## 3 Results
### Case Studies  
In the following, a few case studies regarding different types of hearing loss are presented. Firing rates are depicted with respect to fiber index (y-axes) and time (x-axes). The fibers are ordered by their origin from apex (bottom) to base (top), which corresponds to low and high frequencies, respectively. Figures 4-7 show firing rates for (a) NH, i.e., the reference; (b) unaided hearing, i.e., the baseline; (c) hearing with sole acoustical amplification; (d) hearing with sole electrical stimulation, including residual hearing at low frequencies; and (e) electrical stimulation combined with acoustical amplification. In addition, hearing loss parameters, personalized fitting parameters, and LAPs are shown on the top of the images. In NH, three major clusters of AN firings are observed. First, the largest cluster at the bottom left of the image corresponds to the first two phonemes /n/ and /e/ of the stimulus. The second cluster is located at the top in the middle, i.e., around fiber index 2500 and 0.2 s. It corresponds to the third phoneme, /s/. Finally, the third cluster is shown on the right. It is located at around 0.28 s, and ranges from approximately fiber 500 to fiber 2500. Moreover, a few speckles are observed between the clusters. Figure 4 shows the results for a subject with severe to profound hearing impairment. In particular, most of the IHCs were damaged, which is reflected by I\({}_{f}\) = 39.8 dB and I\({}_{s}\) = 40.2 dB. Moreover, severe CGL was present, which is reflected by O\({}_{f}\) = 30.7 dB and O\({}_{s}\) = 33.2 dB. The unaided LAP(ua) = 99.7% reflected hearing loss close to deafness. With sole acoustical amplification, no improvement was achieved, i.e., LAP(ac) = 99.8%, even with large gain factors \(L_{f}\) = 56.3 dB and \(L_{s}\) = 57.2 dB. Smaller LAPs were obtained for the remaining two options, i.e., LAP(el) = 83.4% and LAP(co) = 83.9%. The combination with acoustical amplification did not outperform sole electrical stimulation, which was due to the absence of substantial residual hearing at low frequencies. Figure 5 reports results for a subject with a complete loss of IHCs in a basal dead region, and a partly loss of IHCs in the remaining cochlear regions. The former is reflected by I\({}_{s}\) = 55.3 dB, and the latter by I\({}_{f}\) = 8.4 dB. The hearing loss is reflected in (b) by the absence  
Figure 4: AN firing rates with regard to fiber index and time. The subject has severe IHCL and CGL. The stimulus was an audio recording of a speaker uttering the word ’nest’, which was scaled to an equivalent sound pressure level of 65 dB (20 uPa). (**a**) Normal hearing reference. (**b**) Unaided hearing, with hearing loss parameters (I\({}_{f}\), I\({}_{s}\), O\({}_{f}\), O\({}_{s}\), and N\({}_{fib}\)). (**c**) Sole acoustical amplification, with amplification parameters (I\({}_{f}\) and I\({}_{s}\)). (**d**) Sole acoustical stimulation, with insertion depth of the CI. (**e**) Electrical stimulation combined with acoustic amplification, with insertion depth of the CI and amplification parameter L\({}_{f}\). LAP refers to the cost-adjusted loss of action potentials. of firing of high frequency fibers, i.e., missing of the /s/-cluster, as well as substantial decrease in neural activity in the lower frequency region. The unaided loss of action potentials LAP(ua) = 63.5%. A better option is acoustic amplification (LAP(ac) = 56.8%). The LAP is larger for options involving cochlear implantation, i.e., 80.4% and 66.3%. Figure 6 reports results for a subject with a moderate flat component, as well as a larger sloping component of CGL. The LAP(ua) was 72.8%, which reflects significant loss of hearing. The speckles that are visible in the NH reference appear to be suppressed in unaided hearing (b). Moreover, the /s/- and /t/-clusters of nerve firings associated with the fricative /s/ and the plosive /t/ appear to be particularly faint in (b).