Implantable Electronic Hearing Aid

This invention relates to an electronic device for improving the hearing of persons who suffer hearing disabilities produced by non-functioning of the inner ear mechanism. The invention utilizes the principle of implanting wire electrodes for transmitting audio stimuli signals directly to the auditory nerve.

Many of the prior devices developed for hearing aids are cosmetically unattractive and are objectionable in terms of internal noise, buzzing and poor tonal quality. In addition, many prior electronic hearing aids overamplify certain portions of the audio spectrum and underamplify others, resulting in severe distortion of sound.

Furthermore, providing aid for persons who have a non-functioning inner ear has posed even more difficult problems due to the complex electrical nature of the cochlea. It has been heretofore proposed that stimulation of the acoustic nerve be accomplished by insertion of hair-size platinum (or other) wires into the cochlea over which an analog voltage is applied representing the audible signal picked up by a miniature microphone. Such a proposal is disclosed in U.S. Pat. No. 3,751,605. However, the analog voltage signal applied to the acoustic nerve quite often results in severe distortion of the original audio signal and lack of fidelity.

An electronic hearing aid device for aiding a person having a hearing disability of the inner ear comprising a receiver for receiving an external audio signal and converting the audio signal into an analog voltage signal. An amplifier is connected to the receiver for receiving the analog voltage signal and amplifying the signal. A plurality of frequency filter networks have inputs connected to the output of the amplifier for receiving the amplified analog voltage signal and breaking the analog signal down into component signals having frequencies corresponding to a predetermined frequency range of each respective filter network. An analog-digital converter network is connected to the output of each filter network for receiving the component signal therefrom and converting the component signal into a digital component signal having a series of digital pulses of the same frequency as the analog component signal. A pin connector member is provided having a plurality of pins. Each pin is connected to an output of an analog-digital filter network for receiving the digital pulse signals therefrom. A plurality of electrode members are implanted in the auditory nerve of the inner ear with an end of one of the electrodes being connected to each of the pins. The distal end of the electrode members are implanted in the auditory nerve of the inner ear so that each component digital signal will be applied to stimulate the portion of the nerve normally accustomed to transmitting the same frequency range of audio signals as in the normal hearing process for interpretation in the hearing center of the brain.

Accordingly, an important objective of the present invention is to provide an electronic device for use as an effective hearing aid for people having a hearing disability of the inner ear.

Still another important objective of the present invention is to provide a hearing aid device for persons having a hearing disability in the inner ear which produces accurate reproduction of audio signals having high fidelity.

Another important objective of the present invention is to provide an electronic hearing aid device which utilizes discrete electrical stimuli to activate the individual fibers or groups of fibers of the auditory nerve to more naturally stimulate the true functioning of the inner ear.

Still another important objective of the present invention is to provide an electronic hearing aid device for hearing disabilities of the inner ear which provides a breakdown of a composite audio signal into a number of component frequency signals within the normal audio spectrum for individually stimulating the auditory nerve fibers producing a more natural transmission of signals for interpretation in the normal hearing process.

The construction designed to carry out the invention will be hereinafter described, together with other features thereof.

The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings forming a part thereof, wherein an example of the invention is shown and wherein:

FIG. 1 is a sectional view illustrating the insertion of a portion of the hearing aid device of the present invention in the human ear,

FIG. 2 is an enlarged view of FIG. 1 illustrating the connection of the electrical transmission electrodes of the present invention implanted adjacent the basilar membrane of the inner ear,

FIG. 2A is a view of a cross-section of an enlargement of the cochlea (inner ear) showing a proposed access for the distal end of the implanted electrode into the acoustic (eighth carnial) nerve,

FIG. 3 is a schematic diagram illustrating an electrical circuit for an electronic hearing device constructed in accordance with the present invention, and

FIG. 4 is a schematic diagram illustrating an analog to digital converter circuit for use in an electronic hearing aid device constructed in accordance with the present invention.

