Yes, when you're learning something new, the brain uses resources (all the chemical and biological necessities to grow new neural connections).
This could mean that your thinking performance decreases, temporarily, while your brain is allocating more blood circulation / glucose consumption, etc ...
Sleep also plays a role, too ... As new learning connections get "consolidated" during certain phases of sleep ...
So yes, I'd say that your suspicion is correct. It's almost like the brain is a computer - and performance can lag when resources are diverted to do new tasks ...
I am asking this because of something that has recently happened to my grade.
My two disciplines are chess and theology. Normally my Bullet grade is just over 1800. But when I was reading and reflecting on a History of the Waldenses from 1622 recently my Bullet ability slipped and I struggled to stay over 1700.
Having finished the book, my Bullet grade is back over 1800. As far as I know, I have done nothing different. Certainly I have done no additional chess study.
It's not as simple as "the two ways of thought are incompatible" - I am now reading a different theological treatise with; it seems; no ill effect on my grade.
Is there any literature on; or other psychological explanation for; this sort of thing? Was this random chance, or might the two types of thinking have clashed somehow?
All ideas welcomed.