RESUMO
Background and Objectives@#Natural and synthetic speech signals effectively stimulate cortical auditory evoked potential (CAEP). This study aimed to select the speech materials for CAEP and identify CAEP waveforms according to gender of speaker (GS) and gender of listener (GL). @*Subjects and Methods@#Two experiments including a comparison of natural and synthetic stimuli and CAEP measurement were performed of 21 young announcers and 40 young adults. Plosive /g/ and /b/ and aspirated plosive /k/ and /p/ were combined to /a/. Six bisyllables–/ga/-/ka/, /ga/-/ba/, /ga/-/pa/, /ka/-/ba/, /ka/-/pa/, and /ba/-/pa/–were formulated as tentative forwarding and backwarding orders. In the natural and synthetic stimulation mode (SM) according to GS, /ka/ and /pa/ were selected through the first experiment used for CAEP measurement. @*Results@#The correction rate differences were largest (74%) at /ka/-/ pa/ and /pa/-/ka/; thus, they were selected as stimulation materals for CAEP measurement. The SM showed shorter latency with P2 and N1-P2 with natural stimulation and N2 with synthetic stimulation. The P2 amplitude was larger with natural stimulation. The SD showed significantly larger amplitude for P2 and N1-P2 with /pa/. The GS showed shorter latency for P2, N2, and N1-P2 and larger amplitude for N2 with female speakers. The GL showed shorter latency for N2 and N1-P2 and larger amplitude for N2 with female listeners. @*Conclusions@#Although several variables showed significance for N2, P2, and N1-P2, P1 and N1 did not show any significance for any variables. N2 and P2 of CAEP seemed affected by endogenous factors.
RESUMO
Since noise-induced hearing loss (NIHL) is one of prevalent issues in the occupational settings, hearing protection device (HPD) has been widely used to reduce noise exposure levels and to prevent developing NIHL. This review study aimed to introduce several types of the HPD in terms of current trends, its variety and functions, and application. Including a brief history of the HPD, we explain its two types, i.e., passive and active functions, in the first part of main body. The passive HPD has a flat attenuation across the overall frequency range, whereas the active HPD effectively preserves communication components such as meaningful speech with low intensity stimuli while filtering out the high levels of noise. In the second part of the main body, we discuss some negative issues of hearing functions when users are wearing the HPD. In detail, the active HPD does not much degrade the hearing performance for speech detection/recognition and sound source localization compared to the passive HPD. Rather, reduced sound (or music) quality is improved with active one in general. In the final part, we mention that although various applications in the special fields such as factory, mining, army, airplane, and music have been demonstrated, the usage and awareness of HPD in occupational aspect may not follow its fast technological development. Furthermore, most people do not know about either importance or use method of HPD in the non-occupational setting. For these reasons, we conclude that hearing professionals have to access the latest trends of the HPD and to increase their knowledge on it, and thus they should provide the best HPD prescription for the public as well as employees who have to protect their ears from hazard noise impacts.