Intelligible speech encoded in the human brain stem frequency-following response.

The human brain stem frequency-following response (FFR) registers phase-locked neural activity to cyclical auditory stimuli. We show that the FFR can be elicited by word stimuli, and when speech-evoked FFTs are reproduced as auditory stimuli they are heard as intelligible speech. Stimuli were 10 high- and 10 low-probability words drawn from normative verbal responses of university students. Horizontal and vertical dipole FFRs based on 1000 repetitions of each word were recorded from two different participants. Speech-evoked FFRs were evaluated by 80 listeners. The results showed significant effects of FFR participant, word probability, and whether or not words were presented with category cues. Depending on such subject and experimental variables, FFRs were correctly perceived from 5% to 92% of the time.