A variety of noises have been employed for decades in an effort to facilitate habituation, mask, or suppress tinnitus. Many of these sounds have reportedly provided benefit, but success has not been universal. More recently, musical stimuli have been added as a sound therapy component. The potential advantages of using such stimuli, in particular fractal tones, in combination with amplification are discussed in this paper.
Keywords: Amplification, fractal, habituation, modulated, music, stress
|How to cite this article:|
Sweetow RW. The use of fractal tones in tinnitus patient management. Noise Health 2013;15:96-100
| Introduction|| |
Knowledge of tinnitus has progressed over the past two decades from considering tinnitus as a symptom of an ear disorder to the current belief that the generation of tinnitus perception and tinnitus distress, is a function of the brain. This concept has been validated not only by the fact that surgical destruction of the auditory nerve does not necessarily remove the perception of tinnitus, ,, but also by an increasing number of neuroimaging investigations ,, demonstrating widespread activation of neural structures. It is also believed that a key factor in many, if not most, instances of tinnitus is reorganization (neural plasticity) and an increase in central nervous system activity (gain) as a consequence of peripheral attenuation. , In fact, the vast majority of individuals with chronic tinnitus show at least some degree of hearing loss.  Several investigations have demonstrated hyperactivity within auditory pathway structures such as the dorsal cochlear nucleus and the inferior colliculus. ,,
Attempts have been made to restore this missing acoustic stimulation, at least partially, via amplification, filtering, or other means in order to overcome the lack of appropriate stimulation from the ear to the damaged frequency regions in the auditory cortex. Numerous studies have demonstrated various degrees of benefit provided by amplification. ,, There are a number of reasons why hearing aids might be effective in providing relief from tinnitus. Among them are the beliefs that greater neural activity may allow the brain to correct for abnormal reduced inhibition due to outer hair cell damage; an enriched sound environment provided by amplification may minimize maladaptive cortical reorganization; amplification of ambient noise may partially mask tinnitus and is likely to reduce the contrast from tinnitus perception to quiet; and fatigue and stress created by the requirement of extra listening effort may be reduced thus allowing more resources to be allocated to tinnitus coping mechanisms. All of these may facilitate habituation. Furthermore, since the majority of tinnitus sufferers have at least some degree of hearing loss and advances in digital technology allowing for open fittings have expanded the lower range of amplification candidates, hearing aids are frequently a common choice for relief. In the recent Kochkin et al., 2011 study,  of nine tinnitus treatment methods assessed (hearing aids, music, medication, relaxation exercises, counseling, non-wearable sound generators, herbs and dietary supplements, wearable sound generators, and psychological counseling), the most substantial tinnitus amelioration was achieved with hearing aids (34%), followed by the use of music (30%). None of the other treatments achieved an efficacy rating of more than 10%.
There are three distinct goals for sound therapy. The ultimate objective is to completely suppress the tinnitus, while a less gratifying, but still effective (and realistic) goal is to facilitate habituation (the process of adapting to a stimulus thorough repeated exposure). With habituation, either the perception of the tinnitus, or the reaction to the tinnitus is greatly, if not fully, diminished.  The third option is to provide total or partial masking.  Total masking occurs when an external sound is perceived as being louder than the tinnitus, rendering it inaudible when in the presence of the masking stimuli. Partial masking occurs when the loudness of the tinnitus is reduced, but not eliminated by the masker. In addition, masking may divert the patient's attention. Masking employs a narrow band of noise centered around the perceived pitch of the tinnitus in an attempt to provide relief by either completely or partially obscuring the patient's perception of the tinnitus. However, many advocates of behavioral retraining therapies consider full masking of tinnitus to be counterproductive, since for long-term habituation to occur, the stimulus has to be perceived during training.  In addition, masking can interfere with hearing or produce too much distraction. Furthermore, it may only work for a tonal type tinnitus, because if a noise is employed, either broadband or narrow band (in order to limit the overall loudness), it may sound too similar to a "hissing" tinnitus. However, perhaps the greatest limitation of masking is that it typically cannot be constantly or permanently sustained. Therefore, while noise was once considered the most common form of acoustic tinnitus management, other auditory stimuli that can mask or mingle with tinnitus are now being increasingly recommended, utilized, and researched for their long-term benefits.
