The difference in poststimulus suppression between residual inhibition and forward masking.

Introduction: Tinnitus is a widely seen otological symptom that interferes with daily activities and causes discomfort. Tinnitus treatments can be classified into 4 main groups: pharmacological treatments, cognitive and behavioral therapy, psychological treatments, and combined treatment approaches made up of at least 2 of these 3 treatment methods. Objective: The aim of this study was to assess whether it would be possible to develop an individualized treatment method of tinnitus by application of a combined tinnitus signal and music during sleep. Methods: Forty-three ears of 30 patients who had subjective tinnitus were included. The patients were evaluated using Tinnitus Handicap Inventory, Visual Analogue Scale, and Beck Depression Inventory. The psychoacoustic parameters of tinnitus, such as tinnitus frequency and loudness, and minimal masking levels, were determined. The patients were asked to select musical melodies that they liked. The tinnitus frequency of each patient was taken as the central frequency according to ANSI 2004. All sound files were prepared as stereo channels, with 16-bit resolution and 44,100 Hz sampling rate. The root mean square power value of the music and the band noise’s average root mean square power value were equalized with the “Amplification” command, and 70% of the music and 30% of wide/narrow-band noise were mixed as a stereo channel by the “Mix Paste” command. The patients were instructed to listen to that individualized music/narrow-band noise (tinnitus signal) for 2 h during sleep for a duration of 6 months. Results: Tinnitus frequencies of the patients measured prior to treatment and at the second, fourth, and sixth months of follow-up were not significantly different. A statistically significant decrease was seen in tinnitus loudness, minimal masking levels, and residual inhibition during the follow-up. Tinnitus Handicap Inventory scores decreased significantly during follow-up, and the number of patients who complained of tinnitus decreased (p < 0.05). The Visual Analogue Scale scores significantly decreased during follow-up (p < 0.05). Beck Depression Inventory scores decreased significantly during follow-up (p < 0.05). Conclusion: Stimulation of the auditory and limbic systems during sleep by the tinnitus signal combined with individualized musical melodies seems an alternative, effective, and cheap method in the treatment of tinnitus.

IntroductionPsychoacoustic measures are used to quantify tinnitus perception in clinical and research settings. Residual inhibition (RI), for instance, is defined as a temporary reduction in tinnitus loudness after the presentation of an acoustic stimulus. A novel approach was developed recently to assess the minimum sound level producing RI, the minimum residual inhibition level (MRIL), after the repeated presentation of short sounds separated by short periods of silence. Two studies were performed: the objective of the study 1 was to assess the reliability and the reproducibility of this measures as well as others, including the minimum masking level (MML). The objective of study 2 was to assess whether a smoother envelope of the sound would produce similar levels of MML and MRIL and improve listening comfort.MethodsThirty participants with chronic tinnitus completed each study. For study 1, MML and MRIL were obtained at the seven standard audiometric frequencies at around 1-month interval. For study 2, MML and MRIL were obtained using triangular and trapezoidal-shaped NBN signals centered at three different frequencies.ResultsThe mean absolute test-retest difference was 3 dB for both MML and MRIL [Intraclass correlation, ICC (2,1) of 0.70 and 0.84, respectively] for the measures obtained in test and retest (86% of cases for MML and 21% of cases for complete MRIL). While the two types of envelopes provided comparable MRIL, the “triangular” envelope provided more listening comfort.DiscussionIn sum, the novel approach provides quick and reliable MML and MRIL measurement, with the potential benefit of subtyping participants.

Purpose: to verify the sex, age, tinnitus location, presence or absence of hearing loss, its degree, and the psychoacoustic measurements (pitch, loudness, minimum masking level [MML], and residual inhibition [RI]) of patients with chronic tinnitus and their relationships. Methods: the study included subjects of both sexes, aged 25 to 85 years, with complaints of chronic tinnitus, followed up at the health service where the research was conducted. They were submitted to medical history survey, basic audiological assessment, and pitch, loudness, RI, and MML research. The following statistical tests were used: chi-square test, Fisher’s exact test, Wilcoxon-Mann-Whitney U test, Kruskal-Wallis test, and Spearman’s correlation coefficient. The significance level was set at 5% (p≤0.05). Results: the type of tinnitus was associated with the presence or absence of hearing loss (HL), degree of HL, MML, and loudness; age was associated with the presence or absence of HL and its degree. There was a directly weak proportional correlation between loudness and MML, whereas the correlations between pitch and loudness, pitch and MML, and RI and MML were weak and inversely proportional. Conclusion: both the affected subjects and their tinnitus characteristics were heterogeneous. The results indicate that some variables influence one another, which also happens between psychoacoustic measurements.

