SRF301 - Training Cochlear Implant Users' Pitch Discrimination: Effects on Behavioral/Neural Outcomes

Abstract:
Cochlear implants provide excellent speech understanding in quiet for those with moderate to profound sensorineural hearing loss. However, current designs omit key temporal fine structure for pitch discrimination, sound localization, and stream segregation. This study aims to improve timing and rate cues. Five post-lingually deafened adult cochlear implant users completed a training regimen using rate, place, and combined pitch perception cues. A pre- and post-training electroencephalogram (EEG) was administered to examine neural responses to these cues, providing objective measurements following the training. Preliminary findings suggest a trend toward improved rate pitch perception with training.

Summary:
Pitch perception refers to the ability to distinguish differences between frequencies. In normal hearing, individuals can detect frequency differences as small as 0.1% with pure tones. This ability is crucial not only for music enjoyment but also for stream segregation, where listeners focus on specific sounds in noisy environments. This skill is essential for speech comprehension in noise and music perception.

In typical hearing, two main cues help with pitch discrimination: place and rate of stimulation. Place cues assist in recognizing vowel sounds for speech understanding, with the cochlea's basilar membrane organized to detect pitches from high to low. Rate cues, on the other hand, help with sound localization and separating speech from background noise by using the auditory nerve's stimulation pattern. Both temporal (rate) and spectral (place) cues work together to handle complex listening tasks like speech in noise and sound localization.

Cochlear implants (CIs) can provide open-set speech perception for those with severe to profound sensorineural hearing loss. For many, CIs are life-changing devices that open the door to communication. However, current CI designs are not without flaws. The greatest challenges users face include speech perception in noise and music appreciation. In current CI designs, temporal information is sacrificed in favor of spectral information, meaning that these devices provide minimal timing cues and rely heavily on place cues. With current signal processing strategies, the temporal fine structure is discarded in favor of envelope extraction. Missing this crucial cue, CI users struggle significantly with speech in noise and sound localization tasks. The envelope is responsible for much of the speech recognition in normal hearing. Utilizing this cue, CI users can discriminate pitch down to an average of 10%, which is notably poorer than the 0.1% discrimination exhibited by those with typical hearing.

The present study aims to address whether CI users perceive adequate rate, place, and combined rate/place stimulation cues and if improvement can be achieved through training. The project included five post-lingually deafened adult cochlear implant users who followed a training regimen. Each participant received pre- and post-assessment electroencephalograms (EEGs) measuring acoustic change complex (ACC) responses to rate pitch changes using a research processor. After the pre-assessment EEG, participants were sent home with a computer and research processor. The training lasted one month, after which participants returned to complete the same post-assessment EEG. This allowed the collection of both objective neural responses from the EEG and behavioral responses from training data. Preliminary findings suggest a trend toward improved rate pitch perception with training.

In conclusion, while cochlear implants restore speech perception, there remains room for enhancing pitch discrimination, especially through training aimed at improving temporal cue perception.

Brief Summary of Clinical Takeaways:
The clinical takeaway from this session is that, with potential improvements using rate-based cues, cochlear implant manufacturers could alter signal processing strategies to improve speech understanding in noise and enhance music appreciation.