Abstract:
An exemplary embodiment providing one or more improvements includes apparatus and methods for sensing electrical activity in tissue of a person in a manner which is substantially limits or eliminates interference from noise in a surrounding environment.

Description:
RELATED APPLICATIONS  
       [0001]     The present application claims priority from U.S. Provisional Application Ser. No. 60/713,899, filed on Sep. 2, 2005 which is incorporated herein by reference. In addition, U.S. patent application Ser. No. XX (Attorney Docket No. CAM-2) titled A Device and Method for Determining and Improving Present Time Emotional State of a Person which was invented by Ray Caama{hacek over (n)}o et al. and which has the same filing date as the present application, is hereby incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     Devices used for sensing electrical activity in tissue have many uses in modern society. In particular modern electroencephalograms (EEGs) are used for measuring electrical activity in the brains of people for anesthesia monitoring, attention deficit disorder treatment, epilepsy prediction, and sleep monitoring, among other uses. Unfortunately, the complexity and cost of prior modern EEGs typically limits their use to clinics or other facilities where the device can be used on numerous people under the expert attention of a trained medical professional. Using the EEG on numerous people in a clinical setting helps to distribute the cost of the machine to the people which use it. EEGs can cost several thousand dollars.  
         [0003]     Trained personnel are used for setting up and operating EEGs because of the complexities involved. Setting up prior EEGs involves preparing the skin of the person for connection of electrodes. The skin is typically prepared by shaving the hair from the area, sanding the skin to remove the outer surface and applying a conductive gel or liquid to the skin before attaching the electrode to the skin. Such extensive skin preparation is needed because contact resistance between the electrode and the skin must be reduced in order for prior EEGs to work properly. Contact resistance in these prior EEGs typically needs to be 20 k ohms or less.  
         [0004]     Typical prior EEGs are subject to errors caused by electrical and magnetic noise from the environment surrounding the person. Errors are also caused by slight variations in internal components of the EEG and other sources, such as movement of the person during the operation of the EEG. Environmental noise can be caused by 60 Hz power in electrical wiring and lights in the area where the EEG is used, and other sources. Even the friction of any object moving through the air can cause noise from static electricity. Most or all prior EEGs have two electrodes are connected to the person&#39;s head and wires which are run from each of the electrodes to the EEG machine. The routing of the wires and the positions of the noise causing elements in the environment can cause significant errors in the measurements done by the EEG.  
         [0005]     Measuring the electrical activity in the brain is difficult because the electrical signal being measured is many times smaller than the noise in the system. In many instances, the noise is on the order of a few volts or a few tens of volts while the electrical signal being measured is only in the microvolt range. This gives a signal-to-noise ratio of 10ˆ6.  
         [0006]     Prior EEGs have used very precise differential amplifiers, such as instrumentation amplifiers, to measure the electrical signal. The amplifier is referenced to a common reference such as the leg of the user. Each of the two wires from the two electrodes on the person&#39;s head are connected to the inputs of the differential amplifier. The output of the differential amplifier is a voltage relative to the reference which is proportional to the difference in voltage between the two electrodes times a constant. The measurement in this case is very sensitive because the differential amplifier is finding a small difference, the brain signal, between two signals which are 10ˆ6 times as large. These are reasons why small variations in components, the routing of the wires and other factors cause significant errors in the measurement and why prior EEGs are expensive and hard to use.  
         [0007]     Another problem with the prior EEGs is that the 60 Hz noise is amplified at the first stage which saturates the signals before they are subtracted. In prior EEGs, designers go to great lengths to design systems that balance or shield the noise to avoid saturation. Systems which use the principle of subtracting two large numbers in measuring a small number are prone to these kinds of problems.  
         [0008]     The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon reading of the specification and a study of the drawings.  
       SUMMARY  
       [0009]     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements.  
         [0010]     A method is described for sensing electrical activity in tissue of a user. Electrical activity is detected from the tissue between a first point and a second point on skin of the user and a voltage signal is generated in response thereto which contains a signal of interest and undesired signals. The voltage signal is amplified to amplify the signal of interest and undesired signals without substantially amplifying the noise. The amplification results in an output signal.  
         [0011]     Another method is disclosed for sensing electrical activity in tissue of a user in a noise environment that is subjected to electrical noise. A sensor electrode is connected to skin of the user at a first point. A reference electrode is connected to skin of the user at a second point which is in a spaced apart relationship to the first point to allow the sensor electrode to sense the electrical activity in the tissue at the first point relative to the second point. An amplifier is provided which is configured to amplify the electrical activity while substantially reducing the influence from the noise environment.  
