Research suggests that the brain corrects grammar errors while you listen to others speak:
The brain does all kinds of amazing things while you’re not paying attention (you know, like regularly remind you to breathe). But it’s also engaged in less critical but equally interesting tasks, like correcting the grammar of the person sitting across from you at dinner. A University of Oregon study has logged hard evidence that the brain processes and compensates for errors in grammar and syntax without your being aware of it.