CN107193368B - Time-variable coding non-invasive brain-computer interface system and coding mode - Google Patents
Time-variable coding non-invasive brain-computer interface system and coding mode Download PDFInfo
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- CN107193368B CN107193368B CN201710272431.7A CN201710272431A CN107193368B CN 107193368 B CN107193368 B CN 107193368B CN 201710272431 A CN201710272431 A CN 201710272431A CN 107193368 B CN107193368 B CN 107193368B
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Abstract
The invention belongs to the field of brain-computer interfaces, and particularly discloses a non-invasive brain-computer interface coding method of variable-time length coding, aiming at the technical problems of high coding difficulty, difficult demodulation and difficult adaptation to different user electroencephalogram characteristics in the prior art, the non-invasive brain-computer interface coding method is used for sending binary codes which are convenient for computer identification to a computer by the brain, the brain generates two first-stage signals with fixed frequency and fixed stimulation time length, the two first-stage signals respectively correspond to the binary codes, a plurality of first-stage signals form a code element, and the interval between the code elements is calibrated by changing the time length of the first-stage signal at the last bit of the code element or inserting a mark code mode. A variable duration coded non-invasive brain-computer interface system is also disclosed.
Description
Technical Field
The invention relates to the field of brain-computer interfaces, in particular to a non-invasive brain-computer interface system with variable time length coding and a coding mode.
Background
Studies have shown that when subjected to a fixed frequency visual stimulus, the visual cortex of the human brain produces a continuous response that is related to the stimulus frequency (at the fundamental frequency or at multiples of the stimulus frequency). This response is called the Steady State Visual Evoked potential, Steady-State Visual affected Potentials, SSVEP. It can be reliably applied to brain-Computer Interface Systems (BCIs).
In order to receive, detect and analyze an SSVEP signal, the prior art provides an FM-SSVEP stimulator system, which is a steady-state visual stimulator system based on fixed frequencies, and is characterized in that fixed frequencies are respectively used as stimulation signals, then electroencephalogram signals of a brain when the brain is stimulated are collected, data analysis and processing are performed, further, the frequency of the SSVEP signal is obtained, information of the stimulation signals can be fed back by comparing the mark frequency of the SSVEP signal with the frequency of the stimulation signals, and thus, instruction transmission is completed, and the technology can be applied to multiple fields of electroencephalogram dialing, control and the like.
In the previously proposed patent "brain wave command identification method based on SSVEP brain-computer interface", three frequencies (or signals) of "Bit 0", "Bit 1" and "Bit 2" are used to implement binary Bit stream coding and Bit stream end calibration of the stimulation unit, respectively.
However, the encoding method requires more frequencies, the implementation difficulty on a display or other stimulation units is still high, and the "Bit 0", "Bit 1", and "Bit 2" need to be demodulated (three times of filtering is needed) in the decoding process; the processing time required for one demodulation process is long (mainly, the existing computer languages are all based on binary coding, when the binary coding is required to decode signals with three states (or three signals), two-bit binary coding corresponding to the signal with one state is required), and the brain is enabled to generate signals with different three states and convenient identification, so that the difficulty is high for the human brain.
Disclosure of Invention
The invention provides a non-invasive brain-computer interface system and a coding mode of variable-time length coding, aiming at the technical problems of high coding difficulty, difficult demodulation and difficult adaptation to different user electroencephalogram characteristics in the prior art.
The basic scheme provided by the invention is as follows: the non-invasive brain-computer interface coding method of variable time length coding is used for the human brain to send binary codes which are convenient for the computer to identify to the computer, the human brain generates two first-stage signals with fixed frequency and fixed stimulation time length, the two first-stage signals respectively correspond to the binary codes, a plurality of first-stage signals form a code element, and the time length of the first-stage signal of the last bit of the code element is changed or a mark coding mode is inserted to calibrate the interval between the code elements.
The invention has the advantages that the brain-computer interface is a unidirectional brain-computer interface, and is used for receiving signals transmitted by the brain in a unidirectional mode, the interval between the code elements in the scheme needs to be calibrated by prolonging the stimulation time of the last binary signal, compared with the prior art that the interval between the code elements needs to be calibrated by using a single signal, the invention only needs the human brain to generate two first-stage signals with fixed frequency and fixed stimulation time length, the prior art needs the human brain to generate three signals with fixed frequency and fixed stimulation time length, and the way of inserting the mark code means that a stimulation with different stimulation time length from the binary code stimulation time length is inserted between the code elements, the stimulation is called mark code, compared with the time length of changing the first-stage signal of the last bit of the code element, the stimulation provided by the mark code may not be the last bit of the code element, may be other stimulation signals, the way of inserting the mark code means is actually that the binary signal with different stimulation time length (such as '01' or '10's first-stage signal is inserted into a code element which can be used for distinguishing the stimulation source from a serial port which can receive the stimulation signal at the same time length of the code element at the same time as an equivalent light at the end of a command.
