Patent Publication Number: US-2020275856-A1

Title: An intra- and circum-aural eeg brain computer interface

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application claims the benefits of priority of U.S. Provisional Patent Application No. 62/559,133, entitled “An Intra- and Circum-aural EEG Brain Computer Interface” and filed at the United States Patent and Trademark Office on Sep. 15, 2017, the content of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present relates to brain activity recording by electroencephalography. More particularly the present relates to a brain-computer interface for brain activity recording by electroencephalography. 
     BACKGROUND 
     Brain-computer interfaces (BCI) can directly translate human intentions into discrete commands while bypassing the human locomotor system. Most non-invasive BCI systems currently in use are based on electroencephalography (EEG) recording technology using recent developments of mobile EEG solutions. However, current non-invasive BCI systems still have important limitations. Although the current systems may be robust to motions and can make abstraction of human body movements, the current systems can be cumbersome and visible to others which can be inadequate for being used in social settings or during physical activity. Indeed, sensors of mobile EEG-based BCI systems are not inconspicuous enough for use in social settings and can be cumbersome while performing a physical activity such a running, swimming, cycling, etc. 
     For instance, when trying to measure Auditory Steady State Responses (ASSRs) which are recordable electrophysiological responses, at least one electrode  120  such as presented in Prior Art  FIG. 1B  is strategically placed on the human scalp to capture brain activity. ASSRs correspond to the brain activity evoked by one or more stimuli which are characterized by carrier frequencies (Fc) that are amplitude-modulated at a specific frequency (Fm). In practice, when a person is exposed to such stimuli, spectral power of the EEG frequency spectrum that is related to the stimuli will manifest at Fm, and may also appear at its harmonics. ASSRs&#39; recordings and stimuli generations were conducted by using the Multiple Auditory Steady-State Evoked Response, known as the “MASTER System™”, a LabVIEW™ based software developed at the Rotman Research Institute, an international center for the study of human brain function. 
     The MASTER System™ is a data acquisition system designed by Michael S. John and Terrence W. Picton to assess human hearing by recording auditory steady-state responses. The LabVIEW™ based environment simultaneously generates multiple amplitude-modulated and/or frequency-modulated auditory stimuli, acquires electrophysiological responses to these stimuli, displays these responses in the frequency-domain, and determines whether or not the responses are significantly larger than background physiological activity. 
     Prior Art  FIG. 1A  presents various hardware components of the MASTER system  100 . The MASTER System™  100  includes a PC  101 , an acquisition board  104 , a variable gain amplifier  106 , an audiometer  108 , a transducer  110  (usually, earphones or headphones), an EEG amplifier  112 , coaxial cables and audio cables. In addition, as concurrently presented in Prior Art  FIG. 1B , the system  100  uses a set of gold-plated electrodes  120 , such as a captor electrode  122  placed at vertex (Cz), a reference electrode  124  placed on the back of the neck (near hairline) and a ground electrode  126  placed on the clavicle. 
     All components of the MASTER System™  100  are monitored by the single PC  101 . The stimulation signals from the analogue output of the NI-USB 6229 board  104  are attenuated by an operational amplifier  106  with a gain of −0.5, so that they may be delivered to the “CD input” of the audiometer  108 , which enables the operator to adjust the levels of stimuli delivered by a transducer (such as earphones or headphones). In parallel, ASSRs are scalp-recorded by the electrodes ( 122 , 124  and  126 ) placed at vertex (+)  122 , hairline (ref)  124  and clavicle (ground)  126  and are then amplified by the EEG amplifier  112 , before reaching the analogue input of the data acquisition board  104  connected to the computer  101 . Data is processed online with the LabVIEW™ based software. 
     Prior art  FIG. 1C  presents an EEG capture device  140  having circum-aural electrodes positioned on a semi-flexible plastic base material. A conductive paste must be applied to the skin to provide proper electrode contact and an adhesive film (not shown) is applied over the device  140  to secure the device  140  in a desired position and further ensure a proper skin-electrode contact. The electrodes are positioned such as to contact a mastoid area as well as a lower jaw bone area. Movement of the lower jaw bone can compromise the proper positioning of the device  140  and prevent effective brain signal acquisition. Moreover, the shape and size of the device  140  make it visible to others which can be inadequate for being used in social settings. 