         [0012]     A sensor circuit is described for sensing electrical activity in tissue of a user and isolating and amplifying a signal of interest from the sensed electrical activity. The sensor circuit includes a sensor electrode for placing on skin of the user at a first point. A reference electrode for placing at a second point which is a distance away from the first point to allow the sensor electrode to sense the electrical activity and to produce a voltage signal relative to the second point which includes the signal of interest in response. An electronic module of the sensor circuit includes a power source with positive and negative source voltages and a source reference voltage which is electrically connected to the reference electrode. An amplifier is connected to receive power from the power source and to receive the voltage signal from the sensor electrode and the power source reference voltage. The amplifier produces an output signal which is proportional to the voltage signal relative to the power source reference voltage. A filter portion receives the output signal from the amplifier and attenuates electrical activity unrelated to the signal of interest while passing the signal of interest.  
         [0013]     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is an illustration of a system which uses a sensor device which measures electrical activity to determine a present time emotional state of a user.  
         [0015]      FIG. 2  is an illustration of a program which contains a display of a level of the present time emotional state of the user and has controls for media material used in guiding the user in relation to the present time emotional state of the user.  
         [0016]      FIG. 3  is a diagram of one example in which the media material guides the user based on the present time emotional state of the user.  
         [0017]      FIG. 4  is a diagram of another example in which the media material guides the user based on the present time emotional state of the user.  
         [0018]      FIG. 5  is a diagram of yet another example in which the media material guides the user based on the present time emotional state of the user.  
         [0019]      FIG. 6  is a perspective view of the sensor device shown in  FIG. 1 .  
         [0020]      FIG. 7  is a block diagram of the sensor device and a computer shown in  FIG. 1 .  
         [0021]      FIG. 8  is a circuit diagram of an amplifier used in the sensor device shown in  FIG. 7 .  
         [0022]      FIG. 9  is a circuit diagram of a filter stage used in the sensor device shown in  FIG. 7 .  
         [0023]      FIG. 10  is a circuit diagram of a resistor-capacitor RC filter used in the sensor device shown in  FIG. 7 .  
         [0024]      FIG. 11  is a circuit diagram of the amplifier, three filter stages and the RC filter shown in  FIGS. 8, 9  and  10 .  
         [0025]      FIG. 12  is a block diagram of a digital processor of the sensor device shown in  FIG. 7 .  
     
    
     DETAILED DESCRIPTION  
       [0026]     A system  30  which incorporates the present discussion is shown in  FIG. 1 . Exemplary system  30  includes a sensor device  32  which is connected to a user  34  for sensing and isolating a signal of interest from electrical activity in the user&#39;s pre-frontal lobe. The signal of interest has a measurable characteristic of electrical activity, or signal of interest, which relates to a present time emotional state (PTES) of user  34 . PTES relates to the emotional state of the user at a given time. For instance, if the user is thinking about something that causes the user emotional distress, then the PTES is different than when the user is thinking about something which has a calming affect on the emotions of the user. In another example, when the user feels a limiting emotion regarding thoughts, then the PTES is different than when the user feels a state of release regarding those thoughts. Because of the relationship between the signal of interest and PTES, system  30  is able to determine a level of PTES experienced by user  34  by measuring the electrical activity and isolating a signal of interest from other electrical activity in the user&#39;s brain.  
         [0027]     In the present example, sensor device  32  includes a sensor electrode  36  which is positioned at a first point and a reference electrode  38  which is positioned at a second point. The first and second points are placed in a spaced apart relationship while remaining in close proximity to one another. The points are preferably within about 8 inches of one another, and in one instance the points are about 4 inches apart. In the present example, sensor electrode  36  is positioned on the skin of the user&#39;s forehead and reference electrode  38  is connected to the user&#39;s ear. The reference electrode can also be attached to the user&#39;s forehead, which may include positioning the reference electrode over the ear of the user.  
         [0028]     Sensor electrode  36  and reference electrode  38  are connected to an electronics module  40  of sensor device  32 , which is positioned near the reference electrode  38  to that they are located substantially in the same noise environment. The electronics module  40  may be located at or above the temple of the user or in other locations where the electronics module  40  is in close proximity to the reference electrode  38 . In the present example, a head band  42  or other mounting device holds sensor electrode  36  and electronics module  40  in place near the temple while a clip  44  holds reference electrode  38  to the user&#39;s ear. In one instance, the electronics module and reference electrode are positioned relative to one another such that they are capacitively coupled.  
         [0029]     Sensor electrode  36  senses the electrical activity in the user&#39;s pre-frontal lobe and electronics module  40  isolates the signal of interest from the other electrical activity present and detected by the sensor electrode. Electronics module  40  includes a wireless transmitter  46 , ( FIG. 6 ), which transmits the signal of interest to a wireless receiver  48  over a wireless link  50 . Wireless receiver  48 ,  FIG. 1 , receives the signal of interest from electronics module  40  and connects to a port  52  of a computer  54 , or other device having a processor, with a port connector  53  to transfer the signal of interest from wireless receiver  48  to computer  54 . Electronics module  40  includes an LED  55  ( FIG. 6 ), and wireless receiver  48  includes an LED  57  which both illuminate when the wireless transmitter and the wireless receiver are powered.  
