Cochlear Implant Compression Optimization for Music Listening - Maplaw and AGC

Variations in loudness are a fundamental component of the music listening
experience. Cochlear implant (CI) processing, including amplitude
compression, and a degraded auditory system may further degrade these
loudness cues and decrease the enjoyment of music listening. This study
aimed to identify optimal CI sound processor compression settings to
improve music sound quality for CI users. Fourteen adult MED-EL CI
recipients participated (Experiment #1: n=17 ears; Experiment #2: n=11
ears) in the study. A software application using a modified Comparison
Category Rating (CCR) test method allowed participants to compare and rate
the sound quality of various CI compression settings while listening to 25
real-world music clips. The two compression settings studied were: 1)
Maplaw, which informs audibility and compression of soft level sounds, and
2) Automatic Gain Control (AGC), which applies compression to loud sounds.
For each experiment, one compression setting (Maplaw or AGC) was held at
the default while the other was varied according to the values available
in the clinical CI programming software. Experiment #1 compared Maplaw
settings of 500, 1000 (default), and 2000. Experiment #2 compared AGC
settings of 2.5:1, 3:1 (default), and 3.5:1. In Experiment #1, the group
preferred a higher Maplaw setting of 2000 over the default Maplaw setting
of 1000 (p = 0.003) for music listening. There was no significant
difference in music sound quality between the Maplaw setting of 500 and
the default setting (p = 0.278). In Experiment #2, a main effect of AGC
setting was found; however, no significant difference in sound quality
ratings for pairwise comparisons were found between the experimental
settings and the default setting (2.5:1 versus 3:1 at p = 0.546; 3.5:1
versus 3:1 at p = 0.059). CI users reported improvements in music sound
quality with higher than default Maplaw or AGC settings. Thus,
participants preferred slightly higher compression for music listening,
with results having clinical implications for improving music perception
in CI users.