Low Contrast (low + contrast)

Distribution by Scientific Domains


Selected Abstracts


Rapid categorization of achromatic natural scenes: how robust at very low contrasts?

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2005
Marc J.-M.
Abstract The human visual system is remarkably good at categorizing objects even in challenging visual conditions. Here we specifically assessed the robustness of the visual system in the face of large contrast variations in a high-level categorization task using natural images. Human subjects performed a go/no-go animal/nonanimal categorization task with briefly flashed grey level images. Performance was analysed for a large range of contrast conditions randomly presented to the subjects and varying from normal to 3% of initial contrast. Accuracy was very robust and subjects were performing well above chance level (, 70% correct) with only 10,12% of initial contrast. Accuracy decreased with contrast reduction but reached chance level only in the most extreme condition (3% of initial contrast). Conversely, the maximal increase in mean reaction time was ,,60 ms (at 8% of initial contrast); it then remained stable with further contrast reductions. Associated ERPs recorded on correct target and distractor trials showed a clear differential effect whose amplitude and peak latency were correlated respectively with task accuracy and mean reaction times. These data show the strong robustness of the visual system in object categorization at very low contrast. They suggest that magnocellular information could play a role in ventral stream visual functions such as object recognition. Performance may rely on early object representations which lack the details provided subsequently by the parvocellular system but contain enough information to reach decision in the categorization task. [source]


Synchrotron-Based Micro-CT and Refraction-Enhanced Micro-CT for Non-Destructive Materials Characterisation,

ADVANCED ENGINEERING MATERIALS, Issue 6 2009
Bernd R. Müller
Abstract X-ray computed tomography is an important tool for non-destructively evaluating the 3-D microstructure of modern materials. To resolve material structures in the micrometer range and below, high brilliance synchrotron radiation has to be used. The Federal Institute for Materials Research and Testing (BAM) has built up an imaging setup for micro-tomography and -radiography (BAMline) at the Berliner storage ring for synchrotron radiation (BESSY). In computed tomography, the contrast at interfaces within heterogeneous materials can be strongly amplified by effects related to X-ray refraction. Such effects are especially useful for materials of low absorption or mixed phases showing similar X-ray absorption properties that produce low contrast. The technique is based on ultra-small-angle scattering by microstructural elements causing phase-related effects, such as refraction and total reflection. The extraordinary contrast of inner surfaces is far beyond absorption effects. Crack orientation and fibre/matrix debonding in plastics, polymers, ceramics and metal-matrix-composites after cyclic loading and hydro-thermal aging can be visualized. In most cases, the investigated inner surface and interface structures correlate to mechanical properties. The technique is an alternative to other attempts on raising the spatial resolution of CT machines. [source]


Change of Excitability in Brainstem and Cortical Visual Processing in Migraine Exhibiting Allodynia

HEADACHE, Issue 10 2006
Koichi Shibata MD
Background.,Clinical and neurophysiological manifestations of information processing associated with central sensitization are little known. Allodynic migraine (AM) can be caused by the sensitization of trigeminal neuron, but no study has reported on AM between attacks using blink reflex (BR) and pattern-reversal visual evoked potentials (PVEPs). Objective.,We explored the characteristics of AM between attacks associated with central sensitization using BR and PVEP. Methods.,We recruited 13 patients with interictal AM and 15 patients with nonallodynic migraine (NA), and 30 healthy subjects (HS). BRs were obtained using paired pulses delivered at the interstimulus interval (ISI) of 150, 300, and 500 ms. The ratio of the area in the R2 of the second to R2 of the first shock was measured for each ISI. PVEP were recorded with 2 spatial frequencies (0.5 and 4.0 cpd) and 2 low and high contrasts (29% and 98%, respectively). Amplitudes of P100 were measured. Results.,For BR, there were no significant differences in the ratio of the area of the R2 between the sides of stimulation, and the sides of headache. AM patients had less suppression of the R2 at the ISI of 150 and 300 ms when compared with the NA patients and HS. For PVEP, at 0.5, there were significant differences of amplitude between AM patients and HS, and between NA patients and HS in low and high contrast. At 4.0 cpd, there were significant differences of amplitude between AM patients and HS in low contrast, and between AM patients and HS, and NA patients and HS in high contrast. In AM patients, there was a significant difference of amplitude ratio between 0.5 and 4.0 cpd. Conclusions.,Our BR and PVEP study showed that migraine patients exhibiting allodynia may show central sensitization of brainstem trigeminal neuron and have contrast modulating dysfunction during the cortical visual processing of striate and extrastriate on visual cortex in-between attacks. [source]


Use of image analysis techniques for objective quantification of the efficacy of different hair removal methods

INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 2 2007
S. Bielfeldt
In the field of consumer-used cosmetics for hair removal and hair growth reduction, there is a need for improved quantitative methods to enable the evaluation of efficacy and claim support. Optimized study designs and investigated endpoints are lacking to compare the efficacy of standard methods, like shaving or plucking, with new methods and products, such as depilating instruments or hair-growth-reducing cosmetics. Non-invasive image analysis, using a high-performance microscope combined with an optimized image analysis tool, was investigated to assess hair growth. In one step, high-resolution macrophotographs of the legs of female volunteers after shaving and plucking with cold wax were compared to observe short-term hair regrowth. In a second step, images obtained after plucking with cold wax were taken over a long-term period to assess the time, after which depilated hairs reappeared on the skin surface. Using image analysis, parameters like hair length, hair width, and hair projection area were investigated. The projection area was found to be the parameter most independent of possible image artifacts such as irregularities in skin or low contrast due to hair color. Therefore, the hair projection area was the most appropriate parameter to determine the time of hair regrowth. This point of time is suitable to assess the efficacy of different hair removal methods or hair growth reduction treatments by comparing the endpoint after use of the hair removal method to be investigated to the endpoint after simple shaving. The closeness of hair removal and visible signs of skin irritation can be assessed as additional quantitative parameters from the same images. Discomfort and pain rating by the volunteers complete the set of parameters, which are required to benchmark a new hair removal method or hair-growth-reduction treatment. Image analysis combined with high-resolution imaging techniques is a powerful tool to objectively assess parameters like hair length, hair width, and projection area. To achieve reliable data and to reduce well known image-analysis artifacts, it was important to optimize the technical equipment for use on human skin and to improve image analysis by adaptation of the image-processing procedure to the different skin characteristics of individuals, like skin color, hair color, and skin structure. [source]


Looks are important: parasitic assemblages of agromyzid leafminers (Diptera) in relation to mine shape and contrast

JOURNAL OF ANIMAL ECOLOGY, Issue 3 2004
Adriana Salvo
Summary 1We test the hypothesis that leaf mine appearance can affect the risk of leafminers being discovered by parasitoids, and therefore influence parasitic assemblages, using a comparative study of parasitic complexes associated with 28 agromyzid species in Central Argentina. Analyses were based on size, structure (defined as the number of species in host-range categories) and impact (percentage parasitism) of parasitic complexes on leafminers. Mine appearance was defined in terms of shape (linear, linear-blotch, blotch) and colour (high or low contrast with the leaf lamina). 2Irrespective of the agromyzid species involved, significant differences were found in the structure of the parasitoid complexes: specialists were more abundant and generalists rarer than expected in blotch and cryptically coloured mines. 3There were no differences in average parasitoid species richness and parasitism rates among differently coloured or shaped galleries. However, mine appearance significantly affected parasitic assemblage structure, with shape driving generalist species richness and contrast influencing that of specialists. Mine shape also affected parasitism rates, which were highest for generalists in linear mines, and for specialists in blotch mines. The existence of a gradient of discovery from the cryptically coloured blotch mines to the most apparent highly contrasting linear ones was supported by significant correlations of this gradient with richness and parasitism rates of generalist and specialist parasitoids. 4Taxonomic composition of parasitic complexes (analysed through parasitoid species abundance) was separated significantly according to host mine shape. An even more significant classification of assemblages was achieved when the combination of mine shape and colour was considered in the discoverability gradient. 5Our results suggest that despite leaf mines being an ecologically homogeneous resource, their morphology might offer varying degrees of refuge against different parasitoids. [source]


Pretargeted radioimmunoscintigraphy in patients with primary colorectal cancer using a bispecific anticarcinoembryonic antigen CEA X anti-di-diethylenetriaminepentaacetic acid F(ab,)2 antibody,,

CANCER, Issue S4 2010
Frits Aarts PhD
Abstract BACKGROUND: Antibody-based imaging agents are available commercially, but their success has been limited, mainly because of low contrast and the emergence of 2-fluoro-2-deoxy-D-glucose-positron emission tomography (FDG-PET) scanning. In pretargeting, administration of the radionuclide is separated from the antibody, thereby enhancing image contrast and allowing detection at earlier time points after injection. METHODS: The authors conducted an open-label, single-arm trial that assessed a pretargeting procedure in which an anticarcinoembryonic antigen x (anti-CEA x) anti-diethylenetriaminepentaacetic acid (anti-DTPA)-indum (In) antibody was used in combination with a 111In-labeled di-DTPA peptide for the diagnostic imaging of CEA-expressing colorectal cancer. Three patients received the 111In peptide alone to investigate tumor targeting, organ distribution, and clearance of the peptide. Thereafter, 11 patients received the bispecific antibody (bsAb) (5 mg) to pretarget the tumor. After 3 to 5 days, patients were injected with 185 megabecquerels of 111In-labeled peptide to assess the optimal interval for best image quality. RESULTS: Fourteen patients with primary colorectal cancer were enrolled. One of 3 patients who received 111In peptide alone had low-level tumor uptake. In 9 of 11 other patients, tumors were observed. In 1 patient, FDG-PET,positive lymph nodes were observed clearly with pretargeted immunoscintigraphy. Peptide pharmacokinetics revealed enhanced circulating levels of 111In-labeled peptide in patients in the 3-day interval cohort compared with the other cohorts. Tumor-to-background ratios ranged from 3.5 to 6.4 in the 3-day interval group, from 5.1 to 14.2 in the 4-day interval group, and from 3.5 to 3.9 in the 5-day interval group. The best images were acquired with a 4-day interval at 24 hours after injection of the radiolabeled peptide. Grade 1 adverse events were observed in 2 patients. CONCLUSIONS: Imaging of colorectal cancer using a 2-step, pretargeting system produced the best imaging results 24 hours after peptide administration using a 4-day interval between injection of the bsAb and the peptide. Cancer 2010;116(4 suppl):1111,7. © 2010 American Cancer Society. [source]


New paediatric contrast test: Hiding Heidi low-contrast ,face' test

CLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 5 2003
Clinical Research
ABSTRACT Background:,The Hiding Heidi low-contrast ,face' test is a new paediatric contrast test to evaluate the ability to detect objects with low contrast. The purpose of the present study was to compare the Hiding Heidi low-contrast ,face' test (HH) with the Pelli,Robson contrast sensitivity test (PR) and the functional acuity contrast test (FACT) in the low-contrast assessment. Methods:,Thirty university students participated in the present study. The contrast ability was evaluated by using three different methods: HH, PR and FACT. The HH was repeated on two separate occasions to test the repeatability. Results:,There was a significant positive correlation between HH and PR (r = 0.65, P < 0.01); between HH and FACT at 6 cycles per degree (c.p.d.; r = 0.64, P < 0.01); between HH and FACT at 3 c.p.d. (r = 0.91, P < 0.01); and between HH and FACT at 1.5 c.p.d. (r = 0.56, P < 0.01). The paired t -test showed a significant difference between HH and PR (t = ,6.05, P < 0.01); between HH and FACT at 6 c.p.d. (t = ,11.16, P < 0.01); between HH and FACT at 3 c.p.d. (t = ,8.35, P < 0.01); and between HH and FACT at 1.5 c.p.d. (t = ,5.64, P < 0.01). They had good agreement. The HH had a high repeatability. Conclusions:,The HH had a positive correlation but produced significantly different readings when compared with FACT and PR. The features and role of HH in clinical contrast sensitivity assessment are discussed. [source]


Rapid categorization of achromatic natural scenes: how robust at very low contrasts?

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2005
Marc J.-M.
Abstract The human visual system is remarkably good at categorizing objects even in challenging visual conditions. Here we specifically assessed the robustness of the visual system in the face of large contrast variations in a high-level categorization task using natural images. Human subjects performed a go/no-go animal/nonanimal categorization task with briefly flashed grey level images. Performance was analysed for a large range of contrast conditions randomly presented to the subjects and varying from normal to 3% of initial contrast. Accuracy was very robust and subjects were performing well above chance level (, 70% correct) with only 10,12% of initial contrast. Accuracy decreased with contrast reduction but reached chance level only in the most extreme condition (3% of initial contrast). Conversely, the maximal increase in mean reaction time was ,,60 ms (at 8% of initial contrast); it then remained stable with further contrast reductions. Associated ERPs recorded on correct target and distractor trials showed a clear differential effect whose amplitude and peak latency were correlated respectively with task accuracy and mean reaction times. These data show the strong robustness of the visual system in object categorization at very low contrast. They suggest that magnocellular information could play a role in ventral stream visual functions such as object recognition. Performance may rely on early object representations which lack the details provided subsequently by the parvocellular system but contain enough information to reach decision in the categorization task. [source]


Microfabric of folded quartz veins in metagreywackes: dislocation creep and subgrain rotation at high stress

JOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2009
C. A. TREPMANN
Abstract The microfabrics of folded quartz veins in fine-grained high pressure,low temperature metamorphic greywackes of the Franciscan Subduction Complex at Pacheco Pass, California, were investigated by optical microscopy, scanning electron microscopy including electron backscatter diffraction, and transmission electron microscopy. The foliated host metagreywacke is deformed by dissolution,precipitation creep, as indicated by the shape preferred orientation of mica and clastic quartz without any signs of crystal-plastic deformation. The absence of crystal-plastic deformation of clastic quartz suggests that the flow stress in the host metagreywacke remained below a few tens of MPa at temperatures of 250,300 °C. In contrast, the microfabric of the folded quartz veins indicates deformation by dislocation creep accompanied by subgrain rotation recrystallization. For the small recrystallized grain size of ,8 ± 6 ,m, paleopiezometers indicate differential stresses of a few hundred MPa. The stress concentration in the single phase quartz vein is interpreted to be due to its higher effective viscosity compared to the fine-grained host metagreywacke deforming by dissolution,precipitation creep. The fold shape suggests a viscosity contrast of one to two orders of magnitude. Deformation by dissolution,precipitation creep is expected to be a continuous process. The same must hold for folding of the vein and deformation of the vein quartz by dislocation creep. The microfabric suggests dynamic recrystallization predominantly by subgrain rotation and only minor strain-induced grain boundary migration, which requires low contrasts in dislocation density across high-angle grain boundaries to be maintained during climb-controlled creep at high differential stress. The record of quartz in these continuously deformed veins is characteristic and different from the record in metamorphic rocks exhumed in seismically active regions, where high-stress deformation at similar temperatures is episodic and related to the seismic cycle. [source]