Speech-evoked Auditory Brainstem Response; Electrophysiological evidence of upper brainstem facilitative role on sound lateralization in noise

Background and Aim : Sound localization is one of the most important auditory processing ability, which plays approved role in auditory streaming and speech perception in challenging situations like noisy places. In addition to the main role of lower brainstem centers like Superior Olivary Complex in sound lateralization, efferent auditory system effects on improving auditory skills in everyday auditory challenging positions were revealed. This study evaluated noise effects on lateralization scores in correlation with an objective electrophysiologic test (Speech-ABR in noise), which objectively shows cumulative effects of the afferent and efferent auditory system at Inferior Colliculus and upper brainstem pathwayMethods : Fourteen normal hearing subjects in the age range of 18 to 25 participated in this study. Lateralization scores in the quiet and noisy mode were evaluated. Speech-ABR in both ears for quiet mode and three different contralateral noise levels (SNR= +5, 0, -5) were recorded, too. Correlation of lateralization scores and Speech-ABR changes in noise were studied.Results : Significant decrease of lateralization scores with latency increase and amplitude decrease of Speech-ABR transient peaks (V, A, O) were seen with noise presentation. A high positive correlation between lateralization decrease with latency increase of onset peaks (V, A) and amplitude decrease of transient peaks (V, A, O) were found in low signal to noise ratios.Conclusion : The study revealed that in high challenging auditory situations like auditory lateralization in noise, upper brainstem centers and pathways play a facilitative role for main auditory lateralization centers in lower levels.

Keywords:

Sound Lateralization , Speech evoked Auditory Brainstem Response , Noise , auditory efferent system