     Others have developed portable EEG monitoring systems. For instance, Kidmose et al. describe in US Patent publications 2012/0123290 and 2012/0302858 an EEG monitoring system adapted to be carried continuously by a person to be monitored. The system has an implant unit that is located subcutaneously behind the ear of a patient. The implant unit has an electronics part and two electrodes for picking up electrical EEG signals from the brain of the patient. The electronics part has the necessary electronics for sampling the EEG signals measured by the electrodes and transmitting them wirelessly to an external monitoring unit. The monitoring unit resembles a behind-the-ear hearing aid having an earplug and a housing that is placed behind the ear. The housing has a processing unit adapted to receive wirelessly the EEG readings from the implant unit. The housing is connected to the earplug via a sound tube or an electric cord leading to a receiver of the earplug. This allows the monitoring unit to transmit messages, such as alarms or warnings, into the ear of the person carrying the EEG monitoring system. Despite the portability of the system, this system requires surgery to position the electrodes and the electronics part subcutaneously behind the ear of the patient and is invasive. Moreover, the patient cannot easily remove the implant unit at his own will. 
     In U.S. Pat. No. 9,408,552 to Kidmose et al., there is described an earplug having a shell with at least two electrodes adapted to measure brain wave signals. The electrodes are positioned on a contour portion of the shell and are connected to a processor for measuring the signals. The shell is shaped to individually match at least part of the ear canal and the concha of the user. The earplug is connected to a behind-the-ear component and the brain wave signals detected by the electrodes of the earplug are transmitted to the behind-the-ear component for further processing. The shell is made from a flexible material such as plastic or silicon. The electrodes are positioned on or integrated within the surface of the shell and counts at least one reference electrode and at least one detecting electrode. Kidmose et al. present an earplug having more or less five electrodes. The electrodes are made from alloys such as stainless steel, platinum-iridium or noble metals such as silver, titanium, platinum and tungsten. Otherwise, the electrodes can also be made from silver-silver chloride. In order to improve the quality of the signals detected by the electrodes, a conductive gel is applied. Although Kidmose et al. describe a portable and non-invasive brain wave signal measuring device, since the active electrode or captor electrode is positioned in proximity with the reference electrode, the electrodes can only measure localised brain activity produced by cortex generators that are in proximity with the outer ear-canal and may not be appropriate for providing general or extensive brain activity readings. 
     SUMMARY 
     According to one aspect, there is an electroencephalography (EEG) based brain-computer interface for an ear of a user. The interface has a behind-the-ear piece. The behind-the-ear piece has a flexible base that is shaped to fit mostly behind the ear of a user. The flexible base has at least one electrode positioned to contact with a portion of skin covering a temporal bone of the user&#39;s skull when the device is worn and the at least one electrode is selected from a group consisting of a reference electrode, at least one captor electrode and a ground electrode. The reference electrode is configured to measure a first voltage fluctuation. The at least one captor electrode is configured to measure a second voltage fluctuation. The ground electrode is configured to measure a third voltage fluctuation. The flexible base also has a wedge portion that is shaped to contact at least in part an antihelical fold and/or concha of the ear in order to produce and maintain an adequate pressure and contact of the at least one electrode on a portion of skin covering a temporal bone of the user&#39;s skull. The interface is configured to provide the first voltage fluctuation, the second voltage fluctuation and the third voltage fluctuation for determining a brain electrical activity. 
     According to another aspect, there is an electroencephalography (EEG) based brain-computer interface for an ear of a user. The interface has two in-ear pieces. The first in-ear piece has an ear canal engaging member having a reference electrode configured to measure a first voltage fluctuation and being shaped to engage an outer-ear canal of a first ear in order to allow the reference electrode to contact at least in part a wall of an outer ear canal. The second in-ear piece has an ear canal engaging member having at least one captor electrode configured to measure a second voltage fluctuation and being shaped to engage an outer-ear canal of a second ear to allow the at least one captor electrode to contact at least in part a wall of an outer ear canal. One of the first in-ear piece and the second in-ear piece further has a ground electrode configure to measure a third voltage fluctuation. The interface is configured to provide at least one of the first voltage fluctuation, the second voltage fluctuation and third voltage fluctuation for determining a brain electrical activity. 