         [0030]     In the present example, levels of PTES derived from the signal of interest are displayed in a meter  56 , ( FIGS. 1 and 2 ), on a computer screen  58  of computer  54 . In this instance, computer  54 , and screen  58  displaying meter  56  serve as an indicator. Levels of detail of meter  56  can be adjusted to to suit the user. Viewing meter  56  allows user  34  to determine their level of PTES at any particular time in a manner which is objective. The objective feedback obtained from meter  56  is used for guiding the user to improve their PTES and to determine levels of PTES related to particular memories or thoughts which can be brought up in the mind of user  34  when the user is exposed to certain stimuli. Meter  56  includes an indicator  60  which moves vertically up and down a numbered bar  62  to indicated the level of the user&#39;s PTES. Meter  56  also includes a minimum level indicator  64  which indicates a minimum level of PTES achieved over a certain period of time or during a session in which user  34  is exposed to stimuli from media material  66 . Meter  56  can also include the user&#39;s maximum, minimum and average levels of release during a session. Levels of PTES may also be audibly communicated to the user, and in this instance, the computer and speaker serve as the indicator. The levels can also be indicated to the user by printing them on paper.  
         [0031]     In another instance, different release levels relating to reaction to the same media material can be stored over time on a memory device. These different release levels can be displayed next to one another to inform the user on his or her progress in releasing the negative emotions related to the media material.  
         [0032]     In system  30 , media material  66  is used to expose user  34  to stimuli designed to cause user  34  to bring up particular thoughts or emotions which are related to a high level of PTES in the user. In the present example, media material  66  includes audio material that is played though computer  54  over a speaker  68 . Media material  66  and meter  56  are integrated into a computer program  70  which runs on computer  54  and is displayed on computer screen  58 . Media material  66  is controlled using on-screen buttons  72 , in this instance. Computer program  70  also has other menu buttons  74  for manipulation of program functions and an indicator  76  which indicates connection strength of the wireless link  50 . Program  70  is typically stored in memory of computer  54 , this or another memory device can also contain a database for storing self reported journals and self-observed progress.  
         [0033]     In some instances, program  70  may require a response or other input from user  34 . In these and other circumstances, user  34  may interact with program  70  using any one or more suitable peripheral or input device, such as a keyboard  78 , mouse  80  and/or microphone  82 . For instance, mouse  80  may be used to select one of buttons  72  for controlling media material  66 .  
         [0034]     Media material  66  allows user  34  to interact with computer  54  for self or assisted inquiry. Media material  66  can be audio, visual, audio and visual, and/or can include written material files or other types of files which are played on or presented by computer  54 . Media material  66  can be based on one or more processes, such as “The Release Technique” or others. In some instances, generic topics can be provided in the form of audio-video files presented in the form of pre-described exercises. These exercises can involve typical significant life issues or goals for most individuals, such as money, winning, relationships, and many other popular topics that allow the user to achieve a freedom state regarding these topics. The freedom state about the goal can be displayed when a very low level of PTES, (under some preset threshold) is achieved by the user regarding the goal. The release technique is used as an example in some instances; other processes may also be used with the technological approach described herein.  
         [0035]     In one instance, media material  66  involving “The Release Technique” causes user  34  to bring up a limiting emotion or an emotion-laden experience type of PTES, which results in a disturbance in the nervous system of the user. The process then guides user  34  to normalize the nervous system or release the emotion while the user is focused on the perceived cause of the disturbance. When it is determined that the level of PTES, or release level in this instance, is below a preset threshold then the process is completed.  
         [0036]     The signal of interest which relates to the release level PTES are brain waves or electrical activity in the pre-frontal lobe of the user&#39;s brain in the range of 4-12 Hz. These characteristic frequencies of electrical activity are in the Alpha and Theta bands. Alpha band activity is in the 8 to 12 Hz range and Theta band activity is in the 4 to 7 Hz range. A linear relationship between amplitudes of the Alpha and Theta bands is an indication of the release level. When user  34  is in a non-release state, the activity is predominantly in the Theta band and the Alpha band is diminished; and when user  34  is in a release state the activity is predominantly in the Alpha band and the energy in the Theta band is diminished.  
         [0037]     When user  34  releases the emotion, totality of thoughts that remain in the subconscious mind is lowered in the brain as the disturbance is incrementally released from the mind. A high number of thoughts in the subconscious mind results in what is known as unhappiness or melancholy feelings, which are disturbances in the nervous system. A low number of thoughts in the subconscious mind results in what is known as happiness or joyful feelings, which results in a normalization or absence of disturbances in the nervous system.  
