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4.2 Social mechanisms in communication and collaboration 125

Figure 4.9 An external representation used to
signal to others a person's availability.

In addition to monitoring the behaviors of others, people will organize their
work and physical environment to enable it to be successfully monitored by others.
This ranges from the use of subtle cues to more blatant ones. An example of a sub-
tle cue is when someone leaves their dorm or office door slightly ajar to indicate
that they can be approached. A more blatant one is the complete closing of their
door together with a "do not disturb" notice prominently on it, signaling to every-
one that under no circumstances should they be disturbed (see Figure 4.9).

Overhearing and overseeing
People who work closely together also develop various strategies for coordinating
their work, based on an up-to-date awareness of what the others are doing. This is
especially so for interdependent tasks, where the outcome of one person's activity
is needed for others to be able to carry out their tasks. For example, when putting
on a show, the performers will constantly monitor what one another is doing in
order to coordinate their performance efficiently.
The metaphorical expression "closely-knit teams" exemplifies this way of col-
laborating. People become highly skilled in reading and tracking what others are
doing and the information they are attending to. A well-known study of this phe-
nomenon is described by Christian Heath and Paul Luff (1992), who looked at how
two controllers worked together in a control room in the London Underground.
An overriding observation was that the actions of one controller were tied very
closely to what the other was doing. One of the controllers was responsible for the
movement of trains on the line (controller A), while the other was responsible for
providing information to passengers about the current service (controller B). In
many instances, it was found that controller B overheard what controller A was
doing and saying, and acted accordingly-even though controller A had not said
anything explicitly to him. For example, on overhearing controller A discussing a
problem with a train driver over the in-cab intercom system, controller B inferred
from the ensuing conversation that there was going to be a disruption to the service