Objective: To investigate the temporal relationship between speech auditory brainstem responses and acoustic pattern of the phoneme /ba/.
Methods: Speech elicited auditory brainstem responses (Speech ABR) to /ba/ were recorded in 23 normal-hearing subjects. Effect of stimulus intensity was assessed on Speech ABR components latencies in 11 subjects. The effect of different transducers on electromagnetic leakage was also measured.
Results: Speech ABR showed a reproducible onset response (OR) 6ms after stimulus onset. The frequency following response (FFR) waveform mimicked the 500Hz low pass filtered temporal waveform of phoneme /ba/ with a latency shift of 14.6ms. In addition, the OR and FFR latencies decreased with increasing stimulus intensity, with a greater rate for FFR (-1.4ms/10dB) than for OR (-0.6ms/10dB).
Conclusions: A close relationship was found between the pattern of the acoustic stimulus and the FFR temporal structure. Furthermore, differences in latency behaviour suggest different generation mechanisms for FFR and OR.
Significance: The results provided further insight into the temporal encoding of basic speech stimulus at the brainstem level in humans.