It has been proposed that tinnitus is generated by aberrant neural activity that develops among neurons in tonotopic of regions of primary auditory cortex (A1) affected by hearing loss, which is also the frequency region where tinnitus percepts localize (Eggermont and Roberts 2004; Roberts et al., 2010, 2013). These models suggest (1) that differences between tinnitus and control groups of similar age and audiometric function should depend on whether A1 is probed in tinnitus frequency region (TFR) or below it, and (2) that brain responses evoked from A1 should track changes in the tinnitus percept when residual inhibition (RI) is induced by forward masking. We tested these predictions by measuring (128-channel EEG) the sound-evoked 40-Hz auditory steady-state response (ASSR) known to localize tonotopically to neural sources in A1. For comparison the N1 transient response localizing to distributed neural sources in nonprimary cortex (A2) was also studied. When tested under baseline conditions where tinnitus subjects would have heard their tinnitus, ASSR responses were larger in a tinnitus group than in controls when evoked by 500 Hz probes while the reverse was true for tinnitus and control groups tested with 5 kHz probes, confirming frequency-dependent group differences in this measure. On subsequent trials where RI was induced by masking (narrow band noise centered at 5 kHz), ASSR amplitude increased in the tinnitus group probed at 5 kHz but not in the tinnitus group probed at 500 Hz. When collapsed into a single sample tinnitus subjects reporting comparatively greater RI depth and duration showed comparatively larger ASSR increases after masking regardless of probe frequency. Effects of masking on ASSR amplitude in the control groups were completely reversed from those in the tinnitus groups, with no change seen to 5 kHz probes but ASSR increases to 500 Hz probes even though the masking sound contained no energy at 500 Hz (an “off-frequency” masking effect). In contrast to these findings for the ASSR, N1 amplitude was larger in tinnitus than control groups at both probe frequencies under baseline conditions, decreased after masking in all conditions, and did not relate to RI. These results suggest that aberrant neural activity occurring in the TFR of A1 underlies tinnitus and its modulation during RI. They indicate further that while neural changes occur in A2 in tinnitus, these changes do not reflect the tinnitus percept. Models for tinnitus and forward masking are described that integrate these findings within a common framework.

To determine if the characteristics of tinnitus produced by head trauma are specific and exclusive when compared with other origins of tinnitus. Retrospective study using clinic test results and data from the Tinnitus Data Registry compiled from questionnaires, interviews, and testing. Tinnitus produced by head injury was compared with tinnitus of mixed origins, including no known origin. A tinnitus referral clinic where all patients must see an otologist or an ear, nose, and throat physician prior to attending the clinic. All patients had severe to moderately severe constant tinnitus and presented with tinnitus as the primary symptom. No exclusive characteristics were found to describe head injury-induced tinnitus. The tinnitus for the group with head injury was statistically significantly (P = .004) louder and occurred with greater incidence of continuing pain in the ears. The group with head injury also had more episodes of dizziness and a more severe form of tinnitus. However, no marked difference was noted in pitch of tinnitus, complexity (number of sounds) of tinnitus, or the minimum masking level. This retrospective study found that tinnitus induced by head injury was significantly (P = .004) louder than tinnitus induced from other causes but, interestingly, did not require higher levels of masking. The patients with head injury-induced tinnitus more frequently (P = .0003) displayed residual inhibition although the duration of residual inhibition was not different from that of the comparison group. Other symptoms associated with the tinnitus onset were more frequently mentioned by the group with head trauma-induced tinnitus, except for the condition of pressure sensation in the ears. Using a severity questionnaire, the group with head trauma-induced tinnitus rated their tinnitus as being more severe than did the comparison group. However, such things as pitch of the tinnitus, masking level, acceptance of wearable maskers, general hearing level, and complexity of the tinnitus did not distinguish the two groups.

