3.1 Coordination of Behavior

We will frame the discussion of MOVERS-WORLD in terms of Clark's model of joint activities. An example of a joint activity in MOVERS-WORLD is L1 and L2 loading a large box onto the hand-truck.

L1, L2, and HTO1 agree that a large box LBOX1 will be loaded onto the hand-truck. HTO1 must stand the hand-truck before any box can be loaded on top of it. L1 and L2 must jointly engineer the lifting and loading of LBOX1.

The joint activity of L1, L2, and HTO1 is a complex of coordination problems. Coordination of entry and exit times for each of the phases, from lifting the box to loading the box onto the hand-truck after HTO1 maneuvers it into a standing position, are jointly achieved by the participants. L1 and L2 must initiate a sequence of actions at the same time and then, step-by-step, they must execute lift-together and load-together. If they fail to achieve synchronicity, breakdowns will occur and the following phases of action will require explicit agreements (via communication) to re-coordinate the actors.

Depending on the circumstances, each of Clark's [13] (p. 64) four types of coordination devices may be in play for an activity like loading LBOX2 onto the hand-truck. When the hand-truck is standing in the same room as LBOX2, it signals the readiness of the hand-truck for loading (salience). L1 and L2 could communicate to one another when they are ready to begin lifting (explicit agreement). If HTO1 has only done this once before and, on that prior occasion, her job was to ready the hand-truck for loading, then she could assume her job in the current setting is to stand the hand-truck (precedence). Loading a large box onto the hand-truck is a regular problem of coordination among the community of actors in MOVERS-WORLD (convention).

Over time, given their understanding of the current regularities of coordination, the actors are continuously (re)learning the best ways to coordinate behavior. Actors rarely (if ever) have complete theories or agreements on the optimal way to act. Consider a problem situation where two lifters and a hand-truck operator are in a room with an extra-large box and two medium-sized ones. A reasonable way to coordinate behavior is:

1.

A lifter and the hand-truck operator agree to load the hand-truck with the extra-large box.

2.

The lifters lift the extra-large box together.

3.

The lifters load the extra-large box onto the hand-truck.

4.

In parallel:

(a)

The hand-truck operator pushes the hand-truck to the street and stands it up.

(b)

Each lifter carries a medium-sized box to the street and loads it onto the truck.

5.

A lifter and the hand-truck operator agree to load the extra-large box onto the truck.

6.

The lifters unload the extra-large box from the hand-truck.

7.

The lifters load the extra-large box onto the truck.

Achieving this performance level of coordination between actors is an ACHIEVEMENT. This exact scenario may or may not have occurred previously, e.g., the previous time there could have been another box or actor present. Complicating matters, the situation must unfold such that, at every turn in the action, the actors are reasoning about the situation in complementary manners. The degree to which they achieve this depends on how they reason about the conventions at work over each segment of action. The existence of conventions as parts of the common ground is the mechanism by which the community improves its performance as it moves towards optimal solutions. Whether the community achieves optimal solutions -- or, for that matter, given the dynamics of the situation, whether they even exist -- is neither here nor there, for, more often then not, the actors do not know whether they are performing optimally.