Wolfe, J., Baker, S., Caraway, T., Kasulis, H., Mears, A., Smith, J., Swim, L., & Wood, M. (2007). 1-year postactivation results for sequentially implanted bilateral cochlear implant users. Otology & Neurotology.
Objective: Evaluate speech recognition in quiet and in noise for
a group of 12 children, all of whom underwent sequential bilateral cochlear implantation at various ages (range, 1 yr, 8 mo to 9 yr, 6 mo at time of second implant).
Main Outcome Measures: Speech recognition in quiet was evaluated for each ear separately using single-word speech recognition assessments (Multisyllabic Lexical Neighborhood Test and Early Speech Perception Test) via recorded presentation. Speech recognition in noise was assessed for each ear separately and in the bilateral condition by obtaining a spondee recognition threshold in the presence of speech-weighted noise presented at 45 dB hearing level. The primary outcome measure for speech recognition in noise assessment was the signal-to-noise ratio for 50% performance, which was calculated by determining the difference between the presentation level of the noise and the presentation level at which the speech recognition threshold was obtained. The results of these assessments were contrasted between children receiving their second cochlear implant before 4 years of age and children receiving their second cochlear implant after 4 years of age.
Results: A statistically significant difference for speech recognition scores in quiet was obtained between the early implanted ear and the late-implanted ears for children receiving their second cochlear implant after 4 years of age. There was not a statistically significant difference in speech recognition scores in quiet between the early-implanted and late-implanted ears of children receiving their second cochlear before 4 years of age. Both groups of children possessed better speech recognition scores in noise (statistically significant at an > = 0.05) in the bilateral condition relative to either unilateral condition. However, there was not a statistically significant relationship between speech recognition performance in noise and the duration of deafness of the later implanted ear.
Conclusion: Bilateral cochlear implantation allowed for better speech recognition in noise relative to unilateral performance for a group of 12 children who underwent sequential bilateral cochlear implantation at various ages. There was not a statistically significant relationship between speech recognition in noise benefit, which was defined as the difference in performance between the first implanted ear and the bilateral condition and the age at which the second implant was received. Children receiving bilateral cochlear implants younger than 4 years of age achieved better speech recognition in quiet performance for the later implanted ear as compared with children receiving their second cochlear implant after 4 year of age.
Saturday, September 29, 2007
Wolfe et al. (2007) Results for Sequentially Implanted CIs
Are the conclusions of this article supported by its data?
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7 comments:
This article evaluates speech recognition of 12 children who received sequential bilateral cochlear implants. I found many of the subjects addressed in this article interesting, such as the improvement in minimal audible angle (MAA) with bilateral implantation. An improvement in localization was noted after an extended period of time. All groups whether the second implant was before of after 4 years of age, showed a statistically significant improvement in bilateral condition in noise. This is consistent with the principle of binaural squelch or the ability to draw a signal out of noise. Children who received their second implant before 4 years of age had significantly higher speech recognition (in quiet) mean, than children who received their second implant after 4 years of age. I would like to see further studies done with more children assessing speech reception of later 2nd implantation. Overall I would say that binaural implantation warrants further investigation due to improvement with localization, binaural squelch, and possible improved speech reception with earlier implantation in the second ear.
The article did a good job explaining the lack of research and data regarding the benefits of early implantation of bilateral cochlear implants, thus informing the readers that the information they will provide from this study is important and will be applicable.
The study clearly explained the results, how they were obtained, and their significance and applicability. I think their method was well done, and that their results are significant. Their major finding that bilateral implantation before four years of age leads to much improved speech recognition in quiet is compelling enough to warrant more research. Another study that analyzes the scores as the children continue to age would be interesting. I would like to see how the ability to recognize speech in quiet and in noise improves over the course of a longer period.
Wolfe, et. al. have examined the potential benefit of bilateral cochlear implantation in children who receive the devices sequentually. Their findings are promising and support findings from other researchers. However, the low number of subjects in this study raises some concerns and points to the need for further research with more children. The challenge is the number of bilaterally implanted children is low and perhaps difficult to recruit.
The information in the study by Wolfe et al. (2007) has important implications regarding the need for further research about the benefits of sequential bilateral cochlear implants. The size of the groups was a concern. I realize that the availability of sequentially bilateral implanted children are hard to come by, but as it is increasing maybe this study will be a good foundation for future studies with larger sample sizes. Another concern I had is that 1 test was given to 7 of the children in Group A and another test was given to the other 5 (because the first wasn’t developmentally appropriate for them). While they probably test the same thing, a lot of error may have been introduced into the results by doing that. In a group of 12 children the results showed that bilaterally implanted children did significantly better in speech recognition in noise that unilaterally implanted children. This study lays a nice foundation for future research regarding this and other issues.
I don't think the conclusions in this article are supported by the data. The small number of children in this study concerns me. When comparing scores for the first implanted ear versus the second for the 2 groups, they are comparing 3 children to 4 children. (See Figure 2.) They used 2 different tests when testing speech abilities in quiet because 5 subjects could not complete the first test. A closed-set test is much easier to do than an open-set and it's undeterminable how many they got correct by a lucky guess. Although I would like to agree that 2 implants are better than one, the authors state that the time frame on the 2nd implant is not as important and "benefit from bilateral cochlear implantation may not be restricted to children with a short duration of deafness", however, if you look at the improvement for the child that received the 2nd implant at 9;6, their improvement over the year went from 0% to ~10%. To me, that's not much improvement, especially when I compare it to the children who recieved the second implant before age 4. The age range of the children also concerns me. The differences in scores could be due to the large difference in ages when the child recieved the implant. The 2 grouping the authors used (less than 4 years or greater than 4) is not representative of the group they tested. The first group received their second implants at much more similar ages than the later group.
The authors of this article have brought to light the possible benefits of bilateral sequential implantation. The data seems (I say seems because I am just learning about some of the article’s topical components like MAA and don’t quite understand them holistically) to be supported as far as the participants that they worked with. Due to the small number of participants in this study I believe that more studies are warranted before we have a definitive answer as to how much benefit children receive from bilaterally sequentially implanted cochlear devices.
This is a followup to my comments yesterday about spatial unmasking of speech in noise; I promised to find a citation for you.
Bronkhorst and Plomp (1988) measured the intelligibility of sentences in the presence of speech-shaped noise coming from different locations than the speech. The following paraphrase summarizes a thorough but complicated set of measurements: "The intelligibility level difference is not affected by binaural unmasking, but relies on the ear receiving the signal with the best S/N ratio" (original quote on p. 1514). The "intelligibility difference" referred to is a threshold reduction of about 6 dB that occurred when the noise was separated from the speech by 90 degrees of azimuth. Important things to note: a) they explicitly say that one ear accounts for the improvement in intelligibility, and b) they explicitly rule out a role for binaural neural processing ("Binaural unmasking").
Broknhorst, AW and Plomp, R (1988). "The effect of head-induced interaural time and level differences on speech intelligibility in noise", J Acoust Soc Am, 83, 1508-1516.
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