Audiological Profile of Adult Persons with Auditory Neuropathy Spectrum Disorders

BACKGROUND AND OBJECTIVES: The auditory profile of a large number of persons with late onset auditory neuropathy spectrum disorder (ANSD) is recently described in the Indian context. The purpose of study was 1) to profile data on routine audiological parameters, cortical evoked potentials, and temporal processing, 2) to analyze the benefit from hearing aids for persons with ANSD, and 3) to understand the association between benefit from hearing aids and auditory profile. SUBJECTS AND METHODS: Thirty-eight adults with late onset ANSD and a matched group of 40 normally hearing adults participated in the study. Basic audiological tests, recording of cortical evoked potentials, and temporal processing tests were carried out on both groups of participant while only persons with ANSD were fitted with hearing aid. RESULTS: Subjects in the two groups were significantly different on all the audiological parameters. ANSD group seemed to benefit from hearing aids variably. The mean amplitude of N2 was significantly different between normally-hearing participants and patients with ANSD. CONCLUSIONS: Residual temporal processing, particularly amplitude modulation detection seems to be associated with benefit from hearing aids in patients with ANSD.

Cortical Evoked Potentials and Hearing Aids in Individuals with Auditory Dys-Synchrony.

OBJECTIVE: The purpose of the present study was to investigate the relationship between cortical processing of speech and benefit from hearing aids in individuals with auditory dys-synchrony. MATERIALS AND METHODS: Data were collected from 38 individuals with auditory dys-synchrony. Participants were selected based on hearing thresholds, middle ear reflexes, otoacoustic emissions, and auditory brain stem responses. Cortical-evoked potentials were recorded for click and speech. Participants with auditory dys-synchrony were fitted with bilateral multichannel wide dynamic range compression hearing aids. Aided and unaided speech identification scores for 40 words were obtained for each participant. RESULTS: Hierarchical cluster analysis using Ward's method clearly showed four subgroups of participants with auditory dys-synchrony based on the hearing aid benefit score (aided minus unaided speech identification score). The difference in the mean aided and unaided speech identification scores was significantly different in participants with auditory dys-synchrony. However, the mean unaided speech identification scores were not significantly different between the four subgroups. The N2 amplitude and P1 latency of the speech-evoked cortical potentials were significantly different between the four subgroups formed based on hearing aid benefit scores. CONCLUSION: The results indicated that subgroups of individuals with auditory dys-synchrony who benefit from hearing aids exist. Individuals who benefitted from hearing aids showed decreased N2 amplitudes compared with those who did not. N2 amplitude is associated with greater suppression of background noise while processing speech.

Effect of early onset otitis media on brainstem and cortical auditory processing.

BACKGROUND: Otitis media (OM) leads to significant reduction in the hearing sensitivity. The reduced auditory input, if in the early years of life when the auditory neural system is still maturing, may adversely influence the structural as well as functional development of the system. Past research has reported abnormalities in both the structure and function of brainstem nuclei following auditory deprivation, but, it has not necessarily focused on children who had OM in their first year of life. It can also be said that if auditory processing is affected at the brainstem level because of early onset OM (reduced auditory input in the crucial periods of neural development), then, it may be said that auditory processing is also affected at the cortical level because it receives distorted input from the brainstem. Therefore, the purpose of this study was to document the effects of early onset OM on auditory processing, if any, at the brainstem as well as at cortical levels. A related purpose of the study was to investigate the persistence of the effects of early onset OM, if any, on auditory processing. METHODS: A cross sectional approach and a standard group comparison design was used in the study. Thirty children, who had OM between 6 and 12 months of age and who were in the age range of 3.1 - 5.6 years participated in the study. Children with OM were divided into 3 groups based on their age. Click evoked auditory brainstem responses (ABRs) and late latency responses (LLRs) were recorded from these children, and the responses were compared with those from age and gender matched normal children without any history of OM. The data from the 2 groups was statistically analyzed through independent t test. Pearson's Product Moment correlation was computed to examine the relationship between results of ABR and LLR in children with early onset OM. RESULTS: The mean central conduction time was significantly increased and the mean amplitude of wave I and III of ABRs was significantly reduced in children with early onset OM compared to normal children. Also, the latency of all LLR waves was significantly less in children with early onset OM than in normal children. However, significant differences in mean values of either ABR or LLR (latencies or interwave intervals as the case may be) were observed only in 3-year old children. There was a significant, but negative association between central conduction time and latency of LLRs. CONCLUSION: OM in the first year of life leads to negative effects on brainstem signal processing even if it has occurred only for a short duration (maximum of 3 months). In such a situation, auditory cortical structures probably show compensatory changes through central gain to offset the prolonged central conduction time. Although the results of the present study showed that the negative effects of early onset OM (occurring in the first year of life) on auditory processing disappeared by the time the children were 4.1 years, there is need for longitudinal studies on this to confirm the findings.