WO2004098690A1

WO2004098690A1 - Tinnitus treatment

Info

Publication number: WO2004098690A1
Application number: PCT/DK2004/000323
Authority: WO
Inventors: Joachim Neumann; Christian C. BÜRGER
Original assignee: Oticon AS
Current assignee: Oticon AS
Priority date: 2003-05-06
Filing date: 2004-05-06
Publication date: 2004-11-18
Anticipated expiration: 2005-11-06

Abstract

The invention relates to a method for treating tinnitus where a stimulus is provided to the central stages on the auditory pathway, where two input devices may be included for performing the method. The method may comprise controlling the input of the input of the devices according to a predetermined scheme, where information may be sent from one device to the other device and e.g. provide a spatial stimulus or a spectral stimulus is provided. The invention further relates to a system applying the method.

Description

TITLE

Tinnitus treatment

AREA OF THE INVENTION

The invention relates to the area of tinnitus and more specifically to the area of treatment of tinnitus.

BACKGROUND OF THE INVENTION

Tinnitus is the perception of unwanted sounds (tonal, hissing, clicking or roaring) without the presence of an external sound source. The tinnitus can be stable or fluctuating. It can be perceived located on one or both ears, in the head, or outside the head. Persistent tinnitus occurs in approximately 14% of the population and in about 65%o of the hearing impaired population (Holgers and Hakanson, 2002, Axelsson and Ringdahl, 1989, Coles, 1984, Davis, 1989). hi 2-4% of the total population, it is estimated that tinnitus plagues every day. The exact location of the timiitus generator is unknown. Although there are some indications for a peripheral origin, more recent research points toward an origination in the auditory cortex. It has for example not been possible to link audiometric data or otoacoustic emission with tinnitus.

Today the only effective devices available for those suffering from timiitus are masker and noisers, which are described in the following.

Tinnitus masker

Patients with tinnitus typically report that their tinnitus is less audible and less annoying in the present of sounds. Some avoid moments of silence by choosing to live at a trafficked street or by leaving the windows open at night. This masking of the timiitus by daily life sounds motivated the development of tinnitus masker instruments. These instruments use a noise generator a few dB above the individual tinnitus threshold to mask the tinnitus. The frequency content and level of the noise generator thus has to be matched to the properties of the individual timiitus. Since the introduction of tinnitus maskers in the 1970's, a variety of such devices have become commercially available. A tinnitus masker is typically placed in a hearing instrument shell. Products range from "stand alone" maskers for normal hearing to combinations of maskers and hearing instruments for the hearing impaired. Typically, tinnitus maskers are based on a simple analogue noise generator which output is added to the microphone signal or entirely replaces it. Another common type of masker is referred to as a "bedside masker", resembling a small table radio, which generates noise.

Tinnitus noiser The tinnitus noiser does not try to mask the tinnitus but it rather activates the inner ear with a soft broadband noise. The use of the tinnitus noiser is linked to the relatively new concept of the timiitus retraining therapy (Jastreboff, 1990). The tinnitus retraining therapy is based on the attempt to retrain the patients' brain so they treat their tinnitus similar to natural sounds (like most people can adapt to the refrigerator noise in their kitchen). The idea behind the tinnitus retraining therapy is to retrain reflexes involving connections of the auditory nervous system and the limbic (emotional) system. The timiitus retraining therapy requires intensive one-to-one directive counseling of the patient and a therapist. The timiitus noiser is considered as a supporting factor in the therapy.

The tinnitus noiser and masker attempt to provide a peripheral stimulation of the auditory pathway. A number of further suggestions have been made to methods and devices aiming towards a treatment of the tinnitus, so far without much success.

The objective of the present invention is to provide a method and a device for treatment of tinnitus, which brings improvement to the treatment of those suffering from tinnitus.

SUMMARY OF THE INVENTION

According to the invention the objective is achieved by means of the method as defined in claim 1 and the device as defined in claim 10.

