The Effects of Dynamic-range Automatic Gain Control on Sentence Intelligibility With a Speech Masker in Simulated Cochlear Implant Listening.
Nathaniel J Spencer, Kate Helms Tillery, Christopher A Brown
PMID 30204615WHAT IT FOUND
Linked automatic gain control improved sentence intelligibility in noise in simulated bilateral cochlear implant listening.
Multi-band processing helped when gain control was active but not when it was rarely active. Normal-hearing listeners were tested, not implant users.
Key findings
01Channel-linked automatic gain control improved sentence intelligibility at both low and high AGC thresholds.
02Increasing the number of AGC bands improved intelligibility at the low threshold but not at the high threshold.
03Channel-linked AGC improved the better-ear signal-to-noise ratio and interaural level difference statistics, but it increased target dynamic range.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The study used 17 normal-hearing listeners, not people with cochlear implants. It used vocoder simulation, so it did not include real implant factors such as current spread or individual implant experience. The simulation assumed the output was always audible and did not place hard limits on dynamic range, which is a central problem for implant users. Only symmetrical target and masker locations were tested, so it does not show what happens when talkers are on the same side. The vocoder introduced fixed timing cues between ears that may have made sounds seem closer together. It used a fixed pre-processing signal-to-noise ratio with a female target talker and a different female masker talker.
Declared interests
The authors reported no conflicts of interest or financial disclosures; the supplied publication types list NIH extramural research support.
The easy way to misread this
Do not conclude that linked gain control will improve speech understanding for real bilateral cochlear implant users. The study tested normal-hearing listeners with simulated implant processing and did not limit output dynamic range, so audibility problems were not represented.