         [0038]     An exemplary method  84  which makes use of one or more self or assisted inquiry processes is shown in  FIG. 3 . Method  84  begins at a start  86  from which the method moves to a step  88 . At step  88 , program  70  uses stimuli in media material  66  to guide user  34  to bring up thoughts or subjects which causes an emotional disturbance in the PTES such as a limiting emotion. In the present example, media material  66  involves questions or statements directed to user  34  through speaker  68 . In this and other instances, the computer can insert statements about goals or issue which were input by the user into the media material  66 . For example, user  34  may input a goal statement using keyboard  78  and the computer may generate a voice which inserts the goal statement into the media material. In another example, the user may input the goal statement using microphone  82  and the computer may insert the goal statement into the media material.  
         [0039]     Method  84  then proceeds to step  90  where program  70  uses media material  66  to guide user  34  to release the limiting emotions while still focusing on the thought or subject which causes the limiting emotion. From step  90 , the program proceeds to step  92  where a determination is made as to whether user  34  has released the limiting emotions. This determination is made using the signal of interest from sensor device  32 . In the instance case, the level of release is indicated by the position of indicator  60  on bar  62  in meter  56 , as shown in  FIG. 2 . If the meter indicates that user  34  has released the limiting emotions to an appropriate degree, such as below the preset threshold, then the determination at  92  is yes and method  84  proceeds to end at step  94 . If the determination at  92  is that user  34  has not release the limiting emotions to an appropriate degree, then the determination at  92  is no, and method  84  returns to step  88  to again guide the user to bring up the thought or subject causing the limiting emotion. Method  84  can be continued as long as needed for user  34  to release the limiting emotions and achieve the freedom state. Processes can also include clean up sessions in which the user is guided by the media material to release many typical limiting emotions to assist the user in achieving a low thought frequency releasing the limiting emotions.  
         [0040]     By observing meter  56  while attempting to release the limiting emotions, user  34  is able to correlate feelings with the release of limiting emotions. Repeating this process reinforces the correlation so that the user learns what it feels like to release and is able to release effectively with or without the meter  56  by having an increased releasing skill. A loop feature allows the user to click on a button to enter a loop session in which the releasing part of an exercise is repeated continuously. The levels of the user&#39;s PTES are indicated to the user and the levels are automatically recorded during these loop sessions for later review. Loop sessions provide a fast way in which to guide a user to let go of limiting emotions surrounding particular thoughts related to particular subjects. The loop session does not require the user to do anything between repetitions which allows them to maintain the desireable state of low thought activity, or the release state. Loop sessions can be included in any process for guiding the user to improve their PTES.  
         [0041]     Computer  54  is also able to record release levels over time to a memory device to enable user  34  to review the releasing progress achieved during a recorded session. Other sessions can be reviewed along side of more recent sessions to illustrate the progress of the user&#39;s releasing ability by recalling the sessions from the memory device.  
         [0042]     System  30  is also used for helping user  34  to determine what particular thoughts or subjects affect the user&#39;s PTES. An example of this use is a method  100 , shown in  FIG. 4 . Method  100  begins at start  102  from which the method proceeds to step  104 . At step  104 , user  34  is exposed to a session of media content  42  which contains multiple stimuli that are presented to user  34  over time. Method  100  proceeds to step  106  where the levels of PTES of user  34  are determined during the session while the user is exposed to the multiple stimuli. Following step  106  method proceeds to step  108  where stimulus is selected from the media content  42  which resulted in negative affects on the PTES, such as high emotional limitations. Method  100  therefore identifies for the user areas which results in the negative affects on the PTES. Method  100  then proceeds to step  110  where the selected stimuli is used in a process to help the user release the negative emotions. Method  100  ends at step  112 .  
         [0043]     In one example, program  70  uses a method  120 ,  FIG. 5 , which includes a questioning pattern called “Advantages/Disadvantages.” In this method, the media file asks user  34  several questions in sequence related to advantages/disadvantages of a “certain subject”, which causes the user to experience negative emotions. Words or phrases of the “certain subject” can be entered into the computer by the user using one of the input devices, such as keyboard  78 , mouse  80  and/or microphone  82  which allows the computer to insert the words or phrases into the questions. System  30  may also have goal documents that have the user&#39;s goal statements displayed along with the questioning patterns about the goal and release level data of the user regarding the goal. As an example, the user may have an issue which relates to control, such as a fear of being late for an airline flight. In this instance, the user would enter something like “fear of being late for a flight” as the “certain subject.” 
