Contour Element Research Articles

Contour integration deficits at high spatial frequencies in children treated for anisometropic amblyopia.

This study was conducted to reexamine the question of whether children treated for anisometropic amblyopia have contour integration deficits. To do so, we used psychophysical methods that require global contour processing while minimizing the influence of low-level deficits: visibility, shape perception, and positional uncertainty. Thirteen children with anisometropic amblyopia (age: 10.1 ± 1.8 years) and thirteen visually normal children (age: 10.8 ± 2.0 years) participated in this study. The stimuli were closed figures made up of Gabor patches either in noise or on a blank field. The contrast thresholds to detect a circular contour on a blank field, as well as the thresholds of aspect ratio and contour element number to discriminate a circular or elliptical contour in noise, were measured at Gabor spatial frequencies of 1.5, 3, and 6 cpd for amblyopic eyes (AEs), fellow eyes (FEs), and normal control eyes. Visual acuities and contrast sensitivity functions for AEs and FEs and the Randot stereoacuity were measured before testing. The AEs showed contrast deficits and degraded shape perception compared to the FEs at higher spatial frequencies (6 cpd). When the influence of abnormal contrast sensitivity and shape perception were minimized, the AEs showed contour integration deficits at spatial frequencies 3 and 6 cpd. These deficits were not related to basic losses in contrast sensitivity and acuity, stereoacuity, and visual crowding. Besides, no significant difference was found between the fellow eyes of the amblyopic children and the normal control eyes in the performance of contour integration. After eliminating or compensating for the low-level deficits, children treated for anisometropic amblyopia still show contour integration deficits, primarily at higher spatial frequencies, which might reflect the deficits in global processing caused by amblyopia. Contour integration deficits are likely independent of spatial vision deficits. Refractive correction and/or occlusion therapies may not be sufficient to fully restore contour integration deficits, which indicates the need for the development of clinical treatments to recover these deficits.

Topographic Contour Element Features in Patterned Macrostructures of the 18th Century Persian Bulat Steel

Topographic Contour Element Features in Patterned Macrostructures of the 18th Century Persian Bulat Steel

Error Evaluation of the Crown Profile of Logarithmic Generatrix Roller

In order to realize the accurate assessment of the profile error of the crown of the bearing roller, according to the geometric characteristics and the definition of the shape error of the contour element of the logarithmic bus-type roller, based on the principle of least squares, the least squares piece-wise fitting and error evaluation method of the logarithmic bus-type (combined form of the two-segment logarithmic curve) bearing roller crown profile are studied. Firstly, the three-point method is used to determine the curvature of the discrete data points of the convexity curve, and the boundary point of the two logarithmic curves is determined by the curvature difference method. Secondly, the measuring points adjacent to both sides of the dividing point are selected as auxiliary dividing points; the auxiliary dividing points and the corresponding logarithmic curve segment measuring points are fitted together to fit a series of least squares curves and calculate the corresponding errors. Through comparison and judgment, the least square error of the logarithmic bus-type roller profile is finally determined. Finally, through comparison and judgment, the least square error of the logarithmic bus-type roller profile is finally determined. The example results show that the total error of the logarithmic bus-type roller crown profile curve is 0.0071mm. The method in this paper can effectively realize the fitting and error evaluation of the bearing crown profile error, and it also verifies that the logarithmic prime line can reduce the stress concentration and improve the service life of the bearing.

Investigation of Microstructure, Mechanical Properties and Residual Stress in Non-equal-Channel Angular Pressing of 6061 Aluminum Alloy

In equal-channel angular pressing, it is necessary to repeat the process to achieve large strains. However, in non-equal-channel angular pressing (NECAP), the large strains can be achieved without repetition of the process. In this study, the effect of the NECAP on microstructure, mechanical properties and residual stress (RS) of widely used 6061 aluminum alloy sample was investigated. After the NECAP process, yield strength, tensile strength, hardness and uniformity of the hardness distribution increased dramatically and fracture strain and tensile toughness were significantly reduced. The effect of the NECAP on the yield strength was significantly higher than other parameters of the mechanical properties. Also, the microstructure was obtained with more uniformity and with the grain size of 18.5 times smaller relative to the initial sample. The numerical simulation results showed that by increasing friction coefficient, the plastic strain increases. In this study, a very good agreement was obtained between the results of experimental method of contour and finite element method in the RS measuring. In this paper, the RS factor (R.S.F.) was introduced to investigate the RS distribution. With the aid of this factor, one can obtain a general understanding of the RS distribution in one part. In this research, the effect of the friction coefficient on the R.S.F. in surfaces and middle cross section of the NECAPed sample was discussed.

