Patent Publication Number: US-2023137601-A1

Title: Method for detecting an activity of eyes of a user of glasses

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Italian Application No. 102021000027866 filed on Oct. 29, 2021, which application is hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a method for detecting an activity of eyes of a user of glasses. In particular, it relates to a detection method based on the use of electrodes configured to detect electrostatic charge variations generated by movements of the eyes, to a pair of glasses thereof comprising the electrodes and a control unit configured to implement the detection method, and to a computer program product thereof. 
     BACKGROUND 
     As known, electrooculography (EOG) is a technique to measure the corneo-retinal potential (CRP) that exists between the front portion (e.g., comprising the cornea) and the back portion (e.g., comprising the retina) of the human eye. In fact, the eye acts as a dipole where the front pole at the cornea is positive and the back pole at the retina is negative. 
     EOG is a commonly used measure as CRP is higher than the potentials involved in electroencelography (EEG signals) since the eye is placed outside the skull and therefore there is no bone structure that attenuates the electrical signal generated. To measure the eye movement, pairs of electrodes are placed around the eye and in contact with the skin of the face and, for example, a pair of electrodes above and below the eye and a pair of electrodes to the left and right of the eye. 
     In greater detail, when the eye rotates around an own center of rotation (e.g., substantially central to the same eyeball), it generates a CRP variation which is detected through the electrodes. In particular, when the eyelid closes the cornea moves in one direction while when the eyelid opens the cornea moves in the opposite direction, and this generates a CRP variation that is clearly recognizable and associable with this blink. The signal resulting from a blink generally has a low frequency, for example comprised between about 1 Hz and about 13 Hz. 
     Blinks have been shown to be correlated to a person&#39;s mental state, and in particular they are indicative of cognitive states such as relaxation or attention. For example, the Inter-Eye blink interval (IEBI) is a known and reliable biomarker of the degree of concentration of a person intent on performing an activity that requires visual attention, such as watching a film or performing manual work. 
     SUMMARY 
     The detection of movements of the eyes, such as blink, may be relevant for applications aimed at determining the attention level of the user, the risks resulting from sleep and fatigue, visual disturbances or neurodegenerative diseases, or more simply to automatically activate functions in mobile and portable devices. In fact, detecting the movements of the eyes is relevant in applications such as smart glasses where knowing the direction of the gaze of the person who is wearing them is important, as well as acquiring commands provided by the person (e.g., blink, etc.). For example, eye tracking may activate advanced functions for adjusting the focal point of a camera lens or quick reading functions such as zoom and panoramic operations. 
     However, this known measurement technique suffers from the following problems: measurement noise due to alternating electric current at 50 Hz or 60 Hz possibly present in the environment where the measurement is carried out; noise due to head and body movements during the measurement; artifacts in the measurement caused by the operation of electrical apparatuses present in proximity to the electrodes; measurement errors due to contraction of the facial or neck muscles, or to the slipping of the electrodes on the skin due to sweat and eyelid blink. 
     Embodiments provide a method for detecting the activity of eyes of a user of glasses, the glasses and a computer program product that overcome the drawbacks of the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, preferred embodiments are now described, purely by way of non-limiting example, with reference to the attached drawings, wherein: 
         FIG.  1    is a perspective view of a pair of glasses comprising first electrostatic charge variation sensors, according to an embodiment; 
         FIG.  2    is a block diagram schematically illustrating the glasses of  FIG.  1   ; 
         FIG.  3    schematically shows two electrodes of one of the first electrostatic charge variation sensors of  FIG.  1   , relative to an eye of a user exemplarily shown in three different positions; 
         FIG.  4    is a perspective view of a different embodiment of the glasses comprising the first electrostatic charge variation sensors and second electrostatic charge variation sensors; 
         FIG.  5    is a block diagram of a method for detecting an activity of eyes of a user of the glasses of  FIG.  1   , according to an embodiment; 
         FIGS.  6 - 9  and  13    are graphs of electrical signals acquired through the first and second electrostatic charge variation sensors of  FIGS.  1  and  4   ; 
         FIGS.  10 - 12    are respective block diagrams of respective and further embodiments of the method for detecting the activity of eyes of the user of the glasses of  FIG.  1  or  4   . 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
       FIG.  1    shows a pair of glasses  10  wearable on a user&#39;s face (not shown). In particular, the glasses  10  comprise a frame  12  (optional) having a first and a second support portion  12   a  and  12   b  (e.g., of annular shape) which support and/or accommodate a first and, respectively, a second lens  14   a  and  14   b.  For example, the glasses  10  may be prescription or sun glasses, or be smart glasses. 
     The glasses  10  further comprise a main control unit  21  and one or more first electrostatic charge variation sensors electrically coupled to the main control unit  21  and fixed to the frame  12 , and therefore arranged in proximity to the eyes of the user when the latter wears glasses  10 . 
     According to an exemplary embodiment, the main control unit  21  (such as a microprocessor, a microcontroller or a dedicated calculation unit) comprises, coupled to each other, a processing unit  21   a  and a data storage unit  21   b  (such as a memory, e.g. a non-volatile memory) for storing the acquired data. For example, the main control unit  21  is integrated into the frame  12 . 
     In the embodiment exemplarily considered hereinafter and shown in  FIG.  1   , a first left electrostatic charge variation sensor and a first right electrostatic charge variation sensor (shown in  FIG.  1    with the respective references  20   a  and  20   b ) carried by the first and, respectively, by the second support portions  12   a  and  12   b  are exemplarily considered; however, the number of first electrostatic charge variation sensors may be smaller (e.g., only the first left electrostatic charge variation sensor  20   a  is present) or greater (e.g., two or more first electrostatic charge variation sensors for each of the support portions  12   a  and  12   b ). 
