Human Brains Don't Function As Well When Fatigued

An interesting article at Scientific American summarizes an interesting area of psychology/decision making research and its intriguing conclusions:

For instance, it's long been recognized that strenuous cognitive tasks—such as taking the SAT—can make it harder to focus later on. But recent results suggests that these taxing mental activities may be much broader in scope-and may even involve the very common activity of making choices itself. In a series of experiments and field studies, University of Minnesota psychologist Kathleen Vohs and colleagues repeatedly demonstrate that the mere act of making a selection may deplete executive resources. For example, in one study the researchers found that participants who made more choices in a mall were less likely to persist and do well in solving simple algebra problems.

...

In a parallel investigation, Yale University professor Nathan Novemsky and his colleagues suggest that the mere act of resolving tradeoffs may be depleting. For example, in one study, the scientists show that people who had to rate the attractiveness of different options were much less depleted than those who had to actually make choices between the very same options.

I'm still trying to think through how this research can be applied to human factors/user interface design, but to me it suggests that user interface designers should consider not only the dynamic cognitive load a user experiences at any given point while operating some product or system, but also the cumulative cognitive load. In other words, if you burden users with having to make a bunch of choices (even if the choices themselves are not all that taxing) that require frequent shifts in attention, you shouldn't expect those users to be able to perform at peak cognitive levels while busy with one task (obviously) or even after a busy task has just been completed (not so obvious).

Some questions:

1. How long does it take for a person's cognitive capacity to "recharge?"
2. Also, can one build up "cognitive endurance" through training?
3. Is this why people become frustrated at a seemingly exponential rate when, after repeated attempts, something STILL doesn't work?

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