Speech Prosthesis Employing Beta Peak Detection

Abstract

A speech synthesis device detects beta peak firings corresponding to intended vocalizations by a subject having a scalp, a mastoid process and a speech motor cortex. A EEG electrode and a negative electrode are disposed on the scalp of the subject adjacent to the speech motor cortex. A transmitter is electrically coupled to the electrodes, and is configured to transmit wirelessly electronic representations of the neural potentials detected by the electrodes. A remote unit receives the electronic representations of the neural potentials from the transmitter. The remote unit is programmed to: detect beta peaks firings in the neural potentials; correlate the beta peaks firings with beta peaks associated with phonemes, words and phrases; and generate audible representations of the phonemes, words and phrases.

Claims

1. A speech synthesis device for detecting beta peak firings corresponding to intended vocalizations by a subject having a scalp, a mastoid process and a speech motor cortex, comprising: (a) at least one positive EEG electrode and at least one negative electrode disposed on the scalp of the subject adjacent to the speech motor cortex; (b) a transmitter, electrically coupled to the at least one positive EEG electrode and the at least one negative EEG electrode, that is configured to transmit wirelessly electronic representations of the neural potentials detected by the at least one positive EEG electrode and the at least one negative electrode; and (c) a remote unit that includes receiver circuitry that receives the electronic representations of the neural potentials from the transmitter and that is programmed to: (i) detect beta peaks firings in the neural potentials; (ii) correlate the beta peaks firings with beta peaks associated with phonemes, words and phrases; and (iii) generate audible representations of the phonemes, words and phrases.

2. The speech synthesis device of claim 1, wherein the remote unit comprises a cellular telephone.

3. The speech synthesis device of claim 1, wherein the remote unit is further programmed to perform a fast Fourier transform on data received from the at least one positive EEG electrode and at least one negative EEG electrode prior to detecting beta peak firings.

4. The speech synthesis device of claim 1, further comprising at least one second positive EEG electrode.

5. The speech synthesis device of claim 1, wherein the positive electrode is disposed apart from the negative electrode by a predetermined distance.

6. The speech synthesis device of claim 1, wherein the at least one positive electrode is disposed adjacent to the speech motor cortex.

7. The speech synthesis device of claim 1, wherein the negative electrode is disposed adjacent to the mastoid process.

8. The speech synthesis device of claim 1, wherein the beta peak firings are found at frequency domain ranges selected from a list consisting of: 12 Hz to 20 Hz; 20 Hz to 30 Hz; and 12 Hz to 30 Hz.

9. A method for detecting intended vocalizations by a subject having a scalp, a speech motor cortex and a mastoid process, comprising the steps of: (a) applying at least one positive EEG electrode and at least one negative EEG electrode to a preferred electrode placement site so as to detect neural signals corresponding to intended vocalizations; (b) instructing the subject to attempt to make a training vocalization; (c) detecting beta peak firings in the electronic representations of the neural signals; (d) correlating the beta peak firings to beta peak firings associated with phonemes, words and phrases; and (e) generating audible sounds corresponding to the phonemes, words and phrases.

10. The method of claim 9, further comprising the step of performing a fast Fourier transform on data received from the at least one positive EEG electrode and at least one negative EEG electrode prior to the step of detecting beta peak firings.

11. The method of claim 9, further comprising the step of wirelessly transmitting electronic representations of the neural signals to a remote unit, wherein the steps of detecting beta peak firings, correlating beta peak firings and generating audible sounds are performed by the remote unit.

12. The method of claim 11, wherein the remote unit comprises a cellular telephone.

13. The method of claim 9, further comprising the step of applying at least one second positive EEG electrode to the preferred electrode placement site.

14. The method of claim 9, wherein the step of applying at least one positive EEG electrode and at least one negative EEG electrode to a preferred electrode placement site, comprises the steps of applying the at least one positive electrode to the scalp adjacent to the speech motor cortex and applying the at least one negative electrode to the scalp adjacent to the mastoid process.

15. The method of claim 9, further comprising the step of performing a functional MRI on the subject as the subject attempts to make the training vocalization, thereby detecting a preferred electrode placement site.

16. The method of claim 9, wherein the step of detecting the beta peak firings occurs at frequency domain ranges selected from a list consisting of: 12 Hz to 20 Hz; 20 Hz to 30 Hz; and 12 Hz to 30 Hz.

Description

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

[0011] FIG. 1 is a schematic diagram of one embodiment of a speech prosthesis.

[0012] FIG. 2 is a schematic diagram of a multi-electrode embodiment of a speech prosthesis in use.

[0013] FIG. 3 is a graph showing power spectral density vs. frequency of detected neural potentials.

[0014] FIG. 4 is a flowchart showing one embodiment of a method of using a speech prosthesis.

DETAILED DESCRIPTION OF THE INVENTION

[0015] A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. Unless otherwise specifically indicated in the disclosure that follows, the drawings are not necessarily drawn to scale. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of a, an, and the includes plural reference, the meaning of in includes in and on.

[0016] As shown in FIG. 1, one embodiment of a speech prosthesis includes a local unit 100, that is applied to the scalp of a subject 10, and a remote unit 120. The local unit includes a positive EEG electrode 112 and a negative EEG electrode 114 that are coupled to a transmitter 110. The transmitter 110 can include one of the many short distance technologies known to the art, including wireless technologies such as BLUETOOTH, etc. The transmitter 110 transmits neural impulse data from the electrodes 112 and 114 to a remote unit 120, which could include a cellular telephone, a laptop computer on one of many other computing devices known to the art.