     In particular and as better shown in  FIG.  2   , each first electrostatic charge variation sensor  20   a,    20   b  comprises a sensor control unit  15  and two or more electrodes which are spaced from each other, are fixed to the frame  12  and are electrically coupled to the sensor control unit  15 . In the embodiment exemplarily considered hereinafter and shown in  FIGS.  1  and  2   , a first and a second electrode shown with the respective references  22   a  and  22   b  for each first electrostatic charge variation sensor are exemplarily considered; however, the number of electrodes for each first electrostatic charge variation sensor  20   a,    20   b  may be greater (e.g., four electrodes). 
     In use, each electrode  22   a,    22   b  detects a respective electrostatic charge variation caused by movements of the eyes of the user, as better discussed below, and generates a respective detection signal S R  indicative of said electrostatic charge variation. 
     In detail, each electrode  22   a,    22   b  may have a metal surface or be totally metal coated by dielectric material, or even have a metal surface arranged under an external case of the glasses  10 . In any case, during use, each electrode  22   a,    22   b  is electrostatically coupled to the environment having the glasses  10  present therein, and in greater detail to the user&#39;s eye which is closest to said electrode  22   a,    22   b,  in order to detect the induced electrostatic charge variation thereof. 
     According to an embodiment, each electrode  22   a,    22   b  is integrated into the external case of the glasses  10 , and for example comprises a conductive track formed on, or in, a semiconductor material wafer comprised in the glasses  10 . According to a different embodiment, each electrode  22   a,    22   b  is a metal element present in the glasses  10 . Optionally, when a possible use of the glasses  10  in a humid environment (more specifically in water) is envisaged, each electrode  22   a,    22   b  is inserted inside a waterproof case or in any case it is shielded by one or more protective layers, so as to prevent direct contact of the electrode  22   a,    22   b  with water or humidity: in this case, the waterproof case or the one or more protective layers are of a material (e.g., dielectric or insulating material, such as plastics) such that it does not shield the electrostatic charge generated by the user&#39;s eye, which needs to be acquired by the electrode  22   a,    22   b.  Other embodiments are possible, as apparent to the person skilled in the art, so that the electrodes  22   a,    22   b  are electrostatically coupled to the user&#39;s eyes during use. 
     Furthermore, according to an exemplary embodiment, the sensor control unit  15  (such as a microprocessor, a microcontroller or a dedicated calculation unit) comprises, coupled to each other: an interface unit  17  (optional and of known type) electrically coupled to the electrodes  22   a  and  22   b  to interface the latter with the sensor control unit  15  (e.g., the interface unit  17  comprises an amplification circuit and/or an analog-to-digital converter, ADC, not shown); a respective processing unit  16  for processing detection signals S R  acquired through the electrodes  22   a  and  22   b  (and optionally processed through the interface unit  17 ); and a respective data storage unit  18  (such as a memory, e.g. a non-volatile memory) for storing the acquired data. For example, the sensor control unit  15  is integrated into the respective electrostatic charge variation sensor  20   a,    20   b.    
     In detail, each sensor control unit  15  is configured to process (in a per se known manner, for example by amplifying and converting into digital) the respective detection signals S R  acquired through the electrodes  22   a  and  22   b  and to generate a respective first electrostatic charge variation signal S Q,1  indicative of a difference between the detection signals S R  acquired through the first and second electrodes  22   a  and  22   b.  In particular, the first electrostatic charge variation signal S Q,1  is of digital type and is indicative of a difference between the electrostatic charge variations detected through the electrodes  22   a  and  22   b.    
     According to an embodiment, the first and second electrodes  22   a  and  22   b  of each first electrostatic charge variation sensor  20   a,    20   b  are spaced from each other. In particular, the electrodes  22   a  and  22   b  have a first mutual distance D 1  from each other and, for example, are arranged on respective opposite ends of the respective support portion  12   a,    12   b  (e.g., they are diametrically opposite to each other with respect to the respective support portion  12   a,    12   b  of annular shape). For example, the first and second electrodes  22   a  and  22   b  are aligned with each other along a first axis  19  which joins the first and second lenses  14   a  and  14   b  (e.g., which joins the centers, e.g. the barycenter, of the lenses  14   a  and  14   b ). 
     In other words, as schematically shown in  FIG.  3   , the first and second electrodes  22   a  and  22   b  are arranged so that they detect the movements of the eye (indicated in  FIG.  3    with the reference  30 , and comprising eyelids and an eyeball extending in an orbital cavity) of the user when the latter wears the glasses  10 , and for example face opposite sides of the cornea (indicated in  FIG.  3    with the reference  30   a ) and, in greater detail, opposite sides of the pupil. 
     According to an embodiment shown in  FIG.  4   , the glasses  10  further comprise one or more second electrostatic charge variation sensors similar to the first electrostatic charge variation sensors  20   a  and  20   b  and therefore not further described. In the embodiment exemplarily considered hereinafter and shown in  FIG.  4   , a second left electrostatic charge variation sensor and a second right electrostatic charge variation sensor (shown in  FIG.  1    with the respective references  20   c  and  20   d ) carried by the first and, respectively, by the second lenses  14   a,    14   b  are exemplarily considered; however, the number of second electrostatic charge variation sensors may be smaller or greater. 
