human factors

7-24 Handbook of Aviation Human Factors
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10
Pursuit
Compensatory
Average error (mm)
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0
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Blocks of five trials
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FIGURE 7.21 Errors in tracking performance using pursuit and compensatory displays. (From Briggs, G.E. and
Rockway, M.R., J. Exp. Psychol., 71, 165, 1966.)
performance limits, and some that partially describe the human ability to adapt to the properties of
the device that the person is controlling. This function can be used to predict the combined pilot–
aircraft performance. This is a powerful technique with considerable economic benefits. However, it is
not relevant to this chapter as it describes the performance, and not the underlying processes, and only
describes the human performance in compensatory tracking tasks. It also focuses attention on an aspect
of human performance that can be poorer than that of fairly simple control devices. This encourages the
idea of removing the person from the system, rather than appreciating what people can actively contribute,
and designing support systems to overcome their limitations.
7.1.5 Summary and Implications
7.1.5.1 Theory
The cognitive processes underlying the classic HF/E can be relatively simple, but not so simple that
they can be ignored. Cognitive processing is carried out to meet cognitive functions. Five functions are
discussed in this section: distinguishing between stimuli; building up a percept of an external world
containing independent entities with stable properties; naming; choosing an action; and comparison.
This section suggests that these functions could be met with simple tasks using three main cognitive
processes (what happens when these processes are not sufficient has been mentioned briefly and is discussed
in the next main section). The three processes are: deciding between the alternative interpretations
of the evidence; integrating the data from all the sensory sources along with the knowledge about
the possibilities, to an inferred percept that makes the best sense of all the information; and recoding,
that is, translating from one type of code to another.
Furthermore, five other key aspects of cognitive processing have been introduced:
1. Sensory processing is relative rather than absolute.
2. The cognitive functions are not necessarily met by processes in a clearly distinct sequence.
Processes that are “automated” may be carried out in parallel. The processes communicate with
each other via a common “blackboard,” which provides the context within which each process
works, as summarized in Figure 7.22.