The evaluation of the uncertainty of the research method on the geometrical parameters of the embroidery elements

The indirect measurement method of the contour width deformation of the embroidery element is presented in the work. The square-shaped, directly measured, embroidery element is compared to its digital image. Together with the used test methods steps, the reliability criteria for this method are presented as well. The reliability of the method of measuring the geometrical parameters of a closed contour element of an embroidered square shape is evaluated by analyzing its systematic and random errors and by calculating the total standard uncertainty. In assessing the accuracy of the measurement method, there is also a talk about a comprehensive assessment of measurement uncertainty. Measurement uncertainties are considered to be one of the most important parameters of the ability of a method to determine the possibilities of using and applying the method. When measuring the parameters of real samples, the components of total uncertainty related to the characteristics of the specimen (weave, surface density, filling characteristics, direction of the fabric yarn), their variation within certain limits and possible correlation among these components, influence of the standard means, data processing, digital image calibration were evaluated. It has been determined during the research that a negative error ∼2.4% with expanded uncertainty ∼3.3% complying with the requirements of the reliability of the method is typical for the deformation measurement method applied for the measurement of the five (6, 10, 14, 18, and 22 mm) elements of different contour widths. Because of that the evaluation of the uncertainty according its components is useful while analyzing the factors which have an impact on the deformation.

Contour Integration over Time: Psychophysical and fMRI Evidence.

The brain integrates discrete but collinear stimuli to perceive global contours. Previous contour integration (CI) studies mainly focus on integration over space, and CI is attributed to either V1 long-range connections or contour processing in high-visual areas that top-down modulate V1 responses. Here, we show that CI also occurs over time in a design that minimizes the roles of V1 long-range interactions. We use tilted contours embedded in random orientation noise and moving horizontally behind a fixed vertical slit. Individual contour elements traveling up/down within the slit would be encoded over time by parallel, rather than aligned, V1 neurons. However, we find robust contour detection even when the slit permits only one viewable contour element. Similar to CI over space, CI over time also obeys the rule of collinearity. fMRI evidence shows that while CI over space engages visual areas as early as V1, CI over time mainly engages higher dorsal and ventral visual areas involved in shape processing, as well as posterior parietal regions involved in visual memory that can represent the orientation of temporally integrated contours. These results suggest at least partially dissociable mechanisms for implementing the Gestalt rule of continuity in CI over space and time.

Cortical contributions to impaired contour integration in schizophrenia

ObjectivesVisual perceptual organization impairments in schizophrenia (SCZ) are well established, but their neurobiological bases are not. The current study used the previously validated Jittered Orientation Visual Integration (JOVI) task, along with fMRI, to examine the neural basis of contour integration (CI), and its impairment in SCZ. CI is an aspect of perceptual organization in which multiple distinct oriented elements are grouped into a single continuous boundary or shape. MethodsOn the JOVI, five levels of orientational jitter were added to non-contiguous closed contour elements embedded in background noise to progressively increase the difficulty in perceiving contour elements as left- or right-pointing ovals. Multi-site fMRI data were analyzed for 56 healthy control subjects and 47 people with SCZ. ResultsSCZ patients demonstrated poorer CI, and this was associated with increased activation in regions involved in global shape processing and visual attention, namely the lateral occipital complex and superior parietal lobules. There were no brain regions where controls demonstrated more activation than patients. ConclusionsCI impairment in this sample of outpatients with SCZ was related to excessive activation in regions associated with object processing and allocation of visual–spatial attention. There was no evidence for basic impairments in contour element linking in the fMRI data. The latter may be limited to poor outcome patients, where more extensive structural and functional changes in the occipital lobe have been observed.