     Each second electrostatic charge variation sensor  20   c,    20   d  comprises respectively, instead of the first and the second electrodes  22   a  and  22   b,  a third and a fourth electrode  22   c  and  22   d  which are spaced both from each other and with respect to the first and second electrodes  22   a  and  22   b  and which are similar to the first and second electrodes  22   a  and  22   b  (and therefore are not described again in detail). In particular, the third and fourth electrodes  22   c  and  22   d  are radially internal with respect to the first and second electrodes  22   a  and  22   b  with respect to the center of the respective lens  14   a,    14   b.  For example, the third and fourth electrodes  22   c  and  22   d  have a second mutual distance D 2  from each other that is less than the first mutual distance D 1  and, for example, are fixed to the respective lens  14   a,    14   b  so as to face the eye  30  of the user when the latter wears the glasses  10 . For example, the third and fourth electrodes  22   c  and  22   d  are aligned with each other and with the first and second electrodes  22   a  and  22   b  along the first axis  19 , such that the third and fourth electrodes  22   c  and  22   d  are interposed between the first and second electrodes  22   a  and  22   b.  In other words, as schematically shown in  FIG.  4   , when the user wears the glasses  10 , the third and fourth electrodes  22   c  and  22   d  are arranged so as to detect the movements of the eye  30  and for example one faces the lacrimal caruncle and the other faces the opposite end of the eye  30  with respect to the lacrimal caruncle. In this embodiment, each sensor control unit  15  is further configured, similarly to what has been previously described for the first and second electrodes  22   a  and  22   b,  to process (in a per se known manner, for example by amplifying and converting into digital) the respective detection signals S R  acquired through the third and fourth electrodes  22   c  and  22   d  and to generate a respective second electrostatic charge variation signal S Q,2  indicative of a difference between the detection signals S R  acquired through the third and fourth electrodes  22   c  and  22   d.  In particular, the second electrostatic charge variation signal S Q,2  is of digital type and is indicative of a difference between the electrostatic charge variations detected through the third and fourth electrodes  22   c  and  22   d.    
     In general, since the eye  30  operates as an electric dipole with a positive pole at the cornea  30   a  and a negative pole at the retina (indicated in  FIG.  3    with the reference  30   b ), the movements of the eye  30  generate electric field variations in the environment surrounding the eye  30 , and these electric field variations induce variations in the induced electrostatic charge which are detectable through the electrodes  22   a  and  22   b  (and through the electrodes  22   c  and  22   d,  if any). Since the electrodes  22   a  and  22   b  (and the electrodes  22   c  and  22   d,  if any) are physically and electrically separated from each other, they are at different distances from each other with respect to the cornea  30   a  and the retina  30   b  and therefore detect electrostatic charge variations which differ from each other. This allows a differential detection of the electrostatic charge variations, as better discussed below. This allows both the movements of the eyes in the absence of blink and the eyelash blinks (or eyelid blinks) of the user to be detected, as it has been shown that each blink corresponds to a respective electrostatic charge variation indicative of the blink. 
     In greater detail, it has been verified that these movements of the eyes  30  in the presence of blinks generate, in each first electrostatic charge variation signal S Q,1  and in succession to each other in a blink period with a duration of less than about 50 ms, two respective peaks having opposite sign with respect to a baseline of this signal. In particular, by exemplarily considering a zero baseline, it is possible to have a first positive peak and a second negative peak or vice versa, as a function of the direction of movement of the eyes  30  and of the positions of the first and second electrodes  22   a  and  22   b.  These first and second consecutive peaks in the blink period define a blink scheme (or pattern) that is indicative of a blink (a voluntary or involuntary blink, as better discussed below). Examples of such blink patterns are provided in  FIGS.  6 - 7 C  and better described below. 
     Instead, the movements of the eyes  30  in the absence of complete closure of the eyelids generate respective peaks, isolated from each other over time, in the second electrostatic charge variation signals S Q,2 . In particular, such peaks in the second electrostatic charge variation signals S Q,2  may be positive or negative (the latter are also referred to as valleys) with respect to respective baselines of the second electrostatic charge variation signals S Q,2  (e.g., here exemplarily considered to be equal to 0), as a function of the direction of movement of the eyes  30  and of the position of the third and the fourth electrodes  22   c  and  22   d.  An example of such peaks in the second electrostatic charge variation signals S Q,2  is provided in  FIG.  9    and is better described below. 
     In use, the main control unit  21  implements a detection method  50  of activity (i.e. of movement or state) of the eyes  30  of the user. 
     An embodiment of the detection method  50  is shown in  FIG.  5    and is now discussed. 
     The detection method  50  is performed iteratively, so as to update the information on the activity of the eyes  30  of the user in real time. For the sake of simplicity, an iteration of the detection method  50 , also referred to as the current iteration, is described below. 
     At a step S 10  of the detection method  50 , the first electrostatic charge variation signals S Q,1  are acquired through the first electrostatic charge variation sensors  20   a  and  20   b.  Hereinafter, the first electrostatic charge variation signal S Q,1  acquired through the first left electrostatic charge variation sensor  20   a  is also indicated with the reference S Q,1a , while the first electrostatic charge variation signal S Q,1  acquired through the first right electrostatic charge variation sensor  20   b  is also indicated with the reference S Q,1b . In particular, the first electrostatic charge variation signals S Q,1a , S Q,1b  are acquired through a scrolling buffer. In detail, at each iteration the first electrostatic charge variation signals S Q,1a , S Q,1b  are acquired in a respective time window for example having a predefined duration equal to a time window period (e.g. equal to a few thousand ms, e.g. comprised between about 900 ms and about 2500 ms and e.g. equal to 1800 ms) greater than the blink period; in other words, at each iteration the first electrostatic charge variation signals S Q,1a , S Q,1b  with a time duration equal to the time window period are considered. At each iteration, the oldest sample of each first electrostatic charge variation signal S Q,1a , S Q,1b  is deleted and a new sample of each first electrostatic charge variation signal S Q,1a , S Q,1b  is stored in the buffer. 
     In greater detail, at the current iteration the detection signals S R  of the first and second electrodes  22   a  and  22   b  of the first electrostatic charge variation sensors  20   a  and  20   b  are generated and the respective first electrostatic charge variation signals S Q,1a , S Q,1b  are calculated as a function of the detection signals S R  (in particular, each first electrostatic charge variation signal S Q,1a , S Q,1b  is equal to, or proportional to, the difference between the detection signals S R  of the first and the second electrodes  22   a  and  22   b  of the respective first electrostatic charge variation sensor  20   a,    20   b ). 