[0017] In use, the subject 10 is trained to mentally attempt to say phrases, words or phonemes and electronic representations of the neural impulses that result for the attempts are sensed by the electrodes 112 and 114, and are transmitted to the remote unit 120 by the transmitter 110. The remote unit 120 digitizes the incoming signal and performs a fast Fourier transform on it thereby generating a frequency domain representation of the signal. In the frequency domain, beta peak firings above a predetermined threshold are detected and the values of the peak firings are stored in association with the phrases, words or phonemes that the subject 10 was attempting to say. After training, the subject 10 may attempt again to say the phrases, words or phonemes for which the subject 10 previously trained. The resulting beta peak firings are then correlated to the stored beta peak firings and corresponding audible sounds corresponding to the detected phrases, words or phonemes are generated by the remote unit 120. In alternate embodiments, the detected phrases, words or phonemes can also be displayed in the form of text or used as controls for other systems (such as turning on lights, fans, etc). In one experimental embodiment, it has been found that the most effective detections of beta peak firings are found in the following frequency ranges: 12 Hz to 20 Hz; 20 Hz to 30 Hz; and 12 Hz to 30 Hz.

[0018] As shown in FIG. 2, more than one positive electrode may be employed. In the figure shown, four positive electrodes (electrodes 112a-112d) are employed. Only one negative electrode 114 is necessary to provide a reference. The positive electrodes 112a-112d are placed on the scalp adjacent to the speech cortex of the subject 10. While a functional MM may be performed on the subject to determine optimal placement of the electrodes 112a-112d, it is generally known that the speech cortex is located slightly in front of and above the ear. Subjects who are right handed tend to exhibit stronger speech-related neural impulses on the left side of the head, whereas subjects who are left handed tend to exhibit stronger speech-related neural impulses on the right side of the head.

[0019] The negative electrode 114 is typically placed adjacent to the mastoid process. This is done because there are no muscles in the area of the scalp adjacent to the mastoid process and, therefore, placement of the negative electrode 114 there eliminates EMG artifacts in the resulting neural impulse signals.

[0020] A graph showing a representative digitized frequency domain signal is shown in FIG. 3. This graph shows power spectral density of the signal as a function of frequency. The beta peaks 210 are at signal values that extend above a predetermined threshold 200.

[0021] As shown in FIG. 4, in one embodiment of a method of using the invention, the electrodes are applied to the placement site so as to detect neural signals corresponding to intended vocalizations 302 and the subject is instructed to attempt to make a training vocalization 304. Beta peak firings are detected 306 and the beta peak firings are correlated with stored beta peak firings 308. The remote unit then generates audible sounds corresponding to the phonemes, words and phrases 310.

[0022] In one experimental embodiment, it was discovered that data recorded from the motor speech area of aphasic locked-in and awake speaking subjects has revealed a consistent lower beta peak frequency of 12 to 20 Hz. This beta peak was shown to be present at the onset of covert speech. Studies in the speaking subject revealed that the beta peaks were also present at the onset, offset and inflection point in words and phrases. This raises the possibility of developing a speech prosthesis using only external recording from the scalp, thus avoiding implantation of electrodes within the brain or on its surface.

[0023] Such a speech prosthesis uses the pattern of beta peak firings to detect 10 or more short words. One embodiment of a system consists of wireless recording of the beta peaks and their transmission to a cell phone app that would detect the beta peaks and their firing patterns and output the corresponding words through the phone speakers.

[0024] In one embodiment, external recordings of beta peaks are sensed from EEG electrodes that are held in position using EEG paste (such as, EC2, Natus Manufacturing, Gort, Co. Galway, Ireland). The active electrode (red wire) is positioned one inch above the negative electrode (green wire) in the direction of the vertex as shown in the subject (who, in this case, is right handed). The common electrode is placed on the right mastoid bone.

[0025] In the experimental embodiment, identification of the site for electrodes was achieved using functional MRI with the mute subject making silent (not imagined) vocalizations on an object naming task while in the MRI scanner. In the experimental embodiment, a speaking subject made repeated movements of his tongue, cheeks and jaw, and locations of vascular activity in the fMRI were unique. In addition the electrode site was narrowed even further to the lateral aspect of the premotor face area that extends from the Sylvian fissure to 1 medially. Thus, the external electrodes are placed over this area on the scalp.

[0026] Recording and Analysis of Data:

[0027] The electrode wires were fed into a CWE amplifier (such as, BMA 200, CWE, Ardmore, Pa., USA). Gain was set at 500, with filters set to 1 Hz to 10 KHz. The output was fed into Neuralynx's Cheetah archiving software. Speech output is recorded with the microphone set at a fixed distance from the subject's mouth and fed into the Cheetah software. During acquisition, a circuit was closed using a button push with the subject's left hand (to avoid contaminating the beta peak due to hand movement, while the right hand remained quiescent). The archived data were analyzed for beta peaks using Neuroexplorer software (version 3.259, NEX Nex Technologies, Madison, Ala., USA). The frequency range was restricted between 12 to 20 Hz The data are analyzed in 150, 200, 250, 300, 350, 400, 450 and 500 ms time bins. The criteria for choosing acceptable responses include peaks that lie in the 14 and 15 Hz region using any time bin, and whose baseline is no higher than 20% of the total peak amplitude using percentage of power spectral density analysis.

[0028] The above described embodiments, while including the preferred embodiment and the best mode of the invention known to the inventor at the time of filing, are given as illustrative examples only. It will be readily appreciated that many deviations may be made from the specific embodiments disclosed in this specification without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is to be determined by the claims below rather than being limited to the specifically described embodiments above.