Aids For Deaf Persons

Abstract

An aid for a deaf person, comprising means for changing electrical signals having a first range of electrical frequencies corresponding to a first range of audio frequency signals used in normal speech into electrical signals having a second range of electrical frequencies different from said first range of electrical frequencies in such a manner that the frequency differences of said first range of electrical frequencies are substantially maintained in said second range of electrical frequencies and for superimposing the changed electrical signals onto electrical signals having frequencies within said second range of electrical frequencies and which correspond to a second range of audio frequency signals used in normal speech.

Description

This invention relates to aids for deaf persons having some residual hearing.

Deafness is conventionally classified as being either of the "conductive" kind, in general involving middle ear malfunctions, or of the "perceptive" kind, involving inner ear or auditory nerve malfunctions. When such malfunctions result in a loss of sensitivity to a part of the speech spectrum, e.g., to high frequency components of the speech spectrum, speech perception, acquisition and production may be impaired.

Conventional hearing aids can compensate for the reduced high frequency sensitivity in conductive deafness by selectively amplifying the high frequency speech components. In perceptive (sensory-neural) deafness, however, such techniques are frequently ineffective because the neural circuits mediating frequencies above a particular level, e.g. above 1,000 cps., are completely inoperative (as opposed to lowered in sensitivity), thus rendering inaccessible to the deaf person sections of the speech spectrum, e.g. the fricatives, essential for intelligibility.

To make better use of any residual hearing (usually low frequency residual hearing) which the perceptively deaf person may possess, various means for producing low frequency correlates of the high frequency sections of the speech spectrum have been proposed. Such prior proposals have involved the transposition of the whole or part of the speech spectrum into the region of residual low frequency hearing, e.g. the region below 1,000 cps., using frequency compression or time domain compression systems. The signals produced by such means, although detectable by the perceptively deaf, are not "speech-like" in character and have accordingly met with only very limited success in assisting the perceptively deaf in the understanding, acquisition and production of speech.

The present invention has as its object to enable an aid to be provided for a person with perceptive deafness but with some residual hearing which will enable normal speech to be reproduced within a restricted frequency range so as to have a more speech-like character than is possible with the prior proposals above referred to.

The present invention provides an aid for a deaf person, comprising means for changing electrical signals having a first range of electrical frequencies corresponding to a first range of audio frequency signals used in normal speech into electrical signals having a second range of electrical frequencies different from said first range of electrical frequencies in such a manner that the frequency differences of said first range of electrical frequencies are substantially maintained in said second range of electrical frequencies and for superimposing the changed electrical signals onto electrical signals having frequencies within said second range of electrical frequencies and which correspond to a second range of audio frequency signals used in normal speech.

The invention also provides a method of recoding audio frequencies used in normal speech as an aid to the deaf, the method comprising translating the audio frequencies used in normal speech into electrical signals, changing those electrical signals having a first range of electrical frequencies corresponding to a first range of said audio frequencies into electrical signals having a second range of electrical frequencies different from said first range of electrical frequencies in such a manner that the frequency differences of said first range of electrical frequencies are substantially maintained in said second range of electrical frequencies and superimposing the changed electrical signals onto electrical signals having frequencies within said second range of electrical frequencies and which correspond to a second range of audio frequency signals used in normal speech.

Although the aid of the present invention is primarily intended to assist those persons suffering from perceptive deafness but having some residual hearing, it is envisaged that the aid might also provide more comfortable hearing as compared with a conventional aid using selective amplification in cases of conductive deafness wherein there is a loss of sensitivity to a part, e.g., the high frequency part, of the speech spectrum.