The invention relates to electronic hearing aid devices for persons who are deaf or suffer partial loss of hearing because of a hearing disability. The present invention is particularly advantageous for aiding persons who have hearing disabilities because of a non-functioning inner ear, but who still have a responsive auditory nerve system. The proposed device of the present invention will enable these persons to hear by the transmitting of electrical impulses directly to the auditory nerve through electrode wires implanted in the auditory nerve system. The non-functioning cochlea will be bypassed altogether. The exact method and most appropriate access to the acoustic nerve must be experimentally researched and established by the medical profession and those accustomed to the art (otologists). It is essential for optimum performance that electrical insulation be maintained between one implanted electrode and another within the acoustic nerve. In this manner, only those groups of nerves intended for stimulation by a limited band of frequencies will be activated.

It is considered a major fault of prior attempts at electrode implantation to insert an electrode or electrodes into the cochlear fluid through the oval or round window. The cochlear fluid is not an insulating liquid, and insulation is therefore not maintained between channels.

In addition, prior devices have applied analog voltages to the electrodes. The cochlea (inner ear) does not have the capability to convert analog voltages to digital pulses for stimulation of acoustic nerve endings. A surgical process for implanting such electrodes is discussed more fully in an article entitled "The Electric Ear" appearing in the April 1974 issue of Newsweek magazine.

It is to be understood, of course, that other techniques may be utilized for transmitting the electrical impulses generated by the electronic device of the present invention, and that the electronic device of the present invention contemplates application to other types of hearing problems.

Referring now in more detail to the drawings, FIG. 1 illustrates a schematic diagram of an electrical circuit embodying the electronic device of the present invention for receiving external audio sound waves and converting the sound waves into digital electrical stimuli which are transmitted over the implanted electrodes. A receiver means 10 is provided by a miniature electronic microphone for receiving the external audio signals or sound waves and converting the audio signal into an analog audio voltage signal. The output 10a of the microphone receiver 10 is connected to the input 12a of a conventional amplifier circuit 12 for amplifying the analog voltage signal. A plurality of frequency filter networks 14a through 14j each has an input connected to an output 12b of the amplifier means 12 for receiving the amplified voltage signals therefrom. Each of the frequency filter networks 14a through 14j provides a band-pass filter for passing only a component voltage signal having a frequency of the range to which each respective network is limited.

In the preferred embodiment, each frequency filter network provides a band-pass filter in increments or "blocks" of 500 hertz (HZ) over the audio spectrum between 0 and 5,000 hertz. Thus, filter network 14a is designed to pass a signal in the frequency range of from 0 to 500 hertz, filter 14b from 500 to 1,000 hertz, filter 14c from 1,000 to 1,500 hertz, network 14d from 1,500 to 2,000 hertz, filter 14e from 2,000 to 2,500 hertz, filter 14f from 2,500 to 3,000 hertz, filter 14g from 3,000 to 3,500 hertz, filter 14h from 3,500 to 4,000 hertz, filter 14i from 4,000 to 4,500 hertz, and filter 14j from 4,500 to 5,000 hertz. The number of frequency networks used and hence frequency blocks provided for depends on what correlation is to be achieved with natural electrical stimuli of the auditory nerve systems and the number of portions thereof that are to be stimulated.

The composite analog voltage signal coming from amplifier 12 will be passed through the various filter networks 14a through 14j and will be broken down into component signals of 500 hertz "blocks" each, which will be contained within the normal audio spectrum between 0 and 5,000 hertz. The filter networks 14a through 14j may be any conventional band-pass filter such as a crystal or tuned circuit. One suitable type of network circuit is manufactured by the Krohn-Hite Corporation of Avon, Mass., series 3340, specifically model 3343R. This filter represents one of the best in laboratory equipment and exceeds the requirements for the purposes of this invention except in special applications.

Other suitable filter networks may be had within the integrated circuitry art to provide miniature frequency filter networks of the required complexity and capability within the size of a "body" type aid.

One such filter for each of the 10 channels in this instance could be constructed with the use of a resistance-capacitance twin-T band pass filter section operating into a high gain tuned audio amplifier, producing a so-called "active filter".

