scholarly journals Simulations of the effect of unlinked cochlear-implant automatic gain control and head movement on interaural level differences

2019 ◽  
Vol 145 (3) ◽  
pp. 1389-1400 ◽  
Author(s):  
Alan W. Archer-Boyd ◽  
Robert P. Carlyon
Keyword(s):  
Cochlear Implant ◽  
Head Movement ◽  
Automatic Gain Control ◽  
Gain Control ◽  
Interaural Level Differences

scholarly journals Further simulations of the effect of cochlear-implant pre-processing and head movement on interaural level differences

2021 ◽  
Author(s):  
Alan Archer-Boyd ◽  
Robert P. Carlyon
Keyword(s):  
Cochlear Implant ◽  
Head Movement ◽  
Automatic Gain Control ◽  
Gain Control ◽  
Release Time ◽  
Dynamic Changes ◽  
Bilateral Cochlear Implant ◽  
Interaural Level Differences ◽  
Range Of Values ◽  
Channel Systems

We simulated the effect of several automatic gain control (AGC) and AGC-like systems and head movement on the output levels, and resulting interaural level differences (ILDs) produced by bilateral cochlear-implant (CI) processors. The simulated AGC systems included unlinked AGCs with a range of parameter settings, linked AGCs, and two proprietary multi-channel systems used in contemporary CIs. The results show that over the range of values used clinically, the parameters that most strongly affect dynamic ILDs are the release time and compression ratio. Linking AGCs preserves ILDs at the expense of monaural level changes and, possibly, comfortable listening level. Multichannel AGCs can whiten output spectra, and/or distort the dynamic changes in ILD that occur during and after head movement. We propose that an unlinked compressor with a ratio of approximately 3:1 and a release time of 300-500 ms can preserve the shape of dynamic ILDs, without causing large spectral distortions or sacrificing listening comfort.

scholarly journals Improving Localization and Speech Reception in Noise for Bilateral Cochlear Implant Recipients

2019 ◽  
Vol 23 ◽  
pp. 233121651983149 ◽  
Author(s):  
Wendy B. Potts ◽  
Lakshmish Ramanna ◽  
Trevor Perry ◽  
Christopher J. Long
Keyword(s):  
Cochlear Implant ◽  
Automatic Gain Control ◽  
Gain Control ◽  
Interaural Level Difference ◽  
Mean Square ◽  
Localization Accuracy ◽  
Speech In Noise ◽  
Speech Reception ◽  
Bilateral Cochlear Implant ◽  
Comparative Survey

This study looked at different methods to preserve interaural level difference (ILD) cues for bilateral cochlear implant (BiCI) recipients. One possible distortion to ILD is from automatic gain control (AGC). Localization accuracy of BiCI recipients using default versus increased AGC threshold and linked AGCs versus independent AGCs was examined. In addition, speech reception in noise was assessed using linked versus independent AGCs and enabling and disabling Autosensitivity™ Control. Subjective information via a diary and questionnaire was also collected about maps with linked and independent AGCs during a take-home experience. Localization accuracy improved in the increased AGC threshold and the linked AGCs conditions. Increasing the AGC threshold resulted in a 4° improvement in root mean square error averaged across all speaker locations. Using linked AGCs, BiCI participants experienced an 8° improvement for all speaker locations and a 19° improvement at the speaker location most affected by the AGC. Speech reception threshold in noise improved by an average of 2.5 dB when using linked AGCs versus independent AGCs. In addition, the effect of linked AGCs on speech in noise was compared with that of Autosensitivity™ Control. The Speech, Spatial, and Qualities of Hearing Scale-12 question comparative survey showed an improvement when using maps with linked AGCs. These findings support the hypothesis that ILD cues may be preserved by increasing the AGC threshold or linking AGCs.

Matching Automatic Gain Control Across Devices in Bimodal Cochlear Implant Users

2016 ◽  
Vol 37 (3) ◽  
pp. 260-270 ◽  
Author(s):  
Lidwien C. E. Veugen ◽  
Josef Chalupper ◽  
Ad F. M. Snik ◽  
A. John van Opstal ◽  
Lucas H. M. Mens
Keyword(s):  
Cochlear Implant ◽  
Automatic Gain Control ◽  
Gain Control

scholarly journals The effect of free-field presentation and processing strategy on a measure of spectro-temporal processing by cochlear-implant listeners

2020 ◽  
Author(s):  
Alan Archer-Boyd ◽  
Tobias Goehring ◽  
Robert P. Carlyon
Keyword(s):  
Cochlear Implant ◽  
Automatic Gain Control ◽  
Free Field ◽  
Gain Control ◽  
Processing Strategy ◽  
Temporal Cues ◽  
Significant Difference ◽  
The Everyday ◽  
Test Retest Reliability ◽  
Psychophysical Test

The STRIPES (Spectro-Temporal Ripple for Investigating Processor EffectivenesS) test is a psychophysical test of spectro-temporal resolution developed for cochlear implant (CI) listeners. Previously, the test has been strictly controlled to minimize the introduction of extraneous, non-spectro-temporal cues. Here, the effect of relaxing many of those controls was investigated to ascertain the generalizability of the STRIPES test. Pre-emphasis compensation was not applied to the spectrum of the STRIPES stimuli, the test was presented over a loudspeaker at a level above the automatic gain control (AGC) threshold of the CI processor, and listeners were tested using the “everyday” setting of their clinical devices. There was no significant difference in STRIPES thresholds measured across conditions for the majority of the CI listeners tested. One listener obtained thresholds above the theoretical spectral limit of performance when listening with their clinical processor. An analysis of longitudinal results showed excellent test-retest reliability over multiple listening sessions. Overall the results show that the STRIPES test is robust to extraneous cues, and that thresholds are reliable over time. Above a threshold limit defined by the filter settings of the CI processor used, no guarantee of the validity can be made of measured thresholds, and thresholds may be more variable. The STRIPES test may be sufficiently robust for use across CI manufacturers and in non-research settings.

scholarly journals Effect of (Mis)Matched Compression Speed on Speech Recognition in Bimodal Listeners

2020 ◽  
Vol 24 ◽  
pp. 233121652094897
Author(s):  
Dimitar Spirrov ◽  
Eugen Kludt ◽  
Eline Verschueren ◽  
Andreas Büchner ◽  
Tom Francart
Keyword(s):  
Speech Recognition ◽  
Cochlear Implant ◽  
Dynamic Range ◽  
Automatic Gain Control ◽  
Hearing Aid ◽  
Gain Control ◽  
Time Constants ◽  
Hearing Devices ◽  
Testing Condition ◽  
Speech Recognition In Noise

Automatic gain control (AGC) compresses the wide dynamic range of sounds to the narrow dynamic range of hearing-impaired listeners. Setting AGC parameters (time constants and knee points) is an important part of the fitting of hearing devices. These parameters do not only influence overall loudness elicited by the hearing devices but can also affect the recognition of speech in noise. We investigated whether matching knee points and time constants of the AGC between the cochlear implant and the hearing aid of bimodal listeners would improve speech recognition in noise. We recruited 18 bimodal listeners and provided them all with the same cochlear-implant processor and hearing aid. We compared the matched AGCs with the default device settings with mismatched AGCs. As a baseline, we also included a condition with the mismatched AGCs of the participants’ own devices. We tested speech recognition in quiet and in noise presented from different directions. The time constants affected outcomes in the monaural testing condition with the cochlear implant alone. There were no specific binaural performance differences between the two AGC settings. Therefore, the performance was mostly dependent on the monaural cochlear implant alone condition.

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