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Neural suppression of distractors surrounding the spotlight: Evidence from steady-state visual evoked potentials
JunBang Zhao,ZhiJun Zhang,Chen Zhang,Yi Tang,ZhiFang Liu
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-012-5078-2
Abstract: The present study investigated the allocation of spatial attention using steady-state visual evoked potentials (SSVEPs). The SSVEP is elicited in visual cortical areas by a repetitive flicker having the same fundamental frequency as the driving stimulus. Two flickers were applied with the letter stream presented in the center of the monitor and the distractor presented on either the left or right side of the target. Participants were instructed to detect the target letter in the letter stream. The distance of the two flickers was manipulated. The results show that the amplitudes of the SSVEPs elicited by the distractor were enhanced when it was in the closest position and suppressed when it was at a farther distance. But the amplitudes rebounded at the farthest distance. Meanwhile, the SSVEP elicited by the target flicker remained stable independent of the distance of the distractor. Thus, the present study indicates that focused attention involves neural suppression surrounding the classic “spotlight”, and the SSVEP paradigms open new avenues for studying the attentional suppression mechanism.
Dissipative production of a maximally entangled steady state  [PDF]
Y. Lin,J. P. Gaebler,F. Reiter,T. R. Tan,R. Bowler,A. S. S?rensen,D. Leibfried,D. J. Wineland
Physics , 2013, DOI: 10.1038/nature12801
Abstract: Entangled states are a key resource in fundamental quantum physics, quantum cryp-tography, and quantum computation [1].To date, controlled unitary interactions applied to a quantum system, so-called "quantum gates", have been the most widely used method to deterministically create entanglement [2]. These processes require high-fidelity state preparation as well as minimizing the decoherence that inevitably arises from coupling between the system and the environment and imperfect control of the system parameters. Here, on the contrary, we combine unitary processes with engineered dissipation to deterministically produce and stabilize an approximate Bell state of two trapped-ion qubits independent of their initial state. While previous works along this line involved the application of sequences of multiple time-dependent gates [3] or generated entanglement of atomic ensembles dissipatively but relied on a measurement record for steady-state entanglement [4], we implement the process in a continuous time-independent fashion, analogous to optical pumping of atomic states. By continuously driving the system towards steady-state, the entanglement is stabilized even in the presence of experimental noise and decoherence. Our demonstration of an entangled steady state of two qubits represents a step towards dissipative state engineering, dissipative quantum computation, and dissipative phase transitions [5-7]. Following this approach, engineered coupling to the environment may be applied to a broad range of experimental systems to achieve desired quantum dynamics or steady states. Indeed, concurrently with this work, an entangled steady state of two superconducting qubits was demonstrated using dissipation [8].
Face-Evoked Steady-State Visual Potentials: Effects of Presentation Rate and Face Inversion  [PDF]
L. Forest Gruss,Matthias J. Wieser,Stefan R. Schweinberger,Andreas Keil
Frontiers in Human Neuroscience , 2012, DOI: 10.3389/fnhum.2012.00316
Abstract: Face processing can be explored using electrophysiological methods. Research with event-related potentials has demonstrated the so-called face inversion effect, in which the N170 component is enhanced in amplitude and latency to inverted, compared to upright, faces. The present study explored the extent to which repetitive lower-level visual cortical engagement, reflected in flicker steady-state visual evoked potentials (ssVEPs), shows similar amplitude enhancement to face inversion. We also asked if inversion-related ssVEP modulation would be dependent on the stimulation rate at which upright and inverted faces were flickered. To this end, multiple tagging frequencies were used (5, 10, 15, and 20 Hz) across two studies (n = 21, n = 18). Results showed that amplitude enhancement of the ssVEP for inverted faces was found solely at higher stimulation frequencies (15 and 20 Hz). By contrast, lower frequency ssVEPs did not show this inversion effect. These findings suggest that stimulation frequency affects the sensitivity of ssVEPs to face inversion.