Advantageous embodiments are defined in the dependent claims 2-9 and 11-17. The invention aims at providing a stimulus to the central stages on the auditory pathway - as opposed to a simple noise source that aims at peripheral stimulation, i.e. a masker or a noiser. The central stimulation can be achieved by manipulating the naturally occurring sound in such a way that the attention of the listener is stirred up. The invention does thus not necessarily require additional noise.

The method maybe based on a single ear-level device or on two ear-level devices. These two devices may be working independent of each other or in a co-ordinated fashion. The method may include controlling the output of the devices according to a predetermined scheme. Further the information may be sent from one device to the other device or even from each device and received by the other device.

According to the method a spatial or a spectral stimulus may be provided. Further a sound level stimulus may be provided. Still further a frequency and/or phase stimulus may be provided.

According to the system of the invention the device or devices being part of the system may comprise means for generating the signals and outputting the signals as mentioned above in connection with the method.

The invention will be described more detailed in the following description of preferred embodiments with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Block diagram of a spatial stimulation algorithm; FIG. 2 Four possible time courses for the direction selector; FIG. 3 Block diagram of the spectral stimulation algorithm; FIG. 4 Two possible time courses for the frequency shift selector;

FIG. 5 Block diagram of a pair of devices with additional noise source. DESCRIPTION OF A PREFERRED EMBODIMENT

The algorithms proposed in the following utilize a technology providing the possibility of exchanging information between two ear level instruments. This link is used to yield a stimulation that aims at the central stages of the auditory pathway.

The invention aims at providing a stimulus to the central stages on the auditory pathway - as opposed to a simple noise source that aims at peripheral stimulation. The central stimulation can be achieved by manipulating the naturally occurring sound in such a way that the attention of the listener is stirred up. The algorithms proposed in the following can for example utilize a technology that is about to emerge: the possibility to exchange low-bit-rate information between two ear level instruments. This low-bit-rate or another type of link is helpful to yield a stimulation that aims at the central stages of the auditory pathway.

Although there is no necessity to implement the invention in the signal path of a hearing instrument, this seems natural because (a) about half the number of people suffering from tinnitus have a hearing impairment, (b) the requirement to provide a transparent sound in an occluded ear is easily met by a hearing instrument and (c) a quick acting and low-distortion maximum power output limitation will probably be appreciated by most people suffering from tinnitus.

Spatial Stimulation with connected devices

With reference to FIG. 1 the solution comprises two connected devices. Both instruments have a spatial filter that is coordinated by the direction selector in the master instrument. The spatial stimulation algorithm filters the signals in both devices in order to dynamically manipulate the perceived direction of the naturally occurring sound. This approach requires a link between the signal processing in two devices. This linkage can for example be realized by a low-bit-rate wireless connection. The timing of this communication is not very critical if the simulated direction fluctuates slowly.

The direction selector creates a time varying direction, which is used to select or control the corresponding FIR filter in each of the two devices. FIG. 2 shows four possible time courses of the direction selector. Spectral Stimulation with connected devices

A spectral stimulation is based on dynamic modifications of the frequency transfer function within the instrument. One possible realization is shown in FIG. 3. This solution comprises two connected devices. Both instruments shift the spectra of the processed signals towards higher or lower frequencies. The size of the spectral shift is determined by the frequency shift selector in the master instrument. hi a straightforward realization, one could multiply the signal in both devices with a pure tone. The magnitude of the frequency shift has to be individually chosen to yield a noticeable, but not disturbing effect. The time course of the frequency selector can be chosen similarly as sketched before or as depicted in FIG. 4.

Another implementation could be based on spectral filtering in the two instruments, which emphasizes one frequency region and deemphasizes another frequency region.

These algorithms also attempt to create a central stimulation. They change the spectral properties of the incoming sound signal.

Sound Level Stimulation with connected devices

This algorithm manipulates the level of the incoming sounds. This algorithm resembles an automatic gain control (AGC) circuit, hi an AGC, the level of the input signal is used to calculate the appropriate amount of amplification. In the Sound Level Stimulation of a tinnitus device, the amplification however does not entirely depend on the input signal, but also on the sound level difference selector in the master device. Both the block diagram and the time course greatly correspond to the previous figures.

