Deep Learning methods are getting more and more extensively applied to medical imaging tasks. Nevertheless, very frequently medical images appear unlabelled making it difficult for AI algorithms to utilize the features of the images for classification purposes. Thus, such limitations make it almost impossible to develop robust and accurate algorithm for medical image classification. In this study, we have used a semi-supervised learning method Meta Pseudo Labels which allowed us to train models with a limited amount of labelled data extracted from chest X-ray images. The approach has demonstrated promising results achieving 92.5% of accuracy on the data labelled only for 16%. Additionally, we have also implemented the Transfer Learning approach to obtain higher accuracy on data labelled for only 0.5%. The approach involved initializing the model with the weights obtained from training it on a dataset with higher portion of labelled data. The approach has been proven to be successful averagely increasing the model accuracy on 0.5% of labeled data by 26 percent.

Human action recognition (HAR) is an active and crucial field of computer vision due to its various applications, such as smart surveillance and human-computer interaction. Recently, the human skeleton, which is compact and intuitive for representing actions and body movements, has been widely used in numerous HAR frameworks. Despite the great success of the skeleton-based HAR, several challenges remain, such as intra-class variability and inter-class similarity. In this paper, we address this task by first proposing a discriminative representation of the action-snippet (i.e., the very short sequence) that captures meaningful characteristics of human pose and body transition. We then employ adequate deep sequential neural networks (DSNNs) to thoroughly learn the temporal relation of action-snippets in a whole sequence. In experiments, the results show that the proposed approach achieves high recognition rates on benchmark datasets while maintaining good computational efficiency (i.e., lightweight networks and high recognition speed).

Brain-Computer Interface (BCI) systems have a great impact on improving people’s lives. One of the popular BCI implementations is the Event-Related Potential (ERP)-based spelling system which decodes electroencephalogram (EEG) signals to identify a target character. The effectiveness of BCI systems highly depends on the single trial decoding accuracy; however, the EEG signals are contaminated with diverse artifacts which leads to a poor signal-to-noise ratio. Therefore, various filtering algorithms (e.g., FFT, CSP, Laplacian, PCA) have been applied to find the optimal subset of feature spaces in the temporal and spatial domains. These preprocessing steps could efficiently discard the artifacts and have shown superior performance with typical linear classifiers. However, there is a risk that the informative subspace can be also eliminated by the unsupervised learning process, and this algorithm is not proper to be employed in the end-to-end deep-learning architectures where all modules are differentiable. This study aims to propose a generalized deep neural network model by denoising the ERP signals and initializing the Convolutional Neural Network (CNN) model parameters based on the autoencoder. Proposed CNN models indicate - 98.2% spelling performance and - 91.5% single trial accuracy which outperformed the state-of-the-art CNN models.

Convolutional neural networks (CNNs) have recently been applied to electroencephalogram (EEG)-based brain-computer interfaces (BCIs). EEG is a noninvasive neuroimaging technique, which can be used to decode user intentions. Because the feature space of EEG data is highly dimensional and signal patterns are specific to the subject, appropriate methods for feature representation are required to enhance the decoding accuracy of the CNN model. Furthermore, neural changes exhibit high variability between sessions, subjects within a single session, and trials within a single subject, resulting in major issues during the modeling stage. In addition, there are many subject-dependent factors, such as frequency ranges, time intervals, and spatial locations at which the signal occurs, which prevent the derivation of a robust model that can achieve the parameterization of these factors for a wide range of subjects. However, previous studies did not attempt to preserve the multivariate structure and dependencies of the feature space. In this study, we propose a method to generate a spatiospectral feature representation that can preserve the multivariate information of EEG data. Specifically, 3-D feature maps were constructed by combining subject-optimized and subject-independent spectral filters and by stacking the filtered data into tensors. In addition, a layer-wise decomposition model was implemented using our 3-D-CNN framework to secure reliable classification results on a single-trial basis. The average accuracies of the proposed model were 87.15% (±7.31), 75.85% (±12.80), and 70.37% (±17.09) for the BCI competition data sets IV_2a, IV_2b, and OpenBMI data, respectively. These results are better than those obtained by state-of-the-art techniques, and the decomposition model obtained the relevance scores for neurophysiologically plausible electrode channels and frequency domains, confirming the validity of the proposed approach.