Network Filtering for Big Data: Triangulated Maximally Filtered Graph  [PDF]
Guido Previde Massara,T. Di Matteo,Tomaso Aste
Computer Science , 2015,
Abstract: We propose a network-filtering method, the Triangulated Maximally Filtered Graph (TMFG), that provides an approximate solution to the Weighted Maximal Planar Graph problem. The underlying idea of TMFG consists in building a triangulation that maximizes a score function associated with the amount of information retained by the network. TMFG uses as weights any arbitrary similarity measure to arrange data into a meaningful network structure that can be used for clustering, community detection and modeling. The method is fast, adaptable and scalable to very large datasets, it allows online updating and learning as new data can be inserted and deleted with combinations of local and non-local moves. TMFG permits readjustments of the network in consequence of changes in the strength of the similarity measure. The method is based on local topological moves and can therefore take advantage of parallel and GPUs computing. We discuss how this network-filtering method can be used intuitively and efficiently for big data studies and its significance from an information-theoretic perspective.
Investigation and Comparison of Recording Time of Steady State Evoked Potentials Using Three Methods of Kalman, Ziarani and adaptive  [PDF]
Ali Reza Mehri,Dariush Shahbazi-Gahrouei,Leila Ghaedi
Audiology , 2007,
Abstract: Background and Aim: Hearing assessment in infants and children younger than two years is an impor-tant issue, because the golden time of the language learning and speaking is under the age of two. Steady state auditory evoked potentials (SSAEPs) is one of the best ways of the objective hearing assess-ment for infants and young children. The need for long time of stimulation and recording re-stricted the clinical uses of this method. Therefore, the reduction of the recording time is a common prob-lem. SSAEP signals are contaminated with background EEG signals of the brain and nervous sys-tem. To discriminate these signals the approach is using averaging method.Materials and Methods: In this work two adaptive methods were programmed and tried on (SSAEP) sig-nals. The first method was the work of the Ziarani et al. and the second was the enhanced Kalman fil-ter. To assess suggested methods and to compare them with traditional averaging one, two sets of clini-cal signals prepared with Rotmen research group in university of Toronto were applied. Results: The speed of the extraction of the SSAEP signals with the Ziarani method is 1.6 times faster than the averaging method. The extraction time of the enhanced adaptive Kalman filter is 13.1 times faster than currently used averaging methods. Conclusion: The Kalman filter method seems to be more reliable than the other two methods. In addi-tion, this new application of the Kalman filter in hearing assessment could be more beneficial and faster than other methods as an objective method.
Assessing the quality of steady-state visual-evoked potentials for moving humans using a mobile electroencephalogram headset  [PDF]
Yuan-Pin Lin,Yijun Wang,Chun-Shu Wei,Tzyy-Ping Jung
Frontiers in Human Neuroscience , 2014, DOI: 10.3389/fnhum.2014.00182
Abstract: Recent advances in mobile electroencephalogram (EEG) systems, featuring non-prep dry electrodes and wireless telemetry, have enabled and promoted the applications of mobile brain-computer interfaces (BCIs) in our daily life. Since the brain may behave differently while people are actively situated in ecologically-valid environments versus highly-controlled laboratory environments, it remains unclear how well the current laboratory-oriented BCI demonstrations can be translated into operational BCIs for users with naturalistic movements. Understanding inherent links between natural human behaviors and brain activities is the key to ensuring the applicability and stability of mobile BCIs. This study aims to assess the quality of steady-state visual-evoked potentials (SSVEPs), which is one of promising channels for functioning BCI systems, recorded using a mobile EEG system under challenging recording conditions, e.g., walking. To systematically explore the effects of walking locomotion on the SSVEPs, this study instructed subjects to stand or walk on a treadmill running at speeds of 1, 2, and 3 mile (s) per hour (MPH) while concurrently perceiving visual flickers (11 and 12 Hz). Empirical results of this study showed that the SSVEP amplitude tended to deteriorate when subjects switched from standing to walking. Such SSVEP suppression could be attributed to the walking locomotion, leading to distinctly deteriorated SSVEP detectability from standing (84.87 ± 13.55%) to walking (1 MPH: 83.03 ± 13.24%, 2 MPH: 79.47 ± 13.53%, and 3 MPH: 75.26 ± 17.89%). These findings not only demonstrated the applicability and limitations of SSVEPs recorded from freely behaving humans in realistic environments, but also provide useful methods and techniques for boosting the translation of the BCI technology from laboratory demonstrations to practical applications.