         [0044]     Series of questions related to advantages and disadvantage can be alternated until the state of release, or other PTES, is stabilized as low as possible, that is with the greatest amount of release. Method  120 , shown in  FIG. 5 , starts at a start  122  from which it proceeds to step  124  where program  70  asks user  34  “What advantage/disadvantage is it to me to feel limited by the certain subject?” Program  70  then waits for feedback from the user through one of the input devices.  
         [0045]     Program then proceeds to step  126  where program  70  asks user  34  “Does that bring up a wanting approval, wanting control or wanting to be safe feeling?” Program  70  waits for a response from user  34  from the input device and deciphers which one of the feelings the user responds with, such as “control feeling” for instance. Method  120  then proceeds to step  128  where program  70  questions the user based on the response given to step  128  by asking “Can you let that wanting control feeling go?” in this instance. At this point method  120  proceeds to step  130  where sensor device  32  determines the signal of interest to determine the release level of user  34 . The release level is monitored and the media file stops playing when the release level has stabilized at its lowest point. At this time method  120  proceeds to step  132  and the session is complete. When the session is complete, user  34  will feel a sense of freedom regarding the certain subject. If some unwanted emotional residue is left, this same process can be repeated until complete freedom regarding the issue is realized by the user.  
         [0046]     The above method is an example of “polarity releasing” in which an individual is guided to think about positives and negatives about a certain subject or particular issue, until the mind gives up on the negative emotions generated by the thoughts. There are other polarity releasing methods, such as “Likes/Dislikes” and other concepts and methods that help user&#39;s to achieve lower though frequency which may also be used along with a sensor device such as sensor device  32  for the purposes described herein.  
         [0047]     Program  70  can store the history of responses to media on a memory device, and combine multiple iterations of responses to the same media in order to create a chart of improvement for user  34 . Plotting these responses on the same chart using varying colors and dimensional effects demonstrates to user  34  the various PTES reactions over time to the same media stimulus, demonstrating improvement.  
         [0048]     Program  70  can store reaction to live content as well. Live content can consist of listening to a person or audio in the same physical location, or listening to audio streaming over a telecommunications medium like telephone or the Internet, or text communications. Program  70  can send the PTES data from point-to-point using a communication medium like the Internet. With live content flowing in one direction, and PTES data flowing in the other, the deliverer of live content has a powerful new ability to react and change the content immediately, depending on the PTES data reaction of the individual. This deliverer may be a person or a web server application with the ability to understand and react to changing PTES.  
         [0049]     Program  70  can detect the version of the electronic module  40  latently, based on the type of data and number of bytes being sent. This information is used to turn on and off various features in the program  70 , depending on the feature&#39;s availability in the electronic module  40 .  
         [0050]     With certain types of computers and when certain types of wireless links are used, an incompatibility between wireless receiver  48  and computer  54  may occur. This incompatibility between an open host controller interface (OHCI) of the computer  54  and a universal host controller interface (UHCI) chip in the wireless receiver  48  causes a failure of communication. Program  70  has an ability to detect the symptom of this specific incompatibility and report it to the user. The detection scheme looks for a single response to a ping ‘P’ from the wireless receiver  48 , and all future responses to a ping are ignored. Program  70  then displays a modal warning to the user suggesting workarounds for the incompatibility.  
         [0051]     Program  70  detects the disconnecting of wireless link  50  by continually checking for the arrival of new data. If new data stops coming in, it assumes a wireless link failure, and automatically pauses the media being played and recording of PTES data. On detection of new data coming into the computer  54 , the program  70  automatically resumes the media and recording.  
         [0052]     Program  70  can create exercises and set goals for specific PTES levels. For example, it asks the user to set a target level of PTES and continues indefinitely until the user has reached that goal. Program  70  can also store reactions during numerous other activities. These other activities include but are not limited to telephone conversations, meetings, chores, meditation, and organizing. In addition, program  70  can allow users to customize their sessions by selecting audio, title, and length of session.  
         [0053]     Other computing devices, which can include processor based computing devices, (not shown) can be used with sensor device  32  to play media material  66  and display or otherwise indicate the PTES. These devices may be connected to the sensor device  32  utilizing an integrated wireless receiver rather than the separate wireless receiver  48  which plugs into the port of the computer. These devices are more portable than computer  54  which allows the user to monitor the level PTES throughout the day or night which allows the user to liberate the subconscious mind more rapidly. These computing devices can include a camera with an audio recorder for storing and transmitting data to the receiver to store incidents of reactivity on a memory device for review at a later time. These computing devices can also upload reactivity incidents, intensity of these incidents and/or audio-video recordings of these incidents into computer  54  where the Attachment and Aversions process or other process can be used to permanently reduce or eliminate reactivity regarding these incidents.  
