Longitudinal assessment of spectral ripple discrimination and speech perception evolution in cochlear implant users

Introduction

Psychoacoustic studies have shown that cochlear implant (CI) users’ ability to discriminate spectrally-rippled noise stimuli correlates reasonably well with their speech perception. Non-linguistic tests utilizing spectral ripple have been proposed to be useful for evaluation of CI performance. However, little is known about the evolution of spectral ripple discrimination (SRD) over time after the implantation and its relationship with speech perception rehabilitation. Here, we evaluate longitudinally the evolution of SRD and speech perception in quiet and noise for adult CI users.

Methods

Nine adult CI users attended research sessions, during their first year of rehabilitation, at dates indicated by the clinic (switch-on, one week, one month, two months, three months, six months, nine months and one year after switch-on). Behavioural SRD thresholds were measured using a two-alternative forced-choice paradigm. Speech perception in quiet and in talker-babble noise (10dB SNR and 5dB SNR) was measured using AzBio sentences. Stimuli were presented unilaterally, at most comfortable level as indicated by the participant and sent directly to the CI speech processor via the auxiliary input.

Results

Repeated measures ANOVA indicates that there is a significant time effect in the evolution of SRD (F(7,56)=6.65, p-value<0.0005) and speech perception in quiet and in noise at 10dB SNR (F(7,16.21)=4.45, p-value<0.01; F(6,55.82)=3.16, p-value=0.01). However, speech perception in noise at 5dB SNR showed a slight improvement over time that did not reach statistical significance (F(7,41.66)=1.54, p-value>0.1). Post-hoc tests using the Bonferroni correction revealed that there is an increase in SRD at all sessions compared to the switch-on session, however, statistically significant changes only occur two months after implantation and onwards. Statistically significant changes for speech perception occur one year after implantation for the quiet condition and in noise at 5dB SNR. Pearson’s correlation analysis revealed that SRD at one week after switch on has a strong and significant correlation with speech perception in quiet (r=0.878, p-value=0.002) and in noise at 10dB SNR (r=0.707, p-value=0.05). SRD at one week after switch-on also correlated with speech perception in quiet up to nine months after implantation (r=0.835, p-value=0.038).

Conclusion

Longitudinal assessment of SRD and speech perception indicated that the SRD progression is faster than speech perception in quiet and in noise for adult CI users. SRD even at one week after switch-on showed promising potential estimating speech perception abilities longitudinally. This opens the prospect of using SRD as an objective metric to estimate future speech perception abilities in CI users.