I've been trying to track my cognitive performance, and it turns out simple arithmetic isn't so good at detecting sleep deprivation.

I've been deprived of sleep to the point of starting hallucinations, and my math times went up by about 10%, which is within the noise. However, I was so impaired that I not only soldered the wires on before running them through the cap, but when I undid it, I soldered it right back on without passing them through the cap first.

It seems like different parts of the brain are at work. If you're trying to make sure you're not sleep deprived, I'd look for tasks that lobotomy patients are not good at. I just haven't found any that are easily quantifiable yet.