WO2008109699A2

WO2008109699A2 - Electrode headset

Info

Publication number: WO2008109699A2
Application number: PCT/US2008/055954
Authority: WO
Inventors: Samuel Dean Trewartha; Nathan John Burke; Alan Cc Lee; Peter Noel Cooper; Lori Ann Washbon; Stephen Sapiro; Emir Delic; Nam Hoai Do; Geoffrey Ross Mackellar
Original assignee: Emotiv Systems Pty Ltd
Priority date: 2007-03-06
Filing date: 2008-03-05
Publication date: 2008-09-12
Also published as: WO2008109699A3

Abstract

An electrode headset and electrodes that can be mounted therein are described. The electrode headset is formed from substantially rigid components including some flexibility to snugly embrace a variety of head shapes and sizes, while providing reliable positioning of electrodes according to an electrode placement scheme on a subject's head.

Description

ELECTRODE HEADSET

TECHNICAL FIELD

[0001] This invention relates to an apparatus that can include one or more electrodes.

BACKGROUND

[0002] An electrode system to capture bioelectric signals, such as electroencephalograph (EEG) signals, from a subject generally should address various requirements including safety needs, cost, power consumption, performance, ease of use and subject comfort. In a non-clinical application the relative importance of these factors may be somewhat different to that in a clinical application. For example, in a clinical application the electrodes are applied by a relatively skilled technician, whereas in nonclinical application the electrodes are more likely to be applied by a person with no training or knowledge of correct application or placement of the electrodes. Convenience and subject comfort are also generally more important in a non-clinical application. A patient in a clinical situation is more likely to be tolerant of some level of discomfort or inconvenience when testing and calibrating electrodes than a person in a non-clinical setting.

[0003] Conventional electrodes include passive electrodes and active electrodes.

Passive electrodes follow a simple design principle and include a metal disc with a connecting wire to electronic circuitry. The simplicity makes this type of electrode low cost, although these electrodes are prone to noise and can require numerous noise canceling techniques to achieve satisfactory performance. One noise canceling technique, to minimize impedance at the skin-electrode interface and to minimize interference, involves conditioning the skin where the electrode is to be applied. Typically a scalpel is used to scrape the skin and a liquid disinfectant solution is used to clean the area. Another approach to minimizing impedance and interference at the skin-electrode interface is to fill any gap at the interface with a conductive gel or saline solution that can regulate the impedance.

[0004] Active electrodes include resistive and capacitive active electrodes.

Resistive active electrodes use a direct current path between subject's skin and the input of an operational amplifier to acquire a signal. Capacitive active electrodes do not make contact with the subject's skin, but have a capacitive link between subject's skin and the electrode.

[0005] Active electrodes apply the principle of impedance transformation at the electrode site to improve signal acquisition performance. The electrode plate can be connected to a buffer circuit made from a high input impedance op-amp. The large input impedance of the op-amp can make the impedance at the skin-electrode interface insignificant and stabilize the skin-electrode interface, resulting in improved recording even without use of gel or saline solution. The addition of gel or saline can improve performance even more over passive electrodes. Another advantage of active over passive electrodes is that the impedance of wires connecting active electrodes to an acquisition device can be close to zero, effectively combating interference that can be introduced at this stage. However, the improvements in performance come at the expense of price, as active electrodes require at least one op-amp per electrode, increased power consumption and introduce the need for extra wires to deliver power to the active electrodes. Additionally, because active electrodes are more sensitive than passive electrodes, they can be extremely sensitive to movement, adding artifacts into the acquired signal. Thus, care is needed to ensure firm and stable contact between active electrodes and the skin. If active electrodes are used without a gel or saline solution, it can be difficult to get successful performance, particularly at locations on the head covered with hair.

[0006] Capacitive active electrodes are a fairly recent development in EEG signal acquisition. These electrodes do not require physical contact to be made between the subject and the electrode plate to acquire a signal. Instead, the electrode plate is maintained a predetermined distance away from the head by a highly dielectric material and signals are detected via fluctuations in capacitance.

[0007] A conventional apparatus for applying electrodes to a subject's head includes a flexible cap that covers the subject's entire scalp and includes a strap beneath the chin, so that the cap may be snugly secured to the subject's head. This type of apparatus is typically used in a clinical setting and can include over 100 electrodes for some applications.

SUMMARY

[0008] This invention relates to an apparatus that can include one or more electrodes. In general, in one aspect, the invention features an electrode headset. The electrode headset includes a left band, a right band and a rear band. The left band is configured to position along the left side of a subject's head and extend from approximately the rear center to the front center of the subject's head. The left band includes one or more electrode mounts configured to mount one or more electrodes. The right band is configured to position along the right side of a subject's head and extend from approximately the rear center to the front center of the subject's head. The right band includes one or more electrode mounts configured to mount one or more electrodes. The rear band is attached at a first end to the left band and at a second end to the right band. The rear band is configured to extend across the rear of the subject's head. [0009] Implementations of the invention can realize one or more of the following advantages. The electrode headset described herein can provide suitable electrode placement in an easy to don apparatus. A subject who is untrained as to electrode placement can easily use the electrode headset without the assistance of a trained technician. The electrode headset can apply the necessary pressure to sufficiently press each electrode to the subject's scalp to provide a suitably strong and clear signal, yet is comfortable for the subject wearing the headset.

[0010] The rigid construction not only ensures that the electrodes mounted therein are properly positioned relative to the subject's head and in accordance with a desired electrode placement scheme, but can ensure that the electrodes will remain in a substantially stable position throughout use. The ear notches included in the left and right bands facilitate proper placement on the subject's head. The good contact provided at the electrode-scalp interface can allow noise to settle relatively quickly, and a clean signal can be achieved relatively quickly as compared to prior art systems. [0011] The configuration of the rear portions of the left and right bands assists in maintaining the desired shape of the left and right band, thereby providing predictable and accurate electrode placement.

[0012] The electrode mounts are configured to allow individual electrodes to be easily mounted or replaced, independent of other electrodes mounted within the headset. Accordingly, if a single electrode malfunctions, the individual electrode can be replaced, rather than having to discard the entire electrode headset including all electrodes mounted therein. Additionally, the headset is configured to accommodate a range of head shapes and sizes. [0013] The electrodes described herein are particularly suitable to a non-clinical application, where the subject's comfort and ease of use are important factors, although they can be used in a clinical application as well. The embodiments of dry electrodes described are advantageous for using the electrode headsets described herein, as they can provide a strong and clear signal even through a subject's hair and without use of a wetting fluid. The gimbaled contact can allow a suitable contact to be maintained at the electrode-subject interface, while permitting some relative movement between the electrode headset and the subject's head. The embodiments of wet electrodes described are also suitable for use with the electrode headsets described herein. The wetted conductive pad works well with a subject's hair and leaves the hair only slightly damp upon removal of the electrodes.