Phase Stimulation with connected devices

This algorithm manipulates the phase of the incoming sound. The phase manipulation can be a time varying phase shift or a time varying phase delay of the signal. Both the block diagram and the time course greatly correspond to the previous figures.

Some of the algorithms sketched so far might be unpleasant to listen to or cause dizziness in the listener. A reduction of the central stimulation can be realized by altering (typically reducing) the speed at which a change of direction (or frequency) is performed, by limiting the range of occurring directions (or frequencies) or by other means of reducing the effectiveness of the signal manipulation. Another potential problem is that an input signal is needed to create the central stimulus. The following preferred embodiment does not have these two disadvantages.

Additional noise in two connected devices

Referring to FIG. 5 the solution comprises two connected devices. The noise source can also be replaced with other sound sources, for example via a DAI (Direct Audio Input) and may thus for example come from a tinnitus relieve CD. The additional signal is then used to yield the spatial stimulation. In this embodiment, both instruments have a spatial filter that is coordinated by the direction selector in the master instrument.

Stimulation with disconnected devices

The above mentioned central stimulation can in some extend be achieved by using a single device or disconnected devices that manipulates the direction of the sound, its spectral content, its level or its phase. In any case, a central stimulus is achieved by working together with the other device or with the unaltered signal from the other ear.

Literature references:

Axelsson and Ringdahl, 1989 Tinnitus - a study of its prevalence and characteristics. Br. J Audiol. 23:53-62.

Coles, 1984 Epidemiology of ^'Tinnitus: (1) Prevalence. J. Laryngol. Otol. 9 (suppl): 7-15

Davis, 1989 Ηie prevalence of hearing impairment and reported hearing disability among adults. Int. J. Epidemology 18:911-917.

Jastreboff, 1990 Phantom auditory perception (tinnitus): mechanisms of genertation and perception. Neurosci. Res. 221-254.

Holgers and Hakanson, 2002 Sound stimulation via bone conduction for tinnitus relief: a pilot study. Int. J. Audiology. 41: 293-300.

J. Salvi, Robert F. Burkard, and Samuel A. Reyes (2001) The functional anatomy of tinnitus 141st ASA Meeting, lpPP5. Frank Mirz, Albert Gjedde, Hans Sødkilde-Jørgensen (1999) Functional brain imaging of tinnitus-like perception induced by aversive auditory stimuli. NeuroReport 11 :03, pp

633-637.

Claims

1. A method for treating tinnitus where an acoustic stimulus varying over time is provided to the central stages on the auditory pathway.

2. A method where two output devices are included for performing the method.

3. A method according to claim 2 where the method comprises controlling the output of the devices according to a predetermined scheme.

4. A method according to claim 2 or 3, where information is sent from one device to the other device.

5. A method according to claim 2 or 3, where information is sent from each device and received by the other device.

6. A method according to any of the claims 1-5, where a spatial stimulus is provided.

7. A method according to any of the claims 1-5, where a spectral stimulus is provided.

8. A method according to any of the claims 1-7, where a sound level stimulus is provided.

9. A method according to any of the claims 1-8, where a frequency and/or phase stimulus is provided.

10. A system for treating tinnitus, where the system comprises at least one output device for generating and supplying to a patient an acoustic stimulus varying over time and capable of stimulating the central stages of the auditory pathway.

11. A system according to claim 10 comprising two output devices for generating and supplying the acoustic stimuli.

12. A system according to claim 11, where one device comprise means for transmitting information to the other device and the other device comprises means for receiving the transmitted information.

13. A system according to claim 11 or 12, where each device comprises means for receiving and transmitting information from/to the other device.

14. A device according to any of the claims 10-13, where the device is adapted to provide a spatial stimulus.

15. A device according to any of the claims 10-13, where the device is adapted to provide a spectral stimulus.

16. A device according to any of the claims 10-15, where the device is adapted to provide a sound level stimulus.

17. A method according to any of the claims 10-16, where the device is adapted to provide a frequency and/or phase stimulus.