The effect of a coding strategy that removes temporally masked pulses on speech perception by cochlear implant users

Abstract

Speech recognition in noisy environments remains a challenge for cochlear implant (CI) recipients. Unwanted charge interactions between current pulses in the same and across different electrode channels are likely to impair performance. Here we investigate the effect of reducing the number of current pulses on speech perception. This was achieved by implementing a psychoacoustic temporal-masking model where current pulses in each channel were passed through a temporal integrator to identify and remove pulses that were less likely to be perceived by the recipient. The decision criterion of the temporal integrator was varied to control the percentage of pulses removed in each condition. In experiment 1, speech in quiet was processed with a standard Continuous Interleaved Sampling (CIS) strategy and with 25, 50 and 75% of pulses removed. In experiment 2, performance was measured for speech in noise with the CIS reference and with 50 and 75% of pulses removed. Speech intelligibility in quiet revealed no significant difference between reference and test conditions. For speech in noise, results showed a significant improvement of 2.4 dB when removing 50% of pulses. Performance both in quiet and in noise was not significantly different between the reference and when 75% of pulses were removed. Further, by reducing the overall amount of current pulses by 25, 50, and 75% but accounting for the increase in charge necessary to compensate for the decrease in loudness, estimated average power savings of 21.15, 40.95, and 63.45%, respectively, could be possible for this set of listeners. In conclusion, removing temporally masked pulses may improve speech perception in noise and result in substantial power savings.

Cochlear Implant Research and Development in the Twenty-first Century: A Critical Update

“…Finally, it will be important to determine whether the advances obtained by different approaches are additive-an issue that led one scientist to remark, only half-jokingly, that they had seen so many 5% improvements reported throughout their career that patients should now be scoring more than 100% on speech tests. For example, the various processing algorithms that enhance modulations across time (Koning and Wouters 2016;Lamping et al 2020) or across electrodes (Nogueira et al 2016;Bolner et al 2020;Lopez-Poveda et al 2020) are likely addressing the same basic goal of increasing the contrast in the pattern of electrical stimulation (electrodogram), typically by attenuating or removing lower-amplitude pulses. To the extent that different algorithms attenuate the same pulses their benefits may not sum.…”

“…Koning and Wouters (2016) recently reported a small (1 dB) but significant improvement in the SRT for speech masked by a single talker and for four participants, compared to that for ACE, using a double-blind design. More recently, Lamping et al (2020) developed a strategy that passes the envelope in each channel through a temporal window that has been used to model masking in both normalhearing and CI listeners, and, in each channel, deletes pulses that are likely to be masked. This "Temporal Integrator Processing Strategy (TIPS)" enhances the envelope modulations in each channel and may reduce unwanted charge interactions between pulses in nearby channels.…”

“…This "Temporal Integrator Processing Strategy (TIPS)" enhances the envelope modulations in each channel and may reduce unwanted charge interactions between pulses in nearby channels. Lamping et al (2020) reported that adding the TIPS processing stage to the CIS strategy produced an average of 2.4 dB improvement in the SRT for sentences masked by stationary noise for eight participants, and suggested that it could reduce power consumption substantially. Experimenters but not participants were aware of which condition was being tested.…”

From Microphone to Phoneme: An End-to-End Computational Neural Model for Predicting Speech Perception With Cochlear Implants

“…While the number-of-channels experiment is only one of the basic ways to alter a stimulation strategy, it is a critical benchmark before evaluating more advanced processing strategies. For example, psychoacoustic-ACE (PACE) [66], spatial-ACE (SPACE) [67], and the temporal integration processing strategy (TIPS) [68] all attempt to minimize channel interaction by removing pulses that would be spatially and/or temporally masked by previous pulses. The combined results of the IT analysis and the number-of-channels experiment suggest that the CI-ASR is accurately modelling channel interactions, which would be critical to evaluate and optimize strategies like these.…”