[0014] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

[0015] FIG. 1 is a schematic representation of a signal acquisition system.

[0016] FIG. 2 is a schematic representation of a 10-20 electrode placement system.

[0017] FIGS. 3A-E show an implementation of an electrode headset.

[0018] FIG. 4 shows an electrode placement scheme.

[0019] FIGS. 5A-E show an implementation of an electrode.

[0020] FIGS. 6A-C show alternative implementations of contact elements included in the electrode shown in FIGS. 5A-E.

[0021] FIGS. 7A-B show an alternative electrode.

[0022] FIGS. 8A-B show an alternative electrode.

[0023] FIG. 9 is a schematic representation of a circuit diagram.

[0024] FIGS. 10A-B show an implementation of an electrode housing.

[0025] FIGS. 1 IA-D shown an alternative electrode and electrode mount.

[0026] Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0027] An electrode headset configured to position one or more electrodes mounted in the headset within a predetermined target region on a subject's head and in accordance with a desired electrode placement scheme is described. The electrode headset is formed from a hard material. That is, the electrode headset is formed from a substantially rigid material including at least some flexibility so as to comfortably embrace the subject's head, while applying sufficient pressure between the one more electrodes mounted therein and the subject's head.

[0028] The one or more electrodes can be configured as a dry electrode or a wet electrode, where a dry electrode can obtain a signal without a conductive and typically wet material between the electrode and the subject's skin, and a wet material does require such a conductive material. The electrode headset does not cover the entire upper surface of the subject's head, and can be configured to reduce the region of the head in contact with the electrode headset, while being sufficiently comfortable and acceptable in nonclinical environment.

[0029] FIG. 1 is a schematic representation of a system for detecting and classifying mental states. The system is one example of a system that can employ the electrode headset and/or electrodes described herein. It should be understood however that other systems can use the headset and electrodes described, and the system shown in FIG. 1 is but one implementation for illustrative purposes.

[0030] The system includes a headset 102 configured to position one or more electrodes on a subject's head. The system is configured to operate generally as described in United States Patent Application Serial No. 11/531,238, filed September 12, 2006, entitled "Method and System for Detecting and Classifying the Mental State of a Subject", and United States Patent Application Serial No. 11/531,265, filed September 12, 2006, entitled "Detection Of And Interaction Using Mental States", both of which are incorporated herein in their entirety.

[0031] In one implementation, the one or more electrodes include signal acquisition electrodes configured to detect signals such as electroencephalograph (EEG) signals, electro-oculograph (EOG) signals, or similar electrical potentials in the body. Signals detected by the electrodes in the headset 102 are fed through a sensor interface 104 and digitized by an analog to digital converter 106. Digitized samples of the signal captured by each of the electrodes can be stored during operation of the system 100 in a data buffer 108 for subsequent processing.

[0032] The system 100 further includes a processing system 109 including a digital signal processor 112, a co-processing device 110 and associated memory for storing a series of instructions, otherwise known as a computer program or a computer control logic, to cause the processing system 109 to perform desired functional steps. Notably, the memory includes a series of instructions defining at least one algorithm 114 for detecting and classifying a predetermined type of mental state. Mental states determined by such a classification can include, but are not limited to: emotions; a desire, intention or conscious effort to perform an action such as performing an interaction with a real or virtual object; and a mental state corresponding to an actual movement made by the subject, such as a facial expression, blink, gesture etc. Upon detection of each predefined type of mental state, a corresponding control signal is transmitted to an input/output interface 116. From the input/output interface, the control sign can be transmitted via a wireless transmission device 118 or a wired link (not shown) to a platform 120 for use as a control input by a gaming application, program, simulator or other application.

[0033] In this embodiment, the processing of signals, e.g. the detection or classification of mental states is performed in software and the series of instructions is stored in the memory. In another embodiment, signal processing can be implemented primarily in hardware using, for example, hardware components such as an Application Specific Integrated Circuit (ASIC). Implementation of the hardware state machine so as to perform these functions will be apparent to persons skilled in the relevant art. In yet other embodiments signal processing can be implemented using a combination of both software and hardware.

[0034] In this embodiment the processing system 109 is arranged as separate to the platform 120, however the system 100 can be arranged in a variety of configurations that split the signal processing functionality between various groups of hardware, for example in some embodiments, at least part of the signal processing functionality can be implemented in electronics mounted on the headset 102 or in the platform 120. For example, the apparatus can include a headset assembly that includes the headset, a MUX, A/D converter(s) before or after the MUX, a wireless transmission device, a battery for power supply, and a microcontroller to control battery use, send data from the MUX or A/D converter to the wireless chip, and the like. The apparatus can also include a separate processor unit that includes a wireless receiver to receive data from the headset assembly, and the processing system, e.g., the digital signal processor and the coprocessor. The processor unit can be connected to the platform by a wired or wireless connection. As another example, the apparatus can include a head set assembly as described above, the platform can include a wireless receiver to receive data from the headset assembly, and a digital signal processor dedicated to detection of mental states can be integrated directly into the platform. As yet another example, the apparatus can include a head set assembly as described above, the platform can include a wireless receiver to receive data from the headset assembly, and the mental state detection algorithms are performed in the platform by the same processor, e.g., a general purpose digital processor, that executes the application, programs, simulators or the like. [0035] FIG. 2 shows a scheme 122 of electrode placement corresponding to the international 10-20 electrode placement system (the "10-20 system"). The 10-20 system is based on the relationship between the location of an electrode and the underlying area of cerebral cortex. Each point on the electrode placement scheme 122 indicates a possible scalp electrode position. Each position is indicated by a letter to identify a brain lobe and a number or other letter to identify a hemisphere location. The letters F, T, C, P, and O stand for the frontal, temporal, central, parietal and occipital lobes of the brain. Even numbers refer to the right hemisphere and odd numbers refer to the left hemisphere. The letter Z refers to an electrode placed on the mid-line. The mid-line is a line along the scalp on the sagittal plane originating at the nasion and ending at the inion at the back of the head. The "10" and "20" refer to percentages of the mid- line division. The mid-line is divided into 7 positions, namely, Nasion, Fpz, Fz, Cz, Pz, Oz and Inion, and the angular intervals between adjacent positions are set at 10%, 20%, 20%, 20%, 20% and 10% of the mid-line length respectively. [0036] Electrode Headset

