Effects of site-specific level adjustments on speech recognition with cochlear implants

Area of Science:

• Audiology
• Neuroscience
• Biomedical Engineering

Background:

• Modulation detection thresholds (MDTs) vary across cochlear implant (CI) electrode sites, impacting speech recognition.
• Current site-selection strategies can degrade spectral resolution and frequency-place mapping.
• An alternative approach is needed to improve MDTs without compromising CI processor map integrity.

Purpose of the Study:

• To investigate improving across-site mean MDTs by adjusting stimulation parameters at poorly performing CI sites.
• To test the hypothesis that increasing stimulation levels at poor MDT sites enhances modulation sensitivity and speech recognition.

Main Methods:

• Nine postlingually deafened ears with Nucleus CIs were assessed for MDTs, T levels, and C levels.
• Stimulation levels at the five poorest MDT sites were increased by 5% or 10% of the dynamic range.
• Speech reception thresholds (SRTs) were evaluated using CUNY sentences for site-specific, global, and unadjusted MAPs.

Main Results:

• A 5% site-specific level increase improved group mean SRT by 2.36 dB SNR compared to the unadjusted MAP.
• MDTs at poor sites significantly improved after optimal level adjustment.
• Global level increases or site removal did not improve SRTs.

Conclusions:

• Site-specific T-level adjustments enhance modulation sensitivity at low levels.
• This strategy significantly improves speech recognition thresholds in CI users.
• Site-specific level adjustment is an effective alternative to site-selection for CI speech rehabilitation.