     According to yet another aspect, there is a system for determining a brain activity indicator using a brain-computer interface. The system has an electroencephalography (EEG) based brain-computer interface as defined above, a differential amplifier and a computer device. The amplifier is configured to amplify and convert into a digital form the first voltage fluctuation, the second voltage fluctuation and the third voltage fluctuation provided by the brain-computer interface and to produce associated amplified and converted voltage fluctuations. The computer device is configured to determine a brain electrical activity indicator according to the associated amplified and converted voltage fluctuations. 
     The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which: 
         FIG. 1A  presents a prior art Auditory Steady State Responses (ASSR) recording system; 
         FIG. 1B  presents a prior art gold foil and a prior art gold-plated cup electrodes; 
         FIG. 1C  presents a prior art EEG capture device having circum-aural electrodes positioned on a semi-flexible plastic base material; 
         FIG. 2A  presents an ear device having an in-ear piece and a behind-the-ear piece, according to one embodiment; 
         FIG. 2B  presents an ear device having a behind-the-ear piece, according to an alternate embodiment; 
         FIG. 2C  presents the ear device of  FIG. 2A  or  FIG. 2B  being connected to an ASSR acquisition system, according to one embodiment; 
         FIG. 2D  presents the ear device of  FIG. 2A  or  FIG. 2B  being connected to a differential amplifier for further processing by a computerized system configured to determine a brain electrical activity, according to one embodiment; 
         FIG. 2E  presents an ear device having a two in-ear pieces, according to one embodiment; 
         FIG. 2F  presents alternate in-ear pieces of the in-ear pieces of  FIGS. 2A and 2E , according to one embodiment; 
         FIG. 3A  presents a drawing of a posterior auricle portion of an ear and the various bones of the human skull, in order to describe the positioning of the ear device, according to one embodiment; 
         FIG. 3B  presents two photographic drawings of a person wearing the behind-the-ear pieces of  FIG. 2A  and of  FIG. 2B , according to one embodiment; 
         FIG. 4A  presents a table describing electrodes&#39; placements used for two experiments, «G.P.C» refers to gold-plated cup electrodes, «G.F» refers to gold-foil electrodes and «EAR» refers to ear device electrodes; 
         FIG. 4B  presents a chart depicting Signal-to-noise ratio, in dB, of ASSRs scalp-recorded on subject #1 using gold electrodes (control condition #1 and #2) and the electrodes of the behind-the-ear piece, according to one embodiment; and 
         FIG. 4C  presents a chart depicting Signal-to-noise ratio, in dB, of ASSRs scalp-recorded on subject #3 using gold electrodes (control condition #1 and #2) and the electrodes of the in-ear piece, according to one embodiment. 
     
    
    
     It will be noted that throughout the appended drawings, like features are identified by like reference numerals. 
     DETAILED DESCRIPTION 
     A novel intra- and circum-aural EEG brain computer interface will be described hereinafter. Although the invention is described in terms of specific illustrative embodiment(s), it is to be understood that the embodiment(s) described herein are by way of example only and that the scope of the invention is not intended to be limited thereby. 
     Presented in  FIG. 2A  is an ear device  200  that has an in-ear piece  202  and a behind-the-ear piece  204 , according to one embodiment. The in-ear piece  202  has an ear canal engaging member  206  such as an earplug. The ear canal engaging member  206  is shaped and formed to contact at least in part the walls  300  of an outer ear canal. The ear canal engaging member  206  has an integrated ground electrode  208  and an integrated reference electrode  210 . The integrated ground electrode  208  and integrated reference electrode  210  are strategically positioned within the engaging member  206  such that an adequate pressure from the walls of the outer ear-canal and the concha  306  of the ear provide an effective contact, in order to obtain an adequate impedance matching between the skin and the in-ear electrodes ( 208  and  210 ), as concurrently presented in  FIG. 3A . 
     The behind-the-ear piece  204  is adapted to contact the skin covering the skull opposite or near the antihelical fold  302  of the ear, as presented in  FIGS. 2A and 3A . The behind-the-ear piece  204  is also adapted to contact a portion of the skin covering the temporal bone of the human skull such as the mastoid area  304  as depicted with dotted lines in  FIG. 3A . 