Referring to FIGS. 3A-E, an implementation of an electrode headset 300 is shown. In this implementation, the electrode headset 300 is formed from a hard yet flexible material. FIG. 3A shows a front perspective view and FIG. 3B shows a rear perspective view. FIG. 3E shows a rear view of the electrode headset 300 worn on a subject's head 302. FIGS. 3C and 3D show top and side views respectively. [0037] In this implementation, the electrode headset 300 includes three bands: a left band 304, a right band 306 and a rear band 308. The left band 304 is connected to the rear band 308 by a connector 310. The right band 306 is connected to the rear band by a connector 312. In this implementation, the connectors 310 and 312 are configured to allow relative pivotable movement between the rear band 308 and the left and right bands 304, 306. That is, the rear band 308 can pivot relative to the left and right bands 304, 306 about a horizontal axis 301 in the coronal plane. The left and right bands 304, 306 are not directly connected to one another. [0038] Referring particularly to FIGS. 3D and 3E, each of the left and right bands includes an ear notch configured to position about the subject's ear. For example, in FIG. 3D, a left side view of the electrode headset 300 is shown and the left band 304 includes an ear notch 314. Referring to FIG. 3E, the right band 306 is shown and includes an ear notch 316. The right ear notch 316 is positioned about the subject's right ear 318 when worn by the subject. The left and right ear notches 314, 316 serve to both assist in holding the electrode headset 300 in place when worn, but also serve to facilitate proper positioning of the electrode headset 300 relative to the subject's head 302. [0039] Each of the left and right bands 304, 306 include mounting features to mount one or more electrodes. In one implementation, the electrode mounts are apertures configured to receive and mount an electrode therein. However, it should be noted that other configurations of electrode mounts can be used. For example, an electrode can be mounted to the electrode headset using a clamp, screw or other suitable connection mechanism and/or configuration.

[0040] In the implementation shown, sixteen electrodes 320-350 are shown included in the electrode headset 300. When in use, it is important that the electrodes 320-350 are properly positioned relative to the subject's head 302 to conform to the desired electrode placement scheme. In this example, the desired electrode placement scheme 400 is illustrated in FIG. 4. The reference numerals 320-350 indicating the electrodes included in the electrode headset 300 are repeated on FIG. 4 to show the correspondence of each electrode to the electrode placement scheme. The electrode positions shown in the electrode placement scheme 400 are approximate and the scheme 400 shown is but one example. Electrode placement schemes with more or fewer electrodes in different positions can be used. If a different electrode placement scheme is desired, the electrode mounts included in the left and right bands 304, 306 can be positioned differently accordingly to the different electrode placement scheme. Additionally, if required to satisfy a different electrode placement scheme, the left and right bands can have different configurations that shown in the implementation illustrated. [0041] Referring again to the example shown, in order to achieve positioning of the electrodes 320-350 according to the desired electrode placement scheme 400 on the subject's head 302, it is important the subject properly position the electrode headset 300 on his or her head. By including the ear notches 314, 316 on each of the left and right bands 304, 306, the subject can easily position the electrode headset 300 such that it fits comfortably over the subject's ears. By doing so, the subject has also properly positioned the electrode headset 300 to achieve the desired electrode placement scheme 400. [0042] The rear band 308 is positioned across the rear of the subject's head 302 and extends from the left ear to the right ear when worn. The rear band 308 is configured to hold the left and right bands 304, 306 snugly to the subject's head 302 and provide a tight yet comfortable fit.

[0043] Each of the left and right bands 304, 306 includes a rear portion 305 and

307 respectively having a sideways V-shaped configuration. That is, the rear portion folds back on itself from the center point of the rear toward the ear. The configuration of the rear portion of the left and right bands provides accurate electrode placement, When worn by the subject, the V-shaped rear portion tends to maintain its relative shape and therefore provide predictable and accurate electrode placement. [0044] Additionally, the rear band 308 can house electronic circuitry that is electrically connected to each of the electrodes 320-350 and optionally can house a battery to provide electricity to said electronic circuitry. Each electrode 320-350 is electrically connected to the electronic circuitry housed within the rear band 306. The electronic circuitry can be configured to receive signals from the electrodes 320-350 and provide an output to a processor. The electronic circuitry may also be configured to perform at least some processing of the signals received from the electrodes. For example, referring again to FIG. 1, in some implementations the electronic circuitry mounted on or housed within the electrode headset 300 can be configured to perform some or all of the functions of the sensor interface 104, A/D converter 106, data buffer 108, processing system 109 and/or platform 120.

[0045] In one implementation, the electronic circuitry is housed within the rear band 306 and electrically connected to each electrode mounted therein by one or more wires extending between the electronic circuitry and each electrode. In another embodiment, the physical components electrically connecting the electrodes to the electronic circuitry, e.g., the wires, are embedded within the material forming the components of the electrode headset 300 and can be invisible and inaccessible to a user. This embodiment provides a sleeker, more compact design and functions to protect the wires extending between the electrodes and the electronic circuitry. For example, if the electrode headset 300 is formed from plastic components, wires connecting the electrodes to the electronic circuitry can be embedded within the plastic. Additionally, the electronic circuitry itself can be embedded within the plastic and made invisible to a user, for example, using a flexible printed circuit board (PCB).

[0046] In the implementation shown, the rear band 308 can swivel relative to the left and right bands 304, 306 about the connectors 310 and 312. In another implementation, each of the left and right bands can be formed from a rear and a front component, where the rear and front components are connected to one another in the region of the ear notches 314, 316. The rear and front components can be connected to one another with a connector permitting relative movement between the components, for example, a swivel connector. Providing the ability for the components to move can, in some implementations, allow the electrode headset 300 to fold into a lower profile configuration when not in use, to facilitate packaging or storage. Additionally, providing relative movement between two or more of the components can provide for adjustments in fit or position to compensate for varying head shapes and sizes. [0047] Electrode Placement Scheme

Referring to FIG. 4, an illustrative electrode placement scheme 400 for a subset of the electrode placement positions included in the 10-20 system is shown. The subset of electrode placement positions corresponds to electrode mounts that can be included on the electrode headset 300. In the electrode placement scheme 400 shown, the electrodes 320-350 included in the electrode headset 300 are positioned to mount electrodes to gather information about the subject's facial expression (i.e., facial muscle movement), emotions and cognitive information. The electrode headset 300 can be used with electrodes mounted in all or a subset of the electrode positions. One or more electrodes can be a reference electrode, i.e., an electrode to which signals received from other electrodes can be compared. In one implementation, the reference electrode can bias the subject's body to a known reference potential, e.g., one half of the analog supply voltage. Driven Left Leg (DLL) circuitry can compensate for external effects and keep the subject's body potential stable. The EEG signals can be referenced to the body potential supped by the reference electrode. [0048] Electrode Headset Materials

In one implementation, the electrode headset 300 is substantially formed from a polystyrene material, although other materials can be used including nylon. Optionally, some regions of the electrode headset 300 can be reinforced with an additional layer or extra thickness of the same or a different material, for example, a polystyrene reinforcement layer. Optionally, pads can be included in some regions such that the pads make contact with the subject's head and resist slippage against the subject's head and/or to improve the fit and subject's comfort. In one implementation the pads are formed from silicon.

