A Bootstrapping Method for Improving the Classification Performance of the P300 Speller

Abstract In this paper, we present a novel approach to training classifiers in a speller based on P300 potentials. The method, based on bootstrapping, is a known strategy for generating new samples, but it is rarely used in neurosciences. The study first demonstrates how the performance of the classification task (detecting P300 and Non-P300 classes) could be sub-optimal in the traditional approach. Then, a new method for taking new samples from the training data is proposed. Each classifier is re-trained using balanced sub-groups of individual P300 and non-P300 samples. Data were collected from 14 healthy subjects, using 16 electroencephalography channels. These were filtered in bandpass and decimated. Subsequently, four linear classifiers were trained using the traditional method followed by the proposed one, with 1000, 2000 and 3000 samples per class. Results indicate an improvement in the accuracy and discrimination capacity of discriminative classifiers with the proposed method, maintaining the same statistical properties between the training and test data. By contrast, for generative classifiers, there is no significant difference in the results. Therefore, the proposed method is highly recommended for training discriminative classifiers in spell-based P300 potentials.

Resumen Este artículo presenta un método novedoso para entrenar clasificadores en un deletreador basado en potenciales P300. El método, basado en bootstrapping, es una estrategia conocida para generar nuevas muestras pero escasamente implementado en neurociencias. El estudio muestra cómo el rendimiento de la detección de P300 (frente a No-P300) puede resultar sub-óptimo usando el método tradicional. Luego, se propone un nuevo método donde se toman nuevas muestras a partir de los datos de entrenamiento. Con ellas, se re-entrena al clasificador usando sub-grupos equilibrados de muestras individuales P300 y No-P300. Los datos se recolectaron de 14 sujetos sanos, usando 16 canales de electroencefalografía. Estos fueron filtrados en pasa-banda y diezmados. Posteriormente, cuatro clasificadores lineales fueron entrenados, usando primero el método tradicional y después el método propuesto, con 1000, 2000 y 3000 muestras por clase. Los resultados muestran una mejoría en la precisión y la capacidad de discriminación de clasificadores discriminativos con el método propuesto, manteniendo las mismas propiedades estadísticas entre los datos de entrenamiento y los de prueba. En contraste, para los clasificadores generativos, no existe una diferencia significativa en los resultados. Por consiguiente, el método propuesto es altamente recomendado para entrenar clasificadores discriminativos en deletreadores basados en potenciales P300.

Suturas transconjuntivales del tapete escleral en maculopatía hipotónica tardía tras esclerectomía profunda no perforante / Transconjunctival suturing of the scleral flap in late hypotony maculopathy after non-penetrating deep sclerectomy

CASO CLÍNICO: Un hombre de 63 años desarrolla una maculopatía hipotónica tardía tras una esclerectomía profunda no perforante. La sutura transconjuntival del tapete escleral permite resolver la hipotonía y la normalización de la agudeza visual. DISCUSIÓN: La maculopatía hipotónica puede presentarse de forma diferida tras una cirugía de glaucoma. Las suturas transconjuntivales del tapete escleral son una alternativa en el tratamiento de la hipotonía cuando las medidas conservadoras han fracasado

CLINICAL CASE: A 63-year-old man presents with late hypotony maculopathy after non-penetrating deep sclerectomy. Hypotonia and visual acuity are improved after transconjunctival suturing of the scleral flap. DISCUSSION: Hypotony maculopathy may occur as a late complication after glaucoma surgery. Transconjunctival suturing of the scleral flap can be useful when conservative measures have failed

Transconjunctival suturing of the scleral flap in late hypotony maculopathy after non-penetrating deep sclerectomy. / Suturas transconjuntivales del tapete escleral en maculopatía hipotónica tardía tras esclerectomía profunda no perforante.

CLINICAL CASE: A 63-year-old man presents with late hypotony maculopathy after non-penetrating deep sclerectomy. Hypotonia and visual acuity are improved after transconjunctival suturing of the scleral flap. DISCUSSION: Hypotony maculopathy may occur as a late complication after glaucoma surgery. Transconjunctival suturing of the scleral flap can be useful when conservative measures have failed.