     As further presented in  FIG. 2A , the behind-the-ear piece  204  has a flexible base  211  to which are strategically positioned five captor electrodes ( 212 A,  212 B,  212 C,  212 D,  212 E). The captor electrodes  212 A,  212 B and  212 C are positioned in order to be placed in contact with the skin covering the skull opposite or in proximity with the antihelical fold  302 , when the device  200  worn, as concurrently presented in  FIG. 3A . The captor electrodes  212 D and  212 E are positioned in order to be placed in contact with a portion of the skin covering the temporal bone  304  of the human skull such as the mastoid area, when the device  200  worn. It shall be recognized that the portion of the temporal bone  304  depicted in  FIG. 3A  can differ in shape and size depending on the positioning of the captor electrodes  212 D and  212 E on or within the behind-the-ear piece  204  and the ear morphology of the user. 
     Presented in  FIG. 2B , is an alternate embodiment of the behind-the-ear piece  204 . In this embodiment, the flexible base  211  has three strategically positioned captor electrodes ( 212 F,  212 G,  212 H) in order to be placed in contact with the skin covering the skull opposite or in proximity with the antihelical fold  302 , when the device  200  worn. 
     According to one embodiment, the behind-the-ear piece  204  also has a comfort wedge  214  positioned to contact at least in part the antihelical fold  302  and/or the concha  306  in order to produce and maintain an adequate pressure and contact of the captor electrodes on the skin of the skull opposing the antihelical fold  302  and/or concha  306 . 
     In the embodiment of the behind-the-ear piece  204  presented in  FIG. 2B , the comfort wedge  214  is integral with the flexible base  211 . However, it shall be recognized that in another embodiment, that the comfort wedge  214  may be removeable. Moreover, the comfort wedge  214  can be replaced by any other suitable comfort wedge having a size and shape that corresponds to the space defined between the antihelical fold  302  and/or concha  306  and the opposing skull region of a user. According to yet another embodiment, the flexible base  211  has an integral first comfort wedge having a minimal width and a second comfort wedge that is removably attachable to the first comfort wedge in order to suitably increase a width of the resulting comfort wedge, depending on the ear morphology. 
     In the embodiment of the behind-the-ear piece  204  presented in  FIG. 2B , the comfort wedge  214  is flexible. It shall however be recognized that degree of flexibility of the comfort wedge  214  can differ from one embodiment to another and that in some cases, the comfort wedge  214  can be made from a harder material, without departing from the scope of the present solution. 
     Moreover, in the embodiment presented in  FIG. 2B , the base  211  is flexible. It shall however be recognized that degree of flexibility of the base  211  can differ from one embodiment to another and that in some cases, the base  211  can be made from a harder material, without departing from the scope of the present solution. 
     According to one embodiment, the captor electrodes ( 212 A,  212 B,  212 C,  212 D,  212 E,  212 F,  212 G and/or  212 H) are made of a soft biocompatible polymer material, such as medical grade silicon, filled with a conductive material, such as carbon chopper. The silicon filled with carbon chopper has an adequate conductivity while remaining resilient in order to adapt with comfort to the shape of the posterior auricle of the wearer. According to one embodiment the carbon chopper is mixed with silicon at a weight ratio ranging from 0.5% to 3%. According to another embodiment the carbon chopper is mixed with silicon at a weight ratio ranging from 0.5% to 2%. According to yet another embodiment the carbon chopper is mixed with silicon at a weight ratio ranging from 0.5% to 1%. According to another embodiment, the carbon chopper is mixed with silicon of around a ratio of 0.6%. For instance, for 43 grams of silicon, 0.25 grams of carbon is added. 
     According to one embodiment, the captor electrodes ( 212 A,  212 B,  212 C,  212 D,  212 E,  212 F,  212 G and  212 H) are positioned on the base  211  as depicted in  FIGS. 2A and 2B . However, it shall be recognized that the captor electrodes can be positioned within the base  211  or can also be integral with the base  211 . 
     The shape and size of the ear device  200  is adapted to obtain voltage fluctuation measurements with the electrodes ( 208 ,  210 ,  212 A,  212 B,  212 C,  212 D,  212 E,  212 F,  212 G and  212 H) while seamlessly being worn in and/or around the ear. Indeed, the device  200  generally aims at not being cumbersome to the user and to be used in social setting without drawing too much attention. 
