Clinical evaluation of cochlear implant sound coding taking into account conjectural masking functions, MP3000™

Abstract

Efficacy of the SPEAK and ACE coding strategies was compared with that of a new strategy, MP3000™, by 37 European implant centers including 221 subjects. The SPEAK and ACE strategies are based on selection of 8-10 spectral components with the highest levels, while MP3000 is based on the selection of only 4-6 components, with the highest levels relative to an estimate of the spread of masking. The pulse rate per component was fixed. No significant difference was found for the speech scores and for coding preference between the SPEAK/ACE and MP3000 strategies. Battery life was 24% longer for the MP3000 strategy. With MP3000 the best results were found for a selection of six components. In addition, the best results were found for a masking function with a low-frequency slope of 50 dB/Bark and a high-frequency slope of 37 dB/Bark (50/37) as compared to the other combinations examined of 40/30 and 20/15 dB/Bark. The best results found for the steepest slopes do not seem to agree with current estimates of the spread of masking in electrical stimulation. Future research might reveal if performance with respect to SPEAK/ACE can be enhanced by increasing the number of channels in MP3000 beyond 4-6 and it should shed more light on the optimum steepness of the slopes of the masking functions applied in MP3000.

Figure 1

Distribution of etiology of deafness of 209 subjects. LVAS, large vestibular aquaduct syndrome.

Figure 2

Duration of implant use of 209 subjects before entering the study.

Figure 3

Word scores collected in quiet for the SPEAK/ACE and MP3000 strategies. Number of subjects per language were Dutch (NL) 32, Dutch-Flemish (BE) 19, English (GB) 9, French (FR) 22, German (DE) 57, Italian (IT) 21, Polish (PL) 26, and Spanish (ES) 13. The bars indicate the 95% confidence intervals.

Figure 4

As Fig. 3 but for scores collected in noise at S/N = +10 dB.

Figure 5

As Fig. 3 but S/N at which sentences in noise reach 50% score (Large confidence intervals for the Spanish language, ES, because the number of subjects was 6 rather than 13).

Figure 6

Overall preference for one of the coding strategies. The number of subjects who withdrew from the study (12) has been added to the ACE/SPEAK bar (n total = 221).

Figure 7

Preference for one of the coding strategies in quiet (left-hand panel) and in noise (right-hand panel). The number of subjects who withdrew from the study (12) has been added to the ACE/SPEAK bar (n total = 221).

Figure 8

Battery life as a function of the number of channels used in the SPEAK/ACE and MP3000 strategies. The bars represent 95% confidence intervals. Large confidence intervals correspond to small number of cases.

Figure 9

Distribution of change in battery life with change from SPEAK/ACE to MP3000 strategy across 172 subjects.