Speech Intelligibility Index: A Literature Review

Background and Aim: Speech is known as the most important auditory signal that humans deal with it. Noise can mask speech and prevent spoken information from reaching us. Researchers have been trying to develop indexes to assess speech intelligibility. Speech Intelligibility Index (SII) is one of these indicators and we intend to introduce its nature and applications. Recent Findings: SII is a method that numerically demonstrates the ability to hear speech in difficult listening situations. The number 1.0 indicates that all spoken information is available, while 0.0 indicates that the person does not have access to any information. Hearing loss changes a person’s scores on this index, so we need to use corrective factors to more accurately estimate speech intelligibility. In children, the SII score is different from adults. This indicator can be used in the improvement of hearing aid fitting and more accurate adjustment of cochlear implants. The frequency importance function used to calculate SII has a unique shape in each language. Therefore, SII will also differ in different languages, depending on the nature of each language. Conclusion: SII has emerged as a practical indicator among objective assessments of speech intelligibility. Many have tried to extend and prepare it for use in different groups. Therefore, care should be taken about the use of this index in hearing-impaired people, children, with hearing aids or cochlear implant patients, etc. Evaluation of this index in other languages can help to better adjust the hearing aid based on the characteristics of each language.   Keywords: Speech intelligibility index; hearing loss; children; hearing aid; cochlear implant; language