Instant improvement in monaural spatial hearing abilities through cognitive feedback.

Several studies report that sound localization performance of acute and chronic monauralized normal-hearing listeners can improve through training. Typically, training sessions are administered daily for several days or weeks. While this intensive training is effective, it may also be that monaural localization abilities improve instantly after providing explicit top-down information about the direction dependent change in timbre and level. The aim of the present study was to investigate whether cognitive feedback (i.e., top-down information) could instantly improve sound localization in naive acutely monauralized listeners. Forty-three normal-hearing listeners (experimental group), divided over five different centers, were tested. Two control groups, consisting of, respectively, nine and eleven normal-hearing listeners, were tested in one center. Broadband sounds (0.5-20 kHz) were presented from visible loudspeakers, positioned in azimuth (- 90° to 90°). Participants in the experimental group received explicit information about the noticeable difference in timbre and the poor localization in the monauralized listening condition, resulting in an instant improvement in sound localization abilities. With subsequent roving of stimulus level (20 dB), sound localization performance deteriorated immediately. The reported improvement is related to the context of the localization test. The results provide important implications for studies investigating sound localization in a clinical setting, especially during closed-set testing, and indicate the importance of top-down information.

Bimodal Fitting and Bilateral Cochlear Implants in Children With Significant Residual Hearing: The Impact of Asymmetry in Spatial Release of Masking on Localization.

Purpose This study aimed to gain more insight into the primary auditory abilities of children with significant residual hearing in order to improve decision making when choosing between bimodal fitting or sequential bilateral cochlear implantation. Method Sound localization abilities, spatial release of masking, and fundamental frequency perception were tested. Nine children with bimodal fitting and seven children with sequential bilateral cochlear implants were included in the study. As a reference, 15 children with normal hearing and two children with simultaneous bilateral cochlear implants were included. Results On all outcome measures, the implanted children performed worse than the normal hearing children. For high-frequency localization, children with sequential bilateral cochlear implants performed significantly better than children with bimodal fitting. Compared to children with normal hearing, the left-right asymmetry in spatial release of masking was significant. When the implant was hindered by noise, bimodally fitted children obtained significantly lower spatial release of masking compared to when the hearing aid was hindered by noise. Overall, the larger the left-right asymmetry in spatial release of masking, the poorer the localization skills. No significant differences were found in fundamental frequency perception between the implant groups. Conclusions The data hint to an advantage of bilateral implantation over bimodal fitting. The extent of asymmetry in spatial release of masking is a promising tool for decision making when choosing whether to continue with the hearing aid or to provide a second cochlear implant in children with significant residual hearing.

Unexplained Variation in Benefit of Treatment of Congenital Unilateral Aural Atresia: A Review of the Literature.

OBJECTIVE: A review of published data regarding binaural hearing after treatment of congenital unilateral conductive hearing loss (UCHL) due to aural atresia. Treatment options concern atresia surgery (reconstructive surgery), application of a bone conduction device (BCD), or application of a middle ear implant (MEI). DATA SOURCES: Database PubMed was searched for articles published in English and German between January 1, 1994, and January 1, 2019. STUDY SELECTION: The initial search identified 52 studies, of which 9 met the inclusion criteria. DATA SYNTHESIS: Comparison of studies was based on a structured review. Meta-analysis was not feasible because of the heterogeneity of outcome measures, the limited number of relevant papers (9), and diverse types of treatment (5). CONCLUSIONS: Treatment of UCHL results in bilateral hearing instead of binaural hearing. The large intersubject variability in benefit of treatment is unexplained with a clear improvement in the minority of listeners and a limited improvement or binaural interference in most listeners after atresia repair or amplification with a BCD or MEI.

Spatial Hearing by Bilateral Cochlear Implant Users With Temporal Fine-Structure Processing.

Several studies have demonstrated the advantages of the bilateral vs. unilateral cochlear implantation in listeners with bilateral severe to profound hearing loss. However, it remains unclear to what extent bilaterally implanted listeners have access to binaural cues, e.g., accurate processing of interaural timing differences (ITDs) for low-frequency sounds (<1.5 kHz) and interaural level differences (ILDs) for high frequencies (>3 kHz). We tested 25 adult listeners, bilaterally implanted with MED-EL cochlear implant (CI) devices, with and without fine-structure (FS) temporal processing as encoding strategy in the low-frequency channels. In order to assess whether the ability to process binaural cues was affected by fine-structure processing, we performed psychophysical ILD and ITD sensitivity measurements and free-field sound localization experiments. We compared the results of the bilaterally implanted listeners with different numbers of FS channels. All CI listeners demonstrated good sensitivity to ILDs, but relatively poor to ITD cues. Although there was a large variability in performance, some bilateral CI users showed remarkably good localization skills. The FS coding strategy for bilateral CI hearing did not improve fine-structure ITD processing for spatial hearing on a group level. However, some CI listeners were able to exploit weakly informative temporal cues to improve their low-frequency spatial perception.

