Acceptance of Background Noise, Working Memory Capacity, and Auditory Evoked Potentials in Subjects with Normal Hearing

Background: The acceptable noise level (ANL) test is a method for quantifying the amount of background noise that subjects accept when listening to speech. Large variations in ANL have been seen between normal-hearing subjects and between studies of normal-hearing subjects, but few explanatory variables have been identified. Purpose: To explore a possible relationship between a Swedish version of the ANL test, working memory capacity (WMC), and auditory evoked potentials (AEPs). Research Design: ANL, WMC, and AEP were tested in a counterbalanced order across subjects. Study Sample: Twenty-one normal-hearing subjects participated in the study (14 females and 7 males; aged 20-39 yr with an average of 25.7 yr). Data Collection and Analysis: Reported data consists of age, pure-tone average (PTA), most comfortable level (MCL), background noise level (BNL), ANL (i.e., MCL-BNL), AEP latencies, AEP amplitudes, and WMC. Spearman's rank correlation coefficient was calculated between the collected variables to investigate associations. A principal component analysis (PCA) with Varimax rotation was conducted on the collected variables to explore underlying factors and estimate interactions between the tested variables. Subjects were also pooled into two groups depending on their results on the WMC test, one group with a score lower than the average and one with a score higher than the average. Comparisons between these two groups were made using the Mann-Whitney U-test with Bonferroni correction for multiple comparisons. Results: A negative association was found between ANL and WMC but not between AEP and ANL or WMC. Furthermore, ANL is derived from MCL and BNL, and a significant positive association was found between BNL and WMC. However, no significant associations were seen between AEP latencies and amplitudes and the demographic variables, MCL, and BNL. The PCA identified two underlying factors: One that contained MCL, BNL, ANL, and WMC and another that contained latency for wave Na and amplitudes for waves V and Na-Pa. Using the variables in the first factor, the findings were further explored by pooling the subjects into two groups according to their WMC (WMClow, and WMChigh). It was found that the WMClow had significantly poorer BNL than the WMChigh. Conclusions: The findings suggest that there is a strong relationship between BNL and WMC, while the association between MCL, ANL, and WMC seems less clear-cut.