[0049] The electrode headset 300 described above can be formed from a material exhibiting one or more of the following qualities: highly durable and tough; providing a high degree of functionality; good impact strength and capable of withstanding or resisting moisture and temperature.

[0050] One example of such a material is SLS (Selective Laser Sintering) Cap

Tuff General Purpose 25% Glass Filled Nylon 11 Material available from Envizage, a division of Concentric Asia Pacific, Melbourne, Australia. The SLS Cap Tuff material has a flexural modulus of 2020 Mpa, a tensile modulus of 2460 Mpa and a tensile strength of 38 Mpa. Other materials exhibiting one or more of the qualities described above can be used.

[0051] In another implementation, the Watershed™ 7120 material available from

DSM Somos of New Castle, DE, can be used. The Watershed 7120 material is a durable, strong, semi-transparent, water-resistant resin. Other materials can be used and the ones described are examples.

[0052] Electrode

Referring to FIGS. 5A-F, one implementation of an electrode 570 that can be mounted within the electrode headset 300, or used independent of the electrode headset 300 for a different application, is shown. In this implementation, the electrode 570 is configured as an active resistive electrode. The electrode includes a housing 572, which for illustrative purposes is shown as transparent, including a substantially tubular body 571 and a cap 586. Referring particularly to FIG. 5B, the electrode 570 is shown with the housing 572 removed for illustrative purposes. The electrode 570 includes a printed circuit board (PCB) 584 attached to an electrode plate 582. The PCB 584 includes electronic circuit components forming a sensor circuit. One or more wires can connect to the sensor circuit to provide power to the circuit and permit signals to be sent from the sensor circuit to a signal acquisition system, which can be mounted or housed within the electrode headset 300 or located external to the electrode headset 300. [0053] A flexure element 580 is attached to the underside of the electrode plate

582 and connects on a second end to a gimbaled contact 574. In this implementation the flexure element 580 is a spring, although in other implementations the flexure element can be configured differently. The gimbaled contact 574 includes an upper portion 578 forming a gimbaled connection to the housing 572. A lower portion of the gimbaled contact provides one or more contact elements 576 configured to contact the subject's skin. The flexure element 580 is formed from a conductive material, thereby electrically connecting the gimbaled contact 574 to the electrode plate 582. A conductive path is thereby provided from the subject's skin to the electrode plate 582 via the gimbaled contact 574 and flexure element 580. Bioelectrical potentials from the subject's skin detected by the gimbaled contact 574 are thereby provided to the electrode plate 582 and ultimately to the sensor circuit included in the PCB 584.

[0054] The flexure element 580 can be made from a conductive material, for example, a metal. The electrode plate 582 can be made from a metal or metal alloy and in one implementation is formed from silver-silver-chloride (AgAgCl). [0055] In one implementation, the electrode 570 can function as a dry electrode

570, meaning a sufficient signal can be received at the gimbaled contact 574 and transmitted to the sensor circuit without using a wet, conductive material, i.e., a conductive gel, fluid or wetted contact pad, at the electrode-skin interface; the contact elements 576 can make direct contact with the subject's skin. In another implementation, to improve signal strength, the electrode 570 can function as a wet electrode. That is, the electrode 570 can be used in conjunction with a wet conductive material, such as a conductive gel or fluid or a wetted contact pad. In one particular implementation, a contact pad formed from a material suitable to retain a conductive fluid, e.g. , a felt pad, and wetted with the conductive fluid can be placed between the contact elements 576 and the subject's skin.

[0056] Various embodiments of the contact elements 576 can be used. In an implementation where the electrodes will be used on a subject's head, preferably the contact elements 576 are formed as elongated protrusions as shown, to provide sufficient contact with the subject's skin through the subject's hair. Referring to FIGS. 6A-C, alternative implementations of the contact elements are shown. In FIG. 6 A, the contact elements 587 are substantially cylindrical with rounded ends. In FIG. 6B, the contact elements 588 are substantially triangular shaped. In FIG. 6C, the contact elements 590 are substantially cylindrical and include bulbous tips 592.

[0057] Referring now to FIGS. 5D-F, the housing 570 and gimbaled contact 574 are shown in further detail. The housing includes a substantially tubular body 571 and a cap 586. In the particular implementation shown, the cap 586 includes projections 596 configured to provide a snap fit connection to the tubular body 571, by snapping underneath a rim provided at an upper surface of the tubular body 571. The tubular body 571 includes an interior region configured to receive and house the upper portion 578 of the gimbaled contact 574. The gimbaled contact 574 includes rounded, conical shaped sides, which fit within the lower portion of the interior region of the tubular body 571 and are configured to permit the gimbaled contact 574 to tilt freely in all directions within the housing 572.

[0058] Preferably, to receive a suitable signal, the contact elements 576 are positioned substantially perpendicular to the subject's skin when the electrode headset 300 is worn by the subject. An advantage to the gimbaled contact 574, is that some relative movement between the electrode headset 300 and the subject's head can occur, while maintaining some contact between the contact elements 576 and the subject's skin in the preferred orientation. The flexure element 580 allows the distance from the electrode plate 582 and the contact elements 576 to vary within a certain range determined by the amount of flex permitted by the flexure element 580. Further the gimbaled contact 574 can gimbal, i.e., swivel and/or tilt, within the housing 572. As such, with the distance between the electrode plate 582 and the contact elements 576 permitted to vary, and the gimbaled contact 574 able to tilt, even if the housing 572 changes position such that the tubular body 571 is not substantially perpendicular to the subject's skin, the gimbaled contact 574 can reorientate within the tubular body 571, such that the contact elements 574 maintain a position substantially perpendicular to the subject's skin. Accordingly, the preferred orientation can be maintained and a suitable signal received, even with some shifting of the electrode headset 300. Given that in some applications, particularly in a non-clinical setting, some movement of the subject's head is almost always occurring, the gimbaled contact gives the subject a more enjoyable and hands off experience, as the electrode headset does not require constant adjustment. [0059] In one implementation, the housing 572 is formed from plastic. The gimbaled contact including the contact elements can be formed from a conductive material, for example, metal.

[0060] Referring now to FIGS. 3 A and 5 A, in one implementation, the tubular body 571 of the electrode is configured to friction fit within an electrode aperture (not shown) included in the electrode headset 300. As described above, the electrode apertures can include an annular member that facilitates a friction fit to the outer surface of the tubular body 571. As previously described, each electrode 570 can be independently mounted within and removed from the electrode headset 300, allowing different subsets of electrodes to be used and allowing malfunctioning or broken electrodes 570 to be replaced.