         [0054]     One example of sensor device  32  is shown in  FIGS. 6 and 7 . Sensor device  32  includes sensor electrode  36 , reference electrode  38  and electronics module  40 . The electronics module  40  amplifies the signal of interest by 1,000 to 100,000 times while at the same time insuring that 60 Hz noise is not amplified at any point. Electronics module  40  isolates the signal of interest from undesired electrical activity.  
         [0055]     Sensor device  32  in the present example also includes wireless receiver  48  which receives the signal of interest from the electronics module over wireless link  50  and communicates the signal of interest to computer  54 . In the present example, wireless link  50  uses radiofrequency energy; however other wireless technologies may also be used, such as infrared. Using a wireless connection eliminates the need for wires to be connected between the sensor device  32  and computer  54  which electrically isolates sensor device  32  from computer  54 .  
         [0056]     Reference electrode  38  is connected to a clip  148  which is used for attaching reference electrode  38  to an ear  150  of user  34 , in the present example. Sensor electrode  36  includes a snap or other spring loaded device for attaching sensor electrode  36  to headband  42 . Headband  42  also includes a pocket for housing electronics module  40  at a position at the user&#39;s temple. Headband  42  is one example of an elastic band which is used for holding the sensor electrode and/or the electronics module  40 , another types of elastic bands which provide the same function could also be used, including having the elastic band form a portion of a hat.  
         [0057]     Other types of mounting devices, in addition to the elastic bands, can also be used for holding the sensor electrode against the skin of the user. A holding force holding the sensor electrode against the skin of the user can be in the range of 1 to 4 oz. The holding force can be, for instance, 1.5 oz.  
         [0058]     In another example of a mounting device involves a frame that is similar to an eyeglass frame, which holds the sensor electrode against the skin of the user. The frame can also be used for supporting electronics module  40 . The frame is worn by user  34  in a way which is supported by the ears and bridge of the nose of the user, where the sensor electrode  36  contacts the skin of the user.  
         [0059]     Sensor electrode  36  and reference electrode  38  include conductive surface  152  and  154 , respectively, that are used for placing in contact with the skin of the user at points where the measurements are to be made. In the present example, the conductive surfaces are composed of a non-reactive material, such as copper, gold, conductive rubber or conductive plastic. Conductive surface  152  of sensor electrode  36  may have a surface area of approximately ½ square inch. The conductive surfaces  152  are used to directly contact the skin of the user without having to specially prepare the skin and without having to use a substance to reduce a contact resistance found between the skin and the conductive surfaces.  
         [0060]     Sensor device  32  works with contact resistances as high as 500,000 ohms which allows the device to work with conductive surfaces in direct contact with skin that is not specially prepared. In contrast, special skin preparation and conductive gels or other substances are used with prior EEG electrodes to reduce the contact resistances to around 20,000 ohms or less. One consequence of dealing with higher contact resistance is that noise may be coupled into the measurement. The noise comes from lights and other equipment connected to 60 Hz power, and also from friction of any object moving through the air which creates static electricity. The amplitude of the noise is proportional to the distance between the electronics module  40  and the reference electrode  38 . In the present example, by placing the electronics module over the temple area, right above the ear and connecting the reference electrode to the ear, the sensor device  32  does not pick up the noise, or is substantially unaffected by the noise. By positioning the electronics module in the same physical space with the reference electrode and capacitively coupling the electronics module with the reference electrode ensures that a local reference potential  144  in the electronics module and the ear are practically identical in potential. Reference electrode  38  is electrically connected to local reference potential  144  used in a power source  158  for the sensor device  32 .  
         [0061]     Power source  158  provides power  146  to electronic components in the module over power conductors. Power source  158  provides the sensor device  32  with reference potential  144  at 0 volts as well as positive and negative source voltages, −VCC and +VCC. Power source  158  makes use of a charge pump for generating the source voltages at a level which is suitable for the electronics module.  
         [0062]     Power source is connected to the other components in the module  40  though a switch  156 . Power source  158  can include a timer circuit which causes electronics module  40  to be powered for a certain time before power is disconnected. This feature conserves power for instances where user  34  accidentally leaves the power to electronics module  40  turned on. The power  146  is referenced locally to measurements and does not have any reference connection to an external ground system since sensor circuit  32  uses wireless link  50 .  
         [0063]     Sensor electrode  36  is placed in contact with the skin of the user at a point where the electrical activity in the brain is to be sensed or measured. Reference electrode  38  is placed in contact with the skin at a point a small distance away from the point where the sensor electrode is placed. In the present example, this distance is 4 inches, although the distance may be as much as about 8 inches. Longer lengths may add noise to the system since the amplitude of the noise is proportional to the distance between the electronics module and the reference electrode. Electronics module  40  is placed in close proximity to the reference electrode  38 . This causes the electronics module  40  to be in the same of electrical and magnetic environment is the reference electrode  38  and electronics module  40  is connected capacitively and through mutual inductance to reference electrode  38 . Reference electrode  38  and amplifier  168  are coupled together into the noise environment, and sensor electrode  36  measures the signal of interest a short distance away from the reference electrode to reduce or eliminate the influence of noise on sensor device  32 . Reference electrode  38  is connected to the 0V in the power source  158  with a conductor  166 .  
