Von Bezold assimilation effect reverses in stereoscopic conditions

Lightness contrast and lightness assimilation are opposite phenomena: in contrast, grey targets appear darker when bordering bright surfaces (inducers) rather than dark ones; in assimilation, the opposite occurs. The question is: which visual process favours the occurrence of one phenomenon over the other? Researchers provided three answers to this question. The first asserts that both phenomena are caused by peripheral processes; the second attributes their occurrence to central processes; and the third claims that contrast involves central processes, whilst assimilation involves peripheral ones. To test these hypotheses, an experiment on an IT system equipped with goggles for stereo vision was run. Observers were asked to evaluate the lightness of a grey target, and two variables were systematically manipulated: (i) the apparent distance of the inducers; and (ii) brightness of the inducers. The retinal stimulation was kept constant throughout, so that the peripheral processes remained the same. The results show that the lightness of the target depends on both variables. As the retinal stimulation was kept constant, we conclude that central mechanisms are involved in both lightness contrast and lightness assimilation

Pesquisa e desenvolvimento da heveicultura no Brasil.

O inicio da pesquisa com seringueira no Brasil deu-se em 1937, quando foram desenvolvidas, em Fordlandia e Belterra no Estado do Para, as primeiras acoes de pesquisa entao voltadas para o controle de surtos epidemicos do fungo Microcyclus ulei ocorridos na regiao. A partir de 1946, o Instituto Agronomico do Norte (IAN) assumiu e deu sequencia aos trabalhos desenvolvidos pela Companhia Ford, dando inicio a segunda fase dos trabalhos com seringueira na regiao Norte. Na regiao Nordeste, especificamente no Estado da Bahia, os trabalhos com seringueira iniciaram-se em 1951, com a criacao do Instituto Agronomico do Leste (IPEAL), enquanto na regiao Centro-Sul, particularmente no Estado de Sao Paulo, o marco inicial dos trabalhos de pesquisa com seringueira deve-se ao Instituto Agronomico de Campinas (IAC), em 1942. A vitalizacao da pesquisa se fez sentir a partir de 1975 com a criacao do Centro Nacional de Pesquisa de Seringueira (CNPSe), atualmente Centro Nacional de Pesquisa de Seringueira e Dende (CNPSD), apos acordo entre a Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA) e a Superintendencia da Borracha (SUDHEVEA).bitstream/item/83140/1/Pesquisa-e-Desenvolvimento-da-Heveicultura-no-Brasil.pd

A New Perceptual Bias Reveals Suboptimal Population Decoding of Sensory Responses

Several studies have reported optimal population decoding of sensory responses in two-alternative visual discrimination tasks. Such decoding involves integrating noisy neural responses into a more reliable representation of the likelihood that the stimuli under consideration evoked the observed responses. Importantly, an ideal observer must be able to evaluate likelihood with high precision and only consider the likelihood of the two relevant stimuli involved in the discrimination task. We report a new perceptual bias suggesting that observers read out the likelihood representation with remarkably low precision when discriminating grating spatial frequencies. Using spectrally filtered noise, we induced an asymmetry in the likelihood function of spatial frequency. This manipulation mainly affects the likelihood of spatial frequencies that are irrelevant to the task at hand. Nevertheless, we find a significant shift in perceived grating frequency, indicating that observers evaluate likelihoods of a broad range of irrelevant frequencies and discard prior knowledge of stimulus alternatives when performing two-alternative discrimination

The `Parahippocampal Place Area' Responds Selectively to High Spatial Frequencies

