Separating peripheral and higher-level effects on speech intelligibility using a hearing loss simulator and an objective intelligibility measure

This paper presents a new method for separating the effects of peripheral hearing loss (HL) and higher-level processes on speech intelligibility (SI). In a previous study, we conducted an SI experiment with 14 older adult (OA) listeners, using speech-in-noise sounds that were either processed with an ideal ratio mask (IRM) enhancement technique or left unprocessed. The current study involved an SI experiment with 15 young, normal-hearing (YNH) listeners. This experiment used simulated HL sounds processed with the WHIS simulator that reflected the hearing level of a specific OA from the previous study. The results showed that the target OA's SI scores were higher than the average YNH scores. This implies that the target OA's higher-level processes may be more effective than those of the average YNH. To understand the characteristics of other OAs, we used the GESI objective intelligibility measure to predict SI. First, we confirmed that GESI could fairly accurately predict the SI scores for both the YNH and OA listeners. Next, we predicted the SI scores of the 14 OA listeners using the parameters estimated in the YNH experiment. The results showed that some OAs had higher SI scores than the average YNH, while one OA had lower scores. These differences in SI scores may reflect variations in the efficiency of higher-level processes.These results imply that WHIS and GESI could facilitate contrastive experiments between YNH and OA listeners, regardless of hearing level. This would allow us to study the effects of higher-level processes in OA listeners individually.