[0061] Referring again to FIGS. 5C-E, the dimensions for one particular implementation of the electrode 570 shall be described. It should be understood however that other dimensions and relative dimensions can be used, and the ones described herein are illustrative of one embodiment. The cap 586 can have an overall height 900 of approximately 2.6 millimeters, including an upper thickness 501 of 1.6 millimeters and an approximate height 502 of the projections of 1 millimeter. The outer diameter 503 of the cap 586 can be approximately 11.2 millimeters. The tubular body 571 can have an overall height 504 of approximately 15 millimeters. The overall outer diameter 505 can be approximately 12.7 millimeters, the inner diameter 506 can be approximately 11.2 millimeters and the inner ring diameter 507 can be approximately 10 millimeters. The gimbaled contact 574 can have an overall height 508 of approximately 8.8 millimeters including an approximate upper portion height 509 of 4.6 millimeters and an approximate contact element height 510 of 4.2 millimeters. The approximate outer diameter 511 of the top of the upper portion can be 10.8 millimeters.

[0062] An electrode headset 300 configured to receive an electrode 570 having the dimensions described above can include electrode apertures having an inner diameter sized to friction fit the tubular body 571 of the electrode 570. Accordingly, for an electrode 570 having a tubular body 571 with an outer diameter of approximately 12.7 millimeters, the inner diameter of the electrode aperture is also approximately 12.7 millimeters. As described above, these dimensions are examples of one embodiment. The inner diameter of the electrode apertures can vary, depending on the electrode to be mounted therein. In one implementation, the electrode apertures can have different inner diameters relative to one another, for example, if different sizes or types of electrodes are intended to be mounted in the various different electrode apertures. [0063] Alternative Electrode

In addition to the electrode 570 described above, other configurations of wet or dry electrodes can be mounted within the electrode headsets described herein. Referring to FIG. 7A, a schematic cross sectional view of another implementation of an electrode that can be used in the electrode headsets described herein, or in another type of mounting structure for the same or a different application, is shown. The electrode assembly 700 includes an electrode plate 702 mounted to a printed circuit board (PCB)

704. The PCB 704 includes electronic circuit components forming a sensor circuit (denoted generally as 706). One or more wires 708 are connected to the sensor circuit 706 to provide power to the circuit 706 and permit signals to be sent to a signal acquisition system. The circuit 706 of the PCB 704 includes at least one electrical contact (not shown) that is configured to be connected to an electrode.

[0064] The electrode can be used to pick up bioelectrical potentials from the skin of a subject, and includes the electrode plate 702. The electrode plate 702 is maintained in electrical contact with at least one contact mounted on the PCB via a conductive medium, for example, a conductive glue 710. On the underside of the electrode plate 702 is mounted a contact pad 712, which is configured to provide a conductive path between the subject's skin and the electrode plate 702 when in use. Preferably the contact pad can hold a conductive liquid, such as saline solution, to improve electrical conductivity. However, in some implementations the electrode assembly can be used without a conductive liquid. The sub-assembly including the PCB 704 and electrode plate 702 can be waterproofed and mounted with the contact pad 712 within a housing 714. [0065] FIG. 7B illustrates a schematic exploded view of the PCB 704, electrode plate 702 and contact pad 712 shown in FIG. 7A. A circuit 706 as depicted in FIG. 9 is formed on the PCB 704. On the underside (or other convenient location) of the PCB 704 is a conductive contact 718. The conductive contact 718 can be made of copper or another suitably conductive material, and is used to make electrical contact between the sensor circuit 706 mounted on the PCB 704 and the electrode plate 702. One embodiment of the electrode plate 702 is made of silver-silver chloride (AgAgCI) and is generally disk-like in shape. An upper surface of the electrode plate 702 is maintained in electrical contact with the contact 718, either directly or via a conductive material such as a silver epoxy conductive glue. The bottom surface of the electrode plate 702 makes contact with the contact pad 712, which can be made from a felt material, or include a felt material layer or portion.

[0066] On the underside of the electrode plate 702 is a generally cylindrical projection 720. The projection 720 is configured to be received into a correspondingly shaped recess 716 formed in the upper side of the contact pad 712. The protrusion 720 is sized to as to be a friction fit with the receiving hole 716 in the contact pad 712, and to thereby provide a secure mounting arrangement for fixing the contact pad 712. The projection 720 also increases the amount of surface area of the electrode plate 702 that makes contact with the contact pad 712, and therefore can increase the quality of signal acquisition. However, in alternative embodiments the mating surfaces of the electrode plate 702 and contact pad 712 can be flat, or can have an alternative shape or can be attached together differently.

[0067] In use the contact pad 712 can absorb and hold electrolytic solution such as saline solution or other electrically conductive liquid and maintain a flexible and high quality conductive link between the subject's skin and the electrode plate 702. The use of conductive liquid assists this process, but may not be essential in some embodiments. The contact pad 712 can be made of an absorbent material, such as a felt sponge. For example, the felt sponge used in a dry printset self inking stamp, or felt used in a poster pen or similar "felt-tipped" pen, have suitable absorption and hardness properties for use in embodiments of the present invention, although other materials can be used. In order to protect the electronics of the electrode assembly from damage and to improve the safety of the electrode, the PCB can be enclosed in a waterproof housing. The waterproofed PCB and the attached electrode plate arrangement is inserted into the housing 714.

[0068] In some embodiments, the electrode casing includes a plastic component of unitary construction. The casing can be tubular in configuration and serve a dual role of ensuring mechanical strength of the electrode arrangement and have an open end that can serve as a feed tube, through which electrolyte solution can be introduced to the contact pad 712. The inside of the recess into which the PCB-electrode arrangement is received can include one or more retaining formations configured to hold the PCB- electrode arrangement and contact pad in place during use. The assembly can include a closure or other means to secure the PCB-electrode arrangement in the housing. Moreover, in one embodiment the housing 714 can be configured to hold the PCB- electrode arrangement in a releasable manner to facilitate replacement of the PCB- electrode arrangement within the housing. The inside of the housing 714 can be provided with teeth or circumferential ribs to hold the PCB-electrode arrangement in place, and allow the PCB-electrode arrangement to be pushed out for replacement. The replacement process requires connecting the replacement PCB-electrode arrangement into the acquisition system. In one implementation, this can be achieved using a known crimping or modular wiring/connector systems.

