COGNITIVE WORKLOAD AND PERFORMANCE
Cognitive workload describes an individual’s mental response to a task. Cognitive task load describes the cognitive demands inherent in the task. The individual’s cognitive workload is greatly influenced by the task’s cognitive demands, with the task’s cognitive demands driving the individual’s cognitive workload up or down. However, the task keeps its associated cognitive demands no matter what the cognitive workload levels of the individual or individuals who perform it. Thus, changing the cognitive workload of an individual will not alter the cognitive load of the task—it remains the same. But, changing the cognitive task load may greatly change the resulting cognitive workload of the individual.
Both cognitive workload and cognitive task load may influence performance. When an individual interacts with a task, typically some level of output is required of the individual. That is, he is asked to do more than just be present or absent—he needs to take some action or make some decision or perform in some other (usually measurable) way. Both cognitive workload and cognitive task load have a bearing on this performance output, as shown in the figure below. The role of cognitive workload on performance is direct: if workload is too high or too low, performance may be degraded. The role of cognitive task load on performance may be both indirect and/or direct: if the cognitive demands of the task are too great for the individual to manage, his cognitive workload goes up and his performance is degraded (indirect impact). If the task is simply too hard for anyone, performance in general is restricted (direct impact). Performance may also be poor if cognitive workload becomes too low. Thus, managing either the cognitive workload level of the individual or the cognitive load level of the task can have a beneficial effect on the individual’s performance of the task.
Of course, performance may be influenced by many other things that are external to the individual and the task (such as environment or general working conditions). Similarly, cognitive workload is not determined solely by the cognitive load of the task but may also be impacted by other properties of the individual, either fleeting or stable.
It is useful to consider what happens when cognitive workload is either too low or too high. The figure below shows the hypothesized relationship between cognitive workload and performance under such conditions.
The figure is patterned after the well-known Yerkes-Dodson Law of Arousal with Hebb’s (1955) simplification but the shape of the curve is flatter. Basically, this figure suggests that there exists a “sweet spot” at which both cognitive workload and performance are in acceptable range (indicated by dotted lines). If cognitive workload falls too low, performance suffers (e.g., the individual loses interest, becomes bored, or otherwise fails to perform the task). If cognitive workload rises too high, performance likewise suffers (because the individual no longer can manage the cognitive demands of the task).