838 research outputs found

    Comparative studies on the structure of an upland African stream ecosystem

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    Upland stream systems have been extensively investigated in Europe, North America and Australasia and many of the central ideas concerning their function are based on these systems. One central paradigm, the river continuum concept is ultimately derived from those North American streams whose catchments remain forested with native vegetation. Streams of the tropics may or may not fit the model. They have been little studied. The Amani Nature Reserve in the East Usambara Mountains of north-eastern Tanzania offers an opportunity to bring these naturally forested systems to the attention of the ecological community. This article describes a comparison made between two lengths of the River Dodwe in this area. The work was carried out by a group of postgraduate students from eighteen European and African countries with advice from five staff members, as part of a course organised by the Tropical Biology Association. Rigorous efforts were made to standardise techniques, in a situation where equipment and laboratory facilities were very basic, through a management structure and deliberate allocation of work to specialists in each area.The article offers a summary of invertebrate communities found in the stream and its biomass. Crabs seem to be the key organism in both sections of the streams

    A habituation account of change detection in same/different judgments

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    We investigated the basis of change detection in a short-term priming task. In two experiments, participants were asked to indicate whether or not a target word was the same as a previously presented cue. Data from an experiment measuring magnetoencephalography failed to find different patterns for “same” and “different” responses, consistent with the claim that both arise from a common neural source, with response magnitude defining the difference between immediate novelty versus familiarity. In a behavioral experiment, we tested and confirmed the predictions of a habituation account of these judgments by comparing conditions in which the target, the cue, or neither was primed by its presentation in the previous trial. As predicted, cue-primed trials had faster response times, and target-primed trials had slower response times relative to the neither-primed baseline. These results were obtained irrespective of response repetition and stimulus–response contingencies. The behavioral and brain activity data support the view that detection of change drives performance in these tasks and that the underlying mechanism is neuronal habituation

    Spinal arteriovenous shunts presenting as intracranial subarachnoid haemorrhage

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    Item does not contain fulltextBACKGROUND: In approximately 5% of patients with intracranial subarachnoid haemorrhage (SAH), the cause is another than a ruptured aneurysm or perimesencephalic haemorrhage. One of these causes is a spinal arteriovenous shunt (SAVS). The aim of this study was to investigate the characteristics of patients with SAVS who present with intracranial SAH without symptoms and signs suggesting a spinal cause. METHODS: We systematically reviewed the literature and searched the SAH database of the University Medical Center Utrecht, The Netherlands, for patients with SAVS presenting with intracranial SAH and studied the characteristics of patients with SAVS whose clinical presentation mimicked intracranial SAH caused by rupture of a saccular aneurysm. RESULTS: Thirty-five patients were identified after a review of the literature. In our SAH database, comprising 2142 patients included in the period 1985-2004, we found one patient (0.05%, 95 % CI 0.006- 0.3%). SAH due to SAVS occurred at any age (4-72 years). The SAVS was located at the craniocervical junction in 14 patients, at the cervical level in 11, and at the thoracolumbar level in the remaining 11 patients. The majority of patients (n = 26, 72%) had no disabling deficits at discharge or follow-up. CONCLUSION: Rupture of a SAVS presenting as intracranial SAH is rare and can occur at any age. The SAVS can be located not only at the craniocervical junction or cervical level but also in the thoracolumbar region. Most patients with SAVS presenting as intracranial SAH have a good recovery

    The Flexibility of Nonconsciously Deployed Cognitive Processes: Evidence from Masked Congruence Priming

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    Background: It is well accepted in the subliminal priming literature that task-level properties modulate nonconscious processes. For example, in tasks with a limited number of targets, subliminal priming effects are limited to primes that are physically similar to the targets. In contrast, when a large number of targets are used, subliminal priming effects are observed for primes that share a semantic (but not necessarily physical) relationship with the target. Findings such as these have led researchers to conclude that task-level properties can direct nonconscious processes to be deployed exclusively over central (semantic) or peripheral (physically specified) representations. Principal Findings: We find distinct patterns of masked priming for "novel" and "repeated" primes within a single task context. Novel primes never appear as targets and thus are not seen consciously in the experiment. Repeated primes do appear as targets, thereby lending themselves to the establishment of peripheral stimulus-response mappings. If the source of the masked priming effect were exclusively central or peripheral, then both novel and repeated primes should yield similar patterns of priming. In contrast, we find that both novel and repeated primes produce robust, yet distinct, patterns of priming. Conclusions: Our findings indicate that nonconsciously elicited cognitive processes can be flexibly deployed over both central and peripheral representations within a single task context. While we agree that task-level properties can influence nonconscious processes, our findings sharply constrain the extent of this influence. Specifically, our findings are inconsistent with extant accounts which hold that the influence of task-level properties is strong enough to restrict the deployment of nonconsciously elicited cognitive processes to a single type of representation (i.e. central or peripheral).13 page(s

