Comparison of Click and Chirp Evoked ABR in Normal Hearing and Hearing Impaired Individuals

Abstract

Auditory brainstem responses (ABR) evoked by click stimuli are most commonly evoked potentials used for threshold estimation. It has been reported that the click stimuli doesn't evoked a synchronous neural firing along the basilar membrane and thus resulting in reduced amplitude of ABR wave V. To overcome the reduction in amplitude, chirp stimuli have been developed to compensate the group delays in basilar membrane traveling wave. Thus the present study aimed at Comparing the ABR wave (amplitude, latency and morphology) elicited by click and chirp stimuli in 30 ears with normal hearing and 20 ears with cochlear hearing loss at 80 dBnHL and 40 dB SL at the repetition rates of 11.1/ sec and 30.1/ sec. ABR thresholds obtained by click and chirp in normal hearing and cochlear impaired individuals elicited at 30.1/ sec repetition rate were compared with behavioral thresholds. Also to know whether chirps can evoke any significant neural synchrony in individual with auditory dysynchrony chirp evoked ABR were recorded at 11.1/ sec repetition rate in 10 ears with auditory dysnchrony. The results revealed that there was a significant difference in latencies within and across groups for click and chirp stimuli but there was no significant differences observed in terms of amplitude except for wave I at 11.1/sec repetition rate at 80 dBnHL revealing cochlear processing differences across the groups. There were high correlations between click and chirp evoked with their behavioral thresholds in both normal hearing and hearing impaired subjects suggesting the application of chirp evoked ABR in threshold estimation. Chirp stimuli can evoke better synchrony then click stimuli suggesting the clinical use of chirp evoked ABR in individuals with auditory dysnchrony.