Functional near-infrared spectrometry for auditory speech stimuli in cochlear implant users: a systematic literature review

OBJECTIVE: This study aims to identify the acquisition features of functional near-infrared spectroscopy (fNIRS) in cochlear implant users. METHODS: A systematic literature review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. PubMed, EMBASE, LILACS, Web of Science, Scopus, PsycINFO, IEEE Xplore, Google Scholar, and ProQuest Dissertations & Theses Global were searched using the PECOS acronym. Inclusion criteria encompassed studies involving fNIRS with speech stimuli in cochlear implant users of any age, with information on acquisition parameters and features. Risk of bias assessment was performed using the Joanna Briggs Institute tool. RESULTS: Nineteen studies were included, with thirteen exhibiting a low risk of bias. Noteworthy uniformity was observed in certain fNIRS acquisition features among cochlear implant users, including the waking state (awake), auditory stimuli of words or phrases presented in a free field, visual stimuli displayed during data collection as a secondary task, recording of responses in the bilateral temporal lobe, and a three-centimeter distance between optodes. Variations in acquisition were attributed to differing study purposes. CONCLUSION: This review identifies common acquisition characteristics for fNIRS in cochlear implant users. Multicenter research efforts are advocated to further advance the utility of fNIRS in this population.