The present study was carried out in order to analyze the clinical characteristics of tinnitus both in normal hearing subjects and in patients with hearing loss. The study considered 520 consecutive tinnitus sufferers. The following parameters were considered: age, sex, subjective disturbance caused by tinnitus, subjective judgment of tinnitus intensity, tinnitus laterality, tinnitus duration, tinnitus measurements, normal hearing or associated hearing loss. Among the patients considered, 223 have normal hearing while 297 have a hearing deficit. The hearing impairment was found to be in most cases of sensorineural type. The subjective discomfort is higher in presence of hearing loss. Subjects with hearing loss needed significantly higher masking levels. No evident differences in the residual inhibition (RI) result between the two groups were found. The present study confirms that tinnitus is most frequently associated with hearing loss. The characteristics of tinnitus in normal hearing subjects, except for the subjective judgment of tinnitus intensity, the pitch and the RI, are significantly different for those observed in subjects with hearing loss. The association of tinnitus and hearing deficit seems to increase the perceived severity of the symptom.

The Department of Veterans Affairs (VA) considers tinnitus a disability. Veterans can claim tinnitus as a "service-connected" disability if the tinnitus is thought to be connected to military service. The VA adjudicates each claim and determines whether reasonable evidence exists to support it. Currently, determining the presence of tinnitus is based on subjective reporting-objective measures do not exist. The aim of this study was to develop and document a test for detecting the presence/absence of tinnitus with high confidence. Using our computer-automated, self-guided tinnitus evaluation system, we conducted three phases of testing to compare psychoacoustic measures of tinnitus between participants with versus without tinnitus. Phase 1 measures included loudness match, pitch match, minimum masking level, residual inhibition, Békésy, and forced-choice double staircase. Phases 2 and 3 measures were chosen based on results of the previous phase. The number of tests and time of testing decreased during each successive phase. Differences were seen between groups; most notably, higher low-frequency loudness matches and higher median pitch matches were observed for participants with tinnitus. Results of this study suggest that further efforts can produce a defined psychoacoustic test battery for identifying the presence/absence of tinnitus.

Band-noise masker treatment was used in 101 patients with tinnitus who visited the otolaryngologic clinic of Nippon Medical School Hospital, and the degree of tinnitus was compared before and after treatment.The tinnitus masker was designed so that a band noise ranging from 250 to 5000Hz was divided into 54 sections. The band noise masker was fitted to the tinnitus frequency obtained by the pitch match method and tinnitus was measured before and after masker treatment.1) All patients were relieved of tinnitus while wearing the tinnitus masker, and the tinnitus was completely supressed or diminished (after effect) in 71% for 30min. to several months. 2) The after effect of masking was better in patients whose tinnitus frequencies were within in the frequency range of the band noise masker. 3) There was no correlation between the loudness of tinnitus and the after effect of masking. Even in patients with severe tinnitus of more than 20dB, the after effect of the tinnitus masker was obtained. 4) Tinnitus frequency showed no change after 2hr of masking. 5) In patients whose tinnitus diminished after masker treatment, the loudness balance method with the contralateral ear indicated the change in tinnitus loudness better than that with the ipsilateral ear or with the masking method. 6) The after effect of the masker was more frequently seen in patients whose tinnitogram showed a convergence type or congruence type than in patients who showed other types of tinnitogram.

1. Tinnitus may be the symptom of many different disorders. An accurate assessment of a patient’s history, symptoms, and signs is important to establish a correct diagnosis. The tinnitus handicap inventory (THI) and the visual analog scale (VAS) are very useful tests to evaluate the handicap caused by tinnitus and the entity of tinnitus, respectively. 2. An objective assessment of ear, head, neck, and temporomandibular articulation should be performed. 3. Pure-tone audiometry (the frequency range from 125 to 16 KHz), tympanometry, acoustic middle-ear reflex testing, speech recognition threshold testing, and speech discrimination tests help determine the type of hearing loss and the status of the middle ear. 4. Otoacoustic emission (OAEs) testing allows for precise evaluation of the outer hair cell function. 5. Acufenometry is performed to determine pitch and loudness of tinnitus by defining minimum masking levels (MMLs), loudness discomfort levels (LDLs), and the residual inhibition. 6. Auditory brainstem responses (ABR) are used in selected patients for further evaluation and exclusion of disorders such as vestibular schwannoma. Electrocochleography (ECochG) is used in order to evaluate the electric phenomena of the inner ear.

