Generative Adversarial Maps Improving brain computer interface

This paper presents a new method to improve brain-computer interfaces by creating more training data using advanced machine learning techniques. This helps in better understanding brain signals and enhances the performance of these systems.

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Key Takeaways
  1. 1 Up to now, many methods have been proposed to improve recognition performance in many aspects including preprocessing, feature extraction, feature selection, classification and post-processing aspects .
  2. 2 Qiqi Zhang, Ying Liu applied it for GAN to construct cDCGAN and the CNN was used for discriminative model and the inverse process of CNN was used for generative model .
  3. 3 The TFR of EEG signal ๐‘‹ is fed into our CNN model, and ๐‘™-th convolutional layer is applied to the output of the previous layer ๐‘‹ ๐‘™-1 .
  4. 4 With the development of brain computer interface, many algorithms are proposed to improve its performance.

Introduction

Brain computer interface (BCI) can connect brain and external world by recognizing brain activities and translating it into messages or commands and this process does not depend on normal peripheral nerves and muscles . So how to recognize meaningful brain activities from seemingly meaningless brain electrical signal is a big challenge for BCI field.

In this preliminary study, we take electroencephalography (EEG) and convolutional neural networks (CNN) for example.

However, up to now all the methods to generate artificial EEG signal are based on the combination of the features of raw EEG signal in different trials.

Methodology

Compared with other fields such as computer vision and speech recognition, only very limited number of training samples can be obtained in BCI field, because the subject cannot be asked to perform the same mental task every time for much long time to record brain signal . Fabien Lotte first to generate artificial EEG data by mixing signal segmentation in time domain, and their offline analysis suggested this approach can.

Study Design

To overcome this problem, artificial EEG signal generation methods based on time-frequency representation and analogy method were proposed .

The prior works only considered the temporal features of EEG signal without frequency features, so the Empirical Mode Decomposition (EMD) method was proposed to consider the features in both temporal and frequency domains .

Important Note

Compared with other fields such as computer vision and speech recognition, only very limited number of training samples can be obtained in BCI field, because the subject cannot be asked to perform the same mental task every time for much.

Results & Findings

Up to now, many methods have been proposed to improve recognition performance in many aspects including preprocessing, feature extraction, feature selection, classification and post-processing aspects . Although many achievements have been obtained in this field and many algorithms can get state of the art performance with high classification accuracy in standard dataset or self-recorded dataset, most of the algorithms are only evaluated offline not online running .

  • Up to now, many methods have been proposed to improve recognition performance in many aspects including preprocessing, feature extraction, feature selection, classification and post-processing aspects .
  • Although many achievements have been obtained in this field and many algorithms can get state of the art performance with high classification accuracy in standard dataset.
  • This may attribute to lack of enough data to learn more possible features to make the classifier more robust and reliable, especially for the deep learning.
  • And deep learning model usually has huge numbers of parameters, so the limited training datasets cannot exploit the full potential of deep learning model in BCI.
  • So, we proposed a novel approach in this paper to generate more artificial brain signal data automatically to overcome this data deficiency problem and improve the.
Important Note

And deep learning model usually has huge numbers of parameters, so the limited training datasets cannot exploit the full potential of deep learning model in BCI field .

Important Note

But data scarcity is a big problem confines the ability of these advanced algorithms especially for the deep learning methods, because limited data cannot exploit the full potential of deep learning model in BCI field.

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Practical Applications

However, this approach may cause inadequate high frequency noise at the boundary of two different segments.

I. Introduction

The introduction discusses the challenges in recognizing brain activities for BCI systems due to limited training data. It highlights the need for improved methods to enhance classification performance, particularly using deep learning models that require substantial data.

A. Preprocessing

Preprocessing involves applying continuous wavelet transform to EEG signals to remove noise and extract relevant frequency components, using the complex Morlet wavelet function.

B. Conditional deep convolutional generative adversarial networks (cDCGAN)

This section describes the structure and functioning of cDCGAN, which utilizes CNNs for both generative and discriminative models in the adversarial training process.