The Merits of Bilateral Application of Bone-Conduction Devices in Children With Bilateral Conductive Hearing Loss.

OBJECTIVES: This study aims to characterize lateralization of sounds and localization of sounds in children with bilateral conductive hearing loss (BCHL) when listening with either one or two percutaneous bone conduction devices (BCDs). DESIGN: Sound lateralization was measured with the minimum audible angle test in which children were asked to indicate from which of the two visible speakers the sound originated. Sound localization was measured with a test in which stimuli were presented from speakers that were not visible to the children. In the sound localization test, 150 ms broadband noise bursts were presented, and sound level was roved over a 20-dB range. Because speakers were not visible the localization response was not affected by any visual cue. The sound localization test provides a clear distinction between lateralization and localization of sounds. Ten children with congenital BCHL and one child with acquired BCHL participated. RESULTS: Both lateralization and sound localization were better with bilateral BCDs compared with the unilaterally aided conditions. In the bilateral BCD condition, lateralization was close to normal in nearly all the children. The localization test demonstrated lateralization rather than sound localization behavior when listening with bilateral BCDs. Furthermore, in the unilateral aided condition, stimuli presented at different sound levels were mainly perceived at the same location. CONCLUSIONS: This study demonstrates that, in contrast to listening with two BCDs, children demonstrated difficulties in lateralization of sounds and in sound localization when listening with just one BCD (i.e., one BCD turned off). Because both lateralization and sound localization behavior were tested, it could be demonstrated that these children are more able to lateralize than localize sounds when listening with bilateral BCDs. The present study provides insight in (sub-optimal) sound localization capabilities of children with congenital BCHL in the unilateral-aided and bilateral-aided condition. Despite the sub-optimal results on sound localization, this study underlines the merits of bilateral application of BCDs in such children.

Bilateral bone conduction stimulation provides reliable binaural cues for localization.

This study aimed to characterize binaural hearing abilities with bone conduction stimulation in simulated conductive hearing loss. Bone conduction hearing devices (BCDs) are a common method of rehabilitating conductive hearing loss. However, little is known about the access these devices provide to binaural cues. To study the ability of BCDs to restore access to binaural cues in conductive loss, normal hearing listeners were plugged unilaterally and bilaterally and localization ability was assessed using a non-surgical BCD attached to the mastoid/s via an adhesive (MED-EL, Corp). The results demonstrate that 1) application of the BCD in simulated unilateral conductive hearing loss does not restore access to binaural cues, evidenced by poor localization abilities. 2) bilateral application of BCDs in simulated bilateral conductive hearing loss provides access to binaural cues, 2) unilateral application of BCDs in simulated bilateral conductive hearing loss disrupts these cues and impairs localization performance, The transcutaneous stimulation of the adhesive BCD resulted in decreased access to sound compared to the normal open ear, resulting in asymmetries in aided versus non-aided hearing thresholds. Symmetrical hearing results in improved localization abilities, while asymmetric hearing disrupts sound localization abilities.

Contribution of spectral pinna cues for sound localization in children with congenital unilateral conductive hearing loss after hearing rehabilitation.

