Neural Correlates of Masking Level Differences: Evidence From Auditory Brainstem Responses.

OBJECTIVE

This study aimed to investigate the neural correlates of masking level differences (MLD) by examining their relationship with auditory brainstem responses (ABR) in normal-hearing adults, to better elucidate the underlying brainstem mechanisms involved in MLD.

METHODS

A total of 37 normal-hearing adults aged 18-30 years participated. Auditory evaluations included pure-tone audiometry, tympanometry, MLD testing at 500 Hz under S₀N₀ and SπN₀ conditions, and click-evoked ABR recordings. Correlations between ABR wave latencies (Waves I, III, and V) and interpeak intervals (I-III, III-V, and I-V) with MLD scores were analyzed using Spearman's correlation. Multiple linear regression analyses were conducted in two separate models to evaluate the predictive contribution of ABR components to MLD performance.

RESULTS

The mean MLD was 13.24 ± 2.18 dB, exceeding the clinical threshold for normal performance. No significant gender differences were observed in ABR or MLD measures. A moderate positive correlation was found between ABR Wave V latency and MLD scores (r = 0.58, p < 0.001). In regression analyses, Wave V latency was the only significant predictor of MLD scores (p = 0.003), explaining 28% of the variance. Other ABR components were not significant contributors.

CONCLUSIONS

The results demonstrate that MLD performance is associated with ABR Wave V latency, suggesting that midbrain structures such as the inferior colliculus play a crucial role in binaural auditory processing. These findings support the utility of MLD as a behavioral index of brainstem integrity and its potential role in the evaluation of auditory dysfunction. While further research is needed to confirm these associations in clinical populations, MLD testing may offer valuable diagnostic insights into auditory brainstem dysfunction.