DEVICE FOR ASSESSING PSYCHOPHYSIOLOGICAL RESPONSIVENESS

Abstract

The present invention relates to assessing a psychophysiological responsiveness or non-responsiveness of a subject. A device (10) for assessing a psychophysiological responsiveness of a subject is presented, the device comprising a stimulus unit (11) for providing an electrical stimulus via a first and a second electrode (21, 22) to a skin (100) of the subject; a sensing unit (12) for acquiring an impedance signal (15) indicative of an impedance between the first and the second electrode in response to said electrical stimulus; and an analysis unit (13) adapted to identify an electrical double-layer based on the impedance signal acquired in response to the electrical stimulus and to determine a psychophysiological responsiveness of the subject based on the identified electrical double-layer. It has been found that identifying the presence or absence of an electrical double-layer based on the impedance signal acquired in response to the electrical stimulus can serve as a reliable indicator whether the subject is in a responsive or nonresponsive psychophysiological state. Further, a corresponding method, computer program and system (1) are presented.

Claims

1. Device for assessing a psychophysiological responsiveness of a subject, the device comprising: a stimulus unit for providing an electrical stimulus via a first and a second electrode to a skin of the subject; a sensing unit for acquiring an impedance signal indicative of an impedance between the first and the second electrode in response to said electrical stimulus; and an analysis unit adapted to identify an electrical double-layer based on the impedance signal acquired in response to the electrical stimulus and to determine a state of psychophysiological responsiveness or non-responsiveness of the subject based on the identified electrical double-layer, wherein the analysis unit is configured to identify the electrical double-layer based on a transient behavior of said impedance signal, wherein the analysis unit is adapted to determine the state of psychophysiological responsiveness of the subject based on a transient behavior of a time scale of 1 ms to 5 s, wherein the stimulus unit comprises a voltage source for applying a voltage across the first and the second electrode and/or a current source for applying a current to the first and the second electrode and wherein the stimulus unit is adapted to provide an electrical stimulus comprising a step function from a first voltage to a second voltage or from a first current to a second current.

2. Device according to claim 1, wherein the analysis unit adapted to discriminate between a state of psychophysiological responsiveness and psychophysiological non-responsiveness, wherein an absence of an electrical double-layer is indicative of a state of psychophysiological non-responsiveness of the subject.

3. Device according to claim 1, wherein the analysis unit adapted to discriminate between a state of psychophysiological responsiveness and psychophysiological non-responsiveness, wherein a presence of an electrical double-layer is indicative of a state of psychophysiological responsiveness of the subject.

4. Device according to claim 1, wherein the analysis unit is configured to identify the electrical double-layer by evaluating a voltage barrier indicative of said electrical double-layer based on the impedance signal acquired in response to the electrical stimulus.

5. (canceled)

6. Device according to claim 1, wherein the analysis unit is further adapted to determine the state of psychophysiological responsiveness of the subject based on a transient behavior of a time scale between 10 ms and 2 s, preferably between 20 ms and 500 ms.

7. (canceled)

8. (canceled)

9. Device according to claim 1, wherein the stimulus unit is adapted to provide a voltage and/or current profile.

10. Device according to claim 1, wherein the stimulus unit is adapted to provide an AC electrical excitation.

11. Device according to claim 1, wherein the sensing unit is adapted to acquire a time-variant current and/or voltage between the first and the second electrode.

12. Device according to claim 1, further comprising an output unit for providing information associated with the identified state of psychophysiological responsiveness or non-responsiveness to the subject, the information comprising providing advice how to overcome a state of psychophysiological non-responsiveness.

13. System for assessing a psychophysiological responsiveness of a subject, the system comprising: a first electrode and a second electrode for application to a skin of the subject; and the device for assessing the psychophysiological responsiveness of the subject according to claim 1.