Congenital unilateral conductive hearing loss (UCHL) jeopardizes directional hearing and speech perception in noisy conditions. Potentially, children with congenital UCHL can benefit from fitting a hearing device, such as a bone-conduction device (BCD). However, the literature reports limited benefit from fitting a BCD, and often, surprisingly, relatively good sound localization in the unaided condition is reported. In this study, we hypothesized that the limited benefit with a BCD is related to (i) insufficient access to binaural cues and (ii) relying on monaural spectral pinna cues for sound localization in the horizontal plane. Directional hearing was tested in seventeen children with congenital UCHL (age 6-19) using a percutaneous BCD. Additionally, a mold was placed in the pinna of the normal-hearing ear to diminish direction-dependent spectral pinna cues. Relatively good localization in azimuth was found in the unaided hearing condition in the majority of the children. Sound localization improved when listening with a BCD, and no correlation between age of implantation and aided localization performance was found. When the mold was inserted, the unaided and aided localization abilities of most children deteriorated. Interestingly, in the children with poor localization performance in the unaided condition, sound localization improved significantly with the BCD, and was hardly affected by molding the pinna of the normal-hearing ear. These observations indicate that the majority of these children rely on spectral pinna cues to localize sounds, independent of listening with or without their device. In conclusion, an important reason for the limited benefit of BCD fitting in children with congenital UCHL might be ascribed to an effective coping strategy (use of spectral pinna cues) that still plays a dominant role after BCD fitting.

Sound Localization in Real-Time Vocoded Cochlear-Implant Simulations With Normal-Hearing Listeners.

Bilateral cochlear-implant (CI) users and single-sided deaf listeners with a CI are less effective at localizing sounds than normal-hearing (NH) listeners. This performance gap is due to the degradation of binaural and monaural sound localization cues, caused by a combination of device-related and patient-related issues. In this study, we targeted the device-related issues by measuring sound localization performance of 11 NH listeners, listening to free-field stimuli processed by a real-time CI vocoder. The use of a real-time vocoder is a new approach, which enables testing in a free-field environment. For the NH listening condition, all listeners accurately and precisely localized sounds according to a linear stimulus-response relationship with an optimal gain and a minimal bias both in the azimuth and in the elevation directions. In contrast, when listening with bilateral real-time vocoders, listeners tended to orient either to the left or to the right in azimuth and were unable to determine sound source elevation. When listening with an NH ear and a unilateral vocoder, localization was impoverished on the vocoder side but improved toward the NH side. Localization performance was also reflected by systematic variations in reaction times across listening conditions. We conclude that perturbation of interaural temporal cues, reduction of interaural level cues, and removal of spectral pinna cues by the vocoder impairs sound localization. Listeners seem to ignore cues that were made unreliable by the vocoder, leading to acute reweighting of available localization cues. We discuss how current CI processors prevent CI users from localizing sounds in everyday environments.

Sound-localization performance of patients with single-sided deafness is not improved when listening with a bone-conduction device.

An increased number of treatment options has become available for patients with single sided deafness (SSD), who are seeking hearing rehabilitation. For example, bone-conduction devices that employ contralateral routing of sound (CROS), by transmitting acoustic bone vibrations from the deaf side to the cochlea of the hearing ear, are widely used. However, in some countries, cochlear implantation is becoming the standard treatment. The present study investigated whether CROS intervention, by means of a CROS bone-conduction device (C-BCD), affected sound-localization performance of patients with SSD. Several studies have reported unexpected moderate to good unilateral sound-localization abilities in unaided SSD listeners. Listening with a C-BCD might deteriorate these localization abilities because sounds are transmitted, through bone conduction to the contralateral normal hearing ear, and could thus interfere with monaural level cues (i.e. ambiguous monaural head-shadow cues), or with the subtle spectral localization cues, on which the listener has learned to rely on. The present study included nineteen SSD patients who were using their C-BCD for more than five months. To assess the use of the different localization cues, we investigated their localization abilities to broadband (BB, 0.5-20 kHz), low-pass (LP, 0.5-1.5 kHz), and high-pass filtered noises (HP, 3-20 kHz) of varying intensities. Experiments were performed in complete darkness, by measuring orienting head-movement responses under open-loop localization conditions. We demonstrate that a minority of listeners with SSD (5 out of 19) could localize BB and HP (but not LP) sounds in the horizontal plane in the unaided condition, and that a C-BCD did not deteriorate their localization abilities.

Horizontal sound localization in cochlear implant users with a contralateral hearing aid.

