The influence of the enhancement of onsets on speech intelligibility in cochlear implant users

Cochlear implant (CI) recipients suffer from the inability to understand speech in adverse listening conditions like reverberant rooms or noisy environments but achieve good speech intelligibility (SI) performance in quiet environments. One approach to increase SI in CI patients is to enhance signal by applying noise reduction techniques or distorting the speech envelope in a way to improve SI. We follow the latter approach by enhancing the onsets of the speech envelope to improve the access of CI users to this acoustical landmarks that were shown to be important for speech understanding in normal – hearing listeners. Therefore, an onset envelope enhancement strategy was developed that amplifies the onsets of the speech signal in each frequency band. In this feasibility study, we investigated the influence of onset enhancement by comparing the EE with the reference advanced combined encoder (ACE) strategy with 6 CI users in stationary speech shaped noise (SSN) and in a competitive talker situation. The extraction of the onsets is done on the clean speech signal and the amplified onsets are than added to the noisy mixture of the signal. Hence, a priori knowledge is only used for the peak extraction. Additionally to the onset extraction of the target speaker signal, the onsets of the competitive talker were also extracted from the clean interfering talker signal for the competitive talker task. Results of subjective listening tests with the Dutch LIST sentences showed an increase in speech intelligibility in comparison to the ACE strategy for all CI users in stationary SSN. An alaysis with a repeated measures ANOVA revealed that a significant effect of the factor strategy occurred. There were no other significant main or interaction effects obtained. The results of the competitive talker task, where a female speaker was used as a target speaker and a male as interfering speaker, showed an increase in the speech reception threshold for three different onset enhanced conditions: onsets of the target speaker, onsets of the target and interfering speaker,and onsets of the noisy mixture enhanced. The increase in SI demonstrated the importance of onset cues for CI listeners on SI in adverse listening conditions. Due to the fact that the onset extraction was done on the clean speech signal, further research has to be done to extract the onset cues from the noisy mixture to make the algorithm applicable in noise. The competitive talker situation results suggest that there is a margin for errors in the onset extraction and enhancing the contrast to some extend between the target signal and the background is sufficient to increase SI.status: publishe