14. Method for assessing a psychophysiological responsiveness of a subject, the method comprising the steps of: providing an electrical stimulus via a first and a second electrode to a skin of the subject; acquiring an impedance signal indicative of an impedance between the first and the second electrode in response to said electrical stimulus; and identifying an electrical double-layer based on the impedance signal acquired in response to the electrical stimulus and determining a state of psychophysiological responsiveness or non-responsiveness of the subject based the identified electrical double-layer, wherein the electrical double-layer is identified based on a transient behavior of said impedance signal, wherein the state of psychophysiological responsiveness of the subject is determined based on a transient behavior of a time scale of 1 ms to 5 s, wherein providing the electrical stimulus comprises applying a voltage across the first and the second electrode and/or a current source for applying a current to the first and the second electrode and wherein providing the electrical stimulus further comprises providing an electrical stimulus comprising a step function from a first voltage to a second voltage or from a first current to a second current.

15. Computer program comprising program code means for causing, when said computer program is carried out on a computer, the computer to carry out the steps of obtaining an impedance signal indicative of an impedance between a first and a second electrode in response to an electrical stimulus provided via the first and the second electrode to a skin of a subject; and identifying an electrical double-layer based on the impedance signal acquired in response to the electrical stimulus and determining a state of psychophysiological responsiveness or non-responsiveness of the subject based on the identified electrical double-layer, wherein the electrical double-layer is identified based on a transient behavior of said impedance signal, wherein the state of psychophysiological responsiveness of the subject is determined based on a transient behavior of a time scale of 1 ms to 5 s, wherein providing the electrical stimulus comprises applying a voltage across the first and the second electrode and/or a current source for applying a current to the first and the second electrode and wherein providing the electrical stimulus further comprises providing an electrical stimulus comprising a step function from a first voltage to a second voltage or from a first current to a second current.

16. The method according to claim 14 further comprising discriminating between a state of psychophysiological responsiveness and psychophysiological non-responsiveness, wherein an absence of an electrical double-layer is indicative of a state of psychophysiological non-responsiveness of the subject.

17. The method according to claim 14 further comprising discriminating between a state of psychophysiological responsiveness and psychophysiological non-responsiveness, wherein a presence of an electrical double-layer is indicative of a state of psychophysiological responsiveness of the subject.

18. The method according to claim 14 further comprising identifying the electrical double-layer by evaluating a voltage barrier indicative of said electrical double-layer based on the impedance signal acquired in response to the electrical stimulus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the following drawings

[0038] FIG. 1 shows a schematic diagram of an embodiment of a system for assessing a psychophysiological responsiveness of a subject;

[0039] FIG. 2 shows an exemplary implementation in form of a wearable device such as a smart watch;

[0040] FIG. 3 shows a simplified equivalent electrical circuit of skin tissue including sweat glands;

[0041] FIG. 4 shows an exemplary flow chart of a method for assessing a psychophysiological responsiveness of a subject; and

[0042] FIG. 5A to FIG. 5D show exemplary graphs of provided electrical stimuli and acquired impedance signals in response thereto.

DETAILED DESCRIPTION OF THE INVENTION

[0043] FIG. 1 shows a schematic diagram of a first embodiment of a system 1 for assessing a psychophysiological responsiveness of a subject. The system 1 comprises a device 10 for assessing a psychophysiological responsiveness of the subject as well as a first electrode 21 and a second electrode 22 for application to a skin 100 of the subject.

[0044] The device 10 comprises a stimulus unit 11 for providing an electrical stimulus via the first electrode 21 and the second electrode 22 to the skin 100 of the subject. In the given example, the stimulus unit comprises a voltage source for applying a voltage across the two electrodes 21, 22. The stimulus unit is connected to the first electrode 21 and the second electrode 22 via electrode leads or cables 23, 24. In particular, the stimulus unit 11 is adapted to provide a voltage profile comprising one or more step functions between different voltage levels as exemplary shown in FIG. 5A FIG. 5D.

[0045] The device 10 further comprises a sensing unit 12 for acquiring an impedance signal indicative of an impedance between the first electrode 21 and the second electrode 22. The sensing unit 12 can be a conventional skin conductance sensor as known in the art. The sensing unit can be connected separately to the first electrode 21 and the second electrode 22. However, advantageously, the same electrical connection to the first and the second electrodes 21, 22 via the electrode lead 22, 24 is to be used for both the stimulus unit 11 and the sensing unit 12. In an advantageous embodiment, the sensing unit 12 comprises a series resistor in the electrical path from the stimulus unit to the electrode 22. Hence, this series resistor then forms a voltage divider together with the impedance of the skin 100 of the subject. Thus, a voltage drop across the series resistor or current through the series resistor can be taken as the impedance signal indicative of the impedance of the skin 100 of the subject in response to the electrical stimulus provided by the stimulus unit 11. Hence, the sensing unit 12 does not directly need to measure the conductance or impedance of the skin 100 but determines an impedance signal indicative of the impedance between the first and the second electrode 21, 22 from which the impedance in the first and the second electrode can be derived using known principles.