Various combinations of changed and unchanged signals may be used according to the residual hearing of particular deaf persons. For example, the electrical signals corresponding to an upper audio frequency range, e.g., the electrical signals having frequencies of 4,000 cps. and above and which correspond to that range of audio frequencies which includes the fricatives, may be changed into electrical signals within a lower frequency range and superimposed on the electrical signals within said lower frequency range and which correspond to a lower range of audio frequencies, e.g., the electrical signals having frequencies of from 100 cps, and above and which correspond to that range of audio frequencies which includes the low frequency vowel sounds. In this way, a speech-like recoding of fricative information can be obtained without interfering with the low frequency vowel information.

The changing means may comprise frequency modulating means for modulating an input signal, a single side band filter for filtering the output signal from the modulating means, and demodulating means for demodulating the output signal from the single side band filter. The output signal from the changing means may be superimposed upon the signal within conventional amplifier means. The amplifier means may comprise a pre-amplifier and an amplifier and the output from the changing means may be superimposed upon the signal within the amplifier. Means for providing a choice of outputs within desired frequency ranges may be associated with the amplifier means for rectifying sensitivity losses within the residual hearing range of the deaf person. The means for providing a choice of outputs may comprise a plurality of filters having outputs within different frequency ranges and switch means whereby any one of said filters can be selectively connected with the amplifier means. If desired amplitude compression means may be provided so as to better utilize the dynamic range of the deaf ear.

An aid according to the present invention may comprise a simple hearing aid or a speech training aid. Where the aid comprises a speech training aid it may comprise means whereby both recorded and direct speech can be reproduced within a restricted audio frequency range and/or visual, tactile or like means for aiding the person receiving speech training. Where visual and/or tactile means are provided for aiding the deaf person, the arrangement may be such that the changed electrical signals or the output signals derived when the changed electrical signals are superimposed upon the electrical signals corresponding to said second range of audio frequency signals are used to produce visual and/or tactile information or to control means producing visual and/or tactile information.

In order that the invention may be the more readily understood reference will hereinafter be made by way of example to the accompanying diagrammatic drawings, in which:

FIG. 1 is a diagram illustrating the changing, in an aid according to the present invention, of electrical signals having a first range of electrical frequencies into electrical signals having a second range of electrical frequencies different from the first range and the superimposing of the changed electrical signals onto electrical signals having frequencies within said second range, and

FIG. 2 is an example of a circuit diagram for a hearing or speech training aid according to the present invention.

Referring to FIG. 1 it will be seen that the high frequency components I and J between 4 kilocycles and 5 kilocycles of an input signal have been changed so as to have frequencies of from 0 to 1 kilocycle and have been imposed respectively upon the low frequency components A and B having frequencies below one kilocycle so that a resultant output signal comprises simply A + I and B + J in the low frequency range below 1 kilocycle.

Turning now to FIG. 2 it will be seen that the circuit illustrated comprises an input 1 for an electrical input signal fs which corresponds to an audio signal in the normal range of audio frequencies used in speech and parallel circuit paths 2, 3 for the input signal. The electrical input signal fs is obtained from suitable converter means, e.g., a microphone, which converts an audio input into an electrical output. The circuit path 2 includes a frequency modulator 4 whereby the input signal fs is modulated by a modulating signal fc to give sum and difference signals fc + fs and fc - fs. These sum and difference signals are fed to a single side band filter 5 which filters out signals outside a required frequency range, and passes only a selected range of modulated electrical frequencies. The output signal (fs') from the single side band filter 5 is then passed to demodulator 6 where the output signal from the filter 5 is demodulated by a demodulating signal fc.sub.1 to give an output signal fs' - .DELTA., wherein fc.sub.1 - fc = .DELTA.. The circuit path 3 comprises a pre-amplifier 7 and an amplifier 8 for the input signal fs. The recoded signal fs' - .DELTA. passes to the amplifier 8 by way of resistor 9 and is superimposed upon the pre-amplified input signal fs within the amplifier 8. The amplified signal fs + (fs' - .DELTA.) from the amplifier 8 then passes by way of filter means 10 and an amplitude compressor 11 to an output 12. The filtered signal at the output 12 is then fed to a converter, e.g., a loudspeaker or an earphone which converts the electrical signal to an audio signal. The filter means 10 could comprise simply a single filter adapted to provide a predetermined frequency response. However, in the circuit illustrated, the filter means 10 comprises three filters 10a, 10b, 10c adapted to provide different predetermined frequency responses and switch means 10d whereby any one of said three filters can be selected. This enables the frequency response of the output at 12 to be selected according to the requirements of a deaf person according to the range and extent of residual hearing of the person concerned. It will be understood that whilst the filter means 10 has been shown as comprising three filters, it could if desired comprise more or less filters to give a greater or lesser degree of selection. Thus, where the circuit is for a hearing aid, probably only one filter would be provided at 10 which would be selected according to the requirements of the person for whom the aid is intended. Where on the other hand, the circuit is for a speech-training aid which is likely to be used by different persons, then it is clearly preferable that the filter means 10 comprise a plurality of filters as shown.

