The role of peripheral vision in implicit contextual cuing

Implicit contextual cuing refers to the ability to learn the association between contextual information of our environment and a specific target, which can be used to guide attention during visual search. It was recently suggested that the storage of a snapshot image of the local context of a target underlies implicit contextual cuing. To make such a snapshot, it is necessary to use peripheral vision. In order to test whether peripheral vision can underlie implicit contextual cuing, we used a covert visual search task, in which participants were required to indicate the orientation of a target stimulus while foveating a fixation cross. The response times were shorter when the configuration of the stimuli was repeated than when the configuration was new. Importantly, this effect was still found after 10 days, indicating that peripherally perceived spatial context information can be stored in memory for long periods of time. These results indicate that peripheral vision can be used to make a snapshot of the local context of a targetThis research was supported by a grant from the BIAL Foundation (No. 73/06) and the FCT (SFRH/BPD/22088/2005

Intensity-modulated radiotherapy for breast and head-and-neck cancer

Intensity-modulated radiotherapy (IMRT) is an advanced form of radiotherapy; the beam intensity can thereby be modulated. IMRT can be used to create a highly conformal dose distribution around a tumor, while reducing the dose to the surrounding normal tissue. IMRT can also be used to deliver a heterogeneous dose within the tumor. A higher dose is delivered to areas of high risk, such as a part of the tumor containing more tumor cells. In this thesis, IMRT is applied to the irradiation of breast and oropharyngeal cancer. An IMRT technique for irradiation of breast cancer has been developed, based on the on the division of the tangential fields in four segments shaped by a multi-leaf collimator. The shape of these segments was obtained from an equivalent path length map of the irradiated volume. Using this IMRT technique, a more homogeneous dose distribution was achieved compared to the conventional technique. Furthermore the dose to the lung was reduced. A more complex case is the treatment of oropharyngeal cancer. Different dose levels are delivered to the primary tumor, the volume containing subclinical malignant disease and the lymph nodes. The dose to the spinal cord, brain and parotid gland should be minimized. The relation between the quality of the treatment plan and the number of beams in combination with the number of segments was investigated in order to obtain a clinically acceptable and deliverable plan. Seven beams were sufficient to achieve acceptable dose homogeneity while the dose to the spinal cord and brain was acceptable. The dose to the parotid glands was reduced without compromising the dose to the targets. Special attention should be paid to the localization of the tumor when using IMRT to assure that the dose is delivered at the right location. A margin, taken for geometrical uncertainties, is therefore added to prevent underdosage of the target volumes. Due to this margin, the dose to the surrounding healthy tissues increases. In a theoretical study it was shown that a realistic reduction of this margin might result in a reduction of the probability for radiation induced xerostomia of approximately 20%. In order to reduce the margin, the reliability and toxicity of the use of implanted gold markers for position verification during the irradiation of head-and-neck cancer was investigated. These markers were visualized using an a-Si flat panel imager. No acute major complications were observed. In order to prevent movement of the markers, they should be deep-seated. The random error of the geometric uncertainties obtained without correction during radiotherapy was 1-2 mm. The intrafraction motions of the larynx were investigated during radiotherapy using an a-Si flat panel imager. Motions occurred due to swallowing, breathing, or movement of the tongue. An extra margin of approximately 3.5 mm should be applied to take into account frequent motions, which are probably related to breathing. Two different segmental IMRT techniques have been developed in this thesis for respectively irradiation of the breast and the oropharynx. Both techniques have been implemented clinically. Furthermore, the position verification and intra-fraction motion for head-and-neck irradiation have been investigate

Photocatalytic properties of tin oxide and antimony-doped tin oxide nanoparticles

For the first time it is shown that N-doped SnO2 nanoparticles photocatalyze directly the polymerization of the C=C bonds of (meth)acrylates under visible light illumination. These radical polymerizations also occur when these particles are doped with Sb and when the surfaces of these particles are grafted with methacrylate (MPS) groups. During irradiation with visible or UV light the position and/or intensity of the plasmon band absorption of these nanoparticles are always changed, suggesting that the polymerization starts by the transfer of an electron from the conduction band of the particle to the (meth)acrylate C=C bond. By using illumination wavelengths with a very narrow band width we determined the influence of the incident wavelength of light, the Sb- and N-doping, and the methacrylate (MPS) surface grafting on the quantum efficiencies for the initiating radical formation (F) and on the polymer and particle network formation. The results are explained by describing the effects of Sb-doping, N-doping, and/or methacrylate surface grafting on the band gaps, energy level distributions, and surface group reactivities of these nanoparticles. N-doped (MPS grafted) SnO2 (Sb = 0%) nanoparticles are new attractive photocatalysts under visible as well as UV illumination

A Direct Comparison of Local-Global Integration in Autism and other Developmental Disorders: Implications for the Central Coherence Hypothesis

