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Human observers estimate the illumination direction of rough surfaces rather precisely. When surfaces are rough, the illumination generates visible “texture” from differential shading at the level of the roughness, whereas differential illumination at the level of significant global surface curvature leads to the more familiar “shading.” The shading is used in conventional shape-from-shading (SFS) algorithms, which ignore the illumination texture cue. Because of this simplification, SFS algorithms are typically formulated as global problems (partial differential equations, etc.). Human observers are likely to apply different methods than do these conventional SFS algorithms, however. When the roughness is not isotropic, one expects systematic errors in the visual detection of illumination direction, conceivably giving rise to erroneous shape estimates. Here we addressed this issue through systematic psychophysics on illumination direction detection as a function of the roughness anisotropy. Our expectations were fully borne out, in that the observers committed the predicted systematic errors. These results are precise enough to allow the inference that illumination direction detection is based on second-order statistics—that is, of edge detector (rather than line detector) activity. [ABSTRACT FROM AUTHOR]

Although a two-dimensional picture never fully specifies the actual layout of the depicted threedimensional scene, one is still able to make a three-dimensional interpretation. When a picture is mirrorreflected, the range of plausible scenes possibly corresponding with the depicted scene has not changed with respect to the original depiction. We were curious to find out whether the inherent picture ambiguities would be solved the same way or differently. Participants performed local attitude settings on three sets of pictures: (1) original pictures, (2) left-right mirrored pictures, and (3) up-down mirrored pictures. Pairwise comparison of the pictorial reliefs of the depicted object, reconstructed from the raw settings, revealed dissimilarities. The differences, however, could be drastically diminished by conducting an affine transformation correction taking into account not only the depths, but also the picture plane coordinates. The inherent ambiguities seemed thus to be solved differently between conditions. By factoring out different solutions to the ambiguities, the pictorial reliefs were found to be equivalent. [ABSTRACT FROM AUTHOR]

BACKGROUND: Virulence factors of Helicobacter pylori are associated with peptic ulcer disease and may be also associated with the efficacy of treatment. AIMS: To determine the relation between the vacA and the cagA status of H pylori, clinical disease, and treatment outcome. PATIENTS: 121 patients with H pylori infection and peptic ulcer disease or functional dyspepsia were treated by quadruple antibiotic therapy in two groups for one and two days, respectively. METHODS: DNA was isolated from gastric antral biopsy specimens, taken before and after treatment, and the vacA and cagA status was determined by polymerase chain reaction and reverse hybridisation. RESULTS: Peptic ulcer disease was significantly associated with the vacA s1 type, and cagA positivity, but not with the vacA m type. Treatment efficacy was significantly higher in patients with peptic ulcer disease, or infected with cagA+/vacA s1 strains. CONCLUSIONS: The strong association between the cagA and vacA status and peptic ulcer disease was confirmed. Cure rates seem to be higher for patients with cagA+/vacA s1 H pylori strains, which is consistent with the higher cure rate observed among ulcer patients compared with functional dyspepsia patients. Therefore, treatment studies may require stratification for presence of ulcers as well as H pylori genotypes.