Showing papers by "Gert Pfurtscheller published in 2008"
TL;DR: It can be stated that the SSVEP-based BCI, operating in an asynchronous mode, is feasible for the control of neuroprosthetic devices with the flickering lights mounted on its surface.
Abstract: Brain-computer interfaces (BCIs) are systems that establish a direct connection between the human brain and a computer, thus providing an additional communication channel. They are used in a broad field of applications nowadays. One important issue is the control of neuroprosthetic devices for the restoration of the grasp function in spinal-cord-injured people. In this communication, an asynchronous (self-paced) four-class BCI based on steady-state visual evoked potentials (SSVEPs) was used to control a two-axes electrical hand prosthesis. During training, four healthy participants reached an online classification accuracy between 44% and 88%. Controlling the prosthetic hand asynchronously, the participants reached a performance of 75.5 to 217.5 s to copy a series of movements, whereas the fastest possible duration determined by the setup was 64 s. The number of false negative (FN) decisions varied from 0 to 10 (the maximal possible decisions were 34). It can be stated that the SSVEP-based BCI, operating in an asynchronous mode, is feasible for the control of neuroprosthetic devices with the flickering lights mounted on its surface.
555 citations
01 Jan 2008
TL;DR: This poster presents a probabilistic procedure for estimating the response of the immune system to laser-spot assisted, 3D image analysis of EMTs.
Abstract: Reference EPFL-ARTICLE-164768 URL: http://ijbem.k.hosei.ac.jp/ Record created on 2011-04-08, modified on 2017-05-12
389 citations
TL;DR: This work states that before a BCI can be used for communication and control at home, research must solve several problems, and improvements are on the horizon that expect to see practical BCI systems for a wide range of users and applications.
Abstract: BCI systems let users convert thoughts into actions that do not involve voluntary muscle movement. The systems offer a new means of communication for those with paralysis or severe neuromuscular disorders. BCI technology is a relatively new, fast-growing field of research and applications with the potential to improve the quality of life in severely disabled people. To date, several BCI prototypes exist, but most work only in a laboratory environment. Before a BCI can be used for communication and control at home, research must solve several problems. An important next step is to establish protocols for easily setting up and using BCI systems in a practical environment. Many features, such as electrode positions and frequency components, must be automatically selectable for particular motor imagery. The system must use the fewest number of recording electrodes possible, striving for the optimal single EEG channel. Finally, training time must decrease, perhaps through game-like feedback and automatic detection of artifacts, such as uncontrolled muscle activity. With these improvements, which are on the horizon, we expect to see practical BCI systems for a wide range of users and applications.
214 citations
TL;DR: This work shows how subjects, after performing cue-based feedback training (smiley paradigm), learned to navigate self-paced through the freeSpace virtual environment (VE) and reported the results of three able-bodied subjects.
Abstract: The self-paced control paradigm enables users to operate brain-computer interfaces (BCI) in a more natural way: no longer is the machine in control of the timing and speed of communication, but rather the user is. This is important to enhance the usability, flexibility, and response time of a BCI. In this work, we show how subjects, after performing cue-based feedback training (smiley paradigm), learned to navigate self-paced through the ?freeSpace? virtual environment (VE). Similar to computer games, subjects had the task of picking up items by using the following navigation commands: rotate left, rotate right, and move forward ( three classes). Since the self-paced control paradigm allows subjects to make voluntary decisions on time, type, and duration of mental activity, no cues or routing directives were presented. The BCI was based only on three bipolar electroencephalogram channels and operated by motor imagery. Eye movements (electrooculogram) and electromyographic artifacts were reduced and detected online. The results of three able-bodied subjects are reported and problems emerging from self-paced control are discussed.
199 citations
TL;DR: The set-up of a one-channel NIRS system designed for use as an optical brain-computer interface is described and first measurements of deoxyhemoglobin and oxyhemoglobin changes during mental arithmetic tasks are reported on.
Abstract: Near-infrared spectroscopy (NIRS) is a non-invasive optical technique that can be used to assess functional activity in the human brain. This work describes the set-up of a one-channel NIRS system designed for use as an optical brain-computer interface (BCI) and reports on first measurements of deoxyhemoglobin (Hb) and oxyhemoglobin (HbO(2)) changes during mental arithmetic tasks. We found relatively stable and reproducible hemodynamic responses in a group of 13 healthy subjects. Unexpected observations of a decrease in HbO(2) and increase in Hb concentrations measured over the prefrontal cortex were in contrast to the typical hemodynamic responses (increase in HbO(2), decrease in Hb) during cortical activation previously reported.
