Experimental Section: On the magnetic field distribution generated by a dipolar current source situated in a realistically shaped compartment model of the head

The magnetic field distribution around the head is simulated using a realistically shaped compartment model of the head. The model is based on magnetic resonance images. The 3 compartments describe the brain, the skull and the scalp. The source is represented by a current dipole situated in the visual cortex. The magnetic field distribution due to the source and that due to the volume currents are calculated separately. The simulations are carried out in order to ascertain which matrix of grid points is suitable as a measuring grid. The possibilities studied are grid points situated in a plane, in a surface which follows the contours of the head and in a sphere. This sphere is taken concentric to the sphere which is the best possible fit for the head. Taking into account the relative contribution of the volume currents and the possible accuracy in the positioning of the magnetic field detector, it can be concluded that the best choice is to measure the normal component of the magnetic field at points which are situated in the spherical surface. The results of this study also show that the magnetic field distribution based on a realistically shaped compartment model differs from that based on a compartment model consisting of concentric spheres. In the spherical model of the head no contribution of the volume currents to the component of the field normal to the sphere can be expected. The difference between the results obtained with these two volume conductor models increases with source depth

Relative influence of model assumptions and measurement procedures in the analysis of the MEG

The relative influences of several model parameters and measurement setups on the MEG are studied quantitatively. The influences of the number of grid points of the flux transformer and the accuracy of the measurements are analysed using as criterion a relative difference measure (RDM). In a similar way, using the RDM, the influence of various models is evaluated. The volume conductor, i.e. the head, is described by three different compartment models: the first model consists of concentric spheres, the second of eccentric spheres optimally fitting the individual compartments of the head, and the third consists of realistically shaped compartments. The evaluation of the influence of the model of the source on the MEG is studied by taking either one single current dipole or a set of two current dipoles. The RDM described in the paper is shown to be a valuable measure in the quantitative analysis of MEGs

Talar Fractures in Children: A Possible Injury After Go-Karting Accidents

Item does not contain fulltextGo-karting is an increasingly popular high-energy sport enjoyed by both children and adults. Because of the speeds involved, accidents involving go-karts can lead to serious injury. We describe 6 talar fractures in 4 patients that resulted from go-karting accidents. Talar fractures can cause severe damage to the tibiotalar joint, talocalcaneal or subtalar joint, and the talonavicular joint. This damage can, in turn, lead to complications such as avascular necrosis, arthritis, nonunion, delayed union, and neuropraxia, which have the potential to cause long-term disability in a child.7 p

Cue predictability does not modulate bottom-up attentional capture

Item does not contain fulltextAttention can be involuntarily captured by physically salient stimuli, a phenomenon known as bottom-up attention. Typically, these salient stimuli occur unpredictably in time and space. Therefore, in a series of three behavioral experiments, we investigated the extent to which such bottom-up attentional capture is a function of one’s prior expectations. In the context of an exogenous cueing task, we systematically manipulated participants’ spatial (Experiment 1) or temporal (Experiment 2 and 3) expectations about an uninformative cue, and examined the amount of attentional capture by the cue. We anticipated larger attentional capture for unexpected compared to expected cues. However, while we observed robust attentional capture, we did not find any evidence for a modulation of attentional capture by prior expectation. This suggests that bottom-up attentional capture does not appear modulated by the degree to which the cue is expected or surprising.nul

Cue predictability does not modulate bottom-up attentional capture

Contains fulltext : 197164.pdf (publisher's version ) (Open Access)Attention can be involuntarily captured by physically salient stimuli, a phenomenon known as bottom-up attention. Typically, these salient stimuli occur unpredictably in time and space. Therefore, in a series of three behavioural experiments, we investigated the extent to which such bottom-up attentional capture is a function of one's prior expectations. In the context of an exogenous cueing task, we systematically manipulated participants' spatial (Experiment 1) or temporal (Experiments 2 and 3) expectations about an uninformative cue and examined the amount of attentional capture by the cue. We anticipated larger attentional capture for unexpected compared to expected cues. However, while we observed attentional capture, we did not find any evidence for a modulation of attentional capture by prior expectation. This suggests that bottom-up attentional capture does not appear modulated by the degree to which the cue is expected or surprising.12 p

Cue predictability does not modulate bottom-up attentional capture

Attention can be involuntarily captured by physically salient stimuli, a phenomenon known as bottom-up attention. Typically, these salient stimuli occur unpredictably in time and space. Therefore, in a series of three behavioral experiments, we investigated the extent to which such bottom-up attentional capture is a function of one’s prior expectations. In the context of an exogenous cueing task, we systematically manipulated participants’ spatial (Experiment 1) or temporal (Experiment 2 and 3) expectations about an uninformative cue, and examined the amount of attentional capture by the cue. We anticipated larger attentional capture for unexpected compared to expected cues. However, while we observed robust attentional capture, we did not find any evidence for a modulation of attentional capture by prior expectation. This suggests that bottom-up attentional capture does not appear modulated by the degree to which the cue is expected or surprising