Effect of Noise Spectrum on Cortical Evoked Auditory Potentials in Younger and Older Adults with Normal Hearing Sensitivity

Abstract

Cortical auditory evoked responses (CAEPs) can be employed to study the neural encoding of speech. This on the other hand helps us in understanding the speech processing that happens at higher level. CAEPs can be used on different populations to see how their perception is affected by noise. Older individuals often complain about trouble in understanding speech in noisy situations. These individuals with or without hearing loss usually exhibit difficulty in perception of speech compared to young listeners especially in the presence of background noise. The present study was designed to identify the effect of different type of noise spectrums on the cortical auditory evoked potentials (CAEPs) in younger and older population and its correlation with behavioral measure (speech in noise test results). 15 younger adults and 15 older adults with normal hearing sensitivity participated in the study. Stimulus /ba/ and /da/ stop consonants in four different test environment such as in quiet, high pass noise (>4000 Hz), low pass noise (<200 Hz) and speech noise was used in the study. Latency and amplitude of N1 and P2 were considered for the study. Significant shift in latency and reduction in amplitude was seen in N1 of the older adults. Stimulus condition quiet showed significantly better latency and amplitude compare to other three noise conditions in both the groups. Significant negative correlation was seen between SPIN scores and N1 and P2 latencies. These results indicate, age-related refractory differences in younger and older auditory systems could have reflected in CAEPs. Refractory issues might in turn affect synchronized neural activity and hence result in poorer latency and amplitude. Different noise spectrum affects CAEPs differentially and N1 is most affected by low pass noise and P2 is most affected by high pass noise. The data indicates that use of CAEPs in measuring effect of noise at cortical level and its correlation with speech perception has excellent potential for future research among older adults.