Conclusion: Tinnitus characteristics in normal-hearing patients differ between the groups with unilateral and bilateral complaints.Objectives: The study was to determine the differences between tinnitus characteristics observed in patients with unilateral vs bilateral symptoms and normal hearing threshold, as well as normal results of distortion-product otoacoustic emissions (DPOAEs).Method: The patients answered questions concerning tinnitus duration, laterality, character, accompanying symptoms, and circumstances of onset. The results of tympanometry, auditory brainstem responses, tinnitus likeness spectrum, minimum masking level (MML), and uncomfortable loudness level were evaluated. Records of 380 tinnitus sufferers were examined. Patients with abnormal audiograms and/or DPOAEs were excluded. The remaining 66 participants were divided into groups with unilateral and bilateral tinnitus.Results: Unilateral tinnitus in normal-hearing patients was diagnosed twice more frequently than bilateral. Tinnitus pitch was higher in the group with bilateral tinnitus (p < .001). MML was lower in unilateral tinnitus (p < .05). Mean age of patients was higher in the unilateral tinnitus group (p < .05). Mean tinnitus duration was longer (p < .05) and hypersensitivity to sound was more frequent (p < .05) in the bilateral tinnitus group. Repeated exposure to excessive noise was the most frequent cause in the bilateral tinnitus group.

With care to provide properly chosen masking sounds, masking can help in 60-80% of clinically significant tinnitus cases. There is no universal masker; instead, an individual evaluation of each patient's tinnitus must be performed in order to match the masking sounds to the patient's audiogram and the spectral characteristics of the tinnitus. Successful long-term masking can usually be achieved in patients for whom (1) hearing impairment is not excessive. (2) the tinnitus frequency, FT, can be reliably located, and (3) the tinnitus can be completely masked by a band of noise at or near FT at a low sensation level. Such patients often experience residual inhibition (temporary suppression of tinnitus upon cessation of masking) which may accumulate with sustained use of masking, in some cases becoming permanent. Long-term masking is difficult or impossible for patients whose hearing is so impaired they cannot hear the masker, or those for whom the masking sounds must be presented at unacceptably loud levels to obtain adequate coverage of the tinnitus. There is a great need for additional work to determine what factors influence the effectiveness of masking, in order to improve our ability to provide appropriate masking stimuli even for the difficult cases.

Objectives: Acoustic stimulation or sound therapy is proposed as a main treatment option for chronic subjective tinnitus. To further probe the field of acoustic stimulations for tinnitus therapy, this exploratory study compared 10 Hz amplitude modulated (AM) sounds (two pure tones, noise, music, and frequency modulated (FM) sounds) and unmodulated sounds (pure tone, noise) regarding their temporary suppression of tinnitus loudness. First, it was hypothesized that modulated sounds elicit larger temporary loudness suppression (residual inhibition) than unmodulated sounds. Second, with manipulation of stimulus loudness and duration of the modulated sounds weaker or stronger effects of loudness suppression were expected, respectively.Methods: We recruited 29 participants with chronic tonal tinnitus from the multidisciplinary Tinnitus Clinic of the University of Regensburg. Participants underwent audiometric, psychometric and tinnitus pitch matching assessments followed by an acoustic stimulation experiment with a tinnitus loudness growth paradigm. In a first block participants were stimulated with all of the sounds for 3 min each and rated their subjective tinnitus loudness to the pre-stimulus loudness every 30 s after stimulus offset. The same procedure was deployed in the second block with the pure tone AM stimuli matched to the tinnitus frequency, manipulated in length (6 min), and loudness (reduced by 30 dB and linear fade out). Repeated measures mixed model analyses of variance (ANOVA) were calculated to assess differences in loudness growth between the stimuli for each block separately.Results: First, we found that all sounds elicit a short-term suppression of tinnitus loudness (seconds to minutes) with strongest suppression right after stimulus offset [F(6, 1331) = 3.74, p < 0.01]. Second, similar to previous findings we found that AM sounds near the tinnitus frequency produce significantly stronger tinnitus loudness suppression than noise [vs. Pink noise: t(27) = −4.22, p < 0.0001]. Finally, variants of the AM sound matched to the tinnitus frequency reduced in sound level resulted in less suppression while there was no significant difference observed for a longer stimulation duration. Moreover, feasibility of the overall procedure could be confirmed as scores of both tinnitus loudness and questionnaires were lower after the experiment [tinnitus loudness: t(27) = 2.77, p < 0.01; Tinnitus Questionnaire: t(27) = 2.06, p < 0.05; Tinnitus Handicap Inventory: t(27) = 1.92, p = 0.065].Conclusion: Taken together, these results imply that AM sounds, especially in or around the tinnitus frequency, may induce larger suppression than unmodulated sounds. Future studies should thus evaluate this approach in longitudinal studies and real life settings. Furthermore, the putative neural relation of these sound stimuli with a modulation rate in the EEG α band to the observed tinnitus suppression should be probed with respective neurophysiological methods.

