By Mary Beth O’Sullivan, Professional Education Manager, Cochlear Americas
Berg, K.A., Noble, J.H., Dawant, B.M., Dwyer, R. T., Labadie, R.F., Gifford, R. H.
Journal of the Acoustic Society of America
145 (3), 1556-1564
In today’s busy clinical environment, clinicians who value research-based practice often struggle to keep up with current literature. To help, we’re excited to offer a new ProNews Blog monthly feature – Journal Club! Each month, rotating guest authors will present a current journal article summary.
This month’s Journal Club explores a recent study by the team at Vanderbilt University Medical Center in a March 2019 publication, Speech recognition as a function of the number of channels in perimodiolar electrode recipients. As was pointed out during a recent symposium presentation, the data from this study presents clear and direct clinical implications that can be implemented immediately.
What did the study investigate?
The article presents two different experiments in an effort to examine:
- Number of active electrodes required for best outcomes
- Effect of increasing the default number of maxima from 8 to 16
Why is this important?
Landmark studies¹⁻³ published decades ago evaluated this same question regarding the number of active electrodes to achieve best outcomes. Since that time, it has been standard practice to make clinical decisions based on those findings – namely that performance does not improve with more than 4-8 active electrodes. However, those benchmark studies used straight electrode arrays – not with perimodiolar arrays where the spread of excitation is minimized through closer proximity to the modiolus. With increasing use of perimodiolar arrays and other advances in CI technology, coding strategies, surgical approaches and candidacy criteria, the authors felt it was time for a fresh look at these questions.
How did they do it?
Below summarizes the key elements of study design and demographics:
• 30 subjects, age 24-87
• Minimum of 6 months of use for Experiment I, 3 months for Experiment II
• Placement of array confirmed and electrode-to-modiolus distance measured via imaging and 3D reconstruction
• All current favorite MAPs were 900 Hz rate/25 ms pw; no changes were made.
• Front end features were disabled with the exception of Autosensitivity Control (ASC) and adaptive dynamic range optimization (ADRO).
I. 11 of the 30 subjects participated in Experiment I. Criteria specific to this experiment required that all 22 electrodes were in scala tympani with at least 18 electrodes active in their current favorite MAP.
• 5 MAPs were created based on the current favorite MAP with varying numbers of electrodes activated: 4, 8, 10, 16 and “all on” (consistent with number in use in the favorite MAP). Loudness was adjusted globally.
• Number of maxima matched number of electrodes up to 16 maxima
• Speech perception was evaluated using CNC words, AzBio sentences in Quiet, and AzBio Sentences at +5 SNR.
• Sound quality ratings were assessed using the quick spectral modulation detection (QMSD) test⁴.
II. All 30 subjects participated in Experiment II. In the “all on” condition (at least 18 electrodes active in their preferred MAP), testing was conducted with two conditions.
• Default 8-maxima MAP and 16-maxima MAP.
• Performance with each MAP was evaluated using CNC words and AzBio sentences at +5 SNR.
• Electrode-to-modiolus distance was available for 23 of the 30 subjects.
Based on the study, the graphs below show that increasing the number of electrodes resulted in improved performance and sound quality. Findings were statistically significant in several areas of statistical analyses with the strongest findings demonstrating that the subjects with the electrodes closest to the modiolus had the best performance. The optimal MAP had all electrodes active (per their favorite MAP) with 16 maxima.
The authors hypothesize that perimodiolar electrodes effectively minimize overall charge level requirements which allows better control over the negative effects of channel interaction. This is supported by the findings in this study demonstrating improvements in spectral resolution in the portions of the study that directly assess that feature. It should be noted that by changing the number of maxima to match the number of active electrodes, the participants were utilizing CIS MAPs. The evidence that perimodiolar arrays enable optimal outcomes based on position in the cochlea is great news for patients, and clinicians now have a new and better reference when addressing outcomes when the number of active electrodes is a concern.
Learn more about this exciting clinical strategy by accessing the publication here and stay tuned for next month’s edition of Journal Club!
About our guest author: Mary Beth O’Sullivan is a Professional Education Manager at Cochlear Americas, creating educational opportunities for cochlear implant professionals using research and best practice guidance. Mary Beth has been an audiologist for 20 years, working in clinical settings ranging from large university hospitals to private practice prior to dedicating herself to the education side of the field.
- Fishman, K.E. Shannon, R. V., and Slattery, W.H. (1997). “Speech recognition as a function of the number of electrodes used in the SPEAK cochlear implant speech processor,” J. Speech lang. Hear Res. 4, 1201-1215.
- Friesen, L.M., Shannon, R. V., Baskent, D., and Wang, X. (2001). “Speech recognition in noise as a function of the number of spectral channels: Comparison of acoustic hearing and cochlear implants,” J. Acoust. Soc. Am. 110, 1150-1163.
- Shannon, R.V., Cruz, R.J., and Galvin, J.J. (2011). “Effect of stimulation rate on cochlear implant users’ phoneme, word and sentence recognition in quiet and in noise,” Audiol. Neurotol. 16, 113-123.
- Gifford, R. H., Hedley-Williams, A., Spahr, A.J. (2014). “Clinical assessment of spectral modulation detection for adult cochlear implant recipients: A non-language based measure of performance outcomes,” Int. J. Audiol. 53, 159-164.