[0046] In an embodiment, the stimulus unit 11 and the sensing unit 12 can be implemented as an integral source-meter unit 14. Advantageously, the stimulus unit 11 can comprise a digital-to-analog-converter (DAC). Such a DAC can even be co-integrated in a standard microcontroller (MCU) such as the STM32 series by ST Microelectronics. Correspondingly, the sensing unit 12 can comprise an analog-to-digital-converter (ADC) which may also be co-integrated in a standard microcontroller. Advantageously, the device 10 including the analysis unit 13 can thus be implemented using a microcontroller at low cost. However, the device may also be implemented as a distributed system. For example, data acquired by the sensing may be obtained (i.e. received or retrieved) by a remote processing unit, such as a smartphone running a corresponding app.

[0047] The sensing unit 12 provides the impedance signal 15 as an input to the analysis unit 13 which is adapted to identify an electrical double-layer based on the impedance signal acquired in response to the electrical stimulus provided by the stimulus unit 11 and to determine a state of psychophysiological responsiveness or non-responsiveness of the subject based the identified electrical double-layer. In particular, the analysis unit 13 can be adapted to determine a state of psychophysiological responsiveness or non-responsiveness of the subject based a transient behavior of said impedance signal 15 in response to the electrical the electrical stimulus provided by the stimulus unit 11. In this context, the analysis unit 13 can be adapted to provide a control signal 16 to the stimulus unit 11 for controlling the application of the electrical stimulus. In the alternative, the stimulus unit 11 may provide the analysis unit 13 with information about the provided electrical stimulus, such that the temporal relation between the provided electrical stimulus and the acquired impedance signal can be determined by the analysis unit 13.

[0048] FIG. 2 shows an exemplary implementation of a system 1 for assessing the psychophysiological responsiveness of the subject. For instance, the device can be implemented in form of a smart watch 40, skin conductance sensor wristband or activity tracker and the like. For example, the device may be implemented in the Philips discreet tension indicator (DTI-4) skin conductance sensor wristband. The device 40 comprises a main body 41 and a wristband 42. In the shown embodiment, the first electrode 21 and the second electrode 22, together indicated by reference numeral 20, are arranged on the bottom side of the housing 41 which, when worn by a subject, faces the skin of the subject. However, in an alternative embodiment, one or both electrodes may also be implemented on the wristband 42.

[0049] Referring again to FIG. 1, the skin of the subject 100 comprises the epidermis 102 as the upper portion and the dermis 103 as the lower portion of the skin 100. The topmost layer of the skin 100 as shown in FIG. 1 is the stratum corneum 101. For the case where the subject is in a state of psychophysiological responsiveness, the conductive path 25 within the skin 100 for the measurement of the skin impedance is exemplary shown by arrows. For simplification, the entire skin portion comprising the path 25, underneath the first and second electrodes 21, 22 can be thought of as being filled with a liquid medium comprising sweat as an electrolyte. Within the sweat, ion diffusion occurs when a voltage is applied across the first electrode 21 and the second electrode 22. This space can also be referred to as an interstitial space 103. In the sweat, ion diffusion occurs when an electrical stimulus such as a voltage step or plurality of voltage steps are applied over the first electrode 21 and the second electrode 22. In this context, the presence of a transient in the impedance signal 15 acquired by the sensing unit 12 signals the presence of a salty liquid, i.e. sweat, in the conductive path 25. The transients are caused by the (slow) diffusion of ion in the sweat, corresponding to changes in the electrical stimulus such as the applied voltage profile by lowering the space charge close to the electrodes. The space charge region is indicated by reference numeral 104. The space charge region indicates a region where an electrical double-layer forms. The electrical double-layer in turn provides a voltage barrier or blocking voltage that can be identified based on the impedance signal acquired in response to the electrical stimulus provided by the stimulus unit 11. As indicated in the lower section of FIG. 1, the sweat glands 106, when being filled with sweat as a conductive liquid, provide a conductive path towards the lower layers of the dermis 103.