113 citations
TL;DR: Findings from fMRI at 3T during imagined hand and foot movements are interpreted as evidence that BCI training as a conduit of motor imagery training may assist in maintaining access to SMC in largely preserved somatopy despite complete deafferentation.
Abstract: Although several features of brain motor function appear to be preserved even in chronic complete SCI, previous functional MRI (fMRI) studies have also identified significant derangements such as a strongly reduced volume of activation, a poor modulation of function and abnormal activation patterns. It might be speculated that extensive motor imagery training may serve to prevent such abnormalities. We here report on a unique patient with a complete traumatic SCI below C5 who learned to elicit electroencephalographic signals beta-bursts in the midline region upon imagination of foot movements. This enabled him to use a neuroprosthesis and to "walk from thought" in a virtual environment via a brain-computer interface (BCI). We here used fMRI at 3T during imagined hand and foot movements to investigate the effects of motor imagery via persistent BCI training over 8 years on brain motor function and compared these findings to a group of five untrained healthy age-matched volunteers during executed and imagined movements. We observed robust primary sensorimotor cortex (SMC) activity in expected somatotopy in the tetraplegic patient upon movement imagination while such activation was absent in healthy untrained controls. Sensorimotor network activation with motor imagery in the patient (including SMC contralateral to and the cerebellum ipsilateral to the imagined side of movement as well as supplementary motor areas) was very similar to the pattern observed with actual movement in the controls. We interpret our findings as evidence that BCI training as a conduit of motor imagery training may assist in maintaining access to SMC in largely preserved somatopy despite complete deafferentation.
98 citations
TL;DR: This study investigated how the classification accuracy of a 4-class BCI system can be improved by localizing individual electroencephalogram (EEG) recording positions and found that the use of three SSVEP-harmonics recorded from individual channels yielded significantly higher classification accuracy.
66 citations
TL;DR: In the present study, able‐bodied subjects without any motor imagery experience (naive subjects) were asked to imagine the indicated limb movement for some seconds, revealing a short‐lasting somatotopically specific event‐related desynchronization in the upper mu and/or beta bands.
Abstract: Multi-channel electroencephalography recordings have shown that a visual cue, indicating right hand, left hand or foot motor imagery, can induce a short-lived brain state in the order of about 500 ms. In the present study, 10 able-bodied subjects without any motor imagery experience (naive subjects) were asked to imagine the indicated limb movement for some seconds. Common spatial filtering and linear single-trial classification was applied to discriminate between two conditions (two brain states: right hand vs. left hand, left hand vs. foot and right hand vs. foot). The corresponding classification accuracies (mean ± SD) were 80.0 ± 10.6%, 83.3 ± 10.2% and 83.6 ± 8.8%, respectively. Inspection of central mu and beta rhythms revealed a short-lasting somatotopically specific event-related desynchronization (ERD) in the upper mu and/or beta bands starting ∼300 ms after the cue onset and lasting for less than 1 s.
60 citations
TL;DR: In this work one single Laplacian derivation and a full description of band power values in a broad frequency band are used to detect brisk foot movement execution in the ongoing EEG.
59 citations
31 citations
TL;DR: A tetraplegic patient was able to induce midcentral localized beta oscillations in the electroencephalogram (EEG) after extensive mental practice of foot motor imagery, providing evidence that mentally practice of motor performance is accompanied not only by activation of cortical structures but also by central commands into the cardiovascular system with its nuclei in the brain stem.
TL;DR: The coupling between heart rate (HR) changes and electroencephalographic (EEG) bursts is confirmed in a larger group of preterm infants and semi-automatic detection of burst-to-burst intervals (BBI) is reported on and correlations between BBI and HR changes are found.
28 Apr 2008
TL;DR: In this article, the influence of eye movement direction on patterns of brain activation was investigated by quantifying event-related desynchronization (ERD) in the electroencephalogram (EEG).