Sound therapy is not universally effective. However, the actual benefit from sound therapy remains somewhat elusive. Meta analyses have been conducted on the use of sound therapy. In the Cochrane review  six trials (553 participants) were analyzed. They concluded that no significant change was seen in the change in loudness or the overall severity of tinnitus following the use of sound therapy compared to other interventions such as patient education, relaxation techniques, tinnitus coping strategies, counseling, tinnitus retraining and exposure to environmental sounds. The authors stated that "the lack of quality research in this area, in addition to the common use of combined approaches (hearing therapy plus counseling) in the management of tinnitus are, in part, responsible for the lack of conclusive evidence." Other studies. , (primarily from the psychology literature) have indicated a small, but significant benefit from the addition of sound therapy to other approaches. At least one author  has indicated that "virtually all sound therapies are combined with some form of counseling." Thus, differences in the benefits reported from sound therapies may relate, at least in part, to the effectiveness of counseling, and it is certainly possible that personality characteristics of the patient and perceived psychoacoustic characteristics of the tinnitus may play a yet undefined role.
The purpose of this paper is to propose the use of music, and specifically, unfamiliar music in the form of fractal tones, as a sound therapy tool and to analyze the rationale and considerations that one might contemplate in selecting specific musical stimuli for sound therapy.
Music is considered a reasonable acoustic stimulus for sound therapy since many of the most commonly reported problems occurring as a consequence of tinnitus relate to increased stress and difficulties relaxing, concentrating, and sleeping.  A recent study was conducted examining the relative impact of stress and noise exposure (one of the most frequent causes of tinnitus) on the probability of having tinnitus. The authors reviewed over 2,000 tinnitus patients and concluded that while exposure to both noise and stress were important for the probability and level of tinnitus discomfort, stress was the more important factor in determining whether a patient would transition from being mild or severely impacted.  It has also been reported that long-term stress and coping strategies were the strongest predictors of tinnitus, even stronger than traditional risk factors such as hearing loss, age, gender, and hyperacusis. 
The use of music for setting and altering moods, arousing, and relaxing, is certainly not new. Music is commonly employed in homes, work environments, celebrations, advertisements, romances, movies, athletic locker rooms, shopping malls, and hospitals to soothe, relax, energize and engage. Additionally, music has been actively, and increasingly, employed as a therapeutic treatment for a number of physical and psychological ailments.  Advances in neuroscience and neural imaging have provided a greater understanding of the effects of musical stimuli on the brain and human behavior, including stress. Knowledge about the site of stimulation, neural interactions, and transfer of neural transmitters help explain the behavioral consequences, both positive and negative, of exposure to music. Listening to music can result in physiological changes correlated with relaxation and stress relief.  One reason music is believed to be helpful in reducing stress is because of the wide range of neural structures that are activated including the cerebellum, frontal lobe, limbic system, and auditory cortex. Each of the areas has been identified as being involved in tinnitus perception. ,
Moreover, music is an easy stimulus to alter and certain "rules" have been established about patterns of musical elements, such as slow onset, slower tempo, lower pitch, degree of repetition, and lack of emotional content that, if followed, can produce a desired calming, rather than alerting, effect. ,, Studies have shown that listening to certain types of musical stimuli induces relaxation and heightened concentration in some individuals, but not in others.  Active listening tends to arouse, passive listening tends to soothe. Active listening may distract, passive listening may allow for increased relaxation. It has been recommended that music used for tinnitus management should evoke positive feelings, should be void of vocals, should not contain pronounced bass beats, should be pleasant, but not too interesting or compelling (though for short-term relief attention capturing music can be beneficial), should induce relaxation while reducing tinnitus audibility (best for long-term relief), and should be played at low levels where music blends with tinnitus. , Other suggestions indicate that if music is to be relaxing, it should have a tempo near or below resting heart rate (60-72 beats/min); have a fluid melodic movement, contain a variety of pitches, be self-selected, not have rapid amplitude changes,  and contain an element of uncertainty.  In addition, the fact that sounds (including music) affects people in different ways, due to inherent, learned (and cultural) preferences, should be taken into consideration.
