The Unique Determination of Neuronal Currents in the Brain via Magnetoencephalography

The problem of determining the neuronal current inside the brain from measurements of the induced magnetic field outside the head is discussed under the assumption that the space occupied by the brain is approximately spherical. By inverting the Geselowitz equation, the part of the current which can be reconstructed from the measurements is precisely determined. This actually consists of only certain moments of one of the two functions specifying the tangential part of the current. The other function specifying the tangential part of the current as well as the radial part of the current are completely arbitrary. However, it is also shown that with the assumption of energy minimization, the current can be reconstructed uniquely. A numerical implementation of this unique reconstruction is also presented

Sensitivity of MEG and EEG to Source Orientation

An important difference between magnetoencephalography (MEG) and electroencephalography (EEG) is that MEG is insensitive to radially oriented sources. We quantified computationally the dependency of MEG and EEG on the source orientation using a forward model with realistic tissue boundaries. Similar to the simpler case of a spherical head model, in which MEG cannot see radial sources at all, for most cortical locations there was a source orientation to which MEG was insensitive. The median value for the ratio of the signal magnitude for the source orientation of the lowest and the highest sensitivity was 0.06 for MEG and 0.63 for EEG. The difference in the sensitivity to the source orientation is expected to contribute to systematic differences in the signal-to-noise ratio between MEG and EEG.National Institutes of Health (U.S.) (Grant NS057500)National Institutes of Health (U.S.) (Grant NS037462)National Institutes of Health (U.S.) (Grant HD040712)National Center for Research Resources (U.S.) (P41RR14075)Mind Research Networ

Structural Relaxation in an Amorphous Rapidly Quenched Cobalt-Based Alloy

An amorphous melt-spun Co-based alloy (Metglas 2705 MN) is investigated by Doppler Broadening and Positron Lifetime techniques in order to follow the microstructural changes yielded by isochronal annealings before crystallization. The results are correlated with those of Differential Scanning Calorimetry and Coercive Field measurements. The quenched empty spaces underlined by Lifetime measurements are less than one atomic volume in size and migrate without clustering in larger voids. Both Positron Annihilation and Coercive Field investigations suggest that the overall decrease of free volume related to structural relaxation in this amorphous material, proceeds mainly via compositional short-range ordering. These local chemical rearrangements which lead to a partial disorientation of the magnetic moments act as strong pinning points for Bloch Walls

Empirical investigation of the temporal relations between speech and facial expressions of emotion

Lien vers l'article original : http://link.springer.com/article/10.1007/s12193-010-0050-4Behavior models implemented within Embodied Conversational Agents (ECAs) require nonverbal communication to be tightly coordinated with speech. In this paper we present an empirical study seeking to explore the influence of the temporal coordination between speech and facial expressions of emotions on the perception of these emotions by users (measuring their performance in this task, the perceived realism of behavior, and user preferences).We generated five different conditions of temporal coordination between facial expression and speech: facial expression displayed before a speech utterance, at the beginning of the utterance, throughout, at the end of, or following the utterance. 23 subjects participated in the experiment and saw these 5 conditions applied to the display of 6 emotions (fear, joy, anger, disgust, surprise and sadness). Subjects recognized emotions most efficiently when facial expressions were displayed at the end of the spoken sentence. However, the combination users viewed as most realistic, preferred over others, was the display of the facial expression throughout speech utterance. We review existing literature to position our work and discuss the relationship between realism and communication performance. We also provide animation guidelines and draw some avenues for future work