Comparison of speech processing strategies used in the Clarion implant processor

To evaluate the performance of the various speech processing strategies supported by the Clarion S-Series implant processor.

Five different speech-processing strategies [the Continuous Interleaved Sampler (CIS), the Simultaneous Analog Stimulation (SAS), the Paired Pulsatile Sampler (PPS), the Quadruple Pulsatile Sampler (QPS) and the hybrid (HYB) strategies] were implemented on the Clarion Research Interface platform. These speech-processing strategies varied in the degree of electrode simultaneity, with the SAS strategy being fully simultaneous (all electrodes are stimulated at the same time), the PPS and QPS strategies being partially simultaneous and the CIS strategy being completely sequential. In the hybrid strategy, some electrodes were stimulated using SAS, and some were stimulated using CIS. Nine Clarion CIS users were fitted with the above speech processing strategies and tested on vowel, consonant and word recognition in quiet.

There were no statistically significant differences in the mean group performance between the CIS and SAS strategies on vowel and sentence recognition. A statistically significant difference was found only on consonant recognition. Individual results, however, indicated that most subjects performed worse with the SAS strategy compared with the CIS strategy on all tests. About 33% of the cochlear implant users benefited from the PPS and QPS strategies on consonant and word recognition.

If temporal information were the primary factor in speech recognition with cochlear implants then SAS should consistently produce higher speech recognition scores than CIS. That was not the case, however, because most CIS users performed significantly worse with the SAS strategy on all speech tests. Hence, there seems to be a trade-off between improving the temporal resolution with an increasing number of simultaneous channels and introducing distortions from electrical-field interactions. Performance for some CI users improved when the number of simultaneous channels increased to two (PPS strategy) and four (QPS strategy). The improvement with the PPS and QPS strategies must be due to the higher rates of stimulation. The above results suggest that CIS users are less likely to benefit with the SAS strategy, and they are more likely to benefit from the PPS and QPS strategies, which provide higher rates of stimulation with small probability of channel interaction.