The temporal acoustic pattern of a short speech signal is encoded very accurately in the brainstem. This compound remote response can be recorded on the scalp under the form of speech elicited Auditory Brainstem Response (Speech ABR). Speech ABR is described as the succession of a transient Onset Response (OR) and a sustained Frequency Following Response (FFR). It has been shown that the FFR is the compound phase-locking activity of brainstem cells, and that FFR mimics the periodicity of phonemes (Russo et al., 2004). In Experiment 1 reported here, we confirmed this observation (23 subjects). Experiment 2 showed that Speech ABR to /ba/ components, had different latency-intensity functions (around 15ms for FFR and 7 ms for OR), assuming that these two responses were the result of separate processing streams (11 subjects). In Experiment 3, three stimuli with steady fundamental frequencies (F0) at 133, 375 and 575 Hz vowel were used (12 subjects). Speech ABR showed a reproducible onset response (OR) around 6 ms after stimulus onset, whereas FFR seemed to vanish for high F0. This lack in synchronization gives further evidence that upper brainstem may be the main generator for Speech ABR.

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