Sometimes I can *feel* my brain protesting the strain of doing something. I'm making good progress, as gaijin learning Japanese go. But as my brain tries to decode simple utterances like "between what time and what time is the bank open?" (ginkoo wa nanji kara nanji made des ka?) I can definitely tell: this is not what the old brain wanted to be doing this morning.
Similarly, I can write okay in Japanese once I've figured out the syllables. But I can feel my brain strain to come up with the right bits of hiragana and katakana at any speed.
(Not kanji, of course. I'm only six months in. I know, like, two kanji.)