Early Sentence Recognition in Adult Cochlear Implant Users

Abstract

Normal-hearing subjects listening to acoustic simulations of cochlear implants (CI) can obtain sentence recognition scores near 100% in quiet and in 10 dB signal-to-noise ratio (SNR) noise with acute exposure. However, average sentence recognition scores for real CI listeners are generally lower, even after months of experience, and there is a high degree of heterogeneity. Our aim was to identify the relative importance and strength of factors that prevent CI listeners from achieving early, 1-mo scores as high as those for normal-hearing-listener acoustic simulations.Design: Sentence recognition scores (100 words/list, 65 dB SPL) using CI alone were collected for all adult unilateral CI listeners implanted in our center over a 5-yr period. Sentence recognition scores in quiet and in 10 dB SNR 8-talker babble, collected from 1 to 12 mo, were reduced to a single dependent variable, the "initial" score, via logarithmic regression. "Initial" scores equated to an improved estimate of 1-mo scores, and integrated the time to rise above zero score for poorer performing subjects. Demographic, device, and medical data were collected for 118 subjects who met standard CI candidacy criteria. Computed tomography of the electrode array allowing determination of the insertion depth as an angle, and the presence or absence of scala dislocation was available for 96 subjects. Predictive factors for initial scores were selected using stepwise multiple linear regression. The relative importance of predictive factors was estimated as partial r 2 with a low bias method, and statistical significance tested with type II analysis of variance. Results:The etiologies chronic otitis and autoimmune disease were associated with lower, widely variable sentence recognition scores in the long-term. More than 60% of CI listeners scored >50/100 in quiet at 1 mo. Congenital hearing loss was associated with significantly lower initial scores in quiet (r 2 0.23, p < 0.001), as was longer duration of hearing loss (r 2 0.12, p < 0.001, ˗0.76 pts per year). Initial scores were negatively correlated with insertion depth (r 2 0.09, p < 0.001, ˗0.1 pts per degree), with the highest initial scores being obtained for insertion depths of 300° to 400°. A much greater proportion of scala dislocations was found for perimodiolar arrays compared with straight arrays. Scores were negatively correlated with the proportion of the active electrode array found in scala vestibuli for Nucleus perimodiolar devices (r 2 0.14, p < 0.01, coefficient ˗25). Similar overall results were obtained for sentence recognition scores in noise (+10 dB SNR). The intercept value for the obtained regression functions indicated that CI listeners with the least limiting factors generally scored ~95/100 in quiet and ~90/100 in noise. In addition, CI listeners with insertion angles as low as 315° to 360° could obtain sentence recognition scores >80/100 even at 1 day after activation. Insertion depths of 360° were estimated to produce frequency-place mismatches of about one octave upward shift....

Prognostics Factors of Cochlear Implant in Adults: How Can We Improve Poorer Performers?

“…Our research has shown that the main factors that influence performance are related to circumstances of etiology and duration of deafness, outcomes of surgical intervention of insertion depth and dislocation, and central aspects of linguistic and neurocognitive skills [1]. The variability seen in speech recognition scores are described in Tables 1 and 2.…”

“…If the etiology is not congenital, then the formula is only 90 minus half the number of years of HL. The predictive model is not valid for cases of labyrinthitis (e.g., chronic otitis and autoimmune disease), where the findings of [1] indicated considerable variability and generally poor outcomes. Our evidence from adults suggests a priori that those with congenital HL are expected to yield poor performance scores.…”

“…The model predicts the sentence recognition score of CI users 1 month after activation. It was derived and simplified from the analysis by [1]. The model takes into consideration only the duration of severe-to-profound hearing loss (HL) and one key etiology, congenital hearing loss, which produced significantly lower scores than other etiologies (including "unknown" causes).…”

“…Based on the population data from [1], we generated a distribution of scores assuming ideal electrode position before activation, that is, no dislocation and insertion depth within the recommended limits. The resultant median score was at approximately 70/100 ( Figure 1, raw scores, left).…”

“…A primary aspect of our rehabilitation approach is early identification of the challenges associated with the remediation of adult cochlear implant users who demonstrate poor results on objective measures. A poor performer may be described as one who achieves "…limited performance after taking in account the preoperative biographic factors during counselling the patient and anatomical factors electrode insertion" [1].…”