human factors

Weather Information Presentation 25-13
The concept of perceptual schema—the form of knowledge or mental representation that people use
to assign stimuli to ill-defined categories, a general body of knowledge about a perceptual category,
developing from perceptual experience with examples rather than a strict listing of features (Wickens,
1984)—is important when applied to information supporting effective ATC. Posner and Keele (1968)
suggested that there are two components—a general representation of the mean, and some abstract
representation of the variability. We find that experienced controllers and pilots have developed schema
relative to system states that potentially have significant impact on system operation, such as weather
hazards. Posner and Keele’s research suggests that variability must be addressed directly in training
and display design, and not just the prototypical case. For example, the system developer should fully
understand the system “outlier” states that are important to the user, so that training and display design
properly highlight them.
There is some advantage to top-down, context-driven processing when the user seeks information.
That is, have the user work from top-level displays down to the level of detail needed, rather than just
flash a “chunk” of information on the screen in response to a request. This is because there is strong
research evidence that says that human processing generally follows this model (Wickens, 1984). Closely
related is the concept of holistic processing (Wickens, 1984), which “describes a mode of information
processing in which the whole is perceived directly rather than a consequence of this separate analysis of
its constituent elements” (p. 164). According to Navon (1977), this does not mean that perceptual analysis
of the whole precedes the analysis of the elements, but rather suggests that the conscious perceptual
awareness is initially of the whole and that perception of the elements must follow from a more detailed
analysis. Generally, aviation users seek to process stimuli in a holistic way. The reason for this is to
relieve demands on short-term memory (the “whole” sticks in short-term memory, better than an enumeration
of its parts). If a detail regarding the whole is important, it must be highlighted in some way.
Why do weather graphics seem so important to aviation users Pure human-factors research suggests
that providing information along one dimension—text, color, quality—and then expecting the human
to make an absolute judgment about the stimulus is very difficult. When more dimensions are added,
research suggests that less information is transmitted along each dimension, but more overall information
is conveyed. This lessens the demands on the human; a graphic decision aid uses many dimensions
for this reason. It also matches the structure of the mental model used by the user (Wickens, 1984). With
graphics, it is important that the image given to the user or pilot be accurate at the first time. Research
suggests that subjects place an undue amount of diagnostic weight to the early stimulus, called anchoring.
Subsequent sources of evidence are not given the same amount of weight, but are used only to shift
the anchor slightly in one direction or another (Wickens, 1984). Also, research suggests that the number
of cues has a negative impact on response accuracy. This means cues must be informative and not so
salient that it overrides the information content, reliable and limited to those that are truly diagnostic of
the situation that one wants to convey. Once again, the user must be provided with no more information
than what is needed (Wickens, 1984).
The implication is that information and displays must be unambiguous, context driven, and require
little mental interpretation, such that the structure of the graphical user interface and display must
match the user’s model and task structure, and that the information transmitted must be accurate at
the first time. A goal, of course, is to enhance user awareness of the weather state without negatively
impacting the workload.
25.10 Workload and Time Sharing
Users within the NAS have learnt to be efficient at time sharing and allocating limited attentional
resources. The current ATC system and weather displays have had an important role in this learning
process, because they almost require the user to develop work-around strategies to be effective.
Generally, research on workload suggests that there is a trade-off between maintaining SA and minimizing
workload through automation. The trick is to optimally allocate the workload between human