     At a step S 12 , optional and immediately consecutive to step S 10 , the first electrostatic charge variation signals S Q,1a  and S Q,1b  are filtered to remove the contribution of the alternating electric current possibly present in the environment surrounding the glasses  10 . In fact, if any, the alternating electric current generates respective electrostatic charge variations in the environment, which may be detected by the first electrostatic charge variation sensors  20   a  and  20   b  generating a respective peak, in the frequency domain, in the first electrostatic charge variation signals S Q,1a , S Q,1b  at the frequency of the alternating electric current (i.e. 50 Hz or 60 Hz depending on the country one is in). In particular, the performed filtering may be of low-pass type with a cut-off frequency lower than a first threshold frequency (e.g., equal to about 25 Hz), or of band-pass type with a lower cut-off frequency greater than a second threshold frequency (lower than the first threshold frequency and for example equal to about 1 Hz) and with a higher cut-off frequency lower than the second threshold frequency and for example equal to 20 Hz, or of notch type with a lower cut-off frequency lower than the second threshold frequency and for example equal to 20 Hz, and with a higher cut-off frequency greater than a third threshold frequency (greater than the first threshold frequency and for example equal to about 80 Hz). 
     At a step S 14 , optional and immediately consecutive to step S 12 , the first electrostatic charge variation signals S Q,1a  and S Q,1b  are processed to remove an offset of the latter, and in detail to subtract a respective baseline of the latter (i.e. a reference value, not necessarily constant over time, around which the respective first electrostatic charge variation signal S Q,1a  and S Q,1b  develops; e.g., an average value) from each of them. In this manner, subsequently the variations of the first electrostatic charge variation signals S Q,1a  and S Q,1b  may be taken into account with respect to a zero baseline, and possible offset thereof are not to be considered. 
     At a step S 16 , immediately consecutive to step S 14 , the first electrostatic charge variation signals S Q,1a  and S Q,1b  are processed in a per se known manner to identify any peaks thereof (i.e. positive peaks or negative peaks, the latter also referred to as valleys). In detail, at step S 16 , if any, a number of peaks of the first electrostatic charge variation signals S Q,1a  and S Q,1b  and, for each peak, a respective maximum value and a respective time position (or instant) of this maximum value are identified. Greater details regarding the identification modes of these peaks may be found in the Italian patent document identified by the reference number 102021000012665, of the present Applicant. Alternatively, the portions of the first electrostatic charge variation signals S Q,1a  and S Q,1b  that have a greater value than a threshold value (e.g., a predefined value for example equal to about 200 LSB or a value equal to about 10% of the maximum value of the respective first electrostatic charge variation signal S Q,1a , S Q,1b  in the considered time window) are considered. 
     At a step S 18 , immediately consecutive to step S 16 , it is determined whether a condition on the blink patterns of the first electrostatic charge variation signals S Q,1a  and S Q,1b  is verified. In particular, it is determined whether at least one blink pattern has been detected in at least one of the first electrostatic charge variation signals S Q,1a  and S Q,1b . In other words, it is determined whether a sum of the number of blink patterns of the first electrostatic charge variation signals S Q,1a  and S Q,1b  is non-zero. 
     If the condition on the blink patterns is not verified (i.e. said sum is equal to zero), the current iteration of the detection method  50  ends and the method returns to step S 10  to process the first electrostatic charge variation signals S Q,1a  and S Q,1a  in a subsequent time window. 
     If the condition on the blink patterns is verified (i.e. said sum is greater than zero), the detection method  50  proceeds to a step S 20 . 
     At step S 20 , immediately consecutive to step S 18 , it is verified whether the detected blink patterns of the first electrostatic charge variation signals S Q,1a  and S Q,1b  at the current iteration are indicative of a first condition of the eyes  30  of the user (i.e. whether a voluntary blink, hereinafter also referred to as eye click or more simply click, has occurred). In greater detail, for each pair of consecutive blink patterns of the first electrostatic charge variation signals S Q,1a  and S Q,1b , the first condition is verified if these two blink patterns have a relative time distance greater than a first threshold period that is smaller than the time window period and greater than the blink period (for example it is equal to a few hundred ms, e.g. comprised between about 100 ms and about 800 ms and for example equal to 500 ms). For example, the relative time distance is calculated between reference points of the two blink patterns, similarly to what has been described hereinbelow with reference to the click time distances. Therefore, when the first condition is verified, a click has been detected at the current iteration. 
     A step S 22 , immediately consecutive to step S 20 , is a decision block that verifies whether the first condition has been detected or not at step S 20 . 
     In the present embodiment, if the first condition has not been verified (i.e. no click has been detected) the detection method  50  proceeds to a step S 24 . 
     If the first condition has been verified (i.e. a click has been detected), the detection method  50  proceeds to a step S 32 . 
     Step S 24  refers to a second condition of the eyes  30  of the user (i.e. to an involuntary blink, hereinafter also referred to as eye blink or more simply blink). In general, a blink has a shorter duration than a click as it occurs in an involuntary manner, and involves both eyes simultaneously (unlike the click that is performed with only one eye). In the present embodiment, the first and second conditions are alternative to each other, and therefore the second condition is detected when the first condition is not detected. 
     At step S 24 , an IEBI (“Inter-Eye blink interval”) parameter, of a known type, is therefore calculated as a function of the first electrostatic charge variation signals S Q,1a  and S Q,2a , and in particular as a function of the peaks of the first electrostatic charge variation signals S Q,1a  and S Q,1b . The IEBI parameter is indicative of a blink frequency of the eyes  30  of the user, and in particular is indicative of an average, calculated over a predefined period (e.g., 1 minute), of the distances between blinks that are consecutive to each other over time. 