One "shape" fits all: the orientation bandwidth of contour integration.

The ability of human participants to integrate fragmented stimulus elements into perceived coherent contours (amidst a field of distracter elements) has been intensively studied across a large number of contour element parameters, ranging from luminance contrast and chromaticity to motion and stereo. The evidence suggests that contour integration performance depends on the low-level Fourier properties of the stimuli. Thus, to understand contour integration, it would be advantageous to understand the properties of the low-level filters that the visual system uses to process contour stimuli. We addressed this issue by examining the role of stimulus element orientation bandwidth in contour integration, a previously unexplored area. We carried out three psychophysical experiments, and then simulated all of the experiments using a recently developed two-stage filter-overlap model whereby the contour grouping occurs by virtue of the overlap between the filter responses to different elements. The first stage of the model responds to the elements, while the second stage integrates the responses along the contour. We found that the first stage had to be fairly broadly tuned for orientation to account for our results. The model showed a very good fit to a large data set with relatively few free parameters, suggesting that this class of model may have an important role to play in helping us to better understand the mechanisms of contour integration.

Is 20/20 vision good enough? Visual acuity differences within the normal range predict contour element detection and integration.

Contour integration (CI) combines appropriately aligned and oriented elements into continuous boundaries. Collinear facilitation (CF) occurs when a low-contrast oriented element becomes more visible when flanked by collinear high-contrast elements. Both processes rely at least partly on long-range horizontal connections in early visual cortex, and thus both have been extensively studied to understand visual cortical functioning in aging, development, and clinical disorders. Here, we ask: Can acuity differences within the normal range predict CI or CF? To consider this question, we measured binocular visual acuity and compared subjects with 20/20 vision to those with better-than-20/20 vision (SharpPerceivers) on two tasks. In the CI task, subjects located an integrated shape embedded in varying amounts of noise; in the CF task, subjects detected a low-contrast element flanked by collinear or orthogonal high-contrast elements. In each case, displays were scaled in size to modulate element visibility and spatial frequency (4-12 cycles/deg). SharpPerceivers could integrate contours under noisier conditions than the 20/20 group (p = .0002), especially for high spatial frequency displays. Moreover, although the two groups exhibited similar collinear facilitation, SharpPerceivers could detect the central target with lower contrast at high spatial frequencies (p <. 05). These results suggest that small acuity differences within the normal range--corresponding to about a one line difference on a vision chart--strongly predict element detection and integration. Furthermore, simply ensuring that subjects have normal or corrected-to-normal vision is not sufficient when comparing groups on contour tasks; visual acuity confounds also need to be ruled out.

Modeling and simulation of material degradation in biodegradable wound closure devices

Biodegradable materials have been used as wound closure materials. It is important for these materials to enhance wound healing when the wound is vulnerable, and maintain wound closure until the wound is heal. This article studies the degradation process of bioresorbable magnesium micro-clips for wound closure in voice/laryngeal microsurgery. A novel computational approach is proposed to model degradation of the biodegradable micro-clips. The degradation process that considers both material and geometry of the device as well as its deployment is modeled as an energy minimization problem that is iteratively solved using active contour and incremental finite element methods. Strain energy of the micro-clip during degradation is calculated with the stretching and bending functions in the active contour formulation. The degradation rate is computed from strain energy using a transformation formulation. By relating strain energy to material degradation, the degradation rates and geometries of the micro-clip during degradation can be represented using a simulated degradation map. Computer simulation of the degradation of the micro-clip presented in the study is validated by in vivo and in vitro experiments.

