Proceedings of the Human Factors Society

Limited Attention Capacity Limits Situation Awareness

When people are in engaged highly dynamic environments where lots of things are happening all at once, they may not be able to pay adequate attention to everything simultaneously. We would expect them to allocate their attention to those things they judge to be most important. This insight suggests that limited attentional capacity should limit people’s situation awareness.

In this experiment, I placed participants in a simulated combat environment and tried to manipulate their attentional priorities. In order to assess the impact of these manipulations on situation awareness, I employed a memory probe procedure in which we would occasionally interrupt the simulation and query the participants on details of the tactical situation.

How Do People Maintain Situation Awareness in a Dynamic Environment?

Think about when you are driving on a busy highway. How do you know whether it is safe to change lanes? How do you decide whether the driver of that car coming out of a parking lot is going to wait for you to pass before entering traffic? How do you keep track of a reckless driver speeding and zig-zagging through traffic? These questions are all related to the concept of situation awareness.

Situation awareness is particularly important in the military, especially in the Air Force where the tactical environment is rapidly changing. In the mid-1980’s, pilot situation awareness was a hot topic, but exactly what it was and how cockpit designers could help pilots maintain it were not as yet well understood. For that reason, when I was assigned to the Human Engineering Laboratory at Wright-Patterson Air Force Base, I decided to try to fill in the gaps within our knowledge.

When is a User Interface Good Enough?

During my 20 years as a usability consultant with IBM, it was the rare corporate client that was willing to pay for extensive usability testing. Many clients expected that since we were “user interface experts” we would be able to design a great and usable interface in short order. To cope with the resulting time pressure, we developed several methods for rapidly iterating and evaluating user interface designs. Even so, there remained the question: when do you stop iterating? In other words, when is a user interface good enough?

Scaling Usability Based on Requirements

When a company such as a bank hires a usability engineering consultant, they usually have a specific problem they are trying to solve. One common problem is that customer-service call centers are too expensive to operate. When it is not practical to build a self-service website for their customers, clients will choose instead to redesign their call center agent workstations to make them more efficient. Sometimes, just reducing the amount of time by a few seconds an agent needs to complete a customer service interaction can save the company hundreds of thousands of dollars. The company may even calculate how much time they need to save on certain high-volume customer service interactions in order to achieve their business goals. That targeted time savings then becomes what we call a usability requirement. Of course a usability requirement can also be defined in terms of the number of errors an agent makes using their workstation to complete an interaction, or even just the number of clicks.

Regardless of what the formal usability requirement may be, the usability engineer needs a way to estimate the likelihood that a proposed user interface design will meet that requirement. In other words, is there a way to scale measured performance in a usability test against some criterion so that it represents the probability of achieving a specific usability requirement?