All 10 channels of this type "active filter", along with the microphone and primary audio amplifier could be packaged within a "body" type hearing aid case, and even within the volume of behind-the-ear and eyeglass aid.

The output of each frequency filter network 14a through 14j is connected to a corresponding analog-digital converter circuit 16a through 16j. Each of the analog-digital circuits receives the analog frequency component signal coming from the associated frequency filter network and converts the frequency component signal into a digital component signal having a series of digital pulses of the same frequency as the analog frequency component signal. The analog-digital converter circuit shown generally at 16a through 16j may be any conventional analog to digital converter circuit which will rectify the analog voltage signal providing a series of digital pulses occurring at the same frequency as the original analog signal.

One suitable converter circuit is comprised of a simpled diode rectifier D1, or a transistor gating circuit (or trigger, or switch), whereby a transistor T1 is biased at or slightly below cutoff normally.

When an analog signal from the appropriate filter network (channel) is applied, it will be rectified by the transistor (or diode) switching circuit. Only the positive going portion of the audio sine wave will cause the transistor to conduct. The turn-on threshold of the transistor can therefore be adjusted to allow control of input analog voltage levels, and thus control of background noise.

Voltage level control and time duration limits may also be included in the transistor output (Collector) circuitry, thus maintaining strict control of voltage levels and pulse widths applied to the acoustic nerve.

Each of the analog-digital converter circuits 16a through 16j is connected to a pin connector member 18 having a plurality of pin connections 20a through 20j connected to the corresponding analog-digital converter circuits 16a through 16j for receiving the digital component signal therefrom. The pin connector member 18 is preferably in the form of a female connector 18a which may be implanted in the area of the mastoid bone of the outer ear such as shown in FIG. 1, and a male connector member 18b wherein the pins 20a through 20j are carried by the male connector for insertion into a plurality of matching insert channels 22a through 22j carried within the female connector 18a. In this manner, the electronic circuit elements of the present invention may be removably attached and replaced as a hearing aid device.

It should be noted that another method of female connector implantation could be accomplished by placing it in the ear canal. Implantation in the ear canal may be more cosmetically acceptable than location in the mastoid area.

Connected to the insert channels 22a through 22j of the female coupling 18a are a plurality of corresponding electrode members 24a through 24j which have their remote end surgically implanted adjacent portions of the auditory nerve system B of the inner ear along the basilar membrane C at points a through j. The electrodes transmit each component digital pulse signal at the same portion of the auditory nerve normally accustomed to transmitting like signals in the normal hearing process for interpretation in the hearing center of the brain. Thus, each individual block of digital impulse stimuli will be applied directly to the auditory nerve by way of the imbedded electrodes 24a through 24j which are preferably in the form of platinum wires.

The electronic device constructed in accordance with the present invention proposes that the digital stimuli will more naturally and accurately simulate the functioning of the electrical nature of the cochlea D output to the auditory nerve system. Of course, the microphone 10, the amplifier 12, the frequency filter networks 14a through 14j, and the analog-to-digital converter circuits 16a through 16j, and a suitable power source will be appropriately packaged external to the patient in a package housing A.

It is important to note that the greater the number of individual channels (wires), and thus the greater the synthesis of the input audio signal, then the better the fidelity, or true reproduction of the input signal (s), or tone (s).

The ten individual channels presented in this invention may exceed the current practical state-of-the-art in electrode implantation within the acoustic nerve. The number ten is therefore illustrative, and not intended to be a limitation to the concept.

Likewise, neither is utilization of the audio spectrum between 0-5,000 hertz.

The most beneficial frequency range required by various patients will vary in each case and must be determined by an audiologist.

Thus, it can be seen that an advantageous construction for a hearing aid device can be had in accordance with the present invention for aiding a person having a hearing disability of the inner ear. By breaking down a composite audio signal into component "blocks" of a predetermined frequency range and digitizing each block component of the audio signal for direct application to the auditory nerve by way of imbedded platinum wires, a more natural and accurate simulation of the true functioning of the inner ear can be accomplished.

While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.