The Study Of Loudness Performance On The Physiological Characteristics Of Late Latency Response

The hearing aid and cochlear implantation are the mainly auxiliary approaches for hearing-impaired patients in clinical treat,whose fitting and adjustment need set the hearing threshold and comfortable levels.Usually,the measures of those two parameters need subjectively behavioral test.For special patients lacking of subjective behavior such as infants and the mental handicapped,and electrical response audiometry(ERA)is the efficiently objective measure.However,ERA can only measure the hearing threshold presently,and the objective measure for comfortable levels is still vacant.With the users of hearing aid and cochlear implantation tending to lower in age,to ensure the availability of hearing aid and cochlear implantation,how to achieve the objective measures of comfortable levels is urgent.Auditory evoked potentials(AEP)usually are applied to ERA.Now researches have indicated the AEP amplitude or latency related with loudness or sound intensities,but this relation wasn't stability for individuals.Hence these AEP characteristics haven't yet been efficient loudness test indexes.Animal researches have presented that the amplitude of auditory steady state response(ASSR)appeared habituation,and the habituation degree differed at different sound intensities.The AEP habituation mainly performs that responses attenuate as stimuli replicating.The sound intensities decide the loudness perception from human hearing.Therefor,the loudness response should present on AEP habituation.Studies have been proposed that the late latency response(LLR)of AEP was more proper to habituation study,hence this paper analysed the habituation of LLR under loudness levels at "Most comfortable"?"Loud but comfortable" and "Loud",then extracted the parameters distinguishing the loudness comfortable levels from louder levels,which provided guidance for objective test of loudness comfortable levels.This paper firstly measured the sound intensities corresponding to those three loudness levels for 29 subjects by behavioral loudness test and analysed the relation between loudness levels and sound intensities.EEG was recorded by multichannel,and only EEG from 19 subjects is complete and avaliable to further study because of their limited adaptability to the EEG recording process.This research studied the habituation performance of N100 amplitude,the phase locking value(PLV)and wavelet coherence from LLR at those three loudness levels.The contents are generalized as following:(1)Study of the relation between loudness levels and sound intensities.Measured the sound intensities corresponding to loudness levels at "Most comfortable"?"Loud but comfortable" and "Loud" of 29 subjects by behavioral loudness test to adjust the stimuli intensities during EEG recording.(2)Habituation study of N100 amplitude from LLR at the three loudness levels.Moving superposition averaging was adopt to EEG from 19 subjects to illustrate habituation at three loudness.Defined parameter Vhab to stand for habituation features of amplitude decay velocity.Results indicated that N100 amplitude performed habituation at all loudness levels,and the Vhab of "Loud"was higher than other two loudness,but all results were from EEG after subjects grand average.(3)Habituation study of PLV from LLR at the three loudness levels.In view of individual N100 amplitude habituation not well from part(2),raw data was processed by multichannel noise reduction technology of FASTER and Independence component analysis(ICA).6th order complex gaussian wavelet was adopted to wavelet transform for the data after noise reduction,and the wavelet coefficient from time-frequency dot that LLR appeared most obviously was extracted to calculate the PLVs.results indicated that the PLV of LLR performed habituation under three loudness level at 100 ms and around 5 Hz,but only PLVs at "Most comfortable" was significantly less than PLVs at "Loud"(one-way ANOVA test,p<0.05).(4)Habituation study of wavelet coherence from LLR at the three loudness levels.6th order complex gaussian wavelet was adopted to calculate the wavelet coherence between neighbouring sweeps of LLR,then extending average was executed to wavelet coherence.Study presented that the wavelet coherence of LLR performed habituation under three loudness levels.Averaging the wavelet coherence of 1-50 sweeps and 360-410 sweeps respectively,then respectively set the averaging value as "before decay"and "after decay" samples.Results stated that these two group of samples differed significantly at "Most comfortable" as frequency at 9.2 Hz,time range at 70-110 ms(Wicoxon test,p<0.05).N100 amplitude,the PLV and wavelet coherence of LLR performed various degree habituation at those three loudness.However only PLV and wavelet coherence appeared obviously statistical difference,which can function as potential parameters of measuring loudness comfortable levels.