The training burden of the human brain is increased by forming a signal with fixed frequency and fixed stimulation time length. The thinking of the place where the brain is supposed to be, for example, when trying to think of a square, a signal with fixed frequency is generated, and the stimulation time length is directly the same as the time imagined by the user, so that the problem that the difficulty of generating a signal with fixed frequency by the brain is far greater than the problem of controlling the stimulation time length can be well understood. When encoding (namely when the human brain generates signals), compared with the prior art, the encoding requirement generated by the human brain can greatly reduce the difficulty, and the purpose of reducing the encoding difficulty is achieved.
Because two signals generated by the human brain respectively correspond to binary 'Bit 0' and 'Bit 1', the last Bit is prolonged when the code elements are separated, and only one condition judgment needs to be added when the machine is identified, namely, the separation between the marked code elements is prolonged (or shortened), so that the identification efficiency of the machine can be greatly improved, and the demodulation difficulty is reduced. When the signal is extracted, the final signal (the interval between code elements) can be obtained by extracting the two paths of signals, while the final signal can be obtained by extracting the three paths of signals in the prior art, namely the difficulty of comparison, analysis and sampling is reduced. And the three-way signal is easy to have the condition of signal aliasing, and under the condition, because the signal interval is close, the error code is easy to appear. In the aspect of adapting to different users, the difficulty for the user to regenerate another signal is reduced because the last bit is lengthened (shortened). I.e. two distinguishable signals are generated, enabling a faster adaptation by the user than three distinguishable signals. Namely, each user has individual difference, in practical application, the number of users capable of generating three distinguishable signals is small, long-term training is needed, but the number of users capable of generating two distinguishable signals is far greater than the number of users capable of generating three signals, namely, the requirement on the users is reduced, and the effect of improving the electroencephalogram characteristics suitable for different users is achieved.
The non-invasive brain-computer interface coding method of variable time length coding has the following advantages: 1. when the brain sends out the brain electrical signal, only two distinguishable signals need to be generated, thereby reducing the coding difficulty. 2. When the machine is used for identification, only one condition judgment is needed to be added, information in the electroencephalogram signals can be quickly identified, and the purpose of reducing demodulation difficulty is achieved.
Further, the interval between symbols is scaled by extending the duration of the first phase signal of the last bit of a symbol. Compared with the last bit of the shortened code element, the extension can reduce the difficulty of generating the electroencephalogram by the user.
Furthermore, the human brain generates two first-stage signals with fixed frequency and fixed stimulation time length, and the first-stage signals are generated by the human brain through training the human brain through the stimulation unit. After a certain period of adaptive training, the signals generated by the human brain can be more easily recognized by a machine.
Further, the stimulation unit trains the human brain in the following way, the stimulation unit stimulates the human brain in a binary coding way, and the stimulation unit adopts a unique identification of the binary coding: the 'Bit 0' and the 'Bit 1', the 'Bit 0' and the 'Bit 1' have corresponding fixed frequency and corresponding fixed stimulation time length, the stimulation unit marks the end of an instruction by prolonging the stimulation time corresponding to the 'Bit 0' or the 'Bit 1' of the last Bit of the binary code, and the human brain can send out the signals of the 'Bit 0' and the 'Bit 1' and the prolonged 'Bit 0' and 'Bit 1' without any training.
A variable-duration coded non-invasive brain-computer interface system, comprising:
the stimulation unit is used for stimulating the human brain in a binary coding mode, and adopts a unique identifier of the binary coding: the 'Bit 0' and the 'Bit 1', the 'Bit 0' and the 'Bit 1' have corresponding fixed frequency and corresponding fixed stimulation time length, and the stimulation unit marks the end of an instruction by prolonging the stimulation time corresponding to the 'Bit 0' or the 'Bit 1' of the last Bit of the binary code;
the signal acquisition unit is used for acquiring signals of the human brain;
the decoding unit is used for acquiring the acquired signals of the human brain, finding the 'Bit 0' or 'Bit 1' with the codes being prolonged and segmenting the signals accordingly, and extracting the binary code stream according to the segmented result.
The system has the following advantages that 1, when the brain emits the electroencephalogram signal, only two distinguishable signals need to be generated, and the coding difficulty is reduced. 2. When the machine is used for identification, only one condition judgment is needed to be added, information in the electroencephalogram signals can be quickly identified, and the purpose of reducing demodulation difficulty is achieved.
The system further comprises a signal processing unit, the signal acquisition unit transmits the acquired human brain signals to the signal processing unit, and the signal processing unit performs baseline drift removal processing and band-pass filtering processing on the received human brain signals. After the processing, the recognition rate of the signal can be improved, and the error rate can be reduced.
