Patent No. 3826243 Brainwave analysis and feeback method and apparatus

 

Patent No. 3826243  Brainwave analysis and feeback method and apparatus (Anderson, Jul 30, 1974)

Abstract

A method and apparatus for minimizing spurious responses in brainwave analysis and feedback instruments. A plurality of Fourier amplitude coefficients of the incoming brainwave signals are determined, and these coefficients are appropriately combined to be representative of certain brainwave states and to suppress noise signals that have a relatively wide bandwidth.

Notes:

BACKGROUND OF THE INVENTION

The present invention relates generally to low frequency wave analysis and more particularly to brain wave analyzers. Brain wave signals have been found to be an extremely useful tool for the diagnosis of certain diseases, and for the study of various states of consciousness of healthy animals. In the study of certain diseases and functional disorders of the brain an electroencephalogram (EEG) is commonly recorded. This EEG is obtained by sensing and recording simultaneously a plurality of signals arising from various parts of the brain. A concise review of the clinical implications of electroencephalography is given in the book, "Medical Electroencephalography," by Frederic A. Gibbs and Erna L. Gibbs, Addison-Wesley Publishing Company, Inc., 1969. The recorded signals of such EEG apparatus are extremely complex waveforms, and medical diagnosis from such recordings is normally done by skilled personnel who have had several years of specialized medical training.

It has been found that certain states of consciousness are associated with brain waves in which certain frequency components dominate. A summary of earlier work regarding these states is given by W. Grey Walters in his book, "The Living Brain," W. W. Norton and Company, 1963 and 1953. For example, humans in their normal wide awake state--called beta state--normally exhibit brain waves over a frequency range of from about 12 to 30 Hz. Humans in a relaxed state, with their eyes closed, usually exhibit relatively strong brain waves in the frequency range of 8-12 Hz. This state of consciousness is called the alpha state and the brain waves produced in such state are called alpha waves. For humans in light sleep, brain waves in the range of 6 to 8 Hz are typically produced and these waves are called theta waves. In deep sleep humans typically produce waves in the range of 1 to 4 Hz and these waves are called delta waves.

Joseph Kamiya, Psychology Today, Vol. 1, pages 57-60, April, 1968, has shown that if a person receives external feedback information when certain brain waves are being produced he can learn to discern between certain brain wave states. Furthermore he showed that with the aid of feedback information as to when the alpha wave state is present, many people can learn to control their brain wave states, either emitting or suppressing alpha waves in accord with their will.

Such experiments on trained self-control of alpha waves has been confirmed by Barbara B. Brown, Psychophysiology, Vol. 6, No. 4, pages 442-452, January, 1970. Many subjects have described the alpha wave state as one in which the mind is tranquil, calm and alert, often associated with a pleasant feeling. Devices to facilitate these experiments are called alpha feedback instruments. Typically prior art alpha feedback instruments consist of a sensing means, a means of determining the Fourier amplitude coefficient of a desired frequency component, and a means of displaying or indicating the Fourier amplitude.

A major problem with these prior art devices is that they produce spurious responses due to several different factors including electrode movement, electromyograph signals from muscles, and noise signals generated externally or in the amplifier. A further problem with these prior art devices is that they are difficult to operate because they require critical adjustments of the signal gain because the amplitude of brain wave signals is dependent upon the location of the sensing electrodes and upon the subject.

SUMMARY OF THE INVENTION

The disclosed invention improves the performance of brain wave analysis and feedback instruments by determining a plurality of Fourier amplitude coefficients of a brain wave signal, combining said Fourier amplitude coefficients in a predetermined linear combination to form a composite coefficient, and producing an output signal responsive to said composite coefficient.

Accordingly, it is the object of the invention to provide brain wave analysis and feedback which is indicative of certain brain wave states and which minimizes spurious responses that may arise from electrode movements, muscle potentials, or noise generated either internally or externally.

Another object of the invention is to provide simplified operation of the brain wave feedback instrument so that it can be used and operated by persons without a high degree of prior training. A feature of the invention is that critical adjustments of signal gain are eliminated by providing feedback responsive to predetermined linear combinations of Fourier amplitude coefficients rather than to the amplitude of a single Fourier component as was done in the prior art.

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Although this invention has been disclosed and illustrated with certain brain wave frequencies it is apparent that the principles disclosed here apply to the analysis and indicating the presence of other brain wave frequency combinations. The method has been illustrated with electronic analog computing apparatus, however the method could equally well be carried out by digitizing the incoming brain wave signals and performing the operations described here by suitably programming a general purpose digital computer to carry out the same computations, and activate a suitable indicating device to provide feedback. Although one of the main purposes of this invention is to provide improved brain wave feedback instrumentation, it can be used to minimize or eliminate spurious signals when analyzing brain wave signals directly or analyzing those that have been recorded at an earlier time, as indicated by recorded source 20 of FIG. 2. Since many changes will be apparent to persons skilled in the art, the invention is to be limited only as indicated by the scope of the appended claims.