Dynamical Heterogeneity close to the Jamming Transition in a Sheared Granular Material

The dynamics of a bi-dimensional dense granular packing under cyclic shear is experimentally investigated close to the jamming transition. Measurement of multi-point correlation functions are produced. The self-intermediate scattering function, displaying slower than exponential relaxation, suggests dynamic heterogeneity. Further analysis of four point correlation functions reveal that the grain relaxations are strongly correlated and spatially heterogeneous, especially at the time scale of the collective rearrangements. Finally, a dynamical correlation length is extracted from spatio-temporal pattern of mobility. Our experimental results open the way to a systematic study of dynamic correlation functions in granular materials.Comment: 4 pages, final version accepted for publication in Phys. Rev. Let

Selective Attention and Audiovisual Integration: Is Attending to Both Modalities a Prerequisite for Early Integration?

Interactions between multisensory integration and attention were studied using a combined audiovisual streaming design and a rapid serial visual presentation paradigm. Event-related potentials (ERPs) following audiovisual objects (AV) were compared with the sum of the ERPs following auditory (A) and visual objects (V). Integration processes were expressed as the difference between these AV and (A + V) responses and were studied while attention was directed to one or both modalities or directed elsewhere. Results show that multisensory integration effects depend on the multisensory objects being fully attended—that is, when both the visual and auditory senses were attended. In this condition, a superadditive audiovisual integration effect was observed on the P50 component. When unattended, this effect was reversed; the P50 components of multisensory ERPs were smaller than the unisensory sum. Additionally, we found an enhanced late frontal negativity when subjects attended the visual component of a multisensory object. This effect, bearing a strong resemblance to the auditory processing negativity, appeared to reflect late attention-related processing that had spread to encompass the auditory component of the multisensory object. In conclusion, our results shed new light on how the brain processes multisensory auditory and visual information, including how attention modulates multisensory integration processes

The VST telescope control software in the ESO VLT environment

The VST (VLT Survey Telescope) is a 2.6 m Alt-Az telescope to be installed at Mount Paranal in Chile, in the European Southern Observatory (ESO) site. The VST is a wide-field imaging facility planned to supply databases for the ESO Very Large Telescope (VLT) science and carry out stand-alone observations in the UV to I spectral range. This paper will focus mainly on control software aspects, describing the VST software architecture in the context of the whole ESO VLT control concept. The general architecture and the main components of the control software will be described.Comment: 3 pages, 2 figures, ICALEPCS 2001 Conference, PSN#THAP05

Rapid modulation of sensory processing induced by stimulus conflict

Humans are constantly confronted with environmental stimuli that conflict with task goals and can interfere with successful behavior. Prevailing theories propose the existence of cognitive control mechanisms that can suppress the processing of conflicting input and enhance that of the relevant input. However, the temporal cascade of brain processes invoked in response to conflicting stimuli remains poorly understood. By examining evoked electrical brain responses in a novel, hemifield-specific, visual-flanker task, we demonstrate that task-irrelevant conflicting stimulus input is quickly detected in higher level executive regions while simultaneously inducing rapid, recurrent modulation of sensory processing in the visual cortex. Importantly, however, both of these effects are larger for individuals with greater incongruency-related RT slowing. The combination of neural activation patterns and behavioral interference effects suggest that this initial sensory modulation induced by conflicting stimulus inputs reflects performance-degrading attentional distraction because of their incompatibility rather than any rapid task-enhancing cognitive control mechanisms. The present findings thus provide neural evidence for a model in which attentional distraction is the key initial trigger for the temporal cascade of processes by which the human brain responds to conflicting stimulus input in the environment

Dual Literacy Practices for Dual Language Learners

In early childhood academic settings, literacy practices play a crucial role in the development of emergent literacy skills. Many of the available practices for developing these foundational pre-reading skills are not often inclusive to second language learners. Educators who enter classrooms where dual language exposure is necessary to their curriculum are limited to the types of practices they can utilize to support the development of literacy in two languages. The purpose of this case study was to explore what literacy practices teachers could implement to improve dual literacy development in second language learners. The study began with a foundational understanding of dual literacy development followed by an exploration of current practices that educators were using to support literacy in language immersion settings. The case study included four classroom observations, eight interviews, and a focus group comprised of six educators. The eight classroom interviews were conducted with Grades K‒‍1 immersion teachers from two different elementary schools to collect data on their experiences and available training opportunities that informed their practices in early dual literacy. One recommendation resulting from this study was to provide training opportunities for targeted practices in literacy areas specific to the needs of second language learners

The Temporal Dynamics of Implicit Processing of Non-Letter, Letter, and Word-Forms in the Human Visual Cortex

The decoding of visually presented line segments into letters, and letters into words, is critical to fluent reading abilities. Here we investigate the temporal dynamics of visual orthographic processes, focusing specifically on right hemisphere contributions and interactions between the hemispheres involved in the implicit processing of visually presented words, consonants, false fonts, and symbolic strings. High-density EEG was recorded while participants detected infrequent, simple, perceptual targets (dot strings) embedded amongst a of character strings. Beginning at 130 ms, orthographic and non-orthographic stimuli were distinguished by a sequence of ERP effects over occipital recording sites. These early latency occipital effects were dominated by enhanced right-sided negative-polarity activation for non-orthographic stimuli that peaked at around 180 ms. This right-sided effect was followed by bilateral positive occipital activity for false-fonts, but not symbol strings. Moreover the size of components of this later positive occipital wave was inversely correlated with the right-sided ROcc180 wave, suggesting that subjects who had larger early right-sided activation for non-orthographic stimuli had less need for more extended bilateral (e.g., interhemispheric) processing of those stimuli shortly later. Additional early (130–150 ms) negative-polarity activity over left occipital cortex and longer-latency centrally distributed responses (>300 ms) were present, likely reflecting implicit activation of the previously reported ‘visual-word-form’ area and N400-related responses, respectively. Collectively, these results provide a close look at some relatively unexplored portions of the temporal flow of information processing in the brain related to the implicit processing of potentially linguistic information and provide valuable information about the interactions between hemispheres supporting visual orthographic processing

Subdiffusion and cage effect in a sheared granular material

We investigate experimentally the diffusion properties of a bidimensional bidisperse dry granular material under quasistatic cyclic shear.The comparison of these properties with results obtained both in computer simulations of hard spheres systems and Lenard-Jones liquids and experiments on colloidal systems near the glass transition demonstrates a strong analogy between the behaviour of granular matter and these systems. More specifically, we study in detail the cage dynamics responsible for the subdiffusion in the slow relaxation regime, and obtain the values of relevant time and length scales.Comment: 4 pages, 6 figures, submitted to PR