Further, the device also comprises a feedback module, wherein the feedback module is used for adjusting the matching degree of the natural frequency of the Bit0 and the Bit1 with the electroencephalogram signal. The feedback module is matched with the system, and the electroencephalogram signals matched with the Bit0 and the Bit1 are adjusted according to the personal characteristics of the user so as to adapt to the electroencephalogram characteristics of the user.
Drawings
FIG. 1 is a diagram illustrating the decoding result of a prior art brain-computer interface encoding method;
FIG. 2 is a diagram of the decoded result of the encoding scheme of the brain-computer interface;
FIG. 3 is a spectral diagram of a conventional encoding scheme;
fig. 4 is a spectral diagram of the present invention.
Detailed Description
The present invention will be described in further detail below by way of specific embodiments:
example (b):
the non-invasive brain-computer interface coding method of variable time length coding is used for the human brain to send binary codes convenient for computer identification to a computer, the human brain generates two first-stage signals with fixed frequency and fixed stimulation time length, the two first-stage signals respectively correspond to the binary codes, a plurality of first-stage signals form a code element, and the time length of the first-stage signal of the last bit of the code element is prolonged to calibrate the interval between the code elements.
The human brain generates two first-stage signals with fixed frequency and fixed stimulation time length, a stimulation unit trains the human brain in a following mode, the stimulation unit stimulates the human brain in a binary coding mode, the stimulation unit adopts a unique identifier of binary coding, namely, Bit0 and Bit1 have corresponding fixed frequency and corresponding fixed stimulation time length, the stimulation unit marks the end of an instruction by prolonging the stimulation time corresponding to the last Bit0 or Bit1 of the binary coding, and after training, the human brain can send signals of the Bit0 and the Bit1 and the prolonged Bit0 and Bit 1.
A variable-duration coded non-invasive brain-computer interface system, comprising:
the stimulation unit is used for stimulating the human brain in a binary coding mode, the stimulation unit adopts a unique identifier of binary coding, namely 'Bit 0' and 'Bit 1', the 'Bit 0' and the 'Bit 1' both have corresponding fixed frequency and corresponding fixed stimulation time length, the stimulation unit marks the end of an instruction by prolonging the stimulation time corresponding to the 'Bit 0' or 'Bit 1' of the last Bit of the binary coding, namely the stimulation unit adopts L ED lamps, the L ED lamps are connected with a single chip microcomputer, and the single chip microcomputer controls the L ED lamps to have two flicker frequencies (both have fixed stimulation time lengths) which respectively represent different binary codes.
The signal acquisition unit is used for acquiring signals of the human brain;
the decoding unit is used for acquiring the acquired signals of the human brain, finding out 'Bit 0' or 'Bit 1' with the codes being prolonged and segmenting the signals according to the codes, and extracting a binary code stream according to the segmented result;
the signal processing unit is used for transmitting the acquired human brain signals to the signal processing unit, and performing baseline drift removal processing and band-pass filtering processing on the received human brain signals;
and the feedback module is used for adjusting the matching degree of the natural frequency of the Bit0 and the Bit1 and the electroencephalogram signal.
In this embodiment, the stimulation unit adopts a display capable of emitting light of two colors to provide different stimulation signals to the brain of a person.
The signal acquisition unit mainly comprises an electrode, an electroencephalogram amplifier, a low-pass and band-stop filter, a regulating circuit and a signal acquisition and quantification module, and more devices are arranged in the prior art, and the ADS1299 is adopted as an electroencephalogram signal acquisition device in the embodiment.
The signal processing unit can be directly realized by adopting a single chip microcomputer, and the feedback module can be realized by adjusting a key.
And an FIR filter can also be applied to the present embodiment, reducing the amount of operations of the chip.
Unlike the prior art that uses a filter during decoding, an FIR (english full name: "FFT-Based Overlap-add Method" which can simply and quickly calculate the convolution of a signal and a system function of the filter) filter Based on FFT (fast fourier transform) Overlap can be used in the scheme. In the conventional filter used in the prior art, after each new data is acquired, a filtering operation needs to be performed on all the data again, which wastes processing capacity and makes the prior art have requirements on the computing capacity of the processor. However, in the present invention, the new data is only needed to be added after the existing data after the operation. Processing power is conserved so that BFSK may be implemented on some low power processors.
Specifically, for a general convolution, the computational complexity is: QUOTE
And the computational complexity of the FFT-Based Overlap-add Method is as follows: QUOTE
Wherein QUOTE
For signal period length, N being FFTThe length of the interval.