While music was identified as a preferred "masker" for tinnitus in 1988,  perhaps the first widespread employment of music for tinnitus relief was proposed by Davis, et al., ,, and commercialized by Neuromonics. This approach incorporates a counseling component and a sound therapy component consisting of four pre-recorded music passages that are filtered in accordance with the individuals' hearing loss and delivered via an MP3 player coupled to high fidelity, non-occluding earphones. Many of the principles mentioned above (for example, a relatively slow tempo with no sudden changes in amplitude) to induce relaxation have been utilized in the selection of the pre-recorded musical passages. More recently, Okamoto et al.,  proposed a very different music therapy. It differs from the Neuromonics approach in that it removes (notches) the music out of the frequency regions associated with the tinnitus rather than increasing the intensity in accordance with the hearing loss. In addition, rather than using pre-selected music, it allows the listeners to select music based on their own preference.
While success has been reported success for both approaches, there are potential limitations. In the Neuromonics approach, the patient has only limited choices in the stimuli. This may become a liability if the patient becomes bored or bothered by the repetition of the music. For both therapies, the use of previously recorded music may have an undesired impact on stress reduction because familiar music could evoke memories and potentially negative emotions  or create unwanted distraction. From a practical perspective, since somewhat visually obtrusive headphones (including cords) are currently used in these approaches, some individuals may not be able to use the processor at times where headphones may be considered inappropriate, such as during work. This restriction could perhaps be resolved with the future use of wireless technology.
Another potential limitation is that while the Neuromonics processor modifies the musical signal to compensate for hearing loss, it only provides this stimulation during the limited time it is worn each day (2-4 h is suggested). It does not provide amplification of external stimuli to compensate for the hearing impairment. As stated earlier, current theories suggest that tinnitus generation may result from the peripheral attenuation of auditory input.  This attenuation provokes an increase in central auditory system activity from the dorsal cochlear nucleus through the auditory cortex, as well as a coupling with the limbic system (particularly the hippocampus and amygdala) via collateral connections from the thalamus and other structures.  Stimulation of the thalamus results in release of neurotransmitters, including adrenaline, to produce an autonomic nervous system response associated with stress. 
An alternative approach that incorporates the benefits and rules of music but avoids these potential limitations is the use of fractal tones. Auditory fractal tones utilize harmonic, but not predictable relationships, and are generated by a recursive process where an algorithm is applied multiple times to process its previous output.  The tones (which sound somewhat like wind chimes) are pleasant, but are not associated with music that the listener may hold in memory. They create a melodic chain of tones that repeat enough to sound familiar and follow appropriate musical rules, but vary enough to not be predictable. In addition, the algorithm ensures that no sudden changes appear in tonality or tempo.
The potential application of fractal tones delivered via high-fidelity hearing aids was explored in an experiment to determine if the presence of various acoustic stimuli, including fractal tones, would (1) be perceived as relaxing to tinnitus patients, (2) reduce short term tinnitus annoyance, and (3) lower subjective tinnitus handicap and reaction scores in a 6 month field trial.  The experimental protocol allowed for a comparison of fractal tones alone, fractal tones combined with amplification, broadband (white) noise alone, white noise mixed with amplification, and fractal tones along with amplification and white noise.
Results indicated that fractal tones were effective in promoting relaxation and reducing annoyance from tinnitus. Similar results were also reported by others. , Both fractal tones and white noise reduced tinnitus annoyance (white noise to a greater degree than the fractal tones, likely due to greater masking effects), but the fractal tones were preferred by subjects for longer term use for reasons discussed below. In addition, while the majority of subjects selected slower tempos for relaxation and long-term wear, this choice was not unanimous. This underscores the benefit of providing the individual listener with choices.  Individual preferences for certain types of acoustic stimuli were also emphasized in the Henry et al.,  study in which they reported most, but not all, of their participants clearly preferred certain stimuli over others.
