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Ginger Stickney

Publications and source records attributed to Ginger Stickney.

3 recordsLinked to original sources
PubMed2005

Encoding frequency modulation to improve cochlear implant performance in noise.

Different from traditional Fourier analysis, a signal can be decomposed into amplitude and frequency modulation components. The speech processing strategy in most modern cochlear implants only extracts and encodes amplitude modulation in a limited number of frequency bands. While amplitude modulation encoding has allowed cochlear implant users to achieve good speech recognition in quiet, their performance in noise is severely compromised. Here, we propose a novel speech processing strategy that encodes both amplitude and frequency modulations in order to improve cochlear implant performance in noise. By removing the center frequency from the subband signals and additionally limiting the frequency modulation's range and rate, the present strategy transforms the fast-varying temporal fine structure into a slowly varying frequency modulation signal. As a first step, we evaluated the potential contribution of additional frequency modulation to speech recognition in noise via acoustic simulations of the cochlear implant. We found that while amplitude modulation from a limited number of spectral bands is sufficient to support speech recognition in quiet, frequency modulation is needed to support speech recognition in noise. In particular, improvement by as much as 71 percentage points was observed for sentence recognition in the presence of a competing voice. The present result strongly suggests that frequency modulation be extracted and encoded to improve cochlear implant performance in realistic listening situations. We have proposed several implementation methods to stimulate further investigation. Index Terms-Amplitude modulation, cochlear implant, fine structure, frequency modulation, signal processing, speech recognition, temporal envelope.

Algorithms↗
PubMed2003

Comparison of speech processing strategies used in the Clarion implant processor.

OBJECTIVE: To evaluate the performance of the various speech processing strategies supported by the Clarion S-Series implant processor. DESIGN: 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. RESULTS: 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. CONCLUSIONS: 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.

Acoustic Stimulation↗