Neuroscientists discover a brain signal that indicates whether speech has been understood -- ScienceDaily
To test if human brains actually compute the similarity between words as we listen to speech, the researchers recorded electrical brainwave signals recorded from the human scalp -- a technique known as electroencephalography or EEG -- as participants listened to a number of audiobooks. Then, by analysing their brain activity, they identified a specific brain response that reflected how similar or different a given word was from the words that preceded it in the story.
Crucially, this signal disappeared completely when the subjects either could not understand the speech (because it was too noisy), or when they were just not paying attention to it. Thus, this signal represents an extremely sensitive measure of whether or not a person is truly understanding the speech they are hearing, and, as such, it has a number of potential important applications.