Direct evidence that "speedlines" influence motion mechanisms. (1/11)

Determining the direction of visual motion poses a serious problem for any visual system, given the inherent ambiguities. Geisler (1999) has suggested that motion streaks left in the wake of a moving target provide a rich source of potential information that could aid in resolving direction ambiguities. Here we provide strong experimental evidence that the human visual system does in fact exploit motion streaks in direction discrimination. Masks comprising oriented random noise impeded direction discrimination of moving dots when the masks were oriented parallel to the direction of motion but had very little effect when oriented orthogonal to the direction of motion. The masking effect decreased systematically with increasing bandwidth for the parallel masks and increased with bandwidth for the orthogonal masks. Importantly, these masks had little effect on neither contrast sensitivity for detecting the moving stimuli nor for speed discrimination. Experiments with "Glass patterns" (moire patterns constructed from random dot pairs) confirmed that misleading pattern information can impede motion detection. The results show that the oriented streaks left by moving stimuli provide fundamental information about the direction of visual motion; removing these streaks or augmenting them with erroneous streaks severely confounds motion direction discrimination.  (+info)

Applications of 3D imaging in orthodontics: part I. (2/11)

Part I of this paper describes the background, general concepts, available techniques and the clinical applications of recording external craniofacial morphology in three dimensions. Part II explores the different 3D techniques of imaging the dental arches, and their possible uses in orthodontic diagnosis and treatment.  (+info)

Comparison of three noninvasive methods for measuring scoliosis. (3/11)

The premise behind most noninvasive techniques for the measurement of scoliotic conditions of the spine is that the lateral distortion of the spine relates directly to transverse rib cage deformity within the transverse plane. The focus of this study was to examine this assumption by comparing different noninvasive methods for the assessment of scoliotic curves. The three techniques examined were (1) use of the Scoliometer (SCOL), (2) use of the back-contour device (BCD), and (3) use of moire topographic imaging (MTI). Fourteen subjects (10 female, 4 male) with idiopathic adolescent scoliosis were measured. Posterior-anterior radiographs were obtained for the clinical assessment of all subjects and were subsequently used to determine Cobb angles. Significant correlations between axial trunk rotation and Cobb-angle measurements were observed in the thoracic region (MTI, r = .80, df = 10, P less than .005; BCD, r = .70, df = 10, P less than .025; SCOL, r = .59, df = 10, P less than .025) but were not found within the lumbar region (MTI, r = .42; BCD, r = .17; SCOL, r = .20). Factors other than trunk deformity, such as the posture assumed by the subject during measurement, may have influenced axial trunk rotation. Hence, the techniques appear to provide valid estimations of lateral curvature of the spine in the thoracic region of the trunk but not the lumbar region. The results suggest that the measurement techniques cannot be used interchangeably in clinical recording.  (+info)

Quantifier variables of the back surface deformity obtained with a noninvasive structured light method: evaluation of their usefulness in idiopathic scoliosis diagnosis. (4/11)

New noninvasive techniques, amongst them structured light methods, have been applied to study rachis deformities, providing a way to evaluate external back deformities in the three planes of space. These methods are aimed at reducing the number of radiographic examinations necessary to diagnose and follow-up patients with scoliosis. By projecting a grid over the patient's back, the corresponding software for image treatment provides a topography of the back in a color or gray scale. Visual inspection of back topographic images using this method immediately provides information about back deformity, but it is important to determine quantifier variables of the deformity to establish diagnostic criteria. In this paper, two topographic variables [deformity in the axial plane index (DAPI) and posterior trunk symmetry index (POTSI)] that quantify deformity in two different planes are analyzed. Although other authors have reported the POTSI variable, the DAPI variable proposed in this paper is innovative. The upper normality limit of these variables in a nonpathological group was determined. These two variables have different and complementary diagnostic characteristics, therefore we devised a combined diagnostic criterion: cases with normal DAPI and POTSI (DAPI < or = 3.9% and POTSI < or = 27.5%) were diagnosed as nonpathologic, but cases with high DAPI or POTSI were diagnosed as pathologic. When we used this criterion to analyze all the cases in the sample (56 nonpathologic and 30 with idiopathic scoliosis), we obtained 76.6% sensitivity, 91% specificity, and a positive predictive value of 82%. The interobserver, intraobserver, and interassay variability were studied by determining the variation coefficient. There was good correlation between topographic variables (DAPI and POTSI) and clinical variables (Cobb's angle and vertebral rotation angle).  (+info)

Scale-invariant memory representations emerge from moire interference between grid fields that produce theta oscillations: a computational model. (5/11)

The dorsomedial entorhinal cortex (dMEC) of the rat brain contains a remarkable population of spatially tuned neurons called grid cells (Hafting et al., 2005). Each grid cell fires selectively at multiple spatial locations, which are geometrically arranged to form a hexagonal lattice that tiles the surface of the rat's environment. Here, we show that grid fields can combine with one another to form moire interference patterns, referred to as "moire grids," that replicate the hexagonal lattice over an infinite range of spatial scales. We propose that dMEC grids are actually moire grids formed by interference between much smaller "theta grids," which are hypothesized to be the primary source of movement-related theta rhythm in the rat brain. The formation of moire grids from theta grids obeys two scaling laws, referred to as the length and rotational scaling rules. The length scaling rule appears to account for firing properties of grid cells in layer II of dMEC, whereas the rotational scaling rule can better explain properties of layer III grid cells. Moire grids built from theta grids can be combined to form yet larger grids and can also be used as basis functions to construct memory representations of spatial locations (place cells) or visual images. Memory representations built from moire grids are automatically endowed with size invariance by the scaling properties of the moire grids. We therefore propose that moire interference between grid fields may constitute an important principle of neural computation underlying the construction of scale-invariant memory representations.  (+info)

Measurement of microstrains across loaded resin-dentin interfaces using microscopic moire interferometry. (6/11)

Little is known about the mechanical behavior of resin-dentin interfaces during loading. The presence of relatively compliant hybrid and adhesive layers between stiffer dentin and resin composite should deform more during compressive loading. OBJECTIVE: The objective of this study was to measure changes in microstrain across bonded dentin interfaces in real time using a recently developed microscope moire interferometer. METHOD: This system used a miniature moire interferometer, using two CCD cameras for simultaneous recording of longitudinal and transverse deformation fields, a piezotransducer for fringe shifting and use of a microscope objective with magnification up to 600 x. Small beams (1 mm x 2 mm x 6 mm) of moist resin-bonded dentin covered with cross-lined diffraction grating replica were placed in a miniature compression tester to allow controlled loading from 2 to 37 N while imaging the interference fringe patterns. RESULTS: Resin-dentin interfaces created by bonding dentin with Single Bond/Z100, under compressive loading, exhibited comparatively large strains across the adhesive-hybrid interface. When the wrapped phase maps were unwrapped to permit conversion of fringe order to displacements, the 2-D profiles of strain fields revealed non-uniform strains across the adhesive interface. In the adhesive/hybrid layer zone, the negative strain was larger (i.e. -6000 mu epsilon) than that seen in the adjacent resin composite or underlying mineralized dentin. The changes were elastic because they disappeared when the load was removed. SIGNIFICANCE: Microscopic moire interferometry can be very useful in revealing real-time strain across bonded interfaces under load.  (+info)

Autoindexing the diffraction patterns from crystals with a pseudotranslation. (7/11)

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Direct interaction between the Gulf Stream and the shelfbreak south of New England. (8/11)

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