         [0064]     Sensor electrode  36  senses electrical activity in the user&#39;s brain and generates a voltage signal  160  related thereto which is the potential of the electrical activity at the point where the sensor electrode  36  contacts the user&#39;s skin relative to the local reference potential  144 . Voltage signal  160  is communicated from the electrode  36  to electronics module  40  over conductor  162 . Conductors  162  and  166  are connected to electrodes  36  and  38  in such a way that there is no solder on conductive surfaces  152  and  154 . Conductor  162  is as short as practical, and in the present example is approximately 3 inches long. When sensor device  32  is used, conductor  162  is held a distance away from user  34  so that conductor  162  does not couple signals to or from user  34 . In the present example, conductor  162  is held at a distance of approximately ½″ from user  34 . No other wires, optical fibers or other types of extensions extend from the electronics module  40 , other than the conductors  162  and  166  extending between module  40  and electrodes  36  and  38 , since these types of structure tend to pick up electronic noise.  
         [0065]     The electronics module  40  measures or determines electrical activity, which includes the signal of interest and other electrical activity unrelated to the signal of interest which is undesired. Electronics module  40  uses a single ended amplifier  168 , ( FIGS. 7 and 8 ), which is closely coupled to noise in the environment of the measurement with the reference electrode  38 . The single ended amplifier  168  provides a gain of 2 for frequencies up to 12 Hz, which includes electrical activity in the Alpha and Theta bands, and a gain of less than 1 for frequencies 60 Hz and above, including harmonics of 60 Hz.  
         [0066]     Amplifier  168 ,  FIGS. 8 and 11 , receives the voltage signal  160  from electrode  36  and power  146  from power source  158 . Single ended amplifier  168  generates an output signal  174  which is proportional to voltage signal  160 . Output signal  174  contains the signal of interest. In the present example, voltage signal  160  is supplied on conductor  162  to a resistor  170  which is connected to non-inverting input of high impedance, low power op amp  172 . Output signal  174  is used as feedback to the inverting input of op amp  172  through resistor  176  and capacitor  178  which are connected in parallel. The inverting input of op amp  172  is also connected to reference voltage  144  through a resistor  180 .  
         [0067]     Amplifier  168  is connected to a three-stage sensor filter  182  with an output conductor  184  which carries output signal  174 . The electrical activity or voltage signal  160  is amplified by each of the stages  168  and  182  while undesired signals, such as those 60 Hz and above, are attenuated by each of the stages. Three-stage sensor filter has three stages  206   a,    206   b  and  206   c  each having the same design to provide a bandpass filter function which allows signals between 1.2 and 12 Hz to pass with a gain of 5 while attenuating signal lower and higher than these frequencies. The bandpass filter function allows signals in the Alpha and Theta bands to pass while attenuating noise such as 60 Hz and harmonics of the 60 Hz. The three stage sensor filter  182  removes offsets in the signal that are due to biases and offsets in the parts. Each of the three stages is connected to source voltage  146  and reference voltage  144 . Each of the three stages generates an output signal  186   a,    186   b  and  186   c  on an output conductor  188   a,    186   b  and  188   c,  respectively.  
         [0068]     In the first stage  206   a,    FIGS. 9 and 11 , of three-stage sensor filter  182 , output signal  174  is supplied to a non-inverting input of a first stage op-amp  190   a  through a resistor  192   a  and capacitor  194   a.  A capacitor  196   a  and another resistor  198   a  are connected between the non-inverting input and reference voltage  144 . Feedback of the output signal  186   a  from the first stage is connected to the inverting input of op amp  190   a  through a resistor  200   a  and a capacitor  202   a  which are connected in parallel. The inverting input of op amp  190   a  is also connected to reference voltage  144  through resistor  204   a.    
