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.

The impact of increased cognitive task demands on both performance and cognitive workload
I’d like to read up some more on the temporal relationship between task demands and performance. In the graph, the intersection/interaction occurs post increase in task demands and it looks like though performance decreases marginally before this, it is sustained for just a bit despite the steeper task demands slope. Is there a good place to find more on this?
Thanks!