Different attentional