Abstract
Nowadays, motor imagery (MI) electroencephalogram (EEG) signal classification has become a hotspot in the research field of brain computer interface (BCI). More recently, deep learning has emerged as a promising technique to automatically extract features of raw MI EEG signals and then classify them. However, deep learning-based methods still face two challenging problems in practical MI EEG signal classification applications: (1) Generally, training a deep learning model successfully needs a large amount of labeled data. However, most of the EEG signal data is unlabeled and it is quite difficult or even impossible for human experts to label all the signal samples manually. (2) It is extremely time-consuming and computationally expensive to train a deep learning model from scratch. To cope with these two challenges, a deep transfer convolutional neural network (CNN) framework based on VGG-16 is proposed for EEG signal classification. The proposed framework consists of a VGG-16 CNN model pre-trained on the ImageNet and a target CNN model which shares the same structure with VGG-16 except for the softmax output layer. The parameters of the pre-trained VGG-16 CNN model are directly transferred to the target CNN model used for MI EEG signal classification. Then, front-layers parameters in the target model are frozen, while later-layers parameters are fine-tuned by the target MI dataset. The target dataset is composed of time-frequency spectrum images of EEG signals. The performance of the proposed framework is verified on the public benchmark dataset 2b from the BCI competition IV. The experimental results show that the proposed framework improves the accuracy and efficiency performance of EEG signal classification compared with traditional methods, including support vector machine (SVM), artificial neural network (ANN), and standard CNN.
Highlights
Brain computer interface (BCI), known as brain-machine interface (BMI), enables human brains to directly communicate with external computers or machines
The proposed framework consists of a VGG-16 convolutional neural network (CNN) model pre-trained on the ImageNet and a target CNN model which shares the same structure with VGG-16 except for the softmax output layer
The parameters of the pre-trained VGG-16 CNN model are directly transferred to the target CNN model used for Motor imagery (MI) EEG signal classification
Summary
Brain computer interface (BCI), known as brain-machine interface (BMI), enables human brains to directly communicate with external computers or machines. CNN, as one of the most widely-used deep learning models, is always combined with the extracted features of EEG signal data to provide an improved classification result. Because the CNN model pre-trained on the benchmark dataset like ImageNet can extract universal low-level features, which are useful for most of image classification problems [30]. Shi et al [33] proposed a deep CNN-based transfer learning method for false positive reduction, all the pre-trained layers are transferred to target network and only the last fully connected layer is fine-tuned for the pulmonary nodule classification task.
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