[0050] On the other hand, if the subject is in a state of psychophysiological non-responsiveness, such a sweat path is not available. In this case, if sweat is substantially absent, the conductive path is predominantly through the stratum corneum 101. Hence, ion diffusion does not happen in that case when an electrical stimulus is provided via the first and second electrodes 21, 22. Therefore, the response can be seen as an immediate change and not a slow change that gradually settles at a given value. Hence, the transient behavior, in particular due to the double-layer capacitance, can be evaluated. Further, if the sweat is substantially absent, the voltage barrier of the electrical double-layer, also referred to as ionic double-layer does not form. Hence, the presence or absence of such a voltage barrier can be evaluated.

[0051] FIG. 3 shows a simplified equivalent electrical circuit of skin tissue and sweat glands. The equivalent circuit represents what is seen by the first electrode 21 and the second electrode 22 as the terminals. The skin may be modeled with an R-C circuit comprising a resistor R.sub.0 in parallel with a first series connection of a resistor R.sub.1 and a capacitor C.sub.1, optionally in parallel with a second series connection of a resistor R.sub.2 and a second capacitor C.sub.2. This electrical network has also already been proposed by Comunetti et al. in Characterisation of human skin conductance at acupuncture points, Experientia 51, 328-331, 1995, wherein it was shown that such an electrical network shows the same characteristic as human skin following a voltage step. The shown equivalent circuit is a good approximation if the subject is in a state of psychophysiological responsiveness wherein a capacitance is present due to ion diffusion of sweat in the sweat gland system. However, it has been found that if the subject is in a state of psychophysiological non-responsiveness, the behavior can be modeled by a series resistor only, hence, without the capacitive components by R.sub.1 and C.sub.1 in parallel with R.sub.2 and C.sub.2. For completeness, a resistor R.sub.3 descriptive of a resistance of the stratum corneum is shown in FIG. 3. The stratum corneum can provide a large resistance, for example in the G range. It is to be understood that while a capacitive component can be assumed to be present in any electrical circuit, the capacitance of the stratum corneum is orders of magnitude lower than a capacitive contribution from the sweat gland system, and has thus negligible effect on the switching behavior. In that case, the behavior may be dominated by the resistive component due to the stratum corneum. It should again be highlighted that even though the prior art already discloses that the skin may show a capacitive component in response to an applied voltage step, no analysis is performed to determine a state of psychophysiological responsiveness or non-responsiveness of the subject based on a transient behavior of an impedance signal or voltage barrier indicative of an electrical double-layer.

[0052] Further, the electrical double-layer provides a voltage barrier which can be modeled as a voltage source applied in series with the simplified parallel circuit shown in FIG. 3. A voltage drop across the voltage barrier can easily be identified, for example, by providing a first and a second voltage as electrical stimuli by the stimulus unit and evaluating an impedance signal in response thereto. For example, a sensing unit that evaluates a voltage drop across a reference resistor can be used as described above.

[0053] FIG. 4 shows an exemplary flow chart of a method for assessing a psychophysiological responsiveness of a subject. In a first step S41, an electrical stimulus is provided via a first and a second electrode to a skin of the subject. In a second step S42, an impedance signal indicative of an impedance between the first and the second electrode in response to said electrical stimulus is acquired. In a third step S43, an electrical double-layer is identified based on the impedance signal acquired in response to the electrical stimulus and a state of psychophysiological responsiveness or non-responsiveness of the subject is determined based the identified electrical double-layer.

[0054] For the corresponding computer program, it will be appreciated that a processing unit of a computer does not actively provide or apply an electrical stimulus via the first and the second electrode 21, 22. Nevertheless, a computer program comprising program code means can be adapted to carry out the steps of obtaining (i.e. receiving or retrieving) an impedance signal indicative of an impedance between a first and a second electrode in response to an electrical stimulus provided by the first and the second electrode to a skin of a subject. Hence, an impedance signal in form of an impedance data signal or impedance data can be received by the processing unit or can be actively retrieved for example from a data base for storing said data. The data can be indicative of an impedance between the first and the second electrode which has been acquired in response to an electrical stimulus provided by the first and the second electrode to the skin of the subject. Based on this data, the computer can carry out the steps of identifying an electrical double-layer based on the impedance signal acquired in response to the electrical stimulus and determining a state of psychophysiological responsiveness or non-responsiveness of the subject based on the identified electrical double-layer signal when said computer program is carried out on a computer.

