Speech discrimination score development over time after cochlear implantation

Background:

After receiving cochlear implants (CI), speech discrimination of the CI recipients improves gradually. The knowledge of a normal range for this rate may be relevant for quality control as part of a clinical CI program.

Methods:

We selected 35 functionally deaf adult patients who were fitted with CI, 29 of them with postlingually and 6 with prelingually acquired hearing loss. Speech discrimination was tested with the Freiburger monosyllabic and two-digit numbers speech intelligibility test at timepoints of 1, 3 and 6 months after implantation. The test was performed at 50, 65 and 80 dB speech level. The performance levels were approximated by a function y = a*(1 – exp(-t/τ)). The time constant τ is closely related to the initial slope of the function at t = 0 (i.e. first fitting).

Results:

In postlingually deaf adults, the speech recognition of two-digit numbers at 65 dB increased from 62.5% at 1 month to 84.3% at 3 months and 94.5% at 6 months after implantation. The fit of the function y = a*(1 – exp(-t/τ)) to the data yielded a recovery time τ= 1.2 months for postlingually deaf patients. From the same treatment of the data corresponding to the recognition of monosyllables at 65 dB, the result τ= 1.9 months was derived. The patient cohort of prelingually deaf adults was too small to develop a mathematical function.

Conclusion:

We have shown that for postlingually functionally deaf patients post implantation, the development of speech recognition can be described by the formula y = a*(1 – exp(-t/τ)) and it could therefore be possible to foresee an individual patients improvement in speech recognition. The recovery time τ amounts to 1.2 months for the discrimination numbers and 1.9 months for monosyllables.

Publication History

Publication Date:
18 April 2018 (online)