[0069] Referring to FIGS. 8A-B, an alternative electrode assembly is shown that can be used in an electrode headset described herein, or in a different mounting structure for the same or a different application. The electrode assembly 800 of this embodiment includes a PCB receiving portion 802, a base portion 804 and a cap 806. The PCB receiving portion 802 includes a cavity 808 and is preferably waterproofed, using a material that can also be used to hold the PCB 810 in place in the housing. An opening 814 allows wires 816 to extend to the PCB 810. The floor 818 of the cavity 808 is provided with an aperture 820 to enable an electrical connection to be made between an electrode circuit on the PCB 810 and an electrode plate 822. The PCB receiving portion 802 also includes one or more radial projections 821, described further below. [0070] A cap 806 is provided that is configured so as to close off the cavity 808 and hold the PCB 810 in place within the housing. The base 804 is mounted below the PCB receiving portion 802, and includes a base portion 824 with a through hole 826. The through hole 826 is provided to enable an electrical connection to be made, through the base 804, between a contact of the electrode circuit on the PCB 810 and an electrode plate 822.

[0071] The base 804 also includes a plurality (three in this embodiment) of retaining members 828 that, when the housing is assembled, clip over the edge of the cap 806 and retain the cap 806 in place. The underside of the base 804 further includes an annular flange 830, that defines a recess into which the electrode plate 822 is mounted. The electrode plate 822 can be attached to the bottom of the base 804 using, for example, a conductive glue. In use, sufficient glue is used to mount the electrode plate 822 to the base 804 such that the voids formed by the through holes 826 and 820 are substantially filled and electrical contact is made with a contact of the electrode circuit on the PCB 810. A contact pad 1232 is mounted on the electrode as described in connection with the previous embodiment.

[0072] FIG. 8B depicts the electrode assembly of FIG. 8A in an assembled state.

The electrode housing components can be made from a plastic material such as polyurethane. Such components can be made using from RTV molds created from fabricated styrene masters. Moreover in these embodiments the housings can have one or more electrolyte feed ducts that bypass non- waterproofed electronic components (or be configured to receive an external tube) that can enable electrolyte fluid to be applied to the contact pad of the electrode assembly in use. Such ducts can preferably allow application of the electrolyte fluid without removal of the electrodes from the subject. [0073] It should be noted that since, electrode assemblies can be expensive it is advantageous to enable the number or electrodes to be increased and decreased by the subject to suit his or her needs. For example, an electrode headset in a certain application, e.g., detecting an emotion, may only need eight electrodes, whilst for another application, e.g., additionally detecting a conscious effort such as to move a real or virtual object, or a muscle movement, one or more additional electrodes may be needed. Therefore the electrodes should be mountable and detachable from the headset, e.g. , electrode headset 300, in the manner discussed above. [0074] Circuit Diagram

Referring now to FIG. 9, a schematic circuit diagram is shown for an embodiment of an active electrode for sensing bioelectric potentials. The circuit 900 depicted is suitable for use with an electrode or electrode assembly such as those shown in FIGS. 5A-E, 7A-B and 8A-B. The circuit 900 includes an electrode plate 902, that is maintained in electrical contact (directly or via a conductive path) with the subject's skin. For example, the electrode plate 902 can be the electrode plate 582 of the electrode 570 shown in FIGS. 5A-E, the electrode plate 702 of the electrode assembly 700 shown in FIGS. 7A-B, or the electrode plate 822 of the electrode assembly 800 shown in FIGS. 8A- B.

[0075] The electrode plate 902 provides an input voltage (Vin) that is initially applied to an input protection resistor Rl . The input resistor Rl serves as overcurrent protection in case of electrode malfunction, and protects both the operational amplifier Ul and the subject. In one embodiment, Rl is a 5 kΩ resistor. Rl is connected to a positive terminal of the operational amplifier Ul . Ul is can be set up in a buffer amplifier arrangement. In this example, the buffer amplifier has a gain of 1 , however other gains can be used. The operational amplifier Ul can be a CMOS operational amplifier, which provides a large input impedance, e.g., in the gigaohm range. The operational amplifier Ul also has lower output impedance than a passive electrode, and reduces hum caused by environmental interference, such as power line noise. The operational amplifier can have low intrinsic noise in the frequency range of 0.1 to 40 Hz, in order to enable accurate detection of weak EEG signals such as evoked potentials. The operational amplifier preferably has low drift and low offset voltage.

[0076] In one embodiment, the Ul is a Texas Instruments operational amplifier model no. TLC2201. Alternatively a TLV2211 operational amplifier (also from Texas Instruments) can be used and may be advantageous, as it has a smaller footprint and lower current consumption. As will be known to those skilled in the art other types of operational amplifiers can be used, e.g., a OPA333 operational amplifier (also from Texas Instruments). The circuit 570 includes an optional low pass filter (LPF), which can be used to filter out noise introduced by sources such as radio frequency interference and that can affect the quality of signals required by the electrodes. The circuit 570 also includes optional electro static discharge protection circuitry to protect the operational amplifier Ul in case of electrostatic discharge. The circuit 570 includes a bypass capacitor Cl connected between the power supply signal of operational amplifier Ul and ground to decouple the power supply. [0077] Electrode Assembly Housing

Referring now to FIG. 1OA, a cross-sectional view of one implementation of an electrode assembly housing is shown. As can be seen the main body 1002 of the housing 1000 is generally cylindrical and defines a chamber 1004 into which the PCB, components of the acquisition circuit, an electrode plate and contact pad can be mounted in use. The housing 1000 further includes a radially extending flange 1006 to prevent the electrode assembly from being pushed through an electrode aperture of an electrode headset within which the housing 1000 is mounted. At the top of the chamber 1004 is located a plurality of inwardly extending flanges 1008 to prevent the components installed in the chamber 1004 from being pushed out of the top of the chamber 1004. The inner wall defining the chamber 1004 can include at least one tooth 1010, 1012 or rib(s) to retain the contact pad in the chamber 1004.

[0078] To assemble the electrode assembly, a pre-assembled PCB-electrode plate arrangement can be slid under the flanges 1008 in the direction of arrow 1014 until located in the chamber 1004. The contact pad can be inserted into the bottom of the chamber 1004 in the direction of arrow 1016 and installed in contact with the PCB- electrode plate assembly.