     In particular,  FIG.  6    shows the first electrostatic charge variation signals S Q,1a  and S Q,1b  in the time window of the current iteration, and two blink patterns of the first electrostatic charge variation signals S Q,1a  and S Q,1b  which define a blink. In detail, each blink is defined by a first blink pattern P 1  of one of the first electrostatic charge variation signals (here exemplarily S Q,1a ) and by a second blink pattern P 2  of the other first electrostatic charge variation signal (here exemplarily S Q,1b ), where the first and second blink patterns P 1  and P 2  are less distant from each other than the first threshold period. For example, the time positions t MK1  and t MK2  of the maximum values M K1  and M K2  of the first peaks (indicated in  FIG.  6    with the respective references K 1  and K 2 ) of the first and the second blink patterns P 1  and P 2  of the considered blink are distant from each other by a first time interval T 1  less than the first threshold period. 
     In greater detail, the IEBI parameter is indicative of the average, calculated in the predefined period, of the relative distances (not shown and hereinafter also referred to as blink time distances) between two consecutive blinks, and in detail between respective reference points of the two consecutive blinks. Each reference point may for example be a value such as the time position t MK1 , t MK2 , t MK3  or t MK4  of the maximum value M K1 , M K2 , M K3 , M K4  of the first (K 1  and K 2 ) or of the second (K 3  and K 4 ) peak of the first (P 1 ) or of the second (P 2 ) blink pattern of the blink. For example, the blink time distances used for the calculation of the IEBI parameter may be the distances between the time positions t MK1  of the maximum values M K1  of the first peaks K 1  of the first blink patterns P 1  of two consecutive blinks. 
     In particular, the IEBI parameter is updated at each iteration in which the second condition is verified. For example, at a first iteration (e.g., i=1) of the detection method  50 , the IEBI parameter is set to a predefined value (e.g., equal to 5 s), and at each subsequent iteration in which the occurrence is detected of a blink (e.g., i=N) it is recalculated as a function of both the own value at the immediately preceding iteration (e.g., i=N−1) and the blink time distance calculated at the current iteration (e.g., i=N). 
     At a step S 26 , immediately consecutive to step S 24 , it is determined whether a condition on the IEBI parameter is verified or not, in order to determine an attention (or concentration) state of the user. In particular, it is verified whether the IEBI parameter is greater than an IEBI threshold value (e.g., comprised between about 3 s and about 12 s and for example equal to about 8 s) indicative of a threshold attention level of the user. 
     If the condition on the IEBI parameter is verified (i.e. the IEBI parameter is greater than the IEBI threshold value), a first activity of the eyes  30  of the user is detected (step S 28 ). The first activity of the eyes  30  is indicative of a first attention state of the user which corresponds to a low (or lower) attention level of the user. 
     If the condition on the IEBI parameter is not verified (i.e. the IEBI parameter is lower than, or equal to, the IEBI threshold value), a second activity of the eyes  30  of the user is detected (step S 30 ). The second activity of the eyes  30  is indicative of a second attention state of the user which corresponds to a high (or higher) attention level of the user. 
     As evident, the terms “high” and “low” mentioned in the present description with reference to the attention level are not to be understood in an absolute sense, but rather relatively to each other and in connection with the activity being performed (where the distinction is given by the IEBI threshold value). 
     At step S 32  a relative distance (hereinafter also referred to as the click time distance) between two detected and consecutive clicks of the first electrostatic charge variation signals S Q,1a  and S Q,1b  is calculated as a function of the first electrostatic charge variation signals S Q,1a  and S Q,1b  and in particular as a function of the peaks of the first electrostatic charge variation signals S Q,1a  and S Q,1b . 
     In particular,  FIGS.  7 A- 7 C  each show the first electrostatic charge variation signals S Q,1a  and S Q,1b  in the current time window, and two blink patterns of the first electrostatic charge variation signals S Q,1a  and S Q,1b  which define two respective clicks. In detail, each click is defined by a respective blink pattern (in  FIGS.  7 A- 7 C  indicated for example by P 4 ) of one of the first electrostatic charge variation signals S Q,1a  and S Q,1b , where this blink pattern P 4  is distant from the immediately preceding blink pattern (in  FIGS.  7 A- 7 C  indicated for example by P 3 ) more than the first threshold period. For example, the time positions t MK5  and t MK6  of the maximum values M K5  and M K6  of the first peaks K 5  and K 6  of the considered blink pattern P 4  and, respectively, of the immediately preceding blink pattern P 3  are distant from each other by a second time interval T 2  greater than the first threshold period. The blink pattern P 4  that defines the last considered click may be part of the same first electrostatic charge variation signal of the previous blink pattern P 3  (S Q,1a  in  FIG.  7 A  and S Q,1b  in  FIG.  7 B ) or may be part of a first electrostatic charge variation signal (in  FIG.  7 C , exemplarily S Q,1b ) different from that of the previous blink pattern P 3 . 
     In greater detail, the click time distance is defined between respective reference points of the last two detected clicks (P 3  and P 4  in  FIGS.  7 A- 7 C ). Each reference point may for example be a value such as the time position t MK5 , t MK6 , t MK7  or t MK8  of the maximum value M K5 , M K6 , M K7 , M K8  of the first (K 5  and K 6 ) or of the second (K 7  and K 8 ) peak of the two blink patterns P 3  and P 4  which define said last two consecutive clicks. For example, the click time distance may coincide with the second time interval T 2 . 
     At a step S 34 , immediately consecutive to step S 32 , it is determined whether a condition on the click time distance is verified or not, in order to determine a click mode of the eyes  30  of the user. In particular, it is verified whether the click time distance is less than a click threshold distance (greater than the first threshold period, e.g. comprised between about 200 ms and about 1 s and for example equal to about 700 ms) indicative of a threshold level which identifies a double click (better described hereinbelow). 
