Civil Engineering Reference
In-Depth Information
these cases the screen is so small that the interaction is limited to the few options that can
be displayed, which makes it more difficult to handle.
7.2
SOME USEFUL DESIGN PRINCIPLES IN HUMAN-
COMPUTER INTERACTION
In this chapter we give a brief overview of some important design issues in HCI. Six
design issues are listed below, but in mentioning these, we are only touching on the
surface.
1. Provide an interface that does not violate the user's expectations or mental model.
2. Design a consistent interface. This will improve expectations and reduce user errors.
3. Reduce the memory requirements and memory load of the user.
4. Give feedback to the user, to inform users about what is going on.
5. Design the interface to cater to all types of users. Consider that there are great
differences among individuals in memory and cognitive capabilities.
6. Use direct manipulation to simplify the way information may be accessed and
manipulated by the user. This is one of many great ideas that were implemented at
Xerox Star.
We will now describe these principles in greater detail.
DO NOT VIOLATE THE USER'S MENTAL MODEL
The human-computer dialogue must not violate the user's mental model, the way users
think about the problem. It should not be necessary for the user to translate the
information on the screen, so that it fits with his mental model. As an example, consider
the situation where a company would like to write software for process control of a
mineral flotation process that is used to enrich minerals. This software could then
partially replace the operators who worked with this task.
The programmer who was assigned the topic of writing the software realized that she
was not an expert on mineral enrichment and flotation. She wanted to understand whether
the operators have a mental model of the process, and if she should write the software so
that it would agree with the mental model—and the procedures that were commonly
used, or maybe there are many mental models, one for each operator? If so, she would
like to find out if there are common features between the different models.
To find out, we can observe how operators make decisions about process control
parameters—about temperature, when to add chemicals, and when to finish. A cognitive
task analysis would be a good way to document the operators' expertise and what their
mental models are.
What happens if all mental models are different? In this case the HCI designer can
either select the best model, or try to formulate a new model that will not violate the
existing mental models. This is a difficult task in HCI; it will require much analysis and
evaluation before one can propose a good design solution. But once this is accomplished,
the software will have commercial value.
