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Visual detection of targets moving against structured background fields has been studied with near-monochromatic stimuli, selected so as to isolate the different increment threshold spectral response mechanisms. It is shown that for foveal vision, the red- and green-sensitive mechanisms (pi 5 and pi 4 respectively) yield IMG functions (Barbur and Ruddock, 1980), similar to those found with white light. In contrast, the blue-sensitive (pi 1) mechanism yields a low-frequency IMG response quite unlike that found for the other mechanisms. There is also considerable variation between subjects in this case. Measurements taken 30 degrees off-axis with low (1.4 log trolands) background illumination level, yield a low frequency response IMG function for both rod and cone spectral mechanisms, similar to those found with white light stimuli. At high illumination levels (> 2.2 log trolands) the IMG function for the pi 5-mechanism is shifted to higher spatial frequencies, as is also observed with white light stimuli. A wavelength-selective binocular interaction effect, manifested in the detection of moving targets, is also described, and it is suggested that this may be of value in the study of defective colour vision.
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Stable chromium(VI)-sensitive and -tolerant mutants were obtained by induced mutagenesis of Schizosaccharomyces pombe lysine and leucine auxotrophic heterothallic strains 6chr+ and 9chr+. Eleven of them were selected for further studies. Fast transport of 51CrO4(2-) was detected in a representative sensitive mutant, chr-51S, while the tolerant mutant chr1-66T and the parental strain 6chr+ exhibited significantly lower 51CrO4(2-) uptake. The segregation of tetrads of three selected CrVI-tolerant mutants, chr1-66T, chr1-14T and chr2-04T, strongly indicated that tolerance was determined by single mutations. Random spore analysis proved that the mutations of chr1-66T and chr1-14T were allelic and the mutation of mutant chr2-04T was not allelic with the mutation of chr1-66T. Recombinants carrying the ura4D18 selective marker were created for transformation experiments. Two of them (chr1-661T and chr2-046T) can be used to clone and identify the genes responsible for their CrVI tolerance phenotype.
Cellulose and chromaton-N-super as solid supports for direct determination of the immobilized nickel complexes with dimethylglyoxime and benzyldioxime by diffuse reflection spectroscopy were compared. The advantage of chromaton-N-super with use of benzyldioxime is shown. Detection limit is 0.02 microg/mL. The proposed method was applied for the analysis of soil.
Chromaton-N-super and Silasorb C18 (SMT C18) were compared as solid supports for the direct determination of the immobilized beryllium complexes with eriochrome cyanine R by diffuse reflection spectroscopy. The advantage of Silasorb C18 was shown. A detection limit of 0.0002 microg mL(-1) could be reached in a 100-mL sample. The method was used for the analysis of real water samples.
To assess the effect of the anti-marine-borer timber preservative CCA (a pressure-impregnated solution of copper, chromium, and arsenic compounds) on nontarget epibiota, fouling community development was investigated. Panels of Scots pine treated to target retentions of 12, 24, and 48 kg CCA per m3 of wood (covering the range of retentions recommended for marine use) plus untreated controls were submerged at seven coastal sites (Portsmouth, UK; La Tremblade [two sites], France; Ria Formosa, Portugal; Sagres, Portugal; Kristineberg, Sweden; Athens, Greece). The fouling community on the surfaces of the panels was assessed both qualitatively and quantitatively after 6, 12, and 18 months of exposure. Multivariate statistical methods were used to compare community structure between panel treatments. Panels treated to the three CCA loadings supported very similar fouling assemblages, which in most cases had higher numbers of taxa and individuals than assemblages on untreated panels. No detrimental effects on epibiota due to CCA preservatives were detected at any of the treatment levels at all seven exposure sites, suggesting that the range of environmental conditions at the sites had no bearing on preservative impact on fouling biota. Differences in community structure between CCA-treated and untreated panels may be due to enhanced larval settlement on CCA-treated timber by some species as a result of modifications to the surface properties of the timber by the preservative. Possible reasons for the higher numbers of certain species on the surface of CCA-treated panels are discussed.