Interaural differences in sound arrival time (ITD) and in level (ILD) enable us to localize sounds in the horizontal plane, and can support source segregation and speech understanding in noisy environments. It is uncertain whether these cues are also available to hearing-impaired listeners who are bimodally fitted, i.e. with a cochlear implant (CI) and a contralateral hearing aid (HA). Here, we assessed sound localization behavior of fourteen bimodal listeners, all using the same Phonak HA and an Advanced Bionics CI processor, matched with respect to loudness growth. We aimed to determine the availability and contribution of binaural (ILDs, temporal fine structure and envelope ITDs) and monaural (loudness, spectral) cues to horizontal sound localization in bimodal listeners, by systematically varying the frequency band, level and envelope of the stimuli. The sound bandwidth had a strong effect on the localization bias of bimodal listeners, although localization performance was typically poor for all conditions. Responses could be systematically changed by adjusting the frequency range of the stimulus, or by simply switching the HA and CI on and off. Localization responses were largely biased to one side, typically the CI side for broadband and high-pass filtered sounds, and occasionally to the HA side for low-pass filtered sounds. HA-aided thresholds better than 45 dB HL in the frequency range of the stimulus appeared to be a prerequisite, but not a guarantee, for the ability to indicate sound source direction. We argue that bimodal sound localization is likely based on ILD cues, even at frequencies below 1500 Hz for which the natural ILDs are small. These cues are typically perturbed in bimodal listeners, leading to a biased localization percept of sounds. The high accuracy of some listeners could result from a combination of sufficient spectral overlap and loudness balance in bimodal hearing.

Three-year experience with the Sophono in children with congenital conductive unilateral hearing loss: tolerability, audiometry, and sound localization compared to a bone-anchored hearing aid.

Bone conduction devices (BCDs) are advocated as an amplification option for patients with congenital conductive unilateral hearing loss (UHL), while other treatment options could also be considered. The current study compared a transcutaneous BCD (Sophono) with a percutaneous BCD (bone-anchored hearing aid, BAHA) in 12 children with congenital conductive UHL. Tolerability, audiometry, and sound localization abilities with both types of BCD were studied retrospectively. The mean follow-up was 3.6 years for the Sophono users (n = 6) and 4.7 years for the BAHA users (n = 6). In each group, two patients had stopped using their BCD. Tolerability was favorable for the Sophono. Aided thresholds with the Sophono were unsatisfactory, as they did not reach under a mean pure tone average of 30 dB HL. Sound localization generally improved with both the Sophono and the BAHA, although localization abilities did not reach the level of normal hearing children. These findings, together with previously reported outcomes, are important to take into account when counseling patients and their caretakers. The selection of a suitable amplification option should always be made deliberately and on individual basis for each patient in this diverse group of children with congenital conductive UHL.

Nanogrooved surface-patterns induce cellular organization and axonal outgrowth in neuron-like PC12-cells.

Modulation of a materials surface topography can be used to steer various aspects of adherent cell behaviour, such as cell directional organization. Especially nanometric sized topographies, featuring sizes similar to for instance the axons of the spiral ganglion cells, are interesting for such purpose. Here, we utilized nanosized grooves in the range of 75-500 nm, depth of 30-150 nm, and pitches between 150 nm and 1000 nm for cell culture of neuron-like PC12 cells. The organizational behaviour was evaluated after 7 days of culture by bright field and scanning electron microscopy. Nanotopographies were shown to induce aligned cell-body/axon orientation and an increased axonal outgrowth. Our findings suggest that a threshold for cell body alignment of neuronal cells exists on grooved topographies with a groove width of 130 nm, depth of 70 nm and pitch of 300 nm, while axon alignment can already be induced by grooves with 135 nm width, 52 nm depth and 200 nm pitch. However, no threshold has been found for axonal outgrowth, as all of the used patterns increased outgrowth of PC12-axons. In conclusion, surface nanopatterns have the potential to be utilized as an electrode modification for a stronger separation of cells, and can be used to direct cells towards the electrode contacts of cochlear implants.

Spontaneous behavior in noise and silence: a possible new measure to assess tinnitus in Guinea pigs.

This study describes two experiments that were conducted in search for a behavioral paradigm to test for tinnitus in guinea pigs. Conditioning paradigms are available to determine the presence of tinnitus in animals and are based on the assumption that tinnitus impairs their ability to detect silent intervals in continuous noise. Guinea pigs have not been subjected to these paradigms yet; therefore, we investigated whether guinea pigs could be conditioned in the two-way shuttle-box paradigm to respond to silent intervals in noise. Even though guinea pigs could be trained relatively easy to respond to the presence of a noise interval, training guinea pigs to silent intervals in noise was unsuccessful. Instead, it appeared that they became immobile when the continuous stimulus was suddenly stopped. This was confirmed by the next experiment, in which we subjected guinea pigs to alternating intervals of noise and silence with a random duration between 30 and 120 s. Indeed, guinea pigs were significantly longer immobile during silence compared to during noise. By interpreting immobility as a signature of perceiving silence, we hypothesized that the presence of tinnitus would reduce immobility in silence. Therefore, we unilaterally exposed one group of guinea pigs to an 11-kHz tone of 124 dB sound pressure level for 1 h. A subset of the exposed animals was significantly more active in silence, but also more active in noise, as compared to the control group. The increased mobility during silent intervals might represent tinnitus. However, the increased mobility in noise of this group implies that the observed behavior could have derived from, e.g., an overall increase in activity. Therefore, conducting validation experiments is very important before implementing this method as a new screening tool for tinnitus. Follow-up experiments are discussed to further elucidate the origin of the increased mobility in both silence and noise.

