Envelope Versus Fine Structure Speech Coding Strategy

A Crossover Study

Abstract

Objective: 

The transmission of fine structure information to cochlear implant users is an expanding area of research. Previous studies comparing the fine structure processing (FSP) speech coding strategy to the envelope-based continuous interleaved sampling (CIS) strategy indicated improved speech perception when using the fine structure strategy. Those investigations were performed with an extended frequency spectrum in the low frequencies together with the fine structure strategy. The current study addresses the question whether these improvements are due to the presentation of fine structure per se or rather the extended frequency spectrum. Hence, this cross over study compares the two strategies using an identical frequency spectrum.

Study Design: 

Randomized crossover study.

Patients: 

31 patients were randomly assigned to two groups.

Interventions: 

One group was fitted with a CIS map for 4 weeks, tested and subsequently fitted with a FSP map for 4 weeks. The other group followed the same pattern in reverse.

Main Outcome Measures: 

Test material consisted of sentence tests in noise, monosyllables in quiet and melody recognition.

Results: 

No statistical significance was noted between the different speech coding strategies at an identical frequency spectrum.

Conclusion: 

This study shows that there is no difference in speech perception with FSP compared to CIS at an extended frequency spectrum. Therefore, the extended frequency spectrum in the low frequencies might explain a benefit of FSP observed in previous studies.