## 1 Introduction  
The conductance of sound through the ear may be affected by various pathologies, most of which originate in the outer or middle ear and manifest as an air-bone gap (ABG) in the audiogram. However, inner-ear anomalies might also result in an ABG. A well-known and common inner-ear pathology that causes an ABG is the dehiscence of the superior semicircular canal, in which some of the energy from the stimulus is transferred from the middle ear to the vestibular system instead of to the cochlea duct [1,2]. Similar findings were described in animal models for dehiscence (third window) in all three semicircular canals, as well as in the scala typnani and scala vestibuli [3, 4, 5]. Another example of an ABG originating in the inner ear would be the enlarged vestibular aqueduct (EVA) syndrome that can be associated with ABG in the low-frequency range in the absence of middle-ear dysfunction [6,7]. In these inner-ear anomalies, the bone conduction threshold may improve due to an altered response of the cochlea caused by the third window phenomena [8]. Cochlear implants (CI) are considered the treatment of choice for bilateral severe to profound sensorineural hearing loss (SNHL). In recent years, the CI candidacy criteria have been expanded to include patients with significant residual hearing, mainly in the lower frequencies [9, 10, 11]. However, post-cochlear implantation audiograms in persons with residual hearing often demonstrate larger ABGs with normal tympanometry, without an apparent middle-ear pathology. [PERSON] et al. [12] showed increased air-conduction thresholds after cochlear implantation, while bone-conduction thresholds remained stable; they suggested that the presence of solid electrodes in the scala-typnani increases inner-ear stiffness and hampers sound transduction. In an animal model, [PERSON] et al. [13] demonstrated that cochlear implantation resulted in a 15 dB shift in air-conduction thresholds and only 3-5 dB in bone-conduction thresholds. The ABG increased one week after implantation, suggesting that both the electrode array and post-implantation processes, such as fibrosis, may have contributed to impaired inner-ear mechanics and the deterioration of air-conduction thresholds. Notably, the ABG was also demonstrated objectively through recordings of cochlear microphonics (electrocholeography), using the tip of the electrode array (intra-cochlear) for both air and bone conduction stimuli over a wide band of frequencies [14]. Since some individuals with implants may benefit from a combination of acoustic and electric auditory stimulations (electroacoustic stimulation), these findings might have implications for the surgery strategy, including the selection for the insertion of the electrode array and for recipients' expectations. Sensorineural hearing loss (SNHL) involves structural changes to the cochlear partition [15, 16, 17], including abnormal pectorial membrane in conjunction with degeneration of hair cells [18], fibrosis of stria vascularis [19], or fibrosis of the perilymph [16]. Some of these abnormal structural alterations demonstrate changes in the stiffness and the impedances of the cochlear partition [20, 21, 22], which were manifest mainly in reductions in vibrations at high frequencies and lowering of the partition's resonance frequency. Thus, a diagnostic tool is needed to study the effect of SNHL on the acoustic response of the inner ear. Tympanometry is a common, objective, and non-invasive test that assesses the conductance of sounds through the ear via measurements of acoustic admittance or of acoustic impedance at the plane of the tympan membrane. Typically, using a single frequency of 226 Hz for adults and 800-1000 Hz for infants, tympanometry results can facilitate assessments of tympan membrane integrity, Eustachian tube function, ossicular chain mobility, and stapes motion within the oval window [23]. However, overall test sensitivity and specificity in ossicular chain abnormalities, such as otosclerosis [24] and inner-ear pathologies, are very low [25; 26].