COGNITIVE WORKLOAD, COGNITIVE TASK DEMANDS, AND PERFORMANCE
Most research focuses on the impact on both workload and performance of specific cognitive tasks and their associated cognitive demands. This relationship is shown in the figure below. Stated most simply, what this figure suggests is that two things happen when a task becomes too hard for an individual: first, of course, his performance suffers because he can’t do it. Second, and less obvious, is that as the task becomes more difficult, it most likely encompasses a wider set of cognitive demands, and these expanded cognitive demands drive up the individual’s cognitive workload. So, the performance graph goes down while the workload graph goes up.