The Development and Pilot Testing of a Music Quality Rating Test Battery for New Zealand and Australian MED-EL Cochlear Implant Recipients

Abstract

Many cochlear implant (CI) recipients report the sound quality of their devices to be poor, for listening to music. The latest MED-EL speech processing strategy, Fine Structure Processing (FSP), aims to improve sound quality by encoding some of the low-frequency fine structure (FS) information.

The goals of this study were twofold. The first was to develop a music quality rating test battery (MQRTB) for the New Zealand and Australian populations using commercially available songs. The second was to pilot test the MQRTB in a study comparing the MED-EL speech processing strategies FSP and High Definition Continuous Interleaved Sampling (HDCIS) for music appreciation. The research questions for the second part of this study were: (1) Does familiarity with a speech processing strategy affect musical quality ratings?; (2) Do CI recipients notice a significant difference between FSP and HDCIS when listening to music and if so, what aspects of the sound are different?; (3) Does song familiarity affect the quality ratings of music in CI recipients?; (4) Does music genre affect the quality ratings of music in CI recipients?

The MQRTB used visual analogue scales for the attributes of pleasantness, naturalness, richness, fullness, sharpness, and roughness while listening to a home stereo. The scales were displayed on a computer touchscreen with the stimuli being presented via a home stereo system. There were ten songs in the MQRTB; a familiar and obscure song from each of the following genres: classical, modern, country and western, and common (such as a national anthem or iconic melody) genres, as well as two of the participant’s favourite songs.

Five post-lingually deafened MED-EL SonataTI100 or PulsarCI100 CI recipients using the FSP strategy took part in the FSP versus HDCIS comparison study. Each participant spent three weeks acclimatising to either FSP or HDCIS before completing speech perception testing and the MQRTB task. Following this the participants were switched to the other speech processing strategy to acclimatise to for a further three weeks before re-assessment with the second strategy. At the conclusion of the study, the participants’ speech processors were returned to the pre-study settings. The results of the study showed an effect of acclimatisation on music quality ratings; when the participants were acclimatised to FSP, the group tended to prefer FSP; however, when acclimatised to HDCIS, the participants did not prefer HDCIS. As a group they rated FSP to sound closer to ‘what they would like music to sound like’ than HDCIS, and that HDCIS sounded significantly sharper and rougher than FSP. This suggested that music appreciation was better with FSP, but participants needed to be acclimatised to the strategy first. No effect of familiarity or genre was observed in the averaged group data, however, effects for some individuals were noted.

Overall it would appear that FSP may improve music sound quality for some MED-EL CI recipients, however, it does not solve this issue. The MQRTB was also shown to be an effective tool to assess some aspects of music sound quality.