Tinnitus is the sensation of hearing a "ringing" or "buzzing" in the ears without any external stimuli. Possible causes of tinnitus include hyperactivity in central auditory nuclei, 1 tonotopic reorganization in the auditory cortex, 2 noise exposure, 3 underlying conditions, 4 and use of certain medications. 5 Between 5% and 30% of adults suffer from tinnitus, 6 with about 50% having idiopathic tinnitus. 7www.Shutterstock.com, virtual reality, artificial intelligence, tinnitus.Patients' emotional well-being is affected by tinnitus, 8 including increased anxiety levels. 9 The amygdala and other nonauditory structures in the brain may be involved in tinnitus maintenance by mediating the emotional response in tinnitus patients. 10,11 Novel techniques like the use of vagus nerve implants have been explored for tinnitus mitigation. 12 Although there is no cure for tinnitus yet, effective management techniques include relaxation/mindfulness training, 13 amplification, 14 and sound therapy for both hearing aid users 15 as well as cochlear implant recipients. 16 Sweetow and Sabes 17 evaluated the effects of combining amplification and sound therapy for tinnitus management. The sound therapy included white noise and fractal tones from Widex Zen Therapy. 18 Participants reported a significant reduction in tinnitus annoyance after listening to both sounds but reported feeling more relaxed when hearing the fractal tones. Stress reduction is a significant component in managing chronic health conditions. Distressed patients may turn to social media or mobile applications to explore solutions. 19–22 Techniques for reducing stress can decrease the impact of tinnitus. 23 A randomized controlled trial (RCT) discovered that 16 hours of therapy over two months led to significant reductions in tinnitus measures and reactions to tinnitus. 13 Therapy techniques using virtual reality (VR) have been shown to reduce anxiety in patients with chronic conditions. 24 VR uses specialized equipment that presents visual and auditory information to create specific simulated environments. The use of VR has proven to aid in acute pain management of patients receiving routine and invasive medical procedures. 25 VR also has proven to have significant effects on all affective domains mediated by the limbic system, 26 which is also involved in the perpetuation of tinnitus. 27 Therefore, VR therapy may lessen the engagement of the limbic system in tinnitus perception by delivering relaxation and sound therapy components. The aim of the present study 28 was to explore whether the use of VR combined with conventional sound therapy helped in mitigating tinnitus and reactions to tinnitus as compared to conventional sound therapy alone. STUDY PARTICIPANTS Adults with continuous, chronic, subjective tinnitus were sought as study participants. Adults with hearing aids were recruited if they did not have tinnitus management features programmed into their hearing aids. Twenty adults with both unilateral and bilateral tinnitus (11 males, nine females) between the ages of 18 and 76 years were enrolled in the study. PROCEDURES This study was an RCT with a crossover design. Each participant received two sessions, one week apart. The control intervention provided sound therapy alone, while the experimental intervention provided sound therapy with VR. The sound therapy component used the Zen Aqua program from Widex. The sounds were played for 15 minutes through a computer loudspeaker at a comfortable volume level. The experimental intervention included 15-minute viewings of natural scenes, including flowing streams, lakes, and gorges, presented via VR goggles, while listening to the Zen sounds. Ten participants received the control intervention followed by the experimental intervention and 10 received the experimental intervention followed by the control intervention. Participants' tinnitus loudness, tinnitus functional index (TFI), 29 and minimum masking level (MML) scores were recorded before and after each intervention. RESULTS A multilevel mixed-effects linear regression model accounting for confounding variables revealed that the mean tinnitus loudness and TFI scores reduced significantly (p=0.015 and p=0.043, respectively) after the experimental intervention compared to the control intervention. The MML differences were not statistically significant, but mean values were reduced after the experimental intervention than after the control intervention (p=0.090). DISCUSSION Tinnitus loudness, MMLs, and TFI scores have been used to portray the effectiveness of tinnitus management strategies. 30–32 In the present study, since tinnitus loudness levels and TFI scores improved significantly after receiving the experimental intervention, it can be concluded that these factors are positively affected by combining VR with sound therapy in a controlled setting. While there was no significant improvement in MMLs after the experimental intervention, this could be due to the study procedures causing participants' attention to be focused on their tinnitus. Many tinnitus therapy techniques recommend having an active lifestyle to redirect attention from tinnitus. 33 Previous research has demonstrated that sound therapy, especially fractal tones, can be used to induce relaxation and manage tinnitus. 34,35 In the Sweetow and Sabes study, 17 86% of participants reported feeling relaxed after listening to the wind-chime-like fractal tones. Simonetti et al. 36 discovered a significant reduction in tinnitus handicap inventory (THI) 37 scores after studying the effects of fractal tones on patients with chronic tinnitus. In the present study, participants listened to fractal tones either standalone or with a VR video. Following these interventions, reductions in tinnitus loudness, MMLs, and TFI were present. The emotional and auditory effects of sound therapy can partially explain this trend. For more than two decades, VR has been used to treat conditions such as phobias, 38 anxiety disorders, 24 eating disorders, 39 and intractable pain. 40 A systematic review of 20 studies found VR to be an effective treatment for decreasing acute pain. In 2010, a theoretical framework for the use of VR to manage chronic subjective tinnitus was proposed. 41 Malinvaud et al.42 applied this framework to assess the differences in tinnitus attributes between those receiving VR and those receiving cognitive behavioral therapy (CBT). Without significant differences found between interventions, both interventions showed improvement on THI scores, subjective tinnitus severity scale, and the hospital anxiety and depression scale. 43 The Malinvaud 44 study concluded that VR can be at least as effective as CBT when managing tinnitus. The present study showed significant reductions in tinnitus loudness and TFI for the experimental intervention as compared to the control intervention, supporting these results. LIMITATIONS AND FUTURE DIRECTIONS The present study was conducted in a laboratory setting. Future studies could explore the effects of VR on tinnitus in more natural settings, such as at home. Stimuli can also be presented for a longer duration with more sessions. A longitudinal study would be able to analyze the long-term effects of VR on tinnitus. Future studies could also use a larger participant group. Genetic risk modeling can be used to investigate the biological mechanisms underlying tinnitus. In the present study, participants benefitted from using VR combined with sound therapy for 15 minutes in a laboratory setting. After this intervention, tinnitus loudness levels, MMLs, and TFI scores were reduced when compared to receiving sound therapy alone. Therefore, VR combined with sound therapy is a promising potential technique for managing tinnitus. Future studies could alter the stimuli, mode of delivery, number of sessions, total therapy duration, and number of participants. More trials will be needed before confirming the use of VR and sound therapy to manage tinnitus in a clinical setting.