Source Paper Figures and Captions

Source-paper figure
showed, the whole procedure comprised training part and testing part similar to common processing procedure, but in our proposed method we added data augmentation in training part with limited training data to generate more artificial EEG signal and used this artificial signal as extra training dataset. And to improve the classification accuracy of EEG signal with generated artificial EEG data, the artificial data must have label information. Inspired by the performance of conditional Generative Adversarial Nets (cGAN) and Deep Convolutional Generative Adversarial Networks (DCGAN) in computer vision research [16] [17]. We extended the DCGAN to a conditional version with training data labels and generated the labeled artificial EEG signal.
showed, the whole procedure comprised training part and testing part similar to common processing procedure, but in our proposed method we added data augmentation in training part with limited training data to generate more artificial EEG signal and used this artificial signal as extra training dataset. And to improve the classification accuracy of EEG signal with generated artificial EEG data, the artificial data must have label information. Inspired by the performance of conditional Generative Adversarial Nets (cGAN) and Deep Convolutional Generative Adversarial Networks (DCGAN) in computer vision research [16] [17]. We extended the DCGAN to a conditional version with training data labels and generated the labeled artificial EEG signal.
Source-paper figure
Figure 1. Framework of proposed data augmentation method
Figure 1. Framework of proposed data augmentation method
Source-paper figure
, ๐บ) = ๐”ผ ๐‘ฅ~๐‘ ๐‘‘๐‘Ž๐‘ก๐‘Ž (๐‘ฅ) [๐‘™๐‘œ๐‘”๐ท(๐‘ฅ)] + ๐”ผ ๐‘ง~๐‘ ๐‘ง (๐‘ง) [๐‘™๐‘œ๐‘”(1 -๐ท(๐บ(๐‘ง)))] ๏€จ๏€ฒ๏€ฉ Where ๐‘ ๐‘‘๐‘Ž๐‘ก๐‘Ž is the distribution of training data, ๐ท(๐‘ฅ; ๐œƒ ๐‘‘ ) is discriminative model that can estimate the probability that ๐‘ฅ is from ๐‘ ๐‘‘๐‘Ž๐‘ก๐‘Ž by CNN with parameters ๐œƒ ๐‘‘ , ๐‘ ๐‘ง is the distribution of noise and here we use Gaussian distribution, ๐บ(๐‘ง; ๐œƒ ๐‘” ) is generative model that can generate the artificial data from noise ๐‘ง by inverse CNN with parameters ๐œƒ ๐‘” . To improve the classification accuracy of EEG signal with generated artificial EEG data, the artificial data must have label information. So abovementioned DCGAN is extended to a conditional version with label information, the auxiliary label information ๐‘Œ is feed into both generative model ๐บ and discriminative model ๐ท [17]. The loss function is converted into a conditional version as follows: min ๐บ max ๐ท ๐ฟ(๐ท, ๐บ) = ๐”ผ ๐‘ฅ~๐‘ ๐‘‘๐‘Ž๐‘ก๐‘Ž (๐‘ฅ) [๐‘™๐‘œ๐‘”๐ท(๐‘ฅ|๐‘ฆ ๐‘ง )] + ๐”ผ ๐‘ง~๐‘ ๐‘ง (๐‘ง) [๐‘™๐‘œ๐‘”(1 -๐ท(๐บ(๐‘ง|๐‘ฆ ๐‘‘ )))] ๏€จ๏€ณ๏€ฉ๏€  To avoid overfitting problem on finite dataset during training process, generative model and discriminative model are optimized alternately. In our model, we alternately optimize discriminative model ๐ท and generative model ๐บ by two steps and one step respectively. Theoretically, as long as ๐ท and ๐บ are well-designed and trained effectively, the whole adversarial process can reach the Nash equilibrium. Also at this equilibrium, the distribution of artificial data is same as the training data and the artificial data can be seen as real data because the discriminative model cannot distinguish whether it is artificial data or real data. So we use the generative model to generate artificial data from Gaussian noise as extra training data to augment the size of training data.