To better illustrate the effect of the present invention, we stimulate the human brain (or the human brain starts to imagine and sends out a signal containing a segment of code) according to the existing method (the interval between symbols is identified by "Bit 2", i.e. 3 signals), and then demodulate by the existing coding method and system, the result of demodulation is shown in fig. 1, we can clearly see that the signal aliasing occurs in both 1.2 seconds and 8.4 seconds, in this case, the algorithm with the equivalent amplitude is very easy to misjudge because the signal interval is relatively close. The method provided by the scheme can completely avoid the situation.
The demodulation is performed according to the method and system provided by the invention, and the demodulation result is shown in fig. 2.
We also extract the spectrogram of the existing encoding method (fig. 3) and the spectrogram of the present scheme (fig. 4) for further comparison, and as can be clearly found from the comparison between fig. 3 and fig. 4, there are 3 peaks in fig. 3, i.e. there are three signals, and the distinction degree between the signals (valleys between the peaks) is obviously less obvious than that of fig. 4.
The foregoing is merely an example of the present invention and common general knowledge of known specific structures and features of the embodiments is not described herein in any greater detail. It should be noted that, for those skilled in the art, without departing from the structure of the present invention, several changes and modifications can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicability of the patent. The scope of the claims of the present application shall be determined by the contents of the claims, and the description of the embodiments and the like in the specification shall be used to explain the contents of the claims.
Claims (2)
1. The non-invasive brain-computer interface coding method of the variable time length code, is used for the brain of the people to send the binary code easy to the computer discernment, characterized by, the brain of the people produces two fixed first-phase signals of frequency, stimulating the fixed first-phase signal of time length, two first-phase signals correspond to code of the binary separately, a bit element of composition of a plurality of first-phase signals, mark the interval between the bit elements by lengthening the time length of the first-phase signal of the last bit of bit element;
wherein, the human brain generates two first-stage signals with fixed frequency and fixed stimulation time length, and the first-stage signals are generated by the human brain through training the human brain by the stimulation unit; the stimulation unit trains the human brain in the following way, the stimulation unit stimulates the human brain in a binary coding way, and the stimulation unit adopts a unique identifier of the binary coding: "Bit 0" and "Bit 1", and "Bit 0" and "Bit 1" all have corresponding fixed frequency and corresponding fixed stimulation time length, and the stimulation unit marks the end of an instruction by prolonging the stimulation time corresponding to "Bit 0" or "Bit 1" of the last Bit of the binary code.
2. A variable-duration coded non-invasive brain-computer interface system, comprising:
the stimulation unit is used for stimulating the human brain in a binary coding mode, and adopts a unique identifier of the binary coding: the 'Bit 0' and the 'Bit 1', the 'Bit 0' and the 'Bit 1' have corresponding fixed frequency and corresponding fixed stimulation time length, and the stimulation unit marks the end of an instruction by prolonging the stimulation time corresponding to the 'Bit 0' or the 'Bit 1' of the last Bit of the binary code;
the signal acquisition unit is used for acquiring signals of the human brain;
the decoding unit is used for acquiring the acquired signals of the human brain, finding out 'Bit 0' or 'Bit 1' with the codes being prolonged and segmenting the signals according to the codes, and extracting a binary code stream according to the segmented result;
the signal processing unit is used for transmitting the acquired human brain signals to the signal processing unit, and performing baseline drift removal processing and band-pass filtering processing on the received human brain signals;
and the feedback module is used for adjusting the matching degree of the natural frequency of the Bit0 and the Bit1 and the electroencephalogram signal.
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| CN102512164A (en) * | 2011-11-23 | 2012-06-27 | 电子科技大学 | Coding and identification method for multi-frequency arrangements of SSVEP-BCI (steady state visual evoked potential-brain computer interface) system |
| CN103996054A (en) * | 2014-06-05 | 2014-08-20 | 中南大学 | Electroencephalogram feature selecting and classifying method based on combined differential evaluation |
| CN104887222A (en) * | 2015-05-11 | 2015-09-09 | 重庆大学 | Reversible electroencephalogram analysis method |
| WO2015044851A3 (en) * | 2013-09-25 | 2015-12-10 | Mindmaze Sa | Physiological parameter measurement and feedback system |
| CN105302309A (en) * | 2015-11-05 | 2016-02-03 | 重庆邮电大学 | SSVEP brain-computer interface based brain wave instruction identification method |
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| CN102512164A (en) * | 2011-11-23 | 2012-06-27 | 电子科技大学 | Coding and identification method for multi-frequency arrangements of SSVEP-BCI (steady state visual evoked potential-brain computer interface) system |
| WO2015044851A3 (en) * | 2013-09-25 | 2015-12-10 | Mindmaze Sa | Physiological parameter measurement and feedback system |
| CN103996054A (en) * | 2014-06-05 | 2014-08-20 | 中南大学 | Electroencephalogram feature selecting and classifying method based on combined differential evaluation |
| CN104887222A (en) * | 2015-05-11 | 2015-09-09 | 重庆大学 | Reversible electroencephalogram analysis method |
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