The Influence Of Acoustic Lock-in Processing Disorder On Speech Recognition In Patients With Presbycusis

ObjectiveThis study was to record the speech evoked auditory brainstem response(s-ABR)of normal hearing young and aged people,then compared the frequency following response(FFR)of s-ABR between the two groups,in order to explore the contribution of FFR on revealing possible aging mechanisms of central auditory system.MethodsTwelve normal hearing young adults and aged people respectively(24 ears)were enrolled and s-ABRs(syllable/DA/)were recorded using a SmartEP auditory evoked potential system.Results.The comparison of waveforms between the two groups showed thatthe wave latencies of transient responses in the aged group was longer than that of young group,while the wave latencies of the sustained response,FFR,were of no significant differences.The amplitudes of FFR waves in the aged group were lower than those of in the young group.The FFR spectrum analysis showed that the relative energy of each formant for the aged group was lower than that of in the young group and for some formants.ConclusionCompared with young people,the FFR of aged people showed lower amplitude,meaning that aging can lead to the weakness of the brainstem neurons' spectral encoding ability.It may be one of the mechanisms causing the reduction of speech recognition in presbycusis patients.Objective People with presbycusis(PC)often report difficulties in speech recognition,especially under noisy listening conditions.Investigating the PC-related changes in central representations of envelope signals and temporal fine structure(TFS)signals of speech sounds is critical for understanding the mechanism underlying the PC-related deficit in speech recognition.Frequency-following responses(FFRs)to speech stimulation can be used to examine the subcortical encoding of both envelope and TFS speech signals.This study compared FFRs to speech signals between listeners with PC and those with clinically normal hearing(NH)under either quiet or noise-masking conditions.MethodsFFRs to a 170-ms speech syllable/da/were recorded under either a quiet or noise-masking(with a signal-to-noise ratio(SNR)of 8 dB)condition in 14 older adults with PC and 13 age-matched adults with NH.The envelope(FFRENV)and TFS(FFRTFS)components of FFRs were analyzed separately by adding and subtracting the alternative polarity responses,respectively.Speech recognition in noise was evaluated in each participant.ResultsIn the quiet condition,compared with the NH group,the PC group exhibited smaller FO and H3 amplitudes and decreased stimulus-response(S-R)correlation for FFRENV but not for FFRTFS.Both the H2 and H3 amplitudes and the S-R correlation of FFRENV significantly decreased in the noise condition compared with the quiet condition in the NH group but not in the PC group.Moreover,the degree of hearing loss was correlated with noise-induced changes in FFRTFS morphology.Furthermore,the speech-in-noise(SIN)threshold was negatively correlated with the noise-induced change in H2(for FFRENV)and the S-R correlation for FFRENV in the quiet condition.ConclusionAudibility affects the subcortical encoding of both envelope and TFS in PC patients.The impaired ability to adjust the balance between the envelope and TFS in the noise condition may be part of the mechanism underlying PC-related deficits in speech recognition in noise.FFRs can predict SIN perception performance.