Contour integration and aging: the effects of element spacing, orientation alignment and stimulus duration

The ability to extract contours in cluttered visual scenes, which is a crucial step in visual processing, declines with healthy aging, but the reasons for this decline are not well understood. In three experiments, we examined how the effect of aging on contour discrimination varies as a function of contour and distracter inter-element spacing, collinearity, and stimulus duration. Spiral-shaped contours composed of Gabors were embedded within a field of distracter Gabors of uniform density. In a four alternative forced-choice task, younger and older subjects were required to report the global orientation of the contour. In Experiment 1, the absolute contour element spacing varied from two to eight times the Gabor wavelength and contour element collinearity was disrupted with five levels of orientation jitter. Contour discrimination accuracy was lower in older subjects, but the effect of aging did not vary with contour spacing or orientation jitter. Experiment 2 found that decreasing stimulus durations from 0.8 to 0.04 s had a greater effect on older subjects' performance, but only for less salient contours. Experiment 3 examined the effect of the background on contour discrimination by varying the spacing and orientation of the distracter elements for contours with small and large absolute spacing. As in Experiment, the effect of aging did not vary with absolute contour spacing. Decreasing the distracter spacing, however, had a greater detrimental effect on accuracy in older subjects compared to younger subjects. Finally, both groups showed equally high accuracy when all distracters were iso-oriented. In sum, these findings suggest that aging does not affect the sensitivity of contour integration to proximity or collinearity. However, contour integration in older adults is slower and is especially vulnerable when distracters are denser than contour elements.

Assessing mould costs analysing manufacturing processes of cavities

Pressure die casting mould manufacturing companies have difficulties assessing manufacturing costs for bid generation. In particular, manufacturing effort of mould cavities could hardly be predicted accurately. Due to varying complexity of casting part geometry, processing time of manufacturing cavities appears to be a rather unpredictable factor influencing costs calculation of moulds. This article introduces a novel method for generating and analysing computer-aided design (CAD) models of mould cavities to compute the tool accessibility. Using geometrical information of cavities, working areas for different milling head geometries are determined, and processing times are calculated. Thereupon, a three-step accessibility analysis (AA) has been conducted. Beside the AA method, a CAD-based application of the calculation tool ‘visual form calculator’ (VFC), developed at IFW, is presented. Using the VFC, companies are now able to generate a virtual model of the contour element in order to assess mould costs accurately when analysing manufacturing processes of cavities.

CAD-based cost calculation of mould cavities

This article introduces a method for generating and analyzing CAD models of mould cavities to compute the tool accessibility. Using information about the surface curvature, a determination of working areas for different milling head geometries becomes possible. Relating groups of surfaces with milling heads and specific cutting data allows calculating the manufacturing time of roughing and finishing operations, including the tool change time. Determining the working areas, inaccessible for milling heads, enables to estimate the volume of material that needs to be eroded. A CAD-based application of the calculation tool `Visual Form Calculator’ (VFC), developed at IFW, is presented. Using the VFC, companies of the tool and form making industry are able to generate a virtual model of the contour element in order to analyze the accessibility of the working areas of the cavity and calculate manufacturing costs.

On One More Property of the Ideal Array Element Pattern

An infinite planar array of controlled elements in the form of overlapped subarrays excited through a multiport circuit is considered. It is analytically shown that the contour element (subarray) pattern with an ideal contour shape corresponding to the absence of backward mutual coupling and, as a consequence, to the 100% element efficiency can be exactly formed at a definite amplitude distribution over the densely arranged small ideal subarray radiators in spite of the fact that each such a radiator in the subarray has low efficiency caused by the presence of backward mutual coupling. If the small ideal radiators are controlled directly (without the multiport circuit), the contour pattern can be formed with 100% array efficiency for any shape of the contour. If the radiators are not ideal, then the efficiency of the array shaping the contour pattern is determined by averaging the mismatch efficiency of the uniformly excited array scanning over the region bounded by the contour pattern.

Computational simulation of crack problems by means of the contour element method

The article discusses a contour element method applied to numerical simulations of crack problems in elastic structures. Because the boundary integral equation degenerates for a body with two crack-surfaces occupying the same location, one of the forms of the displacement discontinuity method is implemented. According to the implemented method, resultant forces and dislocation densities, which are placed at mid-nodes of contour segments on one of the crack surfaces, are characterized by the indirect boundary integral equation. Contrarily to internal crack problems, for edge crack problems an edge-discontinuous element is used at the intersection between a crack and an edge to avoid a common node at the intersection. New numerical formulations that are built up on analytical integration are implemented. Therefore, all regular and singular integrals are evaluated only analytically. Tractions and resultant forces at a mid-node of any contour segment are regularized by a nonlocal characterization function. Hence, values of their components are obtained from the modified form of Somigliana’s identity that embraces nonlocal elements and standard elements of kernel matrices used in the boundary element analysis.

