A Study on Simulated Traffic Environment: Assessing Localization Ability from Individuals with Hearing Impairment

Abstract

The present study was taken up to examine localization ability from subjective and objective methods in a simulated road traffic environment. The objectives were formulated as follows: a) To compare the localization errors between ages matched control group and clinical groups b) To assess the localization function index using a standardized questionnaire from control and clinical groups c) To correlate and predict degree of error and localization function index with the audiological findings of participants of the study d) To find the relation between existing protocols in clinic with the adopted test utilized in the current study. Forty participants within age range from 40 to 60 years were involved in the study. The participants were grouped into two groups namely control group and clinical group. Control group comprised of ten participants and all of them had normal hearing sensitivity. Clinical group were sub grouped into three, based on severity of hearing loss i.e. moderate to moderately severe hearing loss 40 to 70 dB HL (mean HL = 61.25 dB HL) (subgroup-1); severe hearing loss 70 to 90 dB HL (mean HL = 77.5 dB HL)(subgroup-2) and profound hearing loss > 90 dB HL (mean HL = 100 dB HL) (subgroup-3). Each subgroup comprised of ten participants. The participants were fitted binaurally with the digital BTE hearing aids. The target stimuli (Truck horn and automobile horn) were presented from five speakers and traffic noise (65 dB SPL and 75 dB SPL) was presented from four speakers as background noise to simulate traffic situation. The localization errors for each horn presented in low and high noise levels were assessed. In addition, localization functional index using the standard questionnaire was obtained from the participants of the study. Further aided SIS and aided audiogram were assessed in binaural condition. The results revealed a degree of localization error; LFI and SIS were significantly reduced with increase in degree of hearing loss. Further localization error significantly reduced with high noise level than low noise level. LFI and DOE were significantly correlated with audiological findings. To be specific, LFI decreased with increased degree of hearing loss; and hearing disability. In addition, LFI decreased with reduced SIS. Further, DOE increased with reduced localization functional index. A regression model was established through which DOE, LFI were predicted from the audiological findings. Interestingly, irrespective of degree of hearing loss, aided thresholds were within speech spectrum. The findings suggests to include localization test to identify degree of localization error instead of considering aided thresholds within speech spectrum for those individuals who seeks a hearing fitness certificate for the purpose of applying driving license. The findings of the study suggests to include localization test in a simulated road traffic condition rather aided audiogram in the present day protocol to issue hearing fitness certificate for hearing impaired individuals who seek for applying driving license. However, the eligibility criteria to issue certificate of hearing fitness for applying driving license is yet to be decided in the upcoming studies.