Generating Visual Flickers for Eliciting Robust Steady-State Visual Evoked Potentials at Flexible Frequencies Using Monitor Refresh Rate  [PDF]
Masaki Nakanishi, Yijun Wang, Yu-Te Wang, Yasue Mitsukura, Tzyy-Ping Jung
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0099235
Abstract: In the study of steady-state visual evoked potentials (SSVEPs), it remains a challenge to present visual flickers at flexible frequencies using monitor refresh rate. For example, in an SSVEP-based brain-computer interface (BCI), it is difficult to present a large number of visual flickers simultaneously on a monitor. This study aims to explore whether or how a newly proposed frequency approximation approach changes signal characteristics of SSVEPs. At 10 Hz and 12 Hz, the SSVEPs elicited using two refresh rates (75 Hz and 120 Hz) were measured separately to represent the approximation and constant-period approaches. This study compared amplitude, signal-to-noise ratio (SNR), phase, latency, scalp distribution, and frequency detection accuracy of SSVEPs elicited using the two approaches. To further prove the efficacy of the approximation approach, this study implemented an eight-target BCI using frequencies from 8–15 Hz. The SSVEPs elicited by the two approaches were found comparable with regard to all parameters except amplitude and SNR of SSVEPs at 12 Hz. The BCI obtained an averaged information transfer rate (ITR) of 95.0 bits/min across 10 subjects with a maximum ITR of 120 bits/min on two subjects, the highest ITR reported in the SSVEP-based BCIs. This study clearly showed that the frequency approximation approach can elicit robust SSVEPs at flexible frequencies using monitor refresh rate and thereby can largely facilitate various SSVEP-related studies in neural engineering and visual neuroscience.
Steady-State Visual Evoked Potentials Can Be Explained by Temporal Superposition of Transient Event-Related Responses  [PDF]
Almudena Capilla,Paula Pazo-Alvarez,Alvaro Darriba,Pablo Campo,Joachim Gross
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0014543
Abstract: One common criterion for classifying electrophysiological brain responses is based on the distinction between transient (i.e. event-related potentials, ERPs) and steady-state responses (SSRs). The generation of SSRs is usually attributed to the entrainment of a neural rhythm driven by the stimulus train. However, a more parsimonious account suggests that SSRs might result from the linear addition of the transient responses elicited by each stimulus. This study aimed to investigate this possibility.
Reliable and Efficient Procedure for Steady-State Analysis of Nonautonomous and Autonomous Systems
J. Dobes,V. Biolkova
Radioengineering , 2012,
Abstract: The majority of contemporary design tools do not still contain steady-state algorithms, especially for the autonomous systems. This is mainly caused by insufficient accuracy of the algorithm for numerical integration, but also by unreliable steady-state algorithms themselves. Therefore, in the paper, a very stable and efficient procedure for the numerical integration of nonlinear differential-algebraic systems is defined first. Afterwards, two improved methods are defined for finding the steady state, which use this integration algorithm in their iteration loops. The first is based on the idea of extrapolation, and the second utilizes nonstandard time-domain sensitivity analysis. The two steady-state algorithms are compared by analyses of a rectifier and a C-class amplifier, and the extrapolation algorithm is primarily selected as a more reliable alternative. Finally, the method based on the extrapolation naturally cooperating with the algorithm for solving the differential-algebraic systems is thoroughly tested on various electronic circuits: Van der Pol and Colpitts oscillators, fragment of a large bipolar logical circuit, feedback and distributed microwave oscillators, and power amplifier. The results confirm that the extrapolation method is faster than a classical plain numerical integration, especially for larger circuits with complicated transients.
Do’s and don’ts in Fourier analysis of steady-state potentials.  [cached]
Michael Bach,Thomas Meigen
Electroneurobiología , 2005,
Abstract: Fourier analysis is a powerful tool in signal analysis that can be fruitfully applied to steady-state evoked potentials (flicker ERG, pattern ERG, VEP etc.). However, there are some inherent theoretical assumptions in the discrete Fourier transform (DFT) that are not necessarily fulfilled in real-world applications. Furthermore, software packages developed for general engineering may be ill-suited and may not fully exploit the information of steady-state recordings.(Article in English).
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