We studied associative visual learning in harnessed honeybees trained with monochromatic lights associated with a reward of sucrose solution delivered to the antennae and proboscis, to elicit the proboscis extension reflex (PER). We demonstrated five properties of visual learning under these conditions. First, antennae deprivation significantly increased visual acquisition, suggesting that sensory input from the antennae interferes with visual learning. Second, covering the compound eyes with silver paste significantly decreased visual acquisition, while covering the ocelli did not. Third, there was no significant difference in the visual acquisition between nurse bees, guard bees, and foragers. Fourth, bees conditioned with a 540-nm light stimulus exhibited light-induced PER with a 618-nm, but not with a 439-nm light stimulus. Finally, bees conditioned with a 540-nm light stimulus exhibited PER immediately after the 439-nm light was turned off, suggesting that the bees reacted to an afterimage induced by prior adaptation to the 439-nm light that might be similar to the 540-nm light.
BACKGROUND: Flickering light stimulation of the retina is known to increase retinal vessel diameter in animals and humans. The aim of the study was to quantify the response of retinal vessel diameter to red-green and blue-green flickering light. METHODS: In 11 normal healthy volunteers (mean age: 25.2+/-6.8 years) retinal arterial and venous diameters were examined by Retinal Vessel Analyzer (IMEDOS Ltd., Weimar, Germany) before, during and after red-green and blue-green flicker stimulation with a frequency of 12 Hz and duration of 10 and 30 s. RESULTS: For red-green flicker at 10 s there was a 2.4+/-1.4% arterial diameter increase at 9.1+/-3.3 s with a return to baseline after 30 s and a 2.4+/-1.1% venous diameter increase at 12.1+/-2.6 s with a return to baseline after 30 s. For red-green flicker at 30 s there was a 3.2+/-1.5% arterial diameter increase at 26.9+/-12.6 s with a return to baseline after 40 s and a 4.9+/-1.8% venous diameter increase at 31.4+/-7.6 s with a return to baseline after 40 s. For blue-green flicker at 10 s there was a 2.0+/-0.7% arterial diameter increase at 10.6+/-5.3 s with a return to baseline after 30 s and a 2.3+/-1.1% venous diameter increase at 12.0+/-5.5 s with a return to baseline after 30 s. For blue-green flicker at 30 s there was a 2.6+/-1.3% arterial diameter increase at 20.7+/-8.0 s with a return to baseline after 40 s and a 3.4+/-2.2% venous diameter increase at 28.8+/-10.5 s with a return to baseline after 40 s. CONCLUSIONS: Retinal vessel diameter dilation is a reproducible response to the applied flicker stimuli. This finding supports the existence of neurovascular coupling in the human retina. Flicker stimulation in either red-green or blue-green might be a useful stimulus for examination of retinal vessel behavior to regulatory demands.
Many teleost fish can adapt their body color to a background color by changing the morphology and density of their skin pigment cells. Melanophore density in fish skin decreases during long-term adaptation to a white background. Although cell death, especially apoptosis, is thought to be involved in these morphological changes, there are no data clearly supporting this mechanism. Using medaka fish, Oryzias latipes, we observed that, on a white background, melanophore size was reduced first and this was followed by a decrease in melanophore density caused by gradual cell death. The process of cell death included loss of cell activity, cell fragmentation, phagocytosis of the fragments, and clearance via the epidermis. Apoptosis was assessed by the appearance of phosphatidylserine on the cell surface of melanophores that had lost motile activity, and DNA fragments involved in cell fragmentation were detected by the TUNEL (TDT-mediated dUTP-biotin nick end-labeling) assay. However, when chemically denervated fish were used, although melanophore size was reduced as expected, cell death was suppressed even on a white background. In skin tissue culture, apoptosis in melanophores was stimulated significantly by norepinephrine, but not by melanin-concentrating hormone. These results indicate that melanophore density decreases by apoptosis, and suggest that sympathetic innervation has an important role in the regulation of apoptosis in melanophores. In analogous fashion, leucophores showed a significant decrease in density with an increase of cell death on a black background. We suggest that apoptosis regulates the balance of pigment cells in the skin of medaka fish to adapt their body color to a particular background.