Investigating the relation between minimum masking levels and hearing thresholds for tinnitus subtyping.

The behaviour of delayed evoked otoacoustic emission (DEOAE) has been studied in normally hearing adults under a conventional forward-masking paradigm, and subjective measurements were carried out additionally for comparison. The clicks served as signals and the noise bursts were used as masker. In different experimental sets, signal and masker intensity, masker duration, and the interval between masker and maskee were altered. At masker levels corresponding to the subjective post-masking threshold of the clicks, the DEOAE was unaffected, i.e. had no noticeable alteration, compared with click stimulation without masking. Even at higher masker levels the inaudible clicks elicited clearly discernible DEOAEs. The forward-masking detection threshold of DEOAE ('DEOAE post-masking threshold') was reached at masker levels approximately 35 dB above the subjective post-masking threshold. The gap between subjective and DEOAE post-masking threshold vis-à-vis the masker level was also evident at different masker durations and different time intervals between masker and maskee. Central neural and peripheral receptor mechanisms are suggested to be the constituents of the masking phenomenon. The neural mechanism is involved at low masker levels. The receptor mechanism effectively joins the neural one at masker levels exceeding the threshold of psychoacoustic masking. The progressive increase in the number of auditory units from the periphery to the centre in the hearing system, linked with an increase in inhibition, can help to explain these effects.