Novel psychoacoustic measure of spectral-temporal processing for discrete regions of the cochlear array: a proof-of-concept study.

INTRODUCTION: Despite the general success of cochlear implantation (CI), the impact of known pathophysiological processes occurring within the cochlea after surgery on hearing outcomes are poorly understood. Previous studies suggested localised intracochlear variations in the electrode-cochlear interface and neurosensory targets may be contributing to poor outcomes for some CI users. Research has highlighted the need to define optimal cochlear biomarkers and behavioural measures to enhance diagnostic and therapeutic approaches for CI users with poor outcomes. The current proof of concept study introduces a novel adaptation of a measure of spectral-temporal processing and aimed to explore its association with electrophysiological measures and speech perception. METHODS: 18 adult CI implant users with 24, 400, 500 and 600 series Cochlear Ltd devices were recruited from a large not-for-profit CI clinic in Australia. Participants completed a "sectional" adaptation of the spectral ripple STRIPES test (secSTRIPES) and bipolar transimpedances (4PI). Original STRIPES stimuli were band-pass filtered for secSTRIPES, targeting discrete high frequency (basal) and low frequency (apical) sections of the electrode array. A linear mixed model approach was used to determine if any relationship existed between localised impedance measures and secSTRIPES scores. Simple linear regression was used to investigate within-subject correlations and the association with conventional measures of speech understanding. RESULTS: Data indicated within-subject sectional variability, with a meaningful difference in secSTRIPES scores for 13 of 18 participants (scores different by >1). Most participants (72%) scored worse on the basal secSTRIPES test. This sectional bias was significant when controlling for age and impedances for 14 CI users with bilateral hearing loss (p= 0.005). There was no statistically significant relationship between 4PI and secSTRIPES scores, however the results suggested there may be positive trend between localised impedance and spectral-temporal processing. The association of secSTRIPES and speech scores was also non-significant, however positive trends between speech and apical STRIPES scores were observed. CONCLUSIONS: This pilot study, the first to describe the sectional adaptation of the STRIPES test, provides sufficient proof of concept for secSTRIPES as a psychoacoustic measure of listening ability in localised sections of the electrode array. While results must be interpreted cautiously due to limitations of the sample size, preliminary findings reveal intracochlear variability in processing performance which warrants further investigation. Following formal validation, secSTRIPES may be beneficial for future research to explore how sectional biases influence overall processing for CI users and as a cochlear biomarker to guide interventions to improve CI performance.