## 4 Discussion  
This study explored the effect of cochlear implantation on middle- and inner-ear mechanics as reflected in WBT and in standard tympanometry. We studied three conditions: normal-hearing ears, implanted ears, and non-implanted ears with severe to profound SNHL. Overall, the findings indicate that WBT measurements were reliable and repeatable in normal ears, implanted ears, and non-implanted ears and were similar for the right and left ears of normal-hearing subjects. Pressure settings (peak and ambient pressure) had insignificant effects on the results, which is not surprising given that almost all ears had normal middle-ear pressure. In normal ears, we demonstrated low absorbance at lower frequencies and two absorbance peaks of 0.6 at approximately 1000 Hz and 0.7 at about 4000 Hz. This pattern is in line with previous reports on WBT in normal-hearing persons [34,35]. While the main effect of pressure was not significant in each group, likely due to minimal differences in the tympanometric peak pressure in each group, the interaction between the groups, frequency, and pressure was, however, significant. This finding may indicate that, while the effect of pressure was not significant within each group, between the groups the differences in absorbance between the ambient and peak pressure across frequency were not similar. The findings for the groups studied in this study enabled us to appreciate the effects of CI surgery, SNHL, and age on WBT. Effects of CI surgery on WBT This impact was derived from the comparisons between the implanted and the contralateral non-implanted ears. Unlike previous reports that used normal-hearing ears, we used matched contra-lateral non-implanted ears of patients with bilateral SNHL as the control group. Comparisons showed decreased absorbance at low frequencies (400-800 Hz) and an increase in absorbance at 1600 Hz. This is in line with reports relating this reduction in absorbance at low frequencies to the presence of the implant in the cochlea inducing an increase in inner-ear stiffness [12, 36, 37, 38]. However, each stage of the CI surgery itself, such as mastoidectomy and posterior tympanotomy, as well as post-operative processes, such as fibrosis, may affect middle- and inner-ear stiffness. [PERSON], as well as [PERSON] [39,40], demonstrated that cortical mastoidectomy and the facial recess approach were found to \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Frequency (Hz)**} & \multirow{2}{*}{**Implanted Ears**} & \multicolumn{2}{c}{**Non-Implanted Ears**} & \multirow{2}{*}{**F (1,28)**} & \multirow{2}{*}{_p-Value_} \\  & & & & \\ \hline
400 & 0.13 \(\pm\) 0.04 & 0.18 \(\pm\) 0.07 & 5.24 & 0.03 \\ \hline
500 & 0.18 \(\pm\) 0.06 & 0.26 \(\pm\) 0.1 & 6.67 & 0.015 \\ \hline
630 & 0.28 \(\pm\) 0.08 & 0.4 \(\pm\) 0.14 & 8.52 & 0.007 \\ \hline
800 & 0.39 \(\pm\) 0.1 & 0.51 \(\pm\) 0.15 & 6.38 & 0.017 \\ \hline
1600 & 0.69 \(\pm\) 0.12 & 0.59 \(\pm\) 0.12 & 5.64 & 0.025 \\ \hline \multirow{2}{*}{**Frequency (Hz)**} & \multirow{2}{*}{**Implanted Ears**} & \multicolumn{2}{c}{**Normal-Hearing Ears ***} & \multirow{2}{*}{**F(1,73)**} & \multirow{2}{*}{_p-Value_} \\  & & & & \\ \hline
1600 & 0.69 \(\pm\) 0.12 & 0.59 \(\pm\) 0.11 & 4.85 & 0.003 \\ \hline
4000 & 0.53 \(\pm\) 0.2 & 0.66 \(\pm\) 0.17 & 4.48 & 0.006 \\ \hline \multirow{2}{*}{**Frequency (Hz)**} & \multicolumn{2}{c}{**Non-implanted Ears**} & \multirow{2}{*}{**Normal-Hearing Ears**} & \multirow{2}{*}{**F (1,69)**} & \multirow{2}{*}{_p-Value_} \\  & & & & \\ \hline
4000 & 0.50 \(\pm\) 0.2 & 0.66 \(\pm\) 0.17 & 4.42 & 0.006 \\ \hline
5000 & 0.46 \(\pm\) 0.16 & 0.56 \(\pm\) 0.13 & 4.04 & 0.009 \\ \hline \hline \end{tabular}  
* For ambient pressure only, implanted ears had significant (_p_ < 0.03) lower absorbance levels for low frequencies (400–800 Hz).  
\end{table} 
Table 3: Average absorbance (across the pressure settings) of the implanted ears, the contra-lateral non-implanted ears, and ears with normal hearing. The F and p values of the differences are also displayed.