Effects of stimulus presentation mode and subcortical laterality in speech-evoked auditory brainstem responses

Objective: Speech-evoked auditory brainstem responses (ABR) are sensitive to the manipulation of stimulus parameters, including how the stimulus is presented, i.e. monaurally or binaurally. Therefore, this parametric study was designed to compare the effect of binaural and monaural stimuli presentation on speech-evoked ABR features in the parallel assessment of subcortical asymmetry of speech stimuli acoustic elements. Design: Electrophysiological responses to the speech syllable /da/ were recorded within three stimulus presentation modes. Study sample: Forty-eight normal hearing monolingual Persian speakers were included in the current study as volunteer cases. Results: Shorter right ear latency was observed for peaks A and E, but the overall response timing was comparable within different stimulus presentation modes. Binaural stimulation generally led to larger response than monaural stimulation and affected the encoding of speech spectral elements. Moreover, no significant interpeak interval difference was observed in the sustained portion of responses. Response to the right and left ear stimulation was highly correlated, and a symmetrical pattern was observed between the two ears. Conclusions: The timing of speech-evoked responses is not related to the stimulus presentation mode; however, binaural stimulation produces more robust responses. Lateral asymmetry in the representation of speech elements was not considerable at the brainstem level.