The weak central coherence hypothesis represents one of the current explanatory models in Autism Spectrum Disorders (ASD). Several experimental paradigms based on hierarchical figures have been used to test this controversial account. We addressed this hypothesis by testing central coherence in ASD (n = 19 with intellectual disability and n = 20 without intellectual disability), Williams syndrome (WS, n = 18), matched controls with intellectual disability (n = 20) and chronological age-matched controls (n = 20). We predicted that central coherence should be most impaired in ASD for the weak central coherence account to hold true. An alternative account includes dorsal stream dysfunction which dominates in WS. Central coherence was first measured by requiring subjects to perform local/global preference judgments using hierarchical figures under 6 different experimental settings (memory and perception tasks with 3 distinct geometries with and without local/global manipulations). We replicated these experiments under 4 additional conditions (memory/perception*local/global) in which subjects reported the correct local or global configurations. Finally, we used a visuoconstructive task to measure local/global perceptual interference. WS participants were the most impaired in central coherence whereas ASD participants showed a pattern of coherence loss found in other studies only in four task conditions favoring local analysis but it tended to disappear when matching for intellectual disability. We conclude that abnormal central coherence does not provide a comprehensive explanation of ASD deficits and is more prominent in populations, namely WS, characterized by strongly impaired dorsal stream functioning and other phenotypic traits that contrast with the autistic phenotype. Taken together these findings suggest that other mechanisms such as dorsal stream deficits (largest in WS) may underlie impaired central coherence

Contribution of peat compaction to relative sea-level rise within Holocene deltas

Modern and forecasted flooding of deltas is accelerated by subsidence of Holocene deposits. Subsidence caused by tectonics, isostasy, sediment compaction and anthropogenic processes, combined with eustatic sea-level rise, results in drowning and increased flood risk within densely populated deltas. Many deltaic sedimentary successions include substantial amounts of peat, which is highly compressible compared to clay, silt and sand. Peat compaction, therefore, may contribute considerably to total delta subsidence. Existing studies are inadequate for quantifying peat compaction across deltas. We present a numerical peat compaction model calibrated with an extensive field dataset. The model quantifies spatial and temporal trends in peat compaction within fluvial-dominated Holocene flood basin sequences of different compositions. Subsidence due to peat compaction is highly variable in time and space, with local rates of up to 15 mm/yr, depending on sedimentary sequence. This is extremely important information for developing sound delta management strategies. Artificial groundwater table lowering may cause substantial additional subsidence. Subsidence due to peat compaction might even exceed estimates of relative sea-level rise, and thus, may seriously increase the risk of delta drowning and human vulnerability to floodin

Brain areas involved in spatial working memory

Spatial working memory entails the ability to keep spatial information active in working memory over a short period of time. To study the areas of the brain that are involved in spatial working memory, a group of stroke patients was tested with a spatial search task. Patients and healthy controls were asked to search through a number of boxes shown at different locations on a touch-sensitive computer screen in order to find a target object. In subsequent trials, new target objects were hidden in boxes that were previously empty. Within-search errors were made if a participant returned to an already searched box; between-search errors occurred if a participant returned to a box that was already known to contain a target item. The use of a strategy to remember the locations of the target objects was calculated as well. Damage to the right posterior parietal and right dorsolateral prefrontal cortex impaired the ability to keep spatial information [`]on-line', as was indicated by performance on the Corsi Block-Tapping task and the within-search errors. Moreover, patients with damage to the right posterior parietal cortex, the right dorsolateral prefrontal cortex and the hippocampal formation bilaterally made more between-search errors, indicating the importance of these areas in maintaining spatial information in working memory over an extended time period.http://www.sciencedirect.com/science/article/B6T0D-4HM7WH2-2/1/b6b13c7b404377bae2b8cf632eb61fe

Network based statistical analysis detects changes induced by continuous theta-burst stimulation on brain activity at rest

We combined continuous theta-burst stimulation (cTBS) and resting state (RS)-fMRI approaches to investigate changes in functional connectivity (FC) induced by right dorsolateral prefrontal cortex (DLPFC)-cTBS at rest in a group of healthy subjects. Seed-based fMRI analysis revealed a specific pattern of correlation between the right prefrontal cortex and several brain regions: based on these results, we defined a 29-node network to assess changes in each network connection before and after, respectively, DLPFC-cTBS and sham sessions. A decrease of correlation between the right prefrontal cortex and right parietal cortex (Brodmann areas 46 and 40, respectively) was detected after cTBS, while no significant result was found when analyzing sham-session data. To our knowledge, this is the first study that demonstrates within-subject changes in FC induced by cTBS applied on prefrontal area. The possibility to induce selective changes in a specific region without interfering with functionally correlated area could have several implications for the study of functional properties of the brain, and for the emerging therapeutic strategies based on transcranial stimulation