A three domain covariance framework for EEG/MEG data

In this paper we introduce a covariance framework for the analysis of EEG and MEG data that takes into account observed temporal stationarity on small time scales and trial-to-trial variations. We formulate a model for the covariance matrix, which is a Kronecker product of three components that correspond to space, time and epochs/trials, and consider maximum likelihood estimation of the unknown parameter values. An iterative algorithm that finds approximations of the maximum likelihood estimates is proposed. We perform a simulation study to assess the performance of the estimator and investigate the influence of different assumptions about the covariance factors on the estimated covariance matrix and on its components. Apart from that, we illustrate our method on real EEG and MEG data sets. The proposed covariance model is applicable in a variety of cases where spontaneous EEG or MEG acts as source of noise and realistic noise covariance estimates are needed for accurate dipole localization, such as in evoked activity studies, or where the properties of spontaneous EEG or MEG are themselves the topic of interest, such as in combined EEG/fMRI experiments in which the correlation between EEG and fMRI signals is investigated.Comment: 25 pages, 8 figures, 1 tabl

Symmetry considerations in the quasi-static approximation of volume conductor theory

In living subjects electromagnetic signals are generated which can be measured electrically with electrodes and normal amplifiers or magnetically, by means of SQUID-magnetometers. The former technique is called EEG (electro-encephalography), the latter MEG (magneto-encephalography). Since the electromagnetic field patterns are dependent on physiological processes inside the body, a study of the electromagnetic field can help to understand these physiological processes. Some theoretical problems which are posed by such a study are considered. The way in which the electromagnetic field is generated is discussed. At a microscopic level, there are different physical mechanisms responsible for the generation of the electromagnetic field. Inside the brain, there are the synaptic interactions of neurons which produce the EEG and MEG. Cardiac potentials and cardiac magnetic induction are generated by the synchronous polarization of cardiac muscle cells

User Generated Diversity. Some reflections on how to improve the quality of amateur productions

The potential of user created content to make a meaningful contribution to media diversity is subject to debates. Central to these debates is the argument of the quality of amateur productions. This article will take a close look at this argument, and make some suggestions on how to improve the quality and utility of amateur productions with regard to the democratic functions of media.user created content, diversity, quality, strategies

The use of the asymptotic expansion to speed up the computation of a series of spherical harmonics

When a function is expressed as an infinite series of spherical harmonics the convergence can be accelerated by subtracting its asymptotic expansion and adding it in analytically closed form. In the present article this technique is applied to two biophysical cases: to the potential distribution in a spherically symmetric volume conductor and to the covariance matrix of biomagnetic measurements

Guilds, product quality and intrinsic value: towards a history of conventions?

"This article addresses the issue of conventions from the perspective of the early modern guilds' regulations related to product quality. Starting from the ideas of François Eymard-Duvernay one specific convention is identified: 'intrinsic value' (i.e., value related to the raw materials used). This convention enabled guild-based artisans to locate product quality in their political standing and, hence, was intimately linked to the (urban) political context. White this may be familiar to the ideas on 'justification' of Boltanski and Thevenot, an historical analysis reveals fundamental conceptual issues. In the seventeenth and eighteenth centuries, both the convention of intrinsic value and the guilds' power to define product quality became obsolete because of (among other things) epistemological transformations. White intrinsic value as a convention was connected to the idea of matter possessing mysterious, religious and creative powers in itself, natural philosophers naturalized matter from the seventeenth century on. As a result, value may have become synonymous with either the products' place in a taxonomy of products or the meaning produced in discourses external to the product. Further research should in any case take fundamental epistemic shifts and shifts in the subject object relationships into consideration." (author's abstract

Productivity development of Swedish distribution system operators in the 21st century : application of the Malmquist index

Nowadays, Data Envelopment Analysis (DEA) is a well-established practice to apply in network regulation. More specifically, DEA can turn out to be a proper tool to evaluate the productivity development of an industry. From the Network Performance Assessment Model to the Revenue Cap Model and passing through a low-powered rate-of-return regime, Sweden experienced a broad range of regulatory scheme. This study is the opportunity to evaluate the impact on the industry of the two mentioned regulatory schemes. Through a Malmquist productivity index, our study encompasses a productivity analysis of the Swedish electricity distribution sector from 2002 to 2017. Besides, a Kruskal-Wallis test and a Tobit regression helped us evaluate if factors such as the ownership type or the customer density could have an influence on the performances of the operators. Among other results, we have demonstrated the low-robustness of the Network Performance Assessment Model and the stability of the industry from the establishment of the Revenue Cap Model onwards. Recommendations to the Swedish Energy Inspectorate are also given such as a revision of the general efficiency requirement imposed to the operators or the inclusion of environmental variables. Furthermore, the results have shown that it is likely that private operators present better performances than municipally-owned and cooperative operators.nhhma

Images of Time and Timelessness: A Musical Reading of Death in Venice

This essay is based on an old, well–known question in aesthetics: how to represent time in its fleetingness without halting, appropriating, objectifying, or transcending it? The question inspires a reading of Thomas Mann’s Death in Venice as the account of a transformation in which a wish to overcome time turns into the erotic desire of being delivered to time. As such, the story reflects the tension between two competing views of music: music as an Apollonian play of time–transcending, auditory forms, and music as the Dionysian art in time. A phenomenological reading of Luchino Visconti’s adaptation of the novella complicates this plainly dualistic opposition. The essay traces how the aesthetic suspension of time is contrasted with, but also depends on, the spectator’s real–time experience. Similarly, the two classical, competing views of music stand in a complex dialectical relation to each other and reflect our existential relation to time