, ๐บ) = ๐”ผ ๐‘ฅ~๐‘ ๐‘‘๐‘Ž๐‘ก๐‘Ž (๐‘ฅ) [๐‘™๐‘œ๐‘”๐ท(๐‘ฅ)] + ๐”ผ ๐‘ง~๐‘ ๐‘ง (๐‘ง) [๐‘™๐‘œ๐‘”(1 -๐ท(๐บ(๐‘ง)))] ๏€จ๏€ฒ๏€ฉ Where ๐‘ ๐‘‘๐‘Ž๐‘ก๐‘Ž is the distribution of training data, ๐ท(๐‘ฅ; ๐œƒ ๐‘‘ ) is discriminative model that can estimate the probability that ๐‘ฅ is from ๐‘ ๐‘‘๐‘Ž๐‘ก๐‘Ž by CNN with parameters ๐œƒ ๐‘‘ , ๐‘ ๐‘ง is the distribution of noise and here we use Gaussian distribution, ๐บ(๐‘ง; ๐œƒ ๐‘” ) is generative model that can generate the artificial data from noise ๐‘ง by inverse CNN with parameters ๐œƒ ๐‘” . To improve the classification accuracy of EEG signal with generated artificial EEG data, the artificial data must have label information. So abovementioned DCGAN is extended to a conditional version with label information, the auxiliary label information ๐‘Œ is feed into both generative model ๐บ and discriminative model ๐ท [17]. The loss function is converted into a conditional version as follows: min ๐บ max ๐ท ๐ฟ(๐ท, ๐บ) = ๐”ผ ๐‘ฅ~๐‘ ๐‘‘๐‘Ž๐‘ก๐‘Ž (๐‘ฅ) [๐‘™๐‘œ๐‘”๐ท(๐‘ฅ|๐‘ฆ ๐‘ง )] + ๐”ผ ๐‘ง~๐‘ ๐‘ง (๐‘ง) [๐‘™๐‘œ๐‘”(1 -๐ท(๐บ(๐‘ง|๐‘ฆ ๐‘‘ )))] ๏€จ๏€ณ๏€ฉ๏€  To avoid overfitting problem on finite dataset during training process, generative model and discriminative model are optimized alternately. In our model, we alternately optimize discriminative model ๐ท and generative model ๐บ by two steps and one step respectively. Theoretically, as long as ๐ท and ๐บ are well-designed and trained effectively, the whole adversarial process can reach the Nash equilibrium. Also at this equilibrium, the distribution of artificial data is same as the training data and the artificial data can be seen as real data because the discriminative model cannot distinguish whether it is artificial data or real data. So we use the generative model to generate artificial data from Gaussian noise as extra training data to augment the size of training data.
Source-paper figure
Figure 2. Comparison between artificial EEG representation and raw EEG time-frequency representation
Figure 2. Comparison between artificial EEG representation and raw EEG time-frequency representation
Source-paper figure
Figure 3. Classification accuracy of testing dataset for different ratio of raw training data and artificial data.
Figure 3. Classification accuracy of testing dataset for different ratio of raw training data and artificial data.
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Frequently Asked Questions

So how to recognize meaningful brain activities from seemingly meaningless brain electrical signal is a big challenge for BCI field. However, up to now all the methods to generate artificial EEG signal are based on the combination of the features of raw.

Fabien Lotte first to generate artificial EEG data by mixing signal segmentation in time domain, and their offline analysis suggested this approach can significantly increase classification accuracy when training data was small . To overcome this problem, artificial EEG signal generation methods.

Up to now, many methods have been proposed to improve recognition performance in many aspects including preprocessing, feature extraction, feature selection, classification and post-processing aspects . Qiqi Zhang, Ying Liu applied it for GAN to construct cDCGAN and the CNN was used.

However, this approach may cause inadequate high frequency noise at the boundary of two different segments. Therefore, cDCGAN is used to generate artificial TFR of EEG signal then the inverse of wavelet transform is applied to generate waveform EEG signal.

And deep learning model usually has huge numbers of parameters, so the limited training datasets cannot exploit the full potential of deep learning model in BCI field . But data scarcity is a big problem confines the ability of these advanced algorithms.

This paper presents a new method to improve brain-computer interfaces by creating more training data using advanced machine learning techniques. This helps in better understanding brain signals and enhances the performance of these systems.