[0055] FIG. 5A to FIG. 5D show exemplary graphs of provided electrical stimuli and acquired impedance signals. The device for providing these electrical stimuli and acquiring the corresponding impedance signals can be a wearable device as exemplarily shown in FIG. 2. For performing a skin conductance measurement, a constant measuring voltage of, for example, 1.048 V can be used. However, when assessing a psychophysiological responsiveness of the subject, the electronic design can be adapted to provide a voltage profile via the first and the second electrode 21, 22 wherein the voltage can be varied, for example lowered in a stepwise manner as indicated by the curve denoted by reference numeral 51.

[0056] In FIG. 5A to FIG. 5D, the horizontal axis denotes time in seconds. The dashed curve 51 denotes the electrical stimulus provided by the stimulus unit via the first and the second electrode to a skin 100 of the subject. The solid lines 52 indicate a skin conductance value as the impedance signal indicative of the impedance between the first and the second electrode in response to said electrical stimulus 51. The vertical axis on the left side denotes a skin conductance value (SC) in arbitrary units corresponding to curve 52. The vertical axis on the right side denotes a voltage indicator of a voltage U as a percentage to a reference voltage in percent [% of Vref.] corresponding to curve 51.

[0057] Compared to a conventional device for measuring a skin conductance, the device can simply be adapted by replacing the reference voltage module for skin conductance measurement with a programmable voltage module, such as a digital-to-analog-converter (DAC). In the shown embodiment, the skin conductance as a special case of the impedance is measured at a sampling rate of about 160 Hz when in a sequence of 10 steps the voltage is lowered from about 1 V down to 0.1 V. The results of such measurements for four human test subjects are shown in FIG. 5A to FIG. 5D. The impedance signals can for example be measured at a sampling rate of 100 Hz or more, preferably 160 Hz. Referring to FIG. 5A and FIG. 5B, the skin conductance traces for persons 1 and 2 on the one hand show an almost immediate stepwise response to voltage changes, as indicated by reference numeral 53. A transient behavior is thus virtually absent. These persons were in a state of psychophysiological non-responsiveness. Artifacts that may occur when switching to a different voltage level may be neglected in the analysis. On the other hand, the skin conductance traces for persons 3 and 4, the settling of the acquired skin conductance value takes up to 10 s. These persons were in a state of psychophysiological responsiveness. In contrast to the stepwise response as indicated by reference numeral 53, the skin conductance for persons 3 and 4 shows a transient behavior as indicated by reference numeral 54.

[0058] An exemplary suitable algorithm to detect the presence of the transient behavior after voltage changes may advantageously use the first derivative of the impedance signal 52. In the absence of transient behavior as shown in FIG. 5A and FIG. 5B, the first derivative will be a small and stable value. However in contrast, in the case of a transient behavior as shown in FIG. 5C and FIG. 5D, the first derivative can be expected to go to a large positive or negative value shortly after the corresponding, here declining, voltage step, and gradually over a couple of seconds declines to a low value.

[0059] In addition or as an alternative to evaluating a transient behavior for identifying the electrical double-layer, it is also possible to evaluate the voltage barrier indicative of said electrical double-layer based on the impedance signal by the skin acquired in response to the electrical stimulus.

[0060] For acquisition of the impedance signal indicative of the skin conductance between the first and the second electrode, a circuit as described in detail in WO 2016/050 551 A1, the content of which is incorporated herein by reference, can be used. Since, in the embodiment described with reference to FIG. 5A to FIG. 5D, the stimulus unit provides a voltage profile, as indicated by dashed curve 51, wherein the voltage is changed, a correction can be applied to account for the different voltage levels by G skin corrected=G skin measuredVref/Vstimulus. For a non responsive state this leads to the increase in skin conductance visible in FIGS. 5A and 5B. For a responsive state this leads to a decrease in skin conductance as visible in FIGS. 5C and 5D. Hence, a change in an absolute value of the determined (corrected) can be evaluated to identify the electrical double-layer. An advantage of this embodiment is that a slow measurement can be performed. Hence, slower and potentially less expensive components may be used. Furthermore, the power consumption can be reduced if a slow sampling rate is sufficient. This is particularly advantageous in wearable devices.

