Optimizing CI Systems for Better Recognition of Soft Speech -the Concept of Broad-Range Mapping

The individual mapping of cochlear implants (CIs) aims to optimize the user's speech understanding. Recent investigations have shown the importance of soft speech: (1) According to Datalog studies, a large proportion of speech components lies in the range below 60 dB, and (2) soft speech represents a separate category in CI outcome, in addition to supra-threshold speech and speech in noise. Soft-speech understanding can be influenced by optimizing T-values or by global parameters (loudness growth and TSPL in the Nucleus system). This study focussed on improving soft speech below 60 dB by optimizing loudness growth.

Speech understanding with varying loudness growth in the speech processor CP11 (Cochlear Ltd.) was compared in 20 experienced adult CI users. The mean soft-speech score based on monosyllabic words at 40 and 50 dB was introduced for quantification.

Six of the 20 patients studied showed significant individual improvement for soft speech when loudness growth was optimized, while none showed a significant decrease under quiet or noisy test conditions.

Actual CI systems offer a broad loudness range of speech understanding. In addition to suprathreshold speech understanding, additional attention should be paid to soft speech, and the result should therefore be confirmed by speech audiometry at low levels.

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