Final answer:
The selective attention factor that refers to how extreme effort may impede attention is known as 'effort'. Excessive effort can lead to stress and limited attentional capacity, hindering one's ability to maintain focus.
Step-by-step explanation:
The selective attention factor that refers to the fact that an extreme effort to accomplish a task may inhibit attention is known as effort. When a task requires significant attention, it places increased energy demands on the brain, and the resources demanded by conscious thought can be seen as a form of effort. Periodically, high-attention activity can be stressful, increasing blood flow and the supply of glucose and oxygen to the brain to meet the heightened mental activity. However, because attention is limited, when too much effort is expended on a task, it can have the paradoxical effect of reducing overall attentional capacity, making it more difficult to maintain focus on other tasks or even aspects of the task at hand.