Cognition: Memory, Attention, and Learning - Foundations for Designing User-Centered Systems - page 149

Finally, we should note again that learning is rarely complete. It is easy to think
that if you have learned to operate a system your learning about that system is
complete. This needn't be so; many users can sometimes perform very compe-
tently with very little knowledge, and other systems, such as UNIX and the Emacs
editor are complex enough that once competent, users can continue to learn new
ways to use them and new components for several years.
5.4.4 Skilled Behavior, Users in Complex Environments
Real human skills are a complex mixture of these levels of learned behavior. In
most cases, routine users will work with an open-loop behavior at the skilled level.
That is, they will be able to perform most tasks in a routine way using existing,
well-used knowledge and not check all of their steps. Their behavior will be open-
loop, that is, they will not check all of their work. They will not close the loop by
checking that things worked correctly because in most cases they no longer need
to. If they do make mistakes, they will be able to recognize them quickly. They
will continue to get faster with practice, but the improvement will be minor. There
will also be some closed-loop behaviors for tasks that are less well practiced, and
in these behaviors users will be more careful and check their work.
For example, airplane pilots often operate at all three levels. Some aspects of
their behavior are automatic; for others they refer to rules and procedures, whilst
for others, particularly in non-routine emergencies, they reason on the basis of
their knowledge about the plane and learn. (In routine emergencies they will use
checklists.)
Rasmussen's ( 1983 ) argument is that good design needs to support all three
levels of operation, not just one. We can also note a social human factor here. If
there are multiple operators, they may operate at different levels at different times
because at the knowledge level they may have different knowledge, which may
give rise to conflict or to strength, depending on how these differences in approach
are resolved.
The knowledge level implies a certain amount of planning activity, but you will
find there are those who believe that people do not engage in planning—arguing
that behavior is situated in a context (e.g., Suchman 1983 ). In other words, they
argue that we perceive the situation and decide what to do then, not on the basis of
some pre-formed plan.
Two responses can be made to this.
• One can do both—have a plan and allow the situation to change it (e.g., per-
forming actions in a different order from that planned).
• Planning seems best related to Rasmussen's knowledge-level, whereas situated
action is 'rule-level' behavior. Again, these are not exclusive options—some
people in some skills may function exclusively at one level, whilst others may
switch between levels at high speed.