Effects Of Interaural Time Difference On Speech Intelligibility Of Hearing-impaired Persons In Noisy Environment

When the target speech and noise come from different directions,the listener can use the difference of their binaural cues to produce spatial release from masking(SRM)and improve speech intelligibility.This masking release is relative to the condition that noise and target speech come from same direction.Interaural time difference(ITD)is one of the important binaural acoustic cues.Changes in ITD may affect speech intelligibility in noise,and there may be individual differences in the ability of different listeners to utilize ITD.In this paper,ITD was changed alone while other spatial cues kept unchanged,the headphone playback method was used to measure the speech reception threshold(SRT)in the noise and the spatial masking release was calculated.First,the effect of ITD on speech intelligibility in noise in normal hearing people was studied,and psychoacoustic experiments were designed to find that:(1)When the noise ITD was fixed at 0 μs,a non-zero ITD(between 100 and 600 μs)was added to the target speech will reduce the SRT,that is,the SRM will be generated,and the SRM will increase with the increase of the ITD of target speech;(2)the ITD of the target speech and noise will take random difference across the frequency band,which will reduce the SRM.The SRM reduces the most when the target speech and noise both have random ITD across different frequency bands;(3)For dynamic ITD,the SRM increases when the modulation rate is slow(0.25,0.5,1 Hz),and the SRM decreases when the modulation rate is fast(2,3 Hz).Then,using the above experimental methods,the effect of ITD on the speech intelligibility in noise of the hearing-impaired people was studied.The SRT of normal listeners who simulated monaural hearing loss(ILD = 15 d B)and patients with different degrees of hearing loss were measured and SRM was calculated.The experimental results showd that:(1)normal listeners with simulated monaural hearing loss can use ITD to generate SRM like normal hearing people,but the SRM is reduced;(2)hearing impaired people can also use ITD to generate SRM,but SRM produced by hearing-impaired people reduces with the hearing loss worsens.Finally,the effect of ITD on speech intelligibility in noise in hearing aid patients was study.A true wireless Bluetooth headphone equipped with a hearing aid algorithm was developed to assist the hearing-impaired people,and the SRT of the hearing-impaired people before and after hearing-aid under non-spatial separation conditions was measured in quiet and noisy environments;Head-related impulse response(HRIR)was used to construction spatial separation angle(0°,-45°,-90°,45°,90°),SRT before and after hearing-aid for hearing-impaired patients was measured in spatial separation conditon.The results showd that:(1)under the condition of non-spatial separation,the hearing-impaired people can obtain the improvement of speech intelligibility from the hearing aid,but the improvement is not obvious in the noise environment;(2)under the condition of spatial separation,the hearingimpaired people can benifit from the binaural aid to get an extra SRM when listen,and effectively improving speech intelligibility in noise.This paper is based on psychoacoustics research,and the study of normal hearing people is helpful to understand the mechanism of the listener to separate the target speech and the noise in the noise.The research on the hearing-impaired people is helpful to understand the causes and solutions of the distortion of binaural hearing of the hearing-impaired people,and provides a reference for the design and optimization of artificial hearing,hearing aids,and hearing detection algorithms.