[0079] FIG. 1OB shows the electrode assembly housing depicted in FIG. 1OA with the electrode components assembled therein. In this implementation, the electrode assembly included in the housing 1000 is the embodiment shown in FIGS. 7A-B. Referring to the same reference numerals of FIGS. 7A-B, the printed circuit board (PCB) 704 is mounted in the topmost position in the chamber 1004, followed by the electrode plate 702. The contact pad 712 is bottom-most in the chamber 1004, and is located in contact with the electrode plate 702. The contact pad 712 is secured in the chamber 1004 by teeth 1010 and 1012, which grip the sides of the contact pad 712. Using such an arrangement, the components can be easily removed from the housing and replaced if a malfunction occurs in the electrode's components. [0080] The headset of the illustrative embodiments depicted use a wired connection to the signal acquisition system, however alternatively a wireless link can be used. It should also be understood that the electrode circuit arrangement, electrodes and electrode headset arrangements described herein can be used in connection in a wide variety of applications outside the implementations described herein. For example the electrode headset arrangement described herein can be used with known electrode arrangements. Moreover the electrode arrangements described herein can be used to detect other types of bioelectric potentials on parts of the body other than the head, e.g. ECG. The electrodes described herein can also be useful for non-human applications. [0081] Electronic Wiring System

As described above, the electrode headset 300 is configured to mount one or more electrodes therein. Each electrode is electrically connected to electronic circuitry that can be configured to receive signals from the electrodes and provide an output to a processor. The electronic circuitry may also be configured to perform at least some processing of the signals received from the electrodes. In some implementations electronic circuitry mounted on or housed within the electrode headset can be configured to perform some or all of the functions of the sensor interface 104, A/D converter 106, data buffer 108, processing system 109 and/or platform 120.

[0082] In one implementation, the electronic circuitry is mounted or housed within the rear band 308 of the electrode headset 300, and electrically connected to each electrode mounted therein by one or more wires extending between the electronic circuitry and each electrode. The wires can be either visible on the exterior or interior of the electrode headset, or can be formed within the electrode headset, for example, by molding within one or more plastic components forming the electrode headset. Preferably, the wiring system exhibits one or more of the following features: a low cost; termination at the electronic module with a connector; flexible and shapeable to fit the contour of the electrode headset; strain relief at the conductor terminations; non-breakable flexible wiring with strain relief, moldable in a rigid headset; noise immunity and having conductor resistance less than 100 ohms.

[0083] In one implementation having eighteen electrodes mounted within an electrode headset, the wiring system includes two connectors accommodating a total of 52 wires. Each wire is multi-stranded and PVC insulated. For example, each multi- stranded wire can include seven 0.26 millimeter diameter conductors. The wires are crimped with receptable contacts and inserted into the connector housing. The wires leading to each electrode board are grouped and twisted together and then stripped at the ends and soldered to the electrode PCB. In one implementation, the wire can be cut to length, crimped, inserted into the connector housing, twisted and stripped by machinery. [0084] In the above implementation, one or more of the following advantages can be realized. The material cost can be minimized (low cost connectors and minimal or no wire wastage, as each wire is cut to the exact length). The wire being flexible can fit the contour of the electrode headset. The manufacturing process is efficient as it can be automated. Twisting the wires can serve to provide noise immunity and efficient placement of the wiring into the headset, as all three wires twisted together is similar to a single mini-cable. The cost of terminating the wire to the electrode board can be minimal, as it can be soldered to the electrode PCB. Strain-relief requirements can be less critical because the wire is multi-stranded, although inexpensive effective strain relief can be provided by threading the wire through another hole in the PCB or alternatively by including a strain relief in the electrode headset molding itself. The wiring assembly can tolerate temperatures of common plastic injection molding processes (e.g., polyethylene at 115 degrees Celsius), as the connectors can be made from nylon and the wire can be PVC insulated and therefore be expected to withstand approximately 150 degrees Celsius. The unique length of the twisted wire to each electrode board can be a convenient guide for fitment of the electrodes and wiring assembly to the electrode headset molding. [0085] Alternative Implementations

In some implementations, the electrode headset 300 can be used to mount an electrode such as the electrode described in U.S. Patent Application Serial No. 11/876,654, entitled "Electrode Conductive Element", filed on October 22, 2007, by Hoai Do, et al, the entire contents of which are hereby incorporated herein by reference in their entirety. Referring to FIGS. 1 IA-F, one implementation of an alternative electrode 1100 that can be mounted within the electrode headset 300 is shown. Providing a conductive fluid between an electrode contact and a location on a subject from which a signal is to be sensed can provide a stronger signal to the electrode. However, depending on the application, using a conductive gel or other wet fluid can be impractical. Further, outside of a medical treatment context, a subject is less likely to agree to having hair removed from the location. A conductive element is described that can be used with an electrode to provide an improved signal from the subject to the electrode, without requiring the subject's hair to be removed and without the discomfort of a liquid gel or other fluid. In some implementations, the conductive element incorporates electrolytic contact. The conductive element can be formed of a non-adhesive material that is sufficiently flexible and compressible to conform to the subject's skin without discomfort when placed in contact with the subject. The material can be one that does not dissolve in water, but is highly water-permeable. For example, the conductive element can be formed of a network of water-insoluble polymer chains, e.g., a hydrogel. The conductive element is formed from a material that can be shaped into a desired configuration, depending on the application. In one example, the conductive element can be formed from a hydrophilic structural polymer.

[0086] Referring to FIG. 1 IA, a perspective side view is shown of an example electrode 1100 including a hydrogel conductive element 1103 and a housing 1102. In the particular implementation shown, the conductive element 1103 has an approximate teardrop-shaped horizontal cross-section. The shape of the conductive element 1103 can facilitate contact with a subject's skin while penetrating through the subject's hair, for example, if used with an electrode to sense EEG signals from the subject's scalp. [0087] Referring to FIG. 1 IB, a cross-sectional side view of the example hydrogel conductive element 1103 and housing 1102 is shown. The housing 1102 can be formed from a non-conductive material that is water-impermeable, durable and biocompatible for skin contact. Example materials include polypropylene, polyethylene, nylon and polystyrene. The housing includes thin walls forming an inner cavity 1107. Within the inner cavity 1107 is housed an electrode plate 1104.

[0088] In this particular example, the electrode plate 1104 includes a nipple- shaped upper portion 1108. The hydrogel conductive element 1102 is shaped to fit over the upper portion 1108, as shown in the cross-sectional view. In this example, the conductive element 1102 fits snugly over the upper portion 1108. The exterior surface 1105 of the hydrogel conductive element contacts a subject's skin and effects an electrolytic connection to the electrode plate 1104. A lower surface 1106 of the electrode plate 1104 is configured to mate with an electrical contact on a mounting apparatus within which the electrode 1100 can be mounted. In some implementations, the electrode plate 1104 is formed from silver/silver chloride. The electrical contact on the mounting apparatus is electrically connected to circuitry to receive signals from the electrode plate 1104. The circuitry can be external to the mounting apparatus, or embedded therein, as is described further below for some particular implementations. Any suitable electrode can be used together with the conductive element, and some different example electrodes are discussed below. [0089] In the implementations shown in FIGS. 1 IA and 1 IB, the housing is configured to facilitate penetrating a hair layer. That is, the housing tapers from its base toward the distal region that makes contact with the subject's scalp. Having a narrow, tapered distal region operates to part the subject's hair and improve scalp contact. Other housing configurations can be used, depending on the particular implementation. [0090] The conductive element 1100 is formed by shaping a hydrogel material into the desired configuration. Examples of hydrogel materials include, but are not limited to: poly-hydroxyethylmethylacrylic (polyHEMA) materials, super-absorbent polymers such as poly-methacrylic acid, hygroscopic materials such as silica gel and porous silicones. The silicone and polyHEMA materials have the following mechanical and electrical properties that are desirable for use in data collection, e.g., EEG data collection: soft, pliable, durable, good set-up times, good conductivity and high quality signals. The material used to form the conductive element 1103 is non-adhesive and can exhibit structural integrity. That is, once formed into a desired shape and configuration, subject to deformation under compression, the conductive element 1103 substantially retains the shape and configuration.