     As presented in  FIG. 2C or 2D , the ear device  200  is adapted to provide to an analysis system  101  or  201  voltage fluctuation measurements indicative of brain activity. The voltage fluctuation measurements are measured by the ground electrode  208 , by the reference electrode  210  and by at least one of the captor electrodes ( 212 A,  212 B,  212 C,  212 D,  212 E,  212 F,  212 G and  212 H) according to a variety of cortex generators and are amplified and converted into a digital form by a differential amplifier  112  or  203 . Based on the amplified and converted voltage fluctuation measurements the data analysis system  101  or  201  can produce electroencephalography recordings. The analysis system  101  or  201 , the differential amplifier  112  or  203  and the ear device  200  are connected via a wire connection or via a wireless connection. 
     According to one embodiment, the analysis system  101  or  201  is adapted to produce a predetermined stimulus and expose the user to the predetermined stimulus. During the predetermined stimulus, the brain-computer interface is configured to measure the voltage fluctuations. The analysis system  101  or  201  then analyses the voltage fluctuations associated to the produced predetermined stimulus. The predetermined stimulus can be a sound stimulus, a visual stimulus or any other kind of stimulus know to produce brain activity. 
     It shall be recognized that in some embodiments, the ground electrode and/or the reference electrode can be positioned on the flexible base  211  and that the in-ear piece  202  may not be required. 
     It shall further be recognized that the data analysis system  201  or  101  can produce electroencephalography recordings based on voltage fluctuation measurements provided by two devices  200  worn by a user on each ear. Indeed, the device  200  can be worn on each ear of the user and the analysis system  201  or  101  may provide EEG results with greater accuracy, particularly when relying on contralateral cross-referencing. Moreover, in one mode of operation, the device  200  having only a ground and a reference electrode is worn on one ear and the device  200  having a suitable number or captor electrodes is worn on the other ear of the user. 
     For instance, in some embodiments, as presented in  FIG. 2E , the ground electrode  208  and the reference electrode  210  are positioned on one in-ear piece  202  that is adapted to be inserted into one of the user&#39;s ears. At least one of the captor electrodes ( 212 A,  212 B,  212 C,  212 D,  212 E,  212 F,  212 G and  212 H) is positioned on another in-ear piece  202  adapted to be inserted into another one of the user&#39;s ears. Notice that the ground electrode  208  can be positioned on either one of the in-ear pieces  202 , without departing from the scope of the present device  200 . 
     In other embodiments, the ground electrode and/or the reference electrode is positioned on one behind-the-ear piece  204  and at least one of the captor electrodes ( 212 A,  212 B,  212 C,  212 D,  212 E,  212 F,  212 G and  212 H) is positioned on another behind-the-ear piece  204 . 
     The data analysis system  201  or  101  is indeed adapted to provide EEG results based on either ipsilateral (same side) EEG readings provided by a device  200  worn on one ear, as presented in  FIG. 2D . The data analysis system  201  is also adapted to provide EEG results based on contralateral (opposite side) EEG readings provided by a device  200  worn on both ears of a user. Indeed, as presented in  FIG. 2E , a first in-ear piece  202  has a reference electrode (R)  210  adapted to measure the voltage fluctuations to be used as the reference electrical potential for the computation of the brain electrical activity. A second in-ear piece  202  has at least one captor electrode (C)  212 A to measure the voltage fluctuations to be used as the active electrical potential for the computation of the brain electrical activity. Either one of the in-ear pieces  202  comprises a ground electrode (G)  208  adapted to measure electrical noise and to prevent power line noise from interfering with the computation of the brain electrical activity. The computation of the brain electrical activity performed by the analysis system  201  corresponds to the difference between the CG voltage and the RG voltage (i.e. CG minus RG). Notice that for contralateral EEG readings one or both of the in-ear pieces  202  can be replaced by a behind-the-ear piece  204 , without departing from the present device  200 . 
     It shall be recognized that the captor electrodes ( 212 A,  212 B,  212 C,  212 D,  212 E,  212 F,  212 G and  212 H) may have any suitable shape, placement or orientation and may vary in number from one embodiment to another without departing from the scope of the present invention. For instance, the placement and number of electrodes as shown in the behind-the-ear pieces  204  of  FIGS. 2A and 2B  produce effective readings among a number of people each having a different yet most common ear morphologies. 