A numerical implementation using mid-node collocation for the hypersingular boundary contour method

A variant of the boundary element method, called the boundary contour method (BCM), offers a further reduction in dimensionality. Consequently, boundary contour analysis of two-dimensional problems does not require any numerical integration at all. In another development, a boundary contour implementation of a regularized hypersingular boundary integral equation (HBIE) using quadratic elements and end-node collocation was proposed and the technique is termed the hypersingular boundary contour method (HBCM). As reported in that work, the approach requires highly refined meshes in order to numerically enforce the stress continuity across boundary contour elements. This continuity requirement is very crucial since the regularized HBIE is only valid at collocation points where the stress tensor is continuous, while the computed stress at the endpoints of a boundary contour element, which is a non-conforming element, is generally not. This paper presents a new implementation of the HBCM for which the regularized HBIE is collocated at the mid-node of a boundary contour element. As the computed stress tensor is continuous at these mid-nodes, there is no need for unusually refined meshes. Some numerical tests herein show that, for the same mesh density, the HBCM using mid-node collocation has a comparable accuracy as the BCM.

Underlying principles of visual shape selectivity in posterior inferotemporal cortex.

Object perception depends on shape processing in the ventral visual pathway, which in monkeys culminates in inferotemporal cortex (IT). Here we provide a description of fundamental quantitative principles governing neural selectivity for complex shape in IT. By measuring responses to large, parametric sets of two-dimensional (2D) silhouette shapes, we found that neurons in posterior IT (Brodmann's areas TEO and posterior TE) integrate information about multiple contour elements (straight and curved edge fragments of the type represented in lower-level areas) using both linear and nonlinear mechanisms. This results in complex, distributed response patterns that cannot be characterized solely in terms of example stimuli. We explained these response patterns with tuning functions in multidimensional shape space and accurately predicted neural responses to the widely varying shapes in our stimulus set. Integration of contour element information in earlier stages of IT represents an important step in the transformation from low-level shape signals to complex object representation.

Apparent position governs contour-element binding by the visual system.

An assumption inherent in many models of visual space is that the spatial coordinates of retinal cells implicitly give rise to the perceptual code for position. The results of the experiments reported here, in which it is shown that retinally non-veridical locations of contour elements are used by the visual system for contour-element binding, lend support to a different view. The visual system does not implicitly code position with reference to the labelled locations of retinal cells, but dynamically extracts spatial position from the aggregate result of local computations. These computations may include local spatial relationships between retinal cells, but are not confined to them; other computations, including position derived from local velocity cues, are combined to code the position of objects in the visual world.

Recognition of melodic transformations: Inversion, retrograde, and retrograde inversion

The melodic transformations of inversion, retrograde, and retrograde inversion occur in pieces of music. An important question is whether such manipulations of melodic material are perceptually accessible to the listener. This study used a short-term recognition-memory paradigm and found that in the easier conditions all these transformations were recognized with better than chance accuracy. The ascending order of difficulty was: inversion, retrograde, retrograde inversion. There was no evidence that listeners distinguish between transforms that preserve the exact interval relationships of the standard stimulus and those that merely preserve its contour (pattern of ups and downs). In view of the order of difficulty of the transforms, two theoretical explanations of performance are possible (1) Listeners may perform the mental transformation required by the recognition task on a representation of the vector of pitches in the standard—an operation that is very like transforming a mental image of the written notation. (2) Listeners may handle inversions differently from the other transformations, comparing the standard and the comparison contour element by contour element, in temporal order. In this view, the temporal dimension would appear to have precedence over the pitch dimension in the musical structure, in consideration of the consequences of disturbing it.