The Sweetow and Sabes results  agreed with the Henry et al.,  data in that their subjects showed a preference for stimuli that were modulated in both the spectral and temporal domains. In the latter study, subjects were presented with a variety of noises and environmental sounds that were filtered and modulated. They found that most, but not all, of their subjects had clear preferences for certain stimuli over others, and most preferred were those that were modulated or temporally varying as opposed to steady state (i.e., pure tones, or filtered or broad band-noise) signals. Modulated signals are characteristic of fractal and other musical stimuli. Reavis, et al.,  indicated that electrical and acoustic suppression was achieved most effectively using dynamically modulated signals. Their results confirmed the conclusions of others. , that temporally patterned sounds such as amplitude and frequency modulated signals may produce highly synchronized and robust cortical responses as opposed to steady state sounds, which produce mostly onset and offset responses in the cortex, and thus may be a more attractive stimulus for this cortical effect. Zeng et al.  also suggested that the temporal characteristics of an electrically generated signal are critical to suppression. Sounds that are too slow produce bursts of activity and those that are too fast show no synchronization, but within a specific range the neurons fire synchronously to the sound stimulus and can produce synchronized, robust neural activity in the auditory cortex. It is possible that there are also optimal properties for an acoustical signal designed for tinnitus relief, though this has yet to be verified.
Preferences for modulated stimuli (as opposed to steady-state signals) for tinnitus relief, may be part of the reason why noise masking has fallen out of favor among some practitioners as an acoustic tinnitus treatment, in addition to the fact that noise does not have the inherent value of inducing relaxation. Interestingly, in the Sweetow and Henderson-Sabes study, noise (similar to the faster tempo fractal tones) reduced short-term annoyance more than other stimuli. The likely cause for this finding was that the steady state noise and faster rhythm provided for more masking because of the shortening (or complete lack) of inter-stimulus intervals. However, only two of the participants opted to have the noise only as a program during the 6 month wearing of the hearing aids, and none of them selected the noise only condition as their preferred setting. This too, may be related to the belief that noise may lack the inherent stress-reducing and relaxation inducing characteristics of music. Thus, the combination of tinnitus annoyance reduction and increased relaxation may be an important factor in long-term acceptance.
Although fractal music differs from conventional music in terms of its familiarity, similar preferences for using music for relaxation and tinnitus sound therapy appear to apply. This includes the finding that sudden variations in amplitude can be disconcerting and counterproductive for sound therapy, lower pitches were found to be more relaxing than higher pitches, and slower tempos were preferred over faster tempos. In addition, subjects preferred major chords rather than minor chords.  Subjects in the Hann, et al.,  investigation compared four well-known baroque musical passages, Bach's Air in G, which is also one of the pre-recorded musical passages contained in the Neuromonics protocol, Albinoni's Adagio, and two of Vivaldi's Four Seasons. Their conclusion was that the major mode was the common musical element for preference. This is consistent with the elements of music most associated with a positive emotional response. ,
Presenting musical stimuli via hearing devices offer some obvious advantages. For example, the hearing deficit can be compensated for by applying the algorithm of the hearing aids to the fractal tones, a potential advantage over pre-recorded CDs. In addition, modern hearing aids are less conspicuous than wearing headphones, particularly those requiring a wired connection to a MP3 player. However, if musical, or other acoustical stimuli are going to be incorporated into hearing aids (so-called combination devices) one must consider whether the limitations of the devices themselves, in particular, bandwidth and dynamic range, create restrictions. Previous investigations  may shed some light on this question. In this study, the majority of subjects preferred the amplitude modulated sounds over the filtered white noise sounds even though the latter stimuli contained several tracks extending to 14 KHz, well beyond the capability of modern hearing aids. Thus, the bandwidth limitations of current hearing aids may not be a critical drawback. Hearing aids have inherent restrictions on dynamic range since their primary purpose is amplifying speech (as opposed to MP3 players or other recording devices). Rather than producing a potential decrement to sound therapy for tinnitus, Hann et al.,  suggest that minimizing the dynamic range is actually a desirable component of sound therapy for tinnitus patients. Considering the fact that hearing impaired patients have loudness recruitment, and many further suffer from hyperacusis, it makes sense that certain tinnitus patients do not wish to be exposed to high intensities. The use of hearing aids with low compression knee points may be of benefit because they will provide additional amplification for very quiet environments, while still offering separate regulation for gain and output for high input intensities.
| Conclusions|| |
Musical stimuli may provide a different, and in some cases, superior option for sound therapies. The use of amplification, combined with flexible music-like signals containing relaxation inducing properties may be a further asset to tinnitus management procedures.
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Robert W Sweetow
Department of Otolaryngology, University of California, San Francisco
Source of Support: The author is a part time consultant for Widex Hearing Aids, Conflict of Interest: None