to see if a number has changed on that display. Thus when cognitive engineers design a system, they consider many kinds of feedback.
Cognitive engineers also consider the context in which a system will be used. If people work in a very noisy (e.g., industrial) environment, then relying on a beep or other sound to get their attention would not be a very good design. Other contexts to consider are the state of the people who will be using the system. How can we design a system that will accommodate all levels of potential users? Can we design the system in such a way that people will be able to use it right away and become better at using it with experience rather than relying on extensive training?
In general, design is an iterative process. Cognitive engineers focus on understanding the cognitive requirements and constraints inherent in the system, designing prototypes, testing those prototypes for usability, and iterating on the designs until production. This human-centered design process is often skipped, either because of a lack of knowledge about the cognitive engineering approach or a perceived lack of time or funding. Usability experts may be brought in after implementation of a system, but it may be difficult to make changes at that point. In fact, a usable system meets the actual requirements. Figure 1 shows how far down in the process implementation should start and how early in the process task analysis and iterative design and testing should start.