[qu4ku]

This may be anecdotal [and sleep deprivation may impact different people differently] but it has a huge impact on me.

I used to use memrise [flash card style memorisation] to learn new words/concepts for years [25minutes, the first thing after waking up, every single day] and I know from experience how sleep, food, hangover, etc. impact my performance.

Sleep has a gigantic impact on my memory, focus and creativity — I believe it is responsible for really high variation in IQ points [10 - 20, but that's my rough guesstimate]. This is a more qualitative assessment but whey I sleep 4 hours it resembles a high level of depression — I lose motivation and all of my natural curiosity is gone [eg. usually, reading/learning brings me happiness, but it's all gone when I'm sleep deprived].

That's why I haven't used an alarm clock for years now.

[kyuudou]

I have similar results and opinions. I feel that there is some kind of "back-end processing" that happens during sleep that is crucial for learning. Also, my sleep tends to be better when I'm doing some kind of workout regularly, although I need to sleep more. If I'm not working out, I can get by easily with 6 hours but if I am, absolutely need 8 hrs min. Makes sense to me since a lot of repair, healing and growth occur while sleeping.