The Impact On Reconstructed AEPs By Stimulus Sequences:Performance Analysis Of Two Deconvolution Methods

Auditory evoked potential(AEP)is a weak potential change of the auditory nerve pathways from the inner ear to the cerebral cortex after receiving acoustic stimuli.Its latencies can reflect the physiological condition of different parts of auditory system.Clinically,AEPs are mainly applied to neonatal hearing screening,assessment of objective hearing and so on.In general,AEP stimulation patterns are divided into conventional and high rates stimulus mode.As for the conventional recording paradigm,the transient AEP can be obtained by superposition averaging method because the response to each stimulus is complete prior to the presentation of the next stimulus.If this condition is not satisfied,overlapping of responses occurs.In this case,the transient AEP cannot be reconstructed by superposition averaging method and the implied AEP may be different from the transien AEP.In order to distinguish both,we called the implied AEP as high order AEP(hAEP).The clinical study of hAEP is promising because high stimulus rates can exert strong stresses on the auditory system which might reveal the pathology in the auditory system at an earlier stage.At present,there are four main deconvolution techniques to acquire the hAEP.Such as Maximum length sequence(m sequence)technique,Quasi-periodic sequence deconvolution(QSD)technique,Continuous loop averaging deconvolution(CLAD)technique and Multi-rate steady state averaging deconvolution(MSAD)technique.The quality of hAEP reconstructed by different deconvolution methods is affected by many factors.In this paper,we studied the effect of the orders of m sequces on noise attuenation and the effect of multi-rate steady state splicing combination modes on the reconstruction of hAEP which were based on the m sequence technique and MSAD method,respectively.1.To evaluate the effect of m sequence's orders on noise attenuation ability,two types of measured data are used.One of them is the spontaneous electroencephalogram(EEG)called simulation data which is acquired after the m sequence of different order(order 5 to 12)stopped stimulating.The other one is the evoked potentials referred to as experimental data stimulated by order 7 and 9 m sequence.Based on two calculation steps(stacking averaging and correlation process)of the m sequence technique,we estimated the noise attenuation ratios(NARs)of this two calculation steps with two types of measured data,respectively.After then we used the experimental data to obtain the linear/nonlinear components and compare them to each other.The results showed that the NAR is essentially independent of the m sequence order and is decided by the total length of valid data or the total recording time.And the result of the similarity comparison of the linear/nonlinear components evoked by order 7 and 9 m sequences indicates that the AEP components are insensitive to the order of m sequence.This study provides a more comprehensive solution for selecting m sequence and promotes betterly the application of non-linear AEPs based on m sequence.2.MSAD method is a newly devepled method to reconstruct the hAEP by transforming the deconvolution process into a matrix inversion problem by linear transformation.Attempting to reconstruct the hAEP evoked by amplitude modulation tone from amplitude modulation AS SR based on MSAD method for the first time,we investigated whether the splicing combinations of multi-rate ASSRs have an effect on the reconstructed hAEPs.Firstly,we recorded the ASSRs of seven different modulation frequencies(70-100 Hz,a step of 5 Hz)to form 15 different splicing combunations acoording to different splicing combination methods.And then we reconstructed the fifteen hAEPs of different splicing combinations.Based on the superposition hypothesis,we used these hAEPs to generate the synthesis ASSRs and analyzed the similarity to the recorded ASSRs under the same stimulus rate by correlation analysis.Finally,to observe the effect of splicing combinations on hAEPs,the hAEPs' waveforms were analyzed from the amplitudes and latencies of the characteristic wave.The results showed that the correlation coefficients between the synthesis ASSRs obtained from the fifteen hAEP templates and the recorded ASSRs with the same stimulus rates ranged from 0.96 to 0.99.The reconstructed hAEPs from various splicing combinations of ASSRs exhibited consistent morphology with three characteristic components.The amplitudes and latencies of these characteristic components have slight difference.The above results showed that the hAEPs were successfully reconstructed from amplitude modulation ASSRs,and the hAEPs were found to be insensitive to the rate combination modes of ASSRs.The reconstructed hAEPs are conducive to promoting the clinical application of amplitude-modulation pure tone and compensates for missing information of the ASSRs in the time domain.