     If the condition on the click time distance is verified (i.e. the click time distance is less than the click threshold distance), a third activity of the eyes  30  of the user is determined (step S 36 ). The third activity is indicative of said double click which corresponds to two voluntary clicks close to each other over time, as shown in  FIG.  8 A  with exemplary reference to the first electrostatic charge variation signal S Q,1a . In other words, the double click is made by two blink patterns between which the respective click time distance (indicated in  FIG.  8 A  with the reference number T 2 ′) is less than the click threshold distance (also referred to as the second threshold period). 
     If the condition on the click time distance is not verified (i.e. the click time distance is greater than, or equal to, the click threshold distance), a fourth activity of the eyes  30  of the user is determined (step S 38 ). The fourth activity is indicative of a single click, i.e. of a voluntary click isolated over time, as shown in  FIG.  8 B  with exemplary reference to the first electrostatic charge variation signal S Q,1a . In greater detail, the single click is made by a blink pattern that has a click time distance (indicated in  FIG.  8 B  with the reference number T 2 ″), with respect to the blink pattern of the immediately preceding click, which is greater than the second threshold period. 
     According to an embodiment of the detection method  50 , shown in  FIG.  10   , a plurality of further steps (indicated as a whole with the reference S 40 ) are further comprised in the detection method  50  between step S 22  and step S 24 . 
     Furthermore, in the present embodiment steps S 10 -S 16  previously described are performed not only for the first electrostatic charge variation signals S Q,1a  and S Q,1b  but also for the second electrostatic charge variation signals S Q,2a  and S Q,2b  acquired through the third and fourth electrodes  22   c  and  22   d  of the second electrostatic charge variation sensors  20   c  and  20   d.  In particular, step S 16  is performed for the second electrostatic charge variation signals S Q,2a  and S Q,2b  in order to detect possible peaks (positive or negative) thereof, similarly to what has been previously described for the detection of blink patterns in the first electrostatic charge variation signals S Q,1a  and S Q,1b . In particular,  FIG.  9    shows an example of second electrostatic charge variation signal (here exemplarily S Q,2a ), wherein two peaks K 9  and K 10  are exemplarily shown, isolated from each other over time and which do not define any blink pattern. For example, the peak K 9  is positive (i.e. the respective maximum value M K9  is greater than 0, i.e. than the baseline of the second electrostatic charge variation signal S Q,2a ) and the peak K 10  is negative (i.e. the respective maximum value M K10  is lower than 0, i.e. than the baseline of the second electrostatic charge variation signal S Q,2a ). 
     At a step S 40   a,  consecutive to step S 22  and interposed between step S 22  and step S 24 , it is verified whether the second electrostatic charge variation signals S Q,2a  and S Q,2b  acquired at the current iteration through the third and fourth electrodes  22   c  and  22   d  are indicative of a third condition of the eyes  30  of the user. In greater detail, the third condition is indicative of a movement of the eyeballs of the eyes  30  in the orbital cavity in the absence of complete closure of the eyelids; in other words, the third condition is correlated to a rotation of the eyeballs which does not require the closure of the eyelids (i.e. the mutual contact of the upper eyelid and of the lower eyelid of each eye  30 ). The third condition is verified if the presence of at least one single peak is identified in each second electrostatic charge variation signal S Q,2a , S Q,2b . This single peak is a peak isolated over time with respect to the other peaks of the second electrostatic charge variation signal S Q,2a , S Q,2b  and which is not part of any blink pattern. In particular, the single peak of the second electrostatic charge variation signal S Q,2a , S Q,2b  is a peak that has no counterpart in the first electrostatic charge variation signals S Q,1a , S Q,1b  (i.e. the first electrostatic charge variation signals S Q,1a , S Q,1b  have no peak at the time position of the single peak of the second electrostatic charge variation signal S Q,2a , S Q,2b ). 
     If the third condition has not been verified (i.e. no movement of the eye  30  has been detected in the absence of complete closure of the eyelids), the detection method  50  proceeds to step S 24  previously described as it is detected that the second condition is verified (i.e. a blink has been detected). 
     If the third condition has been verified (i.e. a movement of the eyes  30  has been detected in the absence of complete closure of the eyelids), the detection method  50  proceeds to a step S 40   b.  Optionally, the method may also proceed simultaneously with both step S 24  and step S 40   b.    
     At step S 40   b,  consecutive to step S 40   a,  the orientation is detected with respect to the baseline of the respective second electrostatic charge variation signal S Q,2a , S Q,2b , of the one or more single peaks detected in the second electrostatic charge variation signals S Q,2a , S Q,2b  which identify respective movements of the eyeballs of the eyes  30  in the absence of complete closure of the eyelids. In detail, exemplarily considering only one second electrostatic charge variation signal S Q,2a , S Q,2b  and only one single peak of the latter, at step S 40   b  it is verified whether the single peak is positive (i.e. whether the respective maximum value is greater than the baseline, here considered zero in view of step S 14 ) or negative (i.e. whether the respective maximum value is lower than the baseline, here considered zero in view of step S 14 ). 
     A step S 40   c,  consecutive to step S 40   b,  is a decision step wherein it is determined whether, for each detected single peak of the second electrostatic charge variation signals S Q,2a , S Q,2b , a fourth condition which exemplarily corresponds to a predefined orientation of said single peak (e.g., positive orientation) is verified. 
     If the fourth condition has been verified (i.e. the single peak is positive), the detection method  50  proceeds to a step S 40   d.    
     If the fourth condition has not been verified (i.e. the single peak is negative), the detection method  50  proceeds to a step S 40   e.    
