Spatial hearing processing: electrophysiological documentation at subcortical and cortical levels

Objective: Recognition of target signal improves when the target and distracted sources are spatially separated, an effect defined as 'spatial release from masking' (SRM). The neural mechanisms underpinning SRM are complicated and still need to be identified. The aim of this study was to identify whether objective correlates of SRM can be recorded in either the brainstem or cortex (or both). Materials and methods: In response to 200 target stimulus blocks, auditory brainstem responses (ABRs), frequency-following responses (FFRs) and cortical auditory evoked potentials (CAEPs) were recorded concurrently from 13 normally hearing adults utilizing two stimulus patterns, flat and staircase, in the presence of randomized distractors at -5, 0, 5, 10 and 15 dB SNR, and in co-located and separated spatial locations. Results: FFR F0 amplitude increased for the flat stimuli at -5 dB SNR, ABR wave V latency decreased for both flat and staircase stimuli in all SNRs and for P1 and N1 latencies due to the noisy CAEPs, drawing any significant conclusion could be subject to further investigation. Conclusion: These findings suggest that SRM can be objectively recorded concurrently in both the brainstem and auditory cortex. It is speculated that the central auditory system can suppress background noise based on spatial information commencing from the brainstem and that this capability is remarkable in more difficulty listing situations. This study may pave the way to evaluate spatial processing electrophysiologically utilizing FFR amplitude, ABR and CAEPs latencies condition to confirmation of the results of this study, at least at the level of the cortex in future investigation.