Single-sided deafness and directional hearing: contribution of spectral cues and high-frequency hearing loss in the hearing ear.

Direction-specific interactions of sound waves with the head, torso, and pinna provide unique spectral-shape cues that are used for the localization of sounds in the vertical plane, whereas horizontal sound localization is based primarily on the processing of binaural acoustic differences in arrival time (interaural time differences, or ITDs) and sound level (interaural level differences, or ILDs). Because the binaural sound-localization cues are absent in listeners with total single-sided deafness (SSD), their ability to localize sound is heavily impaired. However, some studies have reported that SSD listeners are able, to some extent, to localize sound sources in azimuth, although the underlying mechanisms used for localization are unclear. To investigate whether SSD listeners rely on monaural pinna-induced spectral-shape cues of their hearing ear for directional hearing, we investigated localization performance for low-pass filtered (LP, <1.5 kHz), high-pass filtered (HP, >3kHz), and broadband (BB, 0.5-20 kHz) noises in the two-dimensional frontal hemifield. We tested whether localization performance of SSD listeners further deteriorated when the pinna cavities of their hearing ear were filled with a mold that disrupted their spectral-shape cues. To remove the potential use of perceived sound level as an invalid azimuth cue, we randomly varied stimulus presentation levels over a broad range (45-65 dB SPL). Several listeners with SSD could localize HP and BB sound sources in the horizontal plane, but inter-subject variability was considerable. Localization performance of these listeners strongly reduced after diminishing of their spectral pinna-cues. We further show that inter-subject variability of SSD can be explained to a large extent by the severity of high-frequency hearing loss in their hearing ear.

Behavioral responses of deafened guinea pigs to intracochlear electrical stimulation: a new rapid psychophysical procedure.

In auditory research the guinea pig is often preferred above rats and mice because of the easily accessible cochlea and because the frequency range of its hearing is more comparable to that of humans. Studies of the guinea-pig auditory system primarily apply histological and electrophysiological measures. Behavioral animal paradigms, in particular in combination with these histological and electrophysiological methods, are necessary in the development of new therapeutic interventions. However, the guinea pig is not considered an attractive animal for behavioral experiments. Therefore, the purpose of this study was to develop a behavioral task suitable for guinea pigs, that can be utilized in cochlear-implant related research. Guinea pigs were trained in a modified shuttle-box in which a stream of air was used as unconditioned stimulus (UCS). A stream of air was preferred over conventionally used methods as electric foot-shocks since it produces less stress, which is a confounding factor in behavioral experiments. Hearing guinea pigs were trained to respond to acoustic stimuli. They responded correctly within only five sessions of ten minutes. The animals maintained their performance four weeks after the right cochlea was implanted with an electrode array. After systemic deafening, the animals responded in the first session immediately to intracochlear electrical stimulation. These responses were not affected by daily chronic electrical stimulation (CES). In conclusion, the present study demonstrates that guinea pigs can be trained relatively fast to respond to acoustic stimuli, and that the training has a lasting effect, which generalizes to intracochlear electrical stimulation after deafening. Furthermore, it demonstrates that bilaterally deafened guinea pigs with substantial (∼50%) loss of spiral ganglion cells (SGCs), detect intracochlear electrical stimulation.

Amplification options in unilateral aural atresia: an active middle ear implant or a bone conduction device?