         [0069]     Second and third stages  206   b  and  206   c,  respectively, are arranged in series with first stage  206   a.  First stage output signal  186   a  is supplied to second stage  206   b  through resistor  192   b  and capacitor  194   b  to the non-inverting input of op-amp  190   b.  Second stage output signal  186   b  is supplied to third stage  206   c  through resistor  192   c  and capacitor  194   c.  Resistor  198   b  and capacitor  196   b  are connected between the non-inverting input of op-amp  190   b  and reference potential  144 , and resistor  198   c  and capacitor  196   c  are connected between the non-inverting input of op-amp  190   c  and reference potential  144 . Feedback from output conductor  188   b  to the inverting input of op-amp  190   b  is through resistor  200   b  and capacitor  202   b  and the inverting input of op-amp  190   b  is also connected to reference potential  144  with resistor  204   b.  Feedback from output conductor  188   c  to the inverting input of op-amp  190   c  is through resistor  200   c  and capacitor  202   c  and the inverting input of op-amp  190   c  is also connected to reference potential  144  with resistor  204   c.    
         [0070]     Three stage sensor filter  182  is connected to an RC filter  208 ,  FIGS. 10 and 11 , with the output conductor  188   c  which carries the output signal  186   c  from third stage  206   c  of three stage sensor filter  182 ,  FIG. 7 . RC filter  208  includes a resistor  210  which is connected in series to an output conductor  216 , and a capacitor  212  which connects between reference potential  144  and output conductor  216 . RC filter serves as a low pass filter to further filter out frequencies above 12 Hz. RC filter  208  produces a filter signal  214  on output conductor  216 . RC filter  208  is connected to an analog to digital (A/D) converter  218 ,  FIG. 7 .  
         [0071]     A/D converter  218  converts the analog filter signal  214  from the RC filter to a digital signal  220  by sampling the analog filter signal  214  at a sample rate that is a multiple of 60 Hz. In the present example the sample rate is 9600 samples per second. Digital signal  220  is carried to a digital processor  224  on an output conductor  222 .  
         [0072]     Digital processor  224 ,  FIGS. 7 and 12  provides additional gain, removal of 60 Hz noise, and attenuation of high frequency data. Digital processor  224  many be implemented in software operating on a computing device. Digital processor  224  includes a notch filter  230 ,  FIG. 12  which sums 160 data points of digital signal  220  at a time to produce a 60 Hz data stream that is free from any information at 60 Hz. Following notch filter  230  is an error checker  232 . Error checker  232 , removes data points that are out of range from the 60 Hz data stream. These out of range data points are either erroneous data or they are cause by some external source other than brain activity.  
         [0073]     After error checker  232 , digital processor  224  transforms the data stream using a discreet Fourier transformer  234 . While prior EEG systems use band pass filters to select out the Alpha and Theta frequencies, among others, these filters are limited to processing and selecting out continuous periodic functions. By using a Fourier transform, digital processor  224  is able to identify randomly spaced events. Each event has energy in all frequencies, but shorter events will have more energy in higher frequencies and longer events will have more energy in lower frequencies. By looking at the difference between the energy in Alpha and Theta frequencies, the system is able to identify the predominance of longer or shorter events. The difference is then scaled by the total energy in the bands. This causes the output to be based on the type of energy and removes anything tied to amount of energy.  
         [0074]     The Fourier transformer  234  creates a spectrum signal that separates the energy into bins  236   a  to  236   o  which each have a different width of frequency. In one example, the spectrum signal has 30 samples and separates the energy spectrum into 2 Hz wide bins; in another example, the spectrum signal has 60 samples and separates the bins into 1 Hz wide bins. Bins  236  are added to create energy signals in certain bands. In the present example, bins  236  between 4 and 8 Hz are passed to a summer  238  which sums these bins to create a Theta band energy signal  240 ; and bins between 8 and 12 Hz are passed to a summer  242  which sums these bins to create an Alpha band energy signal  244 .  
         [0075]     In the present example, the Alpha and Theta band energy signals  240  and  244  passed to a calculator  246  which calculates (Theta−Alpha)/Theta+Alpha) and produces an output signal  226  on a conductor  228  as a result.  
         [0076]     Output signal  226 ,  FIG. 7 , is passed to wireless transmitter  46  which transmits the output signal  226  to wireless receiver  48  over wireless link  50 . In the present example, output signal  226  is the signal of interest which is passed to computer  54  through port  52  and which is used by the computer to produce the PTES for display in meter  56 .  
         [0077]     Computer  54  may provide additional processing of output signal  226  in some instances. In the example using the Release Technique, the computer  54  manipulates output signal  226  to determine relative amounts of Alpha and Theta band signals in the output signal to determine levels of release experienced by user  34 .  
         [0078]     A sensor device utilizing the above described principles and feature can be used for determining electrical activity in other tissue of the user in addition to the brain tissue just described, such as electrical activity in muscle and heart tissue. In these instances, the sensor electrode is positioned on the skin at the point where the electrical activity is to be measured and the reference electrode and electronics module are positioned nearby with the reference electrode attached to a point near the sensor electrode. The electronics module, in these instances, includes amplification and filtering to isolate the frequencies of the muscle or heart electrical activity while filtering out other frequencies.  
         [0079]     While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.