     If the fourth condition is verified, a fifth activity of the eyes  30  of the user is determined (step S 40   d ). The fifth activity is indicative of a first movement of the eyes  30 . For example, the first movement corresponds to a movement of the cornea  30   a  from right to left relative to the user&#39;s point of view, and/or to a movement of the cornea  30   a  from the third electrode  22   c  to the fourth electrode  22   d  of the second left electrostatic charge variation sensor  20   c;  nevertheless, the orientation of the first movement obviously depends on the position of the third and fourth electrodes  22   c  and  22   d  with respect to the eye  30 , and therefore may also correspond, for example, to a movement of the cornea  30   a  from left to right. 
     If the fourth condition is not verified, a sixth activity of the eyes  30  of the user is determined (step S 40   e ). The sixth activity is indicative of a second movement of the eyes  30 . In particular, the second movement is opposite to the first movement; in other words it is performed in the opposite direction to the first movement. For example, the second movement corresponds to a movement of the cornea  30   a  from left to right, and/or to a movement of the cornea  30   a  from the fourth electrode  22   d  to the third electrode  22   c;  nevertheless, the orientation of the second movement obviously depends on the position of the third and fourth electrodes  22   c  and  22   d  with respect to the eye  30 , and therefore may also correspond, for example, to a movement of the cornea  30   a  from right to left. 
       FIG.  11    shows a further embodiment of the detection method  50 . 
     In the present embodiment, the detection method  50  comprises further steps S 03 -S 07  preceding step S 10  and the glasses  10  further comprise one or more accelerometers (not shown) and one or more gyroscopes (not shown). Hereinafter, exemplary reference is made to the case of an accelerometer and a gyroscope, although a greater number of accelerometers and/or gyroscopes may similarly be considered. In particular, the accelerometer and the gyroscope are fixed to the glasses  10  (for example to the support portions  12   a  and/or  12   b ) and are configured to detect possible movements of the user&#39;s head (e.g., lateral rotations and forward or backward bending of the head, with respect to the torso). 
     At a step S 03 , the main control unit  21  acquires, through the gyroscope, one or more angular velocity signals S ω  indicative of respective angular velocities measured by the gyroscope. These one or more angular velocities are generated by movements of the user&#39;s head, for example with respect to the user&#39;s torso. 
     At a step S 05 , for example performed simultaneously with step S 03 , the main control unit  21  acquires, through the accelerometer, one or more linear acceleration signals S acc  indicative of respective linear accelerations measured by the accelerometer. These one or more linear accelerations are generated by movements of the user&#39;s head, for example with respect to the torso. 
     At a step S 07 , it is determined whether a fifth condition is verified, as a function of the angular velocity signals S ω  and of the linear acceleration signals S acc . The fifth condition is determined when no movements of the user&#39;s head are detected. The determination of the movements of the head from the angular velocity signals S ω  and the linear acceleration signals S acc  is performed in a per se known manner (e.g., through machine learning techniques) and therefore not described in detail herein; nevertheless, details on this aspect may be found for example in the article “Absolute Orientation for Head-Tracking Using Gyroscope, Accelerometer, and Camera”, Fisher, EE 267—Virtual Reality—Stanford University—2018. 
     If the fifth condition is not verified (i.e. movements of the head are detected) the detection method  50  ends and steps S 10 -S 38  are not performed (e.g., the method returns to step S 03 ). 
     If the fifth condition is verified (i.e. no movements of the head, which is immobile, are detected), the detection method  50  proceeds to step S 10  and then the steps shown in  FIG.  5  or  10    are performed. 
     According to an embodiment not shown, the detection method  50  of  FIGS.  5 ,  10  and  11    further comprises a step of controlling, as a function of the detected activity of the eyes  30 , one or more functionalities of the same glasses  10  or of an apparatus (not shown) external to the glasses  10  and operatively coupled thereto (e.g., a smart TV or a smart household appliance). For purely illustrative and non-limiting purposes, the functionalities of the apparatus may comprise providing a sound alarm or activating a standby mode of the apparatus when the first activity (low attention level of the user) is detected, opening a folder or a document or selecting an option of the apparatus through the third and fourth activities (single and double click), and scrolling through the text of a document through the fifth and sixth activities (movements of the eyes  30  without eyelid blinking). 
     The glasses  10  and the detection method  50  previously described allow, owing to the proximity of the electrodes  22   a - 22   d  to the eyes  30 , the movements of the eyes  30  to be detected with high accuracy. In particular, eye activities may be detected indicative of the attention level of the user, of single and double clicks and of movements of the eye  30  in the absence of blink. 
     The possibility, owing to the accelerometer and to the gyroscope, to perform the detection method  50  only in the absence of movements of the user&#39;s head avoids incorrect detections of movement of the eyes, actually due to movements of the head. Furthermore, the fact that the electrodes  22   a - 22   d  are carried by the glasses  10  and are not in contact with the skin of the user&#39;s face prevents detection errors due to the slipping of the same on the skin (e.g., when the latter is humid or sweaty). 
     The detection method  50  requires reduced computational resources to be implemented, and therefore minimizes the electrical consumption required. 
     Finally, it is clear that modifications and variations may be made to the invention described and illustrated herein without thereby departing from the scope of the present invention, as defined in the attached claims. For example, the embodiments described may be combined with each other to obtain further solutions. 
     Steps S 24 -S 38  (as well as steps S 40   a -S 40   e  if any) may be optional. In general, if the first condition is not determined at step S 22 , a blink is detected, and if the first condition is determined at step S 22 , a click is detected. For example, if the first condition is not determined at step S 22 , a blink signal (not shown) is generated which assumes a first value (e.g., 0) indicative of the detection of a blink; if, on the other hand, the first condition is determined at step S 22 , the blink signal is generated with a second value (e.g., 1) indicative of the detection of a click. For example, the blink signal may be used to control the one or more functionalities of the glasses  10  or of the apparatus, similarly to what has been previously described. Following the generation of the blink signal, steps S 24 -S 38  (as well as steps S 40   a -S 40   e  if any) may optionally be performed as previously described. 