Defining the exact mechanisms by which the brain processes visual objects and scenes remains an unresolved challenge. Valuable clues to this process have emerged from the demonstration that clusters of neurons (“modules”) in inferior temporal cortex apparently respond selectively to specific categories of visual stimuli, such as places/scenes. However, the higher-order “category-selective” response could also reflect specific lower-level spatial factors. Here we tested this idea in multiple functional MRI experiments, in humans and macaque monkeys, by systematically manipulating the spatial content of geometrical shapes and natural images. These tests revealed that visual spatial discontinuities (as reflected by an increased response to high spatial frequencies) selectively activate a well-known place-selective region of visual cortex (the “parahippocampal place area”) in humans. In macaques, we demonstrate a homologous cortical area, and show that it also responds selectively to higher spatial frequencies. The parahippocampal place area may use such information for detecting object borders and scene details during spatial perception and navigation.National Institutes of Health (U.S.) (NIH Grant R01 MH6752)National Institutes of Health (U.S.) (grant R01 EY017081)Athinoula A. Martinos Center for Biomedical ImagingNational Center for Research Resources (U.S.)Mind Research Institut

Systematic review and meta-analysis of the diagnostic accuracy of ultrasonography for deep vein thrombosis

Background Ultrasound (US) has largely replaced contrast venography as the definitive diagnostic test for deep vein thrombosis (DVT). We aimed to derive a definitive estimate of the diagnostic accuracy of US for clinically suspected DVT and identify study-level factors that might predict accuracy. Methods We undertook a systematic review, meta-analysis and meta-regression of diagnostic cohort studies that compared US to contrast venography in patients with suspected DVT. We searched Medline, EMBASE, CINAHL, Web of Science, Cochrane Database of Systematic Reviews, Cochrane Controlled Trials Register, Database of Reviews of Effectiveness, the ACP Journal Club, and citation lists (1966 to April 2004). Random effects meta-analysis was used to derive pooled estimates of sensitivity and specificity. Random effects meta-regression was used to identify study-level covariates that predicted diagnostic performance. Results We identified 100 cohorts comparing US to venography in patients with suspected DVT. Overall sensitivity for proximal DVT (95% confidence interval) was 94.2% (93.2 to 95.0), for distal DVT was 63.5% (59.8 to 67.0), and specificity was 93.8% (93.1 to 94.4). Duplex US had pooled sensitivity of 96.5% (95.1 to 97.6) for proximal DVT, 71.2% (64.6 to 77.2) for distal DVT and specificity of 94.0% (92.8 to 95.1). Triplex US had pooled sensitivity of 96.4% (94.4 to 97.1%) for proximal DVT, 75.2% (67.7 to 81.6) for distal DVT and specificity of 94.3% (92.5 to 95.8). Compression US alone had pooled sensitivity of 93.8 % (92.0 to 95.3%) for proximal DVT, 56.8% (49.0 to 66.4) for distal DVT and specificity of 97.8% (97.0 to 98.4). Sensitivity was higher in more recently published studies and in cohorts with higher prevalence of DVT and more proximal DVT, and was lower in cohorts that reported interpretation by a radiologist. Specificity was higher in cohorts that excluded patients with previous DVT. No studies were identified that compared repeat US to venography in all patients. Repeat US appears to have a positive yield of 1.3%, with 89% of these being confirmed by venography. Conclusion Combined colour-doppler US techniques have optimal sensitivity, while compression US has optimal specificity for DVT. However, all estimates are subject to substantial unexplained heterogeneity. The role of repeat scanning is very uncertain and based upon limited data

Putting Youth on the Map: A Pilot Instrument for Assessing Youth Well-Being

Extant measures of adolescent well-being in the United States typically focus on negative indicators of youth outcomes. Indices comprised of such measures paint bleak views of youth and orient action toward the prevention of problems over the promotion of protective factors. Their tendency to focus analyses at a state or county geographic scale produces limited information about localized outcome patterns that could inform policymakers, practitioners and advocacy networks. We discuss the construction of a new geo-referenced index of youth well-being based on positive indicators of youth development. In demonstrating the index for the greater Sacramento, California region of the United States, we find that overall youth well-being falls far short of an optimal outcome, and geographic disparities in well-being appear to exist across school districts at all levels of our analysis. Despite its limitations, the sub-county geographic scale of this index provides needed data to facilitate local and regional interventions