[0091] In one implementation, the conductive element is formed from a material currently used to make disposable contact lenses, for example, polyHEMA with a nominal water content in excess of approximately 20% and saturated in a hydration fluid, such as saline. These materials are particularly rugged mechanically, soft and pliable when hydrated and are able to provide a suitable level of signal quality. Further, these materials are capable of being cast, molded or machined into desired shapes, allowing design flexibility. For example, in EEG application requiring data collection on a subject's scalp, the material can be configured into a shape that can penetrate the hair layer. The material, being soft and compressible, allows the conductive element to conform to a local skin profile and contact skin around remnant hairs. The conductive element is also comfortable and cushions the subject's scalp from the force required to maintain electrical contact.

[0092] In other implementations, the conductive element 1103 can be formed into a different shape, depending on the configuration of the electrode plate and the external circuit type with which it will be used and/or the application. The particular configuration shown in FIGS. 1 IA and 1 IB is but one illustrative example. Of importance though is that the hydrogel material used can be configured into a shape that will maintain its structural integrity. Further, in addition to providing a conductive path for signals from the subject to the electrode plate, the shape itself can perform other functions, e.g., to penetrate the hair layer.

[0093] Advantageously, using materials that are already in use for contact lenses provides a material that is hypoallergenic and approved for biological use in worldwide markets. The materials are currently manufactured in medically controlled environments, and approved hydration materials with benign antibacterial and anti-mold properties are freely available and inexpensive.

[0094] In some implementations, the conductive element 1103 can be repeatedly hydrated by soaking the conductive element 1103 in a custom hydration solution or in a commonly available saline solution suitable for contact lenses. The conductive element 1103 can be hydrated in situ within the electrode 1100 or can be removed, hydrated and replaced within the electrode 1100.

[0095] Referring now to FIGS. 11C and 1 ID, an example of an electrode mount

1112 that can be used in the electrode headset 300 to mount the electrode 1100 is shown. In this implementation, wires extending from the electrode mount 1110 to electronic circuitry mounted on or housed within the electrode headset are embedded within an arm included in the electrode headset 300 or, if a metal arm is used, can be protected within a plastic sheath. A flexible contact element 1114 is exposed within the electrode mount 1110, as shown in FIG. HC.

[0096] The electrode mount 1110 is configured to provide a snap fit connection to the electrode 1100. The contact surface 1106 of the electrode plate 1104 housed within the electrode 1100 makes electrical contact with the flexible contact element 1114 when the electrode 1100 is mounted therein, as shown in FIG. 1 ID. That is, the contact surface 1106 of the electrode plate 1104 electrically couples to the flexible contact element 1114 included within the electrode mount 1110, thereby electrically connecting the conductive assembly 1101 to the electronic circuitry. The conductive element 1103 provides a conductive path for signals from the subject's skin to the electrode plate 1104. Other configurations of electrode mount can be used, and the one described is but one example. [0097] It will be understood that the subject matter disclosed in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects. [0098] A number of embodiments of the invention have been described.

Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. An electrode headset comprising: a left band configured to position along the left side of a subject's head and extend from approximately the rear center to the front center of the subject's head, the left band including one or more electrode mounts configured to mount one or more electrodes; a right band configured to position along the right side of a subject's head and extend from approximately the rear center to the front center of the subject's head, the right band including one or more electrode mounts configured to mount one or more electrodes; and a rear band attached at a first end to the left band and at a second end to the right band, wherein the rear band is configured to extend across the rear of the subject's head.

2. The electrode headset of claim 1, where: the left band further comprises a left ear notch configured to position about a subject's left ear and facilitate placement of the electrode headset on the subject's head; and the right band further comprises a right ear notch configured to position about a subject's left ear and facilitate placement of the electrode headset on the subject's head.

3. The electrode headset of claim 1, where: the one or more electrode mounts included in each of the left and right bands are positioned in accordance with a desired electrode placement scheme.

4. The electrode headset of claim 1, further comprising: one or more electrodes mounted within the one or more electrode mounts included in the left and right bands; and wherein the rear band is further configured to house electronic circuitry electrically connected to each of the one or more electrodes.

5. The electrode headset of claim 4, wherein each of the one or more electrodes positioned within the one or more electrode mounts comprises: an electrode plate; a sensor circuit electrically connected to the electrode plate; a gimbaled contact element; a conductive flexure element connecting the electrode plate and the gimbaled contact element and providing a conductive path therebetween.

6. The electrode headset of claim 1 , wherein the rear band is pivotably attached to the left band and the right band, such that the rear band can pivot relative to the left and rear bands about a horizontal axis in the coronal plane.

7. The electrode headset of claim 1, wherein the electrode headset is formed from a material with sufficient rigidity to hold the one or more electrodes in a desired electrode placement scheme on the subject's head.

8. The electrode headset of claim 7, wherein the electrode headset is formed from a material with sufficient flexibility to flex in response to the electrode headset being positioned on the subject's head such that the left and right bands embrace the subject's head.

9. The electrode headset of claim 1 , wherein the left band and right band each include a back component having a V-shaped configuration.

10. The electrode headset of claim 1, wherein the left band and right band each include a front component having a Y-shaped configuration.

11. The electrode headset of claim 1 , wherein each of the one or more electrodes positioned within the one or more electrode mounts comprises a conductive element formed from a non-adhesive hydrogel material and configured to provide a conductive path for transmitting EEG signals from the subject.

12. The electrode headset of claim 11 , wherein the hydrogel material is selected such that the conductive element retains a desired shape and configuration after more than one use.

13. The electrode headset of claim 11 , wherein the hydrogel material is selected such that the conductive element can be hydrated and re-used repeatedly.

14. The electrode headset of claim 11 , wherein the conductive element is configured to fit around at least a portion of the electrode.

5. The electrode headset of claim 11 , wherein the hydrogel material is selected such that the conductive element is flexible and conforms to the subject's skin under a compressive force and maintains structural integrity for repeated use.