[0061] Optionally, the comparison of such a corrected skin conductance can be made between an average of, for example, the last 4 to 160, preferably the last 10 data points if the impedance signal is measured at a sampling rate of 160 Hz, before and after a voltage step or switch. In the case where no difference can be found, the voltage step can be doubled and the measurement repeated. For example, a sensitivity of an ADC (10 bit . . . 16 bit) in the sensing unit can vary. Hence, in order to yield a detectable effect, the voltage steps provided by the stimulus unit can be doubled in the absence of a measured effect.

[0062] In an embodiment, the analysis can optionally also be combined with an absolute measurement wherein the analysis unit is configured to evaluate whether a skin conductance level is below a predetermined threshold, for example below 1 micro Siemens, otherwise the subject is considered to be in a state of psychophysiological responsiveness

[0063] In a wearable skin conductance sensor, it can be especially important to determine whether a period without skin conductance responses signifies a period of relaxation. For example, the voltage step or generally speaking the electrical stimulus used for assessing the psychophysiological responsiveness of the subject can be applied in a predetermined interval of for example 10s or 7 s during such a skin conductance response (SCR) free period. Hence, a device for skin conductance measurement can be adapted to perform the method proposed herein for assessing a psychophysiological state of the subject after a predetermined period without a skin conductance response. It can thus be verified whether the subject actually is in a period of relaxation or determined whether the subject is in a state of psychophysiological non-responsiveness. A typical skin conductance measurement can take about 7 seconds, from start to end, so a slightly shorter interval can assure that no responses are missed.

[0064] It should be noted that it is not mandatory to apply a voltage profile as shown in FIG. 5A to FIG. 5C. A single voltage step, for example a declining voltage step of 20 to 50 can also be sufficient. For evaluating a transient behavior, the applied voltage can, for example, be lowered in less than 10 ms, preferably in less than 5 ms After such a step a standard measurement voltage for skin conductance measurement can be re-established. A further example of a voltage profile comprises reversing or commutating an applied voltage. An advantage of this embodiment lies in the cost effective implementation, for example, by means of switches for commutating the applied voltage.

[0065] Referring again to FIG. 1, an optional interface or output unit 30 can be provided. For example, the interface can be a data interface which provides data indicative of the state of psychophysiological responsiveness or non-responsiveness of the subject. Such information can also be provided to the user on a human-machine-interface (HMI) for example on the screen of a smartphone. Should a state of non-responsiveness be detected, an advice of how to mitigate this can also be given. For example, simply moistening the area under the electrode with tap water may create a liquid medium in which the transient behavior can be expected to re-appear as well as the psychophysiological responsiveness. It should be noted that executing the method for assessing the psychophysiological responsiveness of the subject can again be used to verify the effectiveness of these measures.

[0066] In conclusion, an advantageous approach for assessing a psychophysiological responsiveness of a subject has been presented that enables the determination a state of psychophysiological responsiveness or non-responsiveness of a subject. The proposed solution can be added to skin conductance measurement devices with limited cost and effort. It should be understood that the device for assessing a psychophysiological responsiveness of the subject can also advantageously be applied in fields where a placement of electrodesin generally the contact of an electrode to the skin of the subjectis to be verified. Exemplary applications include electrocardiogram (ECG), electromyogram (EMG) or electroencephalogram (EEG) applications. Hence, the rather complex procedure of applying wet electrodes or an electrode gel underneath electrodes to ensure a good electrode skin contact can be simplified. A state of psychophysiological responsiveness can thus be equivalent to a good electrode skin contact in particular an electrode-skin contact comprising a capacitive contribution from the skin of the subject. Correct contact to the skin of the subject can thus be verified. In passive methods such as EEG and EEG, an additional stimulus unit for providing an electrical stimulus to the skin of the subject would be required. It should, however, be appreciated that such it is sufficient to temporarily apply a stimulus unit when preparing an actual measurement.

[0067] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0068] In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0069] A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0070] Any reference signs in the claims should not be construed as limiting the scope.