BACKGROUND: There is no consensus on treatment of patients with congenital unilateral aural atresia. Currently, 3 intervention options are available, namely, surgical reconstruction, application of a bone-conduction device (BCD), or application of a middle ear implant. OBJECTIVE: The present study aims to compare the BCD with the application of a middle ear implant. We hypothesized that cross-hearing (stimulating the cochlea by means of bone conduction contralateral to the implanted side) would cause BCD users to have difficulty performing localization tasks. METHODS: Audiologic data of 4 adult patients with a middle ear implant coupled directly to the cochlea were compared with data of 4 adult patients fitted with an osseointegrated BCD. All patients were fitted during adulthood. The emphasis of this study is on directional hearing. RESULTS: The middle ear implant and the BCD improved sound localization of patients with congenital unilateral aural atresia. Unaided scores demonstrate a large variation. CONCLUSION: Our results demonstrate that there was no advantage of the middle ear implant over the BCD for directional hearing in patients who had no amplification in childhood. The BCD users had the best bandwidth.

Bilateral bone conduction devices: improved hearing ability in children with bilateral conductive hearing loss.

OBJECTIVES: The aim of the study was to investigate whether children with bilateral conductive hearing loss benefit from their second device (i.e., the bilateral bone conduction device [BCD]). DESIGN: Speech recognition in noise was assessed in 10 children fitted with bilateral BCDs during childhood. Speech recognition was measured in 2 conditions with both BCDs active. Spatial resolution was tested with the Minimum Audible Angle test in the bilateral and monaural listening conditions. RESULTS: Children demonstrated an improvement in speech recognition when speech was presented from the front and noise was presented from the right-hand side as compared with both speech and noise being presented from the front. The minimum audible angle decreased from 57° in the best monaural condition to 13° in the bilateral condition. CONCLUSIONS: The audiological outcomes demonstrate the advantage of bilateral BCD fitting in children with bilateral conductive hearing loss.

Comparison between a new implantable transcutaneous bone conductor and percutaneous bone-conduction hearing implant.

OBJECTIVES: Despite good results on osseointegration and limited skin reactions with percutaneous bone conductors, there remains room for improvement. Especially in children, adverse events with percutaneous bone conductors might occur more frequently. Transcutaneous bone conductors, if powerful enough, can provide a solution that minimizes adverse events and implant loss. This study compares a new transcutaneous bone conduction hearing aid, the Sophono Alpha 1 (Sophono), with the percutaneous BAHA system (BAHA). METHODS: In our tertiary referral center, 12 patients (age 5-12 yr) with congenital unilateral conductive hearing loss were enrolled in the study as follows: 6 patients with the Sophono and 6 with the BAHA. Both clinical results and audiologic data were gathered. For an objective audiologic comparison between both systems, we used a skull simulator. RESULTS: The skin reactions were comparable between both groups, in 1 implant was lost 1 month after second phase surgery (BAHA). The users received audiologic benefits from both systems. The BAHA-based outcome was slightly better compared with Sophono-based results in sound field thresholds, speech recognition threshold, and speech comprehension at 65 dB. The skull simulator demonstrated that the BAHA device has an output that is 10 to 15 dB higher compared with the Sophono device. CONCLUSION: The Sophono offers appealing clinical benefits of transcutaneous bone conduction hearing; however, the audiologic challenges of transcutaneous application remain, as the Sophono does not exceed percutaneous application regarding audiologic output.

Spiral ganglion cell morphology in guinea pigs after deafening and neurotrophic treatment.

It is well known that spiral ganglion cells (SGCs) degenerate in hair-cell-depleted cochleas and that treatment with exogenous neurotrophins can prevent this degeneration. Several studies reported that, in addition, SGC size decreases after deafening and increases after neurotrophic treatment. The dynamics of these cell size changes are not well known. In a first experiment we measured size, shape (circularity) and intracellular density of SGCs in guinea pigs at various moments after deafening (1, 2, 4, 6, and 8 weeks) and at various cochlear locations. In a second experiment, the effect of treatment with brain-derived neurotrophic factor (BDNF) on SGC morphology was investigated at various cochlear locations in deafened guinea pigs. We found that SGC size gradually decreased after deafening in the basal and middle cochlear turns. Already after one week a decrease in size was observed, which was well before the number of SGCs started to decrease. After BDNF treatment SGCs became noticeably larger than normal throughout the cochlea, including the middle and apical turns, whereas an effect on survival of SGCs was primarily observed in the basal turn. Thus, both after deafening and after neurotrophic treatment a change in size occurs before survival is affected. Morphological changes were not restricted to a subpopulation of SGCs. We argue that although changes in cell size and changes in survival might be manifestations of two separate mechanisms, morphological measures such as size, circularity and intracellular density are indicative for survival and degeneration.