## 4 Discussion  
A simulation study on place-time representations of AN firing rates predicted for different hearing prostheses options and types and degrees of hearing loss was conducted. The prosthesis options were as follows: unaided hearing, acoustic amplification, electrical stimulation, and electrical stimulation combined with acoustic amplification. The hearing loss types were IHCL, CGL, and CS. The firing rates of the individual prosthesis options were compared to NH reference firing rates. Finding the minimum LAP of the AN firing rates served two purposes. First, the fitting parameters of the hearing prostheses were optimized, and second, personalized hearing prosthesis recommendations were obtained. The distinction between the groups 'implant' and 'no implant' is clinically highly relevant. The former group includes subjects for which the prosthesis recommendation involves electrical stimulations. It was found that loss of IHCs was most influential to the 'implant'/'no implant' distinction, followed by CS. The 'implant' group included subjects with a substantial number of damaged IHCs and subjects with severe CS. The estimated threshold of IHCL appeared to be remarkably low as compared to available clinical guidelines that basically suggest implantation for severe or profound hearing loss only. However, it should be noted that I\({}_{\text{I}}\) and I\({}_{\text{s}}\) are not directly comparable to dB HL because they rather refer to spatial density of functional IHCs instead of sound pressure levels. The damage of OHCs appears to influence the implantation recommendation only slightly. Moreover, the distinction between frequency-flat and frequency-sloping components appears to be of limited relevance to the recommendation. Several clinical guidelines regarding the indication of cochlear implantation are reviewed hereafter. In summary, cochlear implantation is indicated for severe to profound hearing loss, which may include individuals with significant residual hearing. For example, [PERSON] et al. found that cochlear-implanted children perform significantly better in speech recognition than their peers with profound hearing loss, i.e., with pure tone average thresholds exceeding 90 dB HL, when using acoustical amplification [26]. However, multiple factors need to be taken into account, including subjects' experience with acoustic amplification; unaided air and bone conduction hearing thresholds; auditory speech recognition; and non-behavioral audiological function such as optoacoustic emissions, immittance testing, and auditory brainstem responses [27]. The recent guideline published by the National Institute for Health and Care Excellence (NICE) suggests that subjects with pure tone thresholds of 80 dB HL or greater at two or more frequencies between 500 Hz and 4 kHz are eligible for cochlear implantation if they do not benefit sufficiently from acoustic amplification [28]. The latter requires for adults a phoneme score of 50% or greater in the [PERSON] word test presented at 70 dB (A), and for children speech language and listening skills that are appropriate for their age, developmental stage, and cognitive abilities. A comprehensive and recent summary of evidence regarding CI candidacy criteria is provided in [27]. The Western Australian Department of Health lists selection criteria for cochlear implantation as (i) moderately severe to profound bilateral sensorineural hearing loss, (ii) little or no benefit from acoustic \begin{table}
\begin{tabular}{c c c} \hline \hline
**Statistic** & **Value** & **95\% Confidence Interval** \\ \hline Sensitivity & 99.48\% & 98.49\% to 99.89\% \\ \hline Specificity & 98.88\% & 97.40\% to 99.63\% \\ \hline Positive likelihood ratio & 88.54 & 37.03 to 211.68 \\ \hline Negative likelihood ratio & 0.01 & 0.00 to 0.02 \\ \hline Positive predictive value & 99.14\% & 97.97\% to 99.64\% \\ \hline Negative predictive value & 99.32\% & 97.94\% to 99.78\% \\ \hline Accuracy & 99.22\% & 98.47\% to 99.66\% \\ \hline \hline \end{tabular}
\end{table}