     The glasses  10  may also comprise a single control unit coupled to the electrodes  22   a - 22   d.  For purely illustrative purposes, this control unit may comprise the main control unit  21  and the sensor control units  15  or it may be the main control unit  21  and the sensor control units  15  may be absent; in these cases, the actions previously described with reference to the sensor control units  15  of the charge variation sensors  20   a,    20   b  are performed by this control unit. 
     Although the case in which the detection method  50  is performed by processing time windows superimposed on each other (scrolling buffer) has been previously described, the previous description applies in a similar manner also to the case of time windows that are consecutive and not superimposed on each other. 
     Furthermore, the number of electrostatic charge variation sensors may be greater than what has been previously considered. In particular, the glasses may comprise one or more third electrostatic charge variation sensors (not shown and similar to the second electrostatic charge variation sensors  20   c  and  20   d ), each of these comprising a respective pair of electrodes (not shown, for example a fifth and a sixth electrode) for an improved detection of the fifth and sixth activities. For example, the fifth and sixth electrodes are spaced from the electrodes  22   a - 22   d,  are radially internal with respect to the first and second electrodes  22   a,    22   b  with respect to the center of the respective lens  14   a,    14   b,  are distant from each other by the second mutual distance D 2  and are fixed to the respective lens  14   a,    14   b  so as to face the eye  30  of the user when the latter wears the glasses  10 . In particular, the fifth and sixth electrodes are angularly equi-spaced with respect to the third and fourth electrodes  22   c  and  22   d  with respect to the center of the respective lens  14   a,    14   b.  For example, the fifth and sixth electrodes are aligned with each other along a second axis (not shown) orthogonal to the first axis, such that they are arranged as a cross with respect to the third and fourth electrodes  22   c,    22   d  where the center of this cross corresponds to the center of the respective lens  14   a,    14   b  (and therefore to a center of the eye  10 , e.g. at the position of the pupil when the user&#39;s gaze is oriented along a direction orthogonal to the face). In this manner the movements of the eyes  30  in the absence of blink may be detected in a more efficient and accurate manner. Similarly to what has already been described for the third and fourth electrodes  20   c  and god, for each third electrostatic charge variation sensor the respective sensor control unit  15  is configured to process respective detection signals S R  acquired through the fifth and sixth electrodes and to generate a respective further second electrostatic charge variation signal indicative of a difference between the detection signals S R  acquired through the fifth and sixth electrodes, and therefore indicative of a difference between the electrostatic charge variations detected through the fifth and sixth electrodes. 
     Furthermore, the glasses  10  may comprise only one first electrostatic charge variation sensor (hereinafter exemplarily considered to be the first left electrostatic charge variation sensor  20   a ). In this case, the detected information refers only to one of the eyes  30  of the user (i.e. to the eye  30  having the first left electrostatic charge variation sensor  20   a  facing thereto). Nevertheless, the information obtained regarding the involuntary activity of one eye (e.g., blink and movements of the eyes in the absence of complete closure of the eyelids) may similarly be considered for the other eye as well, as the involuntary movements of the eyes (both blinks and movements of the eyes in the absence of blink) are generally substantially synchronous and dual. This consideration does not apply instead to voluntary movements of the eyes (e.g., clicks) that are deliberately performed by the user with only one eye. 
     One embodiment of the detection method  50  corresponding to the case in which only the first left electrostatic charge variation sensor  20   a  is present is shown in  FIG.  12   . In particular, when only the first left electrostatic charge variation sensor  20   a  is present the detection method  50  is similar to that previously described (in  FIG.  12    reference is made to the steps shown in  FIG.  5   , although it is clear that what has been said also applies to the embodiments of  FIGS.  10  and  11   ). 
     However, unlike the previously discussed embodiments, in  FIG.  12    steps S 10 -S 16  are performed only for the first electrostatic charge variation signal S Q,1a . 
     Furthermore, the determination of the first condition (previously step S 20 , replaced in  FIG.  12    with the new reference S 20 ′) occurs as a function of the sole first electrostatic charge variation signal S Q,1a . In greater detail, at the current iteration, the first condition is verified (i.e. a click has been detected) if a blink pattern of the first electrostatic charge variation signal S Q,1a , which has a greater time duration than a click threshold period (for example comprised between about 10 ms and about 40 ms, and for example equal to about 20 ms), is present. For example,  FIG.  13    shows the blink pattern (indicated with the reference P 5 ) which has the first peak K 11  with maximum value M K11  at the time position t MK11 , and the second peak K 12  with maximum value M K12  at the time position t MK12 . For purely illustrative and non-limiting purposes, the time duration may be a quantity such as the distance (indicated in  FIG.  13    with the reference T 3 ′) between the time positions t MK11  and t MK12  of the maximum values M K11  and M K12  of the first and the second peaks K 11  and K 12  of the blink pattern P 5 , or the distance (indicated in  FIG.  13    with the reference T 3 ″) between the time positions t JK11  and t JK12  of values of interest J K11  and J K12  of the first and the second peaks K 11  and K 12  of the blink pattern P 5 . For example, the values of interest J K11  and J K12  are points of the first electrostatic charge variation signal S Q,1a  which have a predefined value (e.g., 10% of the maximum value M K11 , M K12  of the respective peak K 11 , K 12 ) and whose time positions t JK11 , t JK12  are preceding and, respectively, following the time positions t MK11 , t MK12  of the maximum values M K11 , M K12  of the respective peaks K 11 , K 12 . As a result, the first condition is verified (i.e. a click has been detected) when the time duration T 3 ′, T 3 ″ of the blink pattern P 5  is greater than the click threshold period. 
     Furthermore, in this embodiment at step S 24  the IEBI parameter is determined as the average, over the predefined period, of the blink time distances, each blink time distance being calculated between two consecutive blink patterns of the first electrostatic charge variation signal S Q,1a , each blink pattern defining a respective blink. 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.