Participants in the study — native-English speaking people aged 18-30 — had their brain activity recorded. Subjects were given 280 experimental sentences, including grammatically correct and incorrect ones. A tone appeared before or after a grammatical faux pas was presented.
When tones appeared after grammatical errors, subjects detected 89% of the errors.
When the tones appear before the grammatical errors, subjects detected only 51% of them. The tones disrupted participants’ ability to declare errors. But, even when the participants did not notice errors, their brains responded to them.