A conventional deaf aid, such as a conventional group hearing aid or group speech training aid, having an auxiliary input connector can readily be converted into an aid according to the present invention by connecting to said auxiliary input connector a separate module comprising a circuit as shown in FIG. 2.

Claims

What is claimed is:

1. An aid for a deaf person, comprising means for changing electrical signals having a first range of electrical frequencies corresponding to a first range of audio frequency signals used in normal speech into electrical signals having a second range of electrical frequencies different from said first range of electrical frequencies without compression so that the frequency differences within said first range of electrical frequencies are substantially maintained in said second range of electrical frequencies and for superimposing the changed electrical signals onto electrical signals having frequencies within said second range of electrical frequencies and which correspond to a second range of audio frequency signals used in normal speech.

2. An aid according to claim 1, wherein electrical signals corresponding to signals in an upper part of the audio frequency range are changed and superimposed upon electrical signals corresponding to audio signals in a lower part of the audio frequency range.

3. An aid according to claim 2, wherein electrical signals having frequencies of from 4,000 cps. and above and corresponding to signals in an upper part of the audio frequency range are changed so as to have frequencies of from 100 cps. and above and wherein the changed electrical signals are superimposed upon electrical signals having frequencies of from 100 cps. and above and corresponding to audio signals in a lower part of the audio frequency range.

4. An aid according to claim 1 wherein the changing means comprises frequency modulating means for modulating an input signal, a single side band filter for filtering the output signal from the modulating means, and demodulating means for demodulating the output signal from the single side band filter.

5. An aid according to claim 1, comprising a first circuit path and a second circuit path, the first circuit path providing said changing means and comprising frequency modulating means for modulating an input signal, a single side band filter for filtering the output signal from the modulating means and demodulating means for demodulating the output signal from the single side band filter and the second circuit path comprising amplifier means for amplifying an input signal, and means whereby the output signal from the first circuit path can be superimposed on the signal within the second circuit path.

6. An aid according to claim 5, wherein said amplifier means comprises a pre-amplifier and an amplifier.

7. An aid according to claim 5, wherein means is associated with said second circuit path for providing a choice of outputs within desired frequency ranges.

8. An aid according to claim 5, wherein there is associated with the second circuit path a plurality of filters having outputs within different frequency ranges and switch means whereby any one of said filters can be selectively connected with said second circuit path to provide an output within a desired frequency range.

9. A method of recoding audio frequencies used in normal speech as an aid to the deaf, the method comprising translating the audio frequencies used in normal speech into electrical signals, changing those electrical signals having a first range of electrical frequencies corresponding to a first range of said audio frequencies into electrical signals having a second range of electrical frequencies different from said first range of electrical frequencies without compression so that the frequency differences within said first range of electrical frequencies are maintained in said second range of electrical frequencies and superimposing the changed electrical signals onto electrical signals having frequencies within said second range of electrical frequencies and which correspond to a second range of audio frequency signals used in normal speech.