For a brain-computer interface (BCI) system, a calibration procedure is required for each individual user before he/she can use the BCI. This procedure requires approximately 20-30 min to collect enough data to build a reliable decoder. It is, therefore, an interesting topic to build a calibration-free, or subject-independent, BCI. In this article, we construct a large motor imagery (MI)-based electroencephalography (EEG) database and propose a subject-independent framework based on deep convolutional neural networks (CNNs). The database is composed of 54 subjects performing the left- and right-hand MI on two different days, resulting in 21 600 trials for the MI task. In our framework, we formulated the discriminative feature representation as a combination of the spectral-spatial input embedding the diversity of the EEG signals, as well as a feature representation learned from the CNN through a fusion technique that integrates a variety of discriminative brain signal patterns. To generate spectral-spatial inputs, we first consider the discriminative frequency bands in an information-theoretic observation model that measures the power of the features in two classes. From discriminative frequency bands, spectral-spatial inputs that include the unique characteristics of brain signal patterns are generated and then transformed into a covariance matrix as the input to the CNN. In the process of feature representations, spectral-spatial inputs are individually trained through the CNN and then combined by a concatenation fusion technique. In this article, we demonstrate that the classification accuracy of our subject-independent (or calibration-free) model outperforms that of subject-dependent models using various methods [common spatial pattern (CSP), common spatiospectral pattern (CSSP), filter bank CSP (FBCSP), and Bayesian spatio-spectral filter optimization (BSSFO)].

Motor imagery (Ml)-based brain-computer interface (BCI) allows users to control external devices using the brain signal patterns induced by the imagination of movements. Since these patterns have high variability between subjects and sessions, the BCI system necessarily requires 20-30 minutes for the calibration process each time the system is used. This time-consuming process requires a high level of the user's concentration; most users experience uncomfortable feelings such as tiredness, exhaustion, and loss of attention, which are symptoms of mental fatigue. In this paper, we introduce a self-paced training that terminates the calibration process within a few minutes. In this training paradigm, users perform MI tasks continuously without an inter-stimulus-interval (ISI). Also, we propose a data selection method to extract the most prominent features from the short calibration data by assuming the data distribution probabilistically and using the prior knowledge of event-related desynchronization (ERD) patterns. The results from 19 subjects indicate that the proposed method gained a comparable classification performance to the conventional method but with a much shorter calibration period (12 min/73.8%, 30 min/76.1%, respectively). In this regard, the proposed method could be of great benefit for real-world BCI applications by providing a quicker calibration process.

As the brain is a unique biological system that reflects the subtle distinctions in the mental attributes of individual humans, electroencephalographic (EEG) signals have been regarded as one of the most promising and potent biometric signals for discriminating between individuals. However, existing EEG-based user-recognition methods present only a limited range of individual distinctions. In this paper, we propose a novel system of decoding cognitive EEG signals for individual identification with high accuracy. Specifically, we investigate the feasibility of our system, which can recognize an individual based on the discriminative patterns of source-level causal connectivity among brain regions, estimated from scalp-level EEG signals. The EEG signals were produced by a steady-state visual evoked potential-inducing grid-shaped top-down paradigm. This system can, in principle, use top-down cognitive features analyzed by individuals' differently characterized neurodynamic causal connectivities. In this paper, we achieved a maximal accuracy of 98.60% on average in 20 subjects, for whom we estimated causal connectivity in 16 brain regions using 5-s intervals of EEG signals. Our system shows promising initial results toward building a practical identification technology able to recognize individuals by means of brain neurodynamics.

Recently, there has been an increased demand for Brain-Machine Interface (BMI) toolboxes for neuroscientifc research. In many BMI applications, speller systems can provide an efficient communication channel for users with disabilities. Here, we introduce an open-source BMI toolbox termed `OpenBMI', which supports the various signal processing chains for common BMI paradigms, such as event-related potentials (ERPs) and steady-state visual evoked potentials (SSVEP). The OpenBMI framework consists of ready-to-use experimental paradigms, offline data analysis techniques, online feedback as well as evaluation modules. The data analysis modules provide essential pre-processing steps (segmentation, baseline correction, etc.) as well as signal processing algorithms such as temporal and spatial filtering, artifact rejection, among others. The experimental paradigms of ERP and SSVEP are available with fully open-sourced demo scripts. Users can easily modify or extend the demo scripts for their needs. In this article, the OpenBMI framework, its features as well as its future development plan is introduced.

A scaler is one of the most important modules in various video applications, such as ultra-high definition TV and scalable video systems. A variety of scaling techniques have been used to increase the video quality when the resolution of the source image has to be up- and down-scaled. Some conventional schemes exploit the property of local block data. Others consider the edge information of the data to be scaled. In this paper, we formulate a scaling problem to minimize the information loss resulting from the resizing process. The loss is considered in both the spatial and the frequency domains, and then it is minimized to optimize the kernel of the scaler. The simulation results show that the proposed algorithm reduces the information loss more than conventional schemes. When compared with the conventional algorithms, the proposed method outperforms those with similar complexity.