     It shall further be recognized that the in-ear piece  202 , can have a variety of shapes and a variety of number of electrodes. For instance, as presented in  FIG. 2F , the in-ear piece  202  can be a customized ear-piece ( 230  and  240 ) that is molded according to the outer-ear canal shape of the user. The in-ear piece  202  can also be a generic ear-piece  250  that is shaped or that has a modifiable shape to adequately fit within the outer-ear canal of all users or for a range of users. As further presented in  FIG. 2F , the in-ear piece  202  can have a plurality of electrodes ( 232  and  234 ) such as the dual electrode ear-piece  230 . The in-ear piece  202  can also comprise a single electrode such as the single electrode ear-pieces ( 240  and  250 ). Depending on the ear device  200  configuration, the single electrode is either a captor electrode, a ground electrode or a reference electrode. Notice that the single electrode ear-piece  240  has one electrode  242  that is shaped to occupy a partial surface of an ear-canal engaging member  244 . However, the single electrode ear-piece  250  has one electrode  252  that is shaped to occupy an entire surface of an ear-canal engaging member  254 . 
     A skilled person shall recognize that if the base  211  were custom molded or printed to properly fit a specific ear morphology the placement and the number of captor electrodes may be reduced to two or three, without departing from the scope of the present ear device  200 . 
     It shall be recognized that the captor electrodes ( 212 A,  212 B,  212 C,  212 D,  212 E,  212 F and  212 G), the ground electrode  208  and the reference electrode  210  can be used as dry or wet electrodes. When used as wet electrodes a conductive paste is be applied to the skin. 
     According to one embodiment, the shape and size of the base  211  and the shape size of the electrodes ( 212 A,  212 B,  212 C,  212 D,  212 E,  212 F,  212 G and  212 H) are defined according to an outer ear impression of a user, in order to obtain a customized fit for the user. According to another embodiment, the shape and size of the bases  211 A and  211 B and the shape and size of the electrodes ( 212 A,  212 B,  212 C,  212 D,  212 E,  212 F,  212 G and  212 H) are defined according to an outer ear impression taken from a plurality of participants in order to obtain an adequate skin contact for a larger group of people. The shape and size of the present behind-the-ear piece  204  presented in  FIGS. 2A and 2B  were determined according to outer ear impressions taken from ten participants. 
     According to one embodiment, the shape and size of the canal engaging member  206  and the shape and size of the ground and reference electrodes ( 208  and  210 ) are defined according to an ear canal impression of a user, in order to obtain a customized fit for the user. According to another embodiment, the shape and size of the canal engaging member  206  and the shape and size of the ground and reference electrodes ( 208  and  210 ) are defined according to an ear canal impression taken from a plurality of participants in order to obtain an adequate skin contact for a larger group of people. The shape and size of the in-ear piece  202  presented in  FIG. 2A  was determined according to in-ear impressions taken from ten participants. 
     Additive manufacturing and casting techniques have been used to produce the present behind-the-ear piece  204 . It shall however be recognized that other techniques such as etching and molding are also possible to produce the behind-the-ear piece  204 . 
     It shall be recognized that the ear device  200  could be integrated with other audio devices, such as hearing aids and headphones, to build next-generation devices that dynamically adapt to the listener&#39;s intentions and cognitive state changes. 
     Experiment 
     The present study evaluates the signal quality of auditory steady state responses (ASSRs) obtained with the unobtrusive ear device  200 , incorporating in- and around-the-ear electrodes and compared to those obtained with well-established gold-plated electrodes. 
     In one experiment, five men aged between 19 years and 29 years and having hearing thresholds below 20 dB HL (from 125 Hz to 8 kHz) were assessed. 
     A typical experiment procedure included two recording sessions which purpose was to compare ASSRs scalp-recorded with the behind-the-ear piece  204  and in-ear piece  202  to those obtained with gold foil  130  or gold-plated cup electrodes  120 . For both experiments, the stimuli consisted of four pure tones (500, 1000, 2000 and 4000 Hz) amplitude modulated at 40 Hz with a depth of 100%. The different placements used for each experiment are reported in the table  400  of  FIG. 4A . 
     Although the ear device  200  signals show lower amplitudes, corresponding signal-to-noise ratios of ASSRs recorded with the ear device  200  were similar to those of ASSRs recorded with gold electrodes ( 120  or  130 ), as presented in graphs  402  and  404  of  FIGS. 4B and 4C . As a consequence, the proposed ear device  200  seems to be a promising candidate for future small, mobile, and unobtrusive BCI platforms. 
     While illustrative and presently preferred embodiment(s) of the invention have been described in detail hereinabove, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.