    Predicting the Effect of Surface Texture on the Qualitative Form of Prehension

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    Reach-to-grasp movements change quantitatively in a lawful (i.e. predictable) manner with changes in object properties. We explored whether altering object texture would produce qualitative changes in the form of the precontact movement patterns. Twelve participants reached to lift objects from a tabletop. Nine objects were produced, each with one of three grip surface textures (high-friction, medium-friction and low-friction) and one of three widths (50 mm, 70 mm and 90 mm). Each object was placed at three distances (100 mm, 300 mm and 500 mm), representing a total of 27 trial conditions. We observed two distinct movement patterns across all trials—participants either: (i) brought their arm to a stop, secured the object and lifted it from the tabletop; or (ii) grasped the object ‘on-the-fly’, so it was secured in the hand while the arm was moving. A majority of grasps were on-the-fly when the texture was high-friction and none when the object was low-friction, with medium-friction producing an intermediate proportion. Previous research has shown that the probability of on-the-fly behaviour is a function of grasp surface accuracy constraints. A finger friction rig was used to calculate the coefficients of friction for the objects and these calculations showed that the area available for a stable grasp (the ‘functional grasp surface size’) increased with surface friction coefficient. Thus, knowledge of functional grasp surface size is required to predict the probability of observing a given qualitative form of grasping in human prehensile behaviour

    Estimating the age of Calliphora vicina eggs (Diptera: Calliphoridae): determination of embryonic morphological landmarks and preservation of egg samples

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    ORCID No. 0000-0002-8917-9646© The Author(s) 2016. Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The attached file is the published version of the article

    Unstaged cancer in the United States: a population-based study

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    <p>Abstract</p> <p>Background</p> <p>The current study examines unstaged disease for 18 cancer sites in the United States according to the influence of age, sex, race, marital status, incidence, and lethality.</p> <p>Methods</p> <p>Analyses are based on 1,040,381 male and 1,011,355 female incident cancer cases diagnosed during 2000 through 2007. Data were collected by population-based cancer registries in the National Cancer Institute's Surveillance, Epidemiology, and End Results Program.</p> <p>Results</p> <p>The level of unstaged disease was greater in more lethal cancers (e.g., liver, esophagus, and pancreas) compared with less deadly cancers (i.e., colon, urinary bladder, and female breast). Unstaged disease increased with age and is greater among non-married patients. Blacks compared with whites experienced significantly higher levels of unstaged cancers of the stomach, rectum, colon, skin (melanoma), urinary bladder, thyroid, breast, corpus, cervix, and ovaries, but lower levels of unstaged liver, lung and bronchial cancers. Males compared with females experienced significantly lower levels of unstaged cancers of the liver, pancreas, esophagus, and stomach, but significantly higher levels of unstaged lung and bronchial cancer and thyroid cancer. The percent of unstaged cancer significantly decreased over the study period for 15 of the 18 cancer sites.</p> <p>Conclusion</p> <p>Tumor staging directly affects treatment options and survival, so it is recommended that further research focus on why a decrease in unstaged disease did not occur for all of the cancer sites considered from 2000 to 2007, and why there are differential levels of staging between whites and blacks, males and females for several of the cancer sites.</p

    Grasping the changes seen in older adults when reaching for objects of varied texture.

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    Old age is associated with reduced mobility of the hand. To investigate age related decline when reaching-to-lift an object we used sophisticated kinematic apparatus to record reaches carried out by healthy older and younger participants. Three objects of different widths were placed at three different distances, with objects having either a high or low friction surface (i.e. rough or slippery). Older participants showed quantitative differences to their younger counterparts - movements were slower and peak speed did not scale with object distance. There were also qualitative differences with older adults showing a greater propensity to stop the hand and adjust finger position before lifting objects. The older participants particularly struggled to lift wide slippery objects, apparently due to an inability to manipulate their grasp to provide the level of precision necessary to functionally enclose the object. These data shed light on the nature of age related changes in reaching-to-grasp movements and establish a powerful technique for exploring how different product designs will impact on prehensile behavior
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