A longitudinal study of speech perception skills and device characteristics of adolescent cochlear implant users

For pediatric cochlear implant (CI) users, CI processor technology, map characteristics, and fitting strategies are known to have a substantial impact on speech perception scores at young ages. It is unknown whether these benefits continue over time as these children reach adolescence.

To document changes in CI technology, map characteristics, and speech perception scores in children between elementary grades and high school, and to describe relations between map characteristics and speech perception scores over time.

A longitudinal design with participants 8-9-yr-old at session 1 and 15-18-yr-old at session 2.

Participants were 82 adolescents with unilateral CIs, who are a subset of a larger longitudinal study. Mean age at implantation was 3.4 yr (range: 1.7-5.4), and mean duration of device use was 5.5 yr (range: 3.8-7.5) at session 1 and 13.3 yr (range: 10.9-15) at session 2.

Speech perception tests at sessions 1 and 2 were the Lexical Neighborhood Test (LNT) presented at 70 dB SPL (LNT-70) and Bamford-Kowal-Bench sentences in quiet (BKB-Q) presented at 70 dB SPL. At session 2, the LNT was also administered at 50 dB SPL (LNT-50), and BKB sentences were administered in noise with a +10 dB SNR (BKB-N). CI processor technology type and CI map characteristics (coding strategy, number of electrodes, threshold levels, and comfort levels) were obtained at both sessions. Electrical dynamic range was computed, and descriptive statistics, correlations, and repeated-measures ANOVAs were employed.

Participants achieved significantly higher LNT and BKB scores, at 70 dB SPL, at ages 15-18 than at ages 8-9 yr. Forty-two participants had 1-3 electrodes either activated or deactivated in their map between test sessions, and 40 had no change in number of active electrodes (mean change: -0.5; range: -3 to +2). After conversion from arbitrary clinical map units to charge-per-phase in nanocoulombs (nC), no significant difference was found for T levels across time. Average comfort levels (C levels) decreased by 19 nC. Seventy-three participants (89%) upgraded their CI processor technology type. At both sessions, significant correlations were found between electrical dynamic range (EDR) and all speech perception measures except LNT-50 (r range: .31 to .47; p < 0.01). Similarly, significant correlations were also found between C levels and all speech perception measures (r range: .29 to .49; p < 0.01). At session 2, a significant correlation was found between processor technology type and the LNT-50 scores (r = .38; p < 0.01).

Significant improvement in speech scores was observed between elementary grades and high school for children who had used a CI since preschool. On average, T levels (nC) and electrode function remained stable for these long-term pediatric users. Analyses of maps did not allow for the determination of the exact cause of C level reductions, though power limitations in new processor systems and changes in perceived loudness over time are possible. Larger EDRs and higher C levels were associated with better speech scores. Newer speech processor technology was associated with better speech scores at a softer level.