable utterance may be more than producing a flawed utterance, which can be easily repaired. These costs include both effort of producing and understanding an utterance, as well as total time for the collaboration.
Clark and Brennan [Clark and Brennan1991] discuss grounding in different media. They point out that different media bring different resources and constraints on grounding as well as having different associated costs. They describe several media (including, face-to-face, telephone, video-teleconference, terminal teleconference, and email) according to whether they have the following properties: copresence (can see the same things), visibility (can see each other), audibility (can hear each other), cotemporality (messages received at the same time as sent), simultaneity (can both parties send messages at the same time or do they have to take turns), sequentiality (can the turns get out of sequence), reviewability (can they review messages, after they have been first received), and reviseability (can the producer edit the message privately before sending). Also, the following costs are considered for these media: formulation costs (how easy is it to decide exactly what to say), production costs (articulating or typing the message), reception costs (listening to or reading the message, including attention and waiting time), understanding costs (interpreting the message in context), start-up costs (initiating a conversation, including summoning the other partner's attention), delay costs (making the receiver wait during formulation), asynchrony costs (not being able to tell what is being responded too), speaker change costs, fault costs, and repair costs. Since different media have different combinations of these constraints and costs, one would expect the principle of least collaborative effort to predict different styles of grounding for use in different media.
Clark and Schaefer [Clark and Schaefer1989] presented an off-line descriptive account of the grounding process in conversation. This was followed up by [Traum1994] with an on-line computational model of grounding in conversation. In order to achieve a kind of predictive model of grounding behavior in a multi-modal context, and relate the grounding process to repair and broaden communicative action beyond just spoken conversation, we need to focus on why an agent would perform a particular communicative act as part of the grounding process. Towards this end, we are collecting and examining data of how grounding is performed in multi-modal collaborative problem solving.