Abstract: Objective This study investigates the influence of eye movement direction on patterns of brain activation. Methods The processing of visual input was investigated by quantifying event-related desynchronization (ERD) in the electroencephalogram (EEG). Cue-based vertical and horizontal eye movements were measured with an eye tracker. Differences between vertical and horizontal eye movements in EEG and eye-tracking data were analyzed. Results The results of this study indicate that vertical and horizontal eye movements result in different ERD and ERS patterns. During the execution of a saccade vertical eye movements are accompanied by a stronger ERS whereas the fixation of the cue is related to stronger ERD after horizontal eye movements. Conclusion The fact that eye movements are correlated with a desynchronization of activity in parietal and occipital areas is reasonable, since visual information processing and visual control of movements take place there. Stronger ERD in the alpha band could be related to the fact that information processing tasks like e.g. reading require mostly horizontal and not vertical eye movements. Significance The differences in the ERD/ERS patterns in relation to the direction of the eye movement should be considered in future investigations and taken into account in the construction of paradigms.
18 Sep 2008
TL;DR: It is shown that the resulting spatialters have to be adapted to each subject and that the combined use of intra-trial and inter-class energy variations of brain sources yield an increase of classification rates for four among eight sub jects.
Abstract: This paper presents a method to recover task-related sources from a multi-class Brain-Computer Interface (BCI) based on motor imagery Our method gathers two common approaches to tackle the multi-class problem: 1) the supervised approach of Common Spatial Pattern (CSP) to discriminate between different tasks; 2) the criterion of statistical independence of non-stationary sources used in Independent Component Analysis (ICA) We show that the resulting spatial filters have to be adapted to each subject and that the combined use of intra-trial and inter-class energy variations of brain sources yield an increase of classification rates for four among eight sub jects
Proceedings Article•
25 Aug 2008TL;DR: It is shown that the use of a priori knowledge about the sources and the performed task increases classification rates compared to previous studies, and gives a general framework to improve Brain-Computer Interfaces and to adapt spatial filtering methods to each subject.
Abstract: This paper presents a general framework to recover task-related sources from a multi-class Brain-Computer Interface (BCI) based on motor imagery. Our method gathers two common approaches to tackle the multi-class problem: 1) the supervised approach of Common Spatial Patterns and Sparse and/or Spectral variants (CSP, CSSP, CSSSP) to discriminate between different tasks; 2) the criterion of statistical independence of non-stationary sources used in Independent Component Analysis (ICA). Our method can exploit different properties of the signals to find the best discriminative linear combinations of sensors. This yields different models of separation. This work aims at comparing these models. We show that the use of a priori knowledge about the sources and the performed task increases classification rates compared to previous studies. This work gives a general framework to improve Brain-Computer Interfaces and to adapt spatial filtering methods to each subject.
30 Sep 2008
TL;DR: D discrete wavelet analysis is applied to extraction of ERS/ERD features from a small number of EEG signals during motor imagery to make use of these features to recognize inputs for BCI (brain-computer interface), based on AR model.
Abstract: ERS and ERD (event-related synchronization and desynchronization) are observed in EEG (electroencephalogram) signals around such events as sensitive stimulus, motions, cognitive actions etc. Usually, ERS/ERD features of EEG are extracted as variances of band-passed signals of several trials. To make use of these features to recognize inputs for BCI (brain-computer interface), we applied discrete wavelet analysis to extraction of ERS/ERD features from a small number of EEG signals during motor imagery. We employed Daubechies, convolution and spline biorthogonal mothers for linear wavelet analysis, also Haar type structural function for morphological wavelet analysis. Then our extraction method was estimated by the pattern recognition based on AR model.
16 Dec 2008
TL;DR: An overview of the Graz BCI used for the control of neuroprosthetic devices is given and a method to overcome the problem of losing the ability to move the elbow is offered.
Abstract: The consequences of a spinal cord injury (SCI) are tremendous for the patients. The loss of motor functions especially of the grasping function leads to a life-long dependency on helping persons and thereby to a dramatic decrease in quality of life. With the help of so-called neuroprostheses, the grasp function can be substantially improved. Nowadys, systems for grasp restoration can only be used by patients with preserved voluntary shoulder and elbow function. In patients with a higher SCI the ability to move the elbow is lost and the number of active control movements decreases. A Brain-Computer Interface (BCI) offers a method to overcome this problem. This work gives an overview of the Graz BCI used for the control of neuroprosthetic devices.
21 Oct 2008
TL;DR: Electroencephalograph signals recorded during miss operation of brain computer interface (BCI) system revealed a feature difference between miss operation and normal operation at the low frequency component and the event-related potential (ERP) such as P300.
Abstract: In this paper, electroencephalograph (EEG) signals recorded during miss operation of brain computer interface (BCI) system was analyzed. As a result, a feature difference between miss operation and normal operation was found at the low frequency component and the event-related potential (ERP) such as P300. Therefore a possibility of the modification of miss operation was confirmed.