Classification of Imaginary Motor Task from Electroencephalographic Signals: A Comparison of Feature Selection Methods and Classification Algorithms / Clasificación de una Motricidad Imaginaria por medio de Señales Electroencefalográficas: Una Comparación de Métodos de Selección de Características y Algoritmos de Clasificación

Abstract: In this work, a Brain Computer interface able to decode imagery motor task from EEG is presented. The method uses time-frequency representation of the brain signal recorded in different regions of the brain to extract important features. Principal Component Analysis and Sequential Forward Selection methods are compared in their ability to represent the feature set in a compact form, removing at the same time unnecessary information. Finally, two method based on machine learning are implemented for the task of classification. Results show that it is possible to decode the mental activity of the subjects with accuracy above 80%. Furthermore, visualization of the main components extracted from the brain signal allow for physiological insights on the activity that take place in the sensorimotor cortex during execution of imaginary movement of different parts of the body.

Resumen: En este trabajo es presentada una Interfaz Cerebro Computadora que tiene la capacidad de decodificar actividades motrices. El método utiliza representación en el dominio de la frecuencia y el tiempo de las señales del cerebro grabadas en distintas regiones de este mismo, con el fin de extraer características importantes. Los métodos: Análisis de Componentes Principales y Selección Secuencial, son comparados en términos de su capacidad para representar características de la señal de una forma compacta, removiendo de esta forma, información innecesaria. Finalmente, dos métodos basados en aprendizaje de máquinas fueron implementados para la clasificación de actividades motrices utilizando solo las señales cerebrales. Los resultados muestran que es posible decodificar la actividad mental en los sujetos con una precisión superior al 80%. Además, la visualización de las componentes principales extraídas de las señales del cerebro permite un analísis de la actividad que toma lugar en la corteza cerebral sensorimotora durante la ejecución de la imaginación de movimientos de distintas partes del cuerpo.

Towards Enzyme-like, Sustainable Catalysis: Switchable, Highly Efficient Asymmetric Synthesis of Enantiopure Biginelli Dihydropyrimidinones or Hexahydropyrimidinones.

Organocatalysts displaying a network of cooperative hydrogen bonds (NCHB) have been employed in an enzyme-like manner for a direct, switchable synthesis of enantiopure hexahydropyrimidinones (HHPMs) or dihydropyrimidinones (DHPMs), which starts at a common, easily accessible α-ureidosulfone stage. The NCHB organocatalyst exploits all its potential as a pure hydrogen-bond biomimetic catalyst even in the presence of organic bases. This one-pot, diastereo- and enantioselective synthetic procedure has been proven to be robust, scalable, highly efficient, and environmentally benign. A straightforward and truly practical entry to enantiopure HHPMs is reported for the first time.

Total hip arthroplasty.

Total hip arthroplasty continues to be an extremely successful procedure, with ever-widening indications and regular improvement in technique, materials, and design. In the past year several studies were published evaluating the results of both cemented and cementless total hip arthroplasty at mid- to long-term follow-up. In addition, careful analysis of basic laboratory studies including finite-element analyses have added to our understanding of materials and design. Specific findings in the past year included poor results with cemented hips in younger patients at long-term follow-up of greater than 16 years. A lower incidence of loosening has been found for cobalt chrome-cemented components compared with titanium-cemented components. No difference was found in the results of metal-backed versus non-metal backed cemented acetabular components, and an increasing incidence of loosening was shown for cemented acetabular components with time. The newer cementless hip arthroplasties showed evidence of learning curve, particularly with regard to innovative design such as acetabular screw rings, whereas porous-coated hemispherical cups appeared to do well. Thigh pain continues to be a problem with cementless designs, and the controversy of titanium versus cobalt chrome for cementless femoral stem designs continues at full tilt.