Two Disparity Channels in Human Visual Cortex With Different Contrast and Blur Sensitivity

Purpose

Our goal is to describe the contrast and blur sensitivity of multiple horizontal disparity subsystems and to relate them to the contrast and spatial sensitivities of their monocular inputs.

Methods

Steady-state visual evoked potential (SSVEP) amplitudes were recorded in response to dynamic random dot stereograms (DRDSs) alternating at 2 Hz between zero disparity and varying magnitudes of crossed disparity for disparity plane and disparity grating stimuli. Half-image contrasts ranged between 2.5% and 80% and over a range of Gaussian blurs from 1.4 to 12 arcmin. Separate experiments measured contrast and blur sensitivity for the monocular half-images.

Results

The first and second harmonics disparity responses were maximal for disparity gratings and for the disparity plane condition, respectively. The first harmonic of the disparity grating response was more affected by both contrast and blur than was the second harmonic of the disparity plane response, which had higher contrast sensitivity than the first harmonic.

Conclusions

The corrugation frequency, contrast, and blur tuning of the first harmonic suggest that it reflects activity of neurons tuned to higher luminance spatial frequencies that are selective for relative disparity, whereas the second harmonic reflects the activity of neurons sensitive to absolute disparity that are driven by low monocular spatial frequencies.

Translational Relevance

SSVEPs to DRDSs provide two objective neural measures of disparity processing, the first harmonic-whose stimulus preferences are similar to those of behavioral stereoacuity-and the second harmonic that represents an independent disparity-specific but not necessarily stereoscopic mechanism.

Cognitive penetrability of scene representations based on horizontal image disparities

The structure of natural scenes is signaled by many visual cues. Principal amongst them are the binocular disparities created by the laterally separated viewpoints of the two eyes. Disparity cues are believed to be processed hierarchically, first in terms of local measurements of absolute disparity and second in terms of more global measurements of relative disparity that allow extraction of the depth structure of a scene. Psychophysical and oculomotor studies have suggested that relative disparities are particularly relevant to perception, whilst absolute disparities are not. Here, we compare neural responses to stimuli that isolate the absolute disparity cue with stimuli that contain additional relative disparity cues, using the high temporal resolution of EEG to determine the temporal order of absolute and relative disparity processing. By varying the observers' task, we assess the extent to which each cue is cognitively penetrable. We find that absolute disparity is extracted before relative disparity, and that task effects arise only at or after the extraction of relative disparity. Our results indicate a hierarchy of disparity processing stages leading to the formation of a proto-object representation upon which higher cognitive processes can act.

Neue hämodynamische Definition der pulmonalen Hypertonie

Eine pathologische Druckerhöhung im pulmonalen Gefäßsystem (pulmonale Hypertonie, PH) wurde bisher definiert durch einen invasiv gemessenen mittleren pulmonalarteriellen Druck (mPAP) ≥25 mm Hg in Ruhe. Auf dem 6th World Symposium on Pulmonary Hypertension (WSPH) in Nizza 2018 wurde eine neue Definition der PH vorgeschlagen, die die Senkung der Obergrenze des normalen mPAP von 24 auf 20 mm Hg beinhaltet.

Obwohl keine Evidenz aus pädiatrischen Studien hierfür vorliegt, wurde diese neue PH-Definition (mPAP >20 mm Hg) aus Gründen der Einheitlichkeit auch von der pädiatrischen „Task Force“ des WSPH 2018 übernommen.

Die vorliegende Stellungnahme der Arbeitsgemeinschaft Pulmonale Hypertonie (AGPH) der Deutschen Gesellschaft für Pädiatrische Kardiologie und angeborene Herzfehler e. V. (DGPK) erläutert die zugrunde liegende Rationale und mögliche Konsequenzen dieser Definitionsänderung. Insbesondere stellt sie klar, dass diese Änderung der Definition aktuell keinen Einfluss auf die Verschreibung von Medikamenten zur gezielten spezifischen Therapie der pulmonalarteriellen Hypertonie hat.

Asymmetries between achromatic and chromatic extraction of 3D motion signals

Motion in depth (MID) can be cued by high-resolution changes in binocular disparity over time (CD), and low-resolution interocular velocity differences (IOVD). Computational differences between these two mechanisms suggest that they may be implemented in visual pathways with different spatial and temporal resolutions. Here, we used fMRI to examine how achromatic and S-cone signals contribute to human MID perception. Both CD and IOVD stimuli evoked responses in a widespread network that included early visual areas, parts of the dorsal and ventral streams, and motion-selective area hMT+. Crucially, however, we measured an interaction between MID type and chromaticity. fMRI CD responses were largely driven by achromatic stimuli, but IOVD responses were better driven by isoluminant S-cone inputs. In our psychophysical experiments, when S-cone and achromatic stimuli were matched for perceived contrast, participants were equally sensitive to the MID in achromatic and S-cone IOVD stimuli. In comparison, they were relatively insensitive to S-cone CD. These findings provide evidence that MID mechanisms asymmetrically draw on information in precortical pathways. An early opponent motion signal optimally conveyed by the S-cone pathway may provide a substantial contribution to the IOVD mechanism.

Sensitivity to Velocity- and Disparity-Based Cues to Motion-In-Depth With and Without Spared Stereopsis in Binocular Visual Impairment

Purpose

Two binocular sources of information serve motion-in-depth (MID) perception: changes in disparity over time (CD), and interocular velocity differences (IOVD). While CD requires the computation of small spatial disparities, IOVD could be computed from a much lower-resolution signal. IOVD signals therefore might still be available under conditions of binocular vision impairment (BVI) with limited or no stereopsis, for example, amblyopia.

Methods

Sensitivity to CD and IOVD was measured in adults who had undergone therapy to correct optical misalignment or amblyopia in childhood (n = 16), as well as normal vision controls with good stereoacuity (n = 8). Observers discriminated the interval containing a smoothly oscillating MID "test" stimulus from a "control" stimulus in a two-interval forced choice paradigm.

Results

Of the BVI observers with no static stereoacuity (n = 9), one displayed evidence for sensitivity to IOVD only, while there was otherwise no sensitivity for either CD or IOVD in the group. Generally, BVI observers with measurable stereoacuity (n = 7) displayed a pattern resembling the control group: showing a similar sensitivity for both cues. A neutral density filter placed in front of the fixing eye in a subset of BVI observers did not improve performance.

Conclusions

In one BVI observer there was preserved sensitivity to IOVD but not CD, though overall only those BVI observers with at least gross stereopsis were able to detect disparity- or velocity-based cues to MID. The results imply that these logically distinct information sources are somehow coupled, and in some cases BVI observers with no stereopsis may still retain sensitivity to IOVD.

Measurement of crosstalk in stereoscopic display systems used for vision research

Studying binocular vision requires precise control over the stimuli presented to the left and right eyes. A popular technique is to segregate signals either temporally (frame interleaving), spectrally (using colored filters), or through light polarization. None of these segregation methods achieves perfect isolation, and so a degree of crosstalk is usually apparent, in which signals intended for one eye are faintly visible to the other eye. Previous studies have reported crosstalk values mostly for consumer-grade systems. Here we measure crosstalk for eight systems, many of which are intended for use in vision research. We provide benchmark crosstalk values, report a negative crosstalk effect in some LCD-based systems, and give guidelines for dealing with crosstalk in different experimental paradigms.

Response of ammonium removal to growth and transpiration of Juncus effusus during the treatment of artificial sewage in laboratory-scale wetlands

The correlation between nitrogen removal and the role of the plants in the rhizosphere of constructed wetlands are the subject of continuous discussion, but knowledge is still insufficient. Since the influence of plant growth and physiological activity on ammonium removal has not been well characterized in constructed wetlands so far, this aspect is investigated in more detail in model wetlands under defined laboratory conditions using Juncus effusus for treating an artificial sewage. Growth and physiological activity, such as plant transpiration, have been found to correlate with both the efficiency of ammonium removal within the rhizosphere of J. effusus and the methane formation. The uptake of ammonium by growing plant stocks is within in a range of 45.5%, but under conditions of plant growth stagnation, a further nearly complete removal of the ammonium load points to the likely existence of additional nitrogen removal processes. In this way, a linear correlation between the ammonium concentration inside the rhizosphere and the transpiration of the plant stocks implies that an influence of plant physiological activity on the efficiency of N-removal exists. Furthermore, a linear correlation between methane concentration and plant transpiration has been estimated. The findings indicate a fast response of redox processes to plant activities. Accordingly, not only the influence of plant transpiration activity on the plant-internal convective gas transport, the radial oxygen loss by the plant roots and the efficiency of nitrification within the rhizosphere, but also the nitrogen gas released by phytovolatilization are discussed. The results achieved by using an unplanted control system are different in principle and characterized by a low efficiency of ammonium removal and a high methane enrichment of up to a maximum of 72.7% saturation.

Adaptation of a constructed wetland to simultaneous treatment of monochlorobenzene and perchloroethene

Mixed groundwater contaminations by chlorinated volatile organic compounds (VOC) cause environmental hazards if contaminated groundwater discharges into surface waters and river floodplains. Constructed wetlands (CW) or engineered natural wetlands provide a promising technology for the protection of sensitive water bodies. We adapted a constructed wetland able to treat monochlorobenzene (MCB) contaminated groundwater to a mixture of MCB and tetrachloroethene (PCE), representing low and high chlorinated model VOC. Simultaneous treatment of both compounds was efficient after an adaptation time of 2 1/2 years. Removal of MCB was temporarily impaired by PCE addition, but after adaptation a MCB concentration decrease of up to 64% (55.3 micromol L(-1)) was observed. Oxygen availability in the rhizosphere was relatively low, leading to sub-optimal MCB elimination but providing also appropriate conditions for PCE dechlorination. PCE and metabolites concentration patterns indicated a very slow system adaptation. However, under steady state conditions complete removal of PCE inflow concentrations of 10-15 micromol L(-1) was achieved with negligible concentrations of chlorinated metabolites in the outflow. Recovery of total dechlorination metabolite loads corresponding to 100%, and ethene loads corresponding to 30% of the PCE inflow load provided evidence for complete reductive dechlorination, corroborated by the detection of Dehalococcoides sp.

Rhamnolipid biosurfactants decrease the toxicity of chlorinated phenols to Pseudomonas putida DOT-T1E

AIMS

To investigate the effect of a mixture of rhamnolipid R1 and R2 biosurfactants produced by a Pseudomonas aeruginosa strain on the toxicity of phenol and chlorophenols to Pseudomonas putida DOT-T1E.

METHODS AND RESULTS

Toxicity was quantified by the effective concentration 50% (EC50), that is the concentration that causes a 50% inhibition of bacterial growth. The presence of 300 mg l(-1) rhamnolipids, that is at about twice their critical micelle concentration (CMC), increased the EC50 of phenol, 4-chlorophenol, 2,4-dichlorophenol and 2,4,5-trichlorophenol by about 12, 19, 32 and 40%, respectively, and consequently reduced the bioavailability and the freely dissolved concentration of the toxic phenolic compounds. The reduction was related to the phenols' octanol-water partition coefficients (K(ow)).

CONCLUSIONS

The reduction in toxicity of the phenols can be explained by a combination of toxin accumulation in biosurfactant micelles and hydrophobic interactions of the phenols with rhamnolipid-based dissolved organic carbon.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results provide evidence that next to the effect of the micelle formation also hydrophobic interactions with rhamnolipid-based dissolved organic carbon affects the bioavailability of the phenols. Quantifying the effect of biosurfactants on the toxicity of hydrophobic compounds such as phenols thus appears to be a useful approach to assess their bioavailable equilibrium concentration.

Function of Contegra valved grafts after unifocalization

BACKGROUND

Can Contegra grafts withstand high pressure?

METHODS

The function of Contegra grafts implanted after unifocalization of major aortopulmonary collateral arteries (MAPCAs) in 10 patients was evaluated. Median age at repair was 194 days and two conduit sizes were used: 12 mm (n = 8) and 14 mm (n = 2). Echocardiography and heart catheterization findings were reviewed.

RESULTS

Two patients died: one early after repair, one late. Death was not graft related. The median duration of observation for survivors was 31 (range 4 - 42) months. The postoperative right ventricular/left ventricular pressure ratio was greater than 75 % in 9 patients. High pressures persisted in 6 survivors. Seven patients underwent interventional dilatation/stenting of pulmonary arteries on 19 occasions. No obstruction was detected in the conduit. Graft valve regurgitation increased in 5 patients, but never exceeded grade 2 (n = 4). Freedom from reoperation for conduit dysfunction/failure was 100 % at month 42.

CONCLUSION

At mid-term follow-up, the Contegra grafts withstood high pressure without significant dysfunction or aneurysmal dilatation requiring surgery. Contegra appears to be an acceptable alternative to the aortic homograft for use after unifocalization of MAPCAs in infancy.

Physiological responses of Juncus effusus (Rush) to chromium and relevance for wastewater treatment in constructed wetlands

Constructed wetlands are increasingly applied for industrial wastewater treatment. However, current knowledge of the stress responses of helophytes to selected toxicants such as dichromate is limited. The goal of the experiments presented here was to characterize the physiological response of Juncus effusus to different concentrations of dichromate dependent upon the growth and constitution of the plants. The growth parameters, shoot length, and dry weight already were strongly affected at low dichromate concentrations of approximately 34 microM. Concentrations of 340 microM impaired chlorophyll fluorescence and a decrease in chlorophyll a started at concentrations higher than 170 microM dichromate. The concentrations of chlorophyll b and carotenoids also were influenced negatively. Thus, the reduction of the pigment content started before any obvious influence on the chlorophyll fluorescence. The highest concentration of dichromate, which caused no permanent inhibition of growth and photosynthesis, was found to be 17 microM K2Cr2O7. In principle, J. effusus is suitable for constructed wetlands to treat chromium-containing wastewater. Because the stress resistance of J. effusus is limited, the maximum concentration of dichromate in the treated wastewater should not exceed 34 microM. The growth parameters, shoot length, and dry weight were sensitive to much lower dichromate concentrations and did react more quickly than the biochemistry-related parameters chlorophyll fluorescence and pigment concentration. Therefore, the example of Juncus effusus shows that the use of only biochemical parameters to define concentration limits for the treatment of dichromate-containing wastewater can lead to incorrect conclusions and result in disturbed long-term operation of the system.

Anaerobic co-reduction of chromate and nitrate by bacterial cultures of Staphylococcus epidermidis L-02

Industrial wastewater is often polluted by Cr(VI) compounds, presenting a serious environmental problem. This study addresses the removal of toxic, mutagenic Cr(VI) by means of microbial reduction to Cr(III), which can then be precipitated as oxides or hydroxides and extracted from the aquatic system. A strain of Staphylococcus epidermidis L-02 was isolated from a bacterial consortium used for the remediation of a chromate-contaminated constructed wetland system. This strain reduced Cr(VI) by using pyruvate as an electron donor under anaerobic conditions. The aims of the present study were to investigate the specific rate of Cr(VI) reduction by the strain L-02, the effects of chromate and nitrate (available as electron acceptors) on the strain, and the interference of chromate and nitrate reduction processes. The presence of Cr(VI) decreased the growth rate of the bacterium. Chromate and nitrate reduction did not occur under sterile conditions but was observed during tests with the strain L-02. The presence of nitrate increased both the specific Cr(VI) reduction rate and the cell number. Under denitrifying conditions, Cr(VI) reduction was not inhibited by nitrite, which was produced during nitrate reduction. The average specific rate of chromate reduction reached 4.4 micromol Cr 10(10 )cells(-1 )h(-1), but was only 2.0 micromol Cr 10(10 )cells(-1 )h(-1) at 20 degrees C. The maximum specific rate was as high as 8.8-9.8 micromol Cr 10(10 )cells(-1 )h(-1). The role of nitrate in chromate reduction is discussed.

Unusual electrocardiogram findings in a preterm infant after fetal tachycardia with hydrops fetalis treated with flecainide

Fetal tachycardia and signs of hydrops fetalis were diagnosed at 29 weeks of gestation. The heart rate normalized by combined treatment with digoxin and flecainide and was followed by improvement of the hydrops. Premature labor led to delivery at 33 weeks of gestation. The newborn infant showed mild respiratory distress and was in a hemodynamically stable condition. Marked QT segment anomalies on the electrocardiogram during the first postnatal days resolved completely within 3 weeks. They were unlikely to be attributable to myocarditis or myocardial infarction. We speculate that these anomalies were caused by the maternal flecainide therapy.

Rotation of the gut: fact or fantasy?

Clinicians, as well as embryologists, believe that normally a process of rotation of the midgut takes place that can be hampered at any stage resulting in the different types of "malrotations." However, a "malrotated" gut has never been observed in normal embryos. Therefore all theories on the normal and abnormal development of the gut are still highly hypothetical. In an attempt to elucidate more clearly which events occur during the development of the gut, the authors studied its embryology in 58 normal rat embryos between the 13th and 20th day of gestation using scanning electron microscopy. In 13 day old rat embryos, the midgut has already formed a loop. It can be subdivided into three parts: the central part with its connections to the stomach and leading to the straight part, with the colorectum on the left and the "small bowel" on the right, and the tip of the loop inside the umbilical cord. These three parts show no signs of developmental synchronization. Each part develops according to its own developmental blueprint: the duodenal and umbilical parts of the midgut show much developmental activity, whereas gross changes of the straight part of the midgut are not seen. This finding is surprising because a process of rotation, if occurring, should result in notable morphological changes especially in this region. Furthermore, the coecum never achieved a position in the upper left abdomen, as is often outlined in schematic drawings. After the return of the bowel into the abdominal cavity, the coecum lies exclusively on the right side of the midline close to the ventral abdominal wall.(ABSTRACT TRUNCATED AT 250 WORDS)

Optical properties of the atmosphere: calculated variability and application to satellite remote sensing of phytoplankton

The radiative transfer equation is solved by the method of successive orders of scattering for several different model atmospheres, taking into account the realistic variability of scattering and absorption. A windruffled ocean surface with whitecaps and with different phytoplankton content is also taken into account. The variation of the ocean-leaving radiance when traveling through the atmosphere is investigated. Calculations are performed at five wavelengths from 0.443 to 0.750 microm, according to the channels of the Coastal Zone Color Scanner (CZCS) on board the Nimbus 7 satellite. The radiance reaching the satellite amounts to only 5% of the radiation that penetrated the ocean, and consequently 95% of the radiation is scattered in the atmosphere or reflected at the ocean surface. Radiance variation at the satellite due to phytoplankton variations lies on the order of 1%, while the radiance variation due to the realistic spread of the optically relevant atmospheric and oceanic constituents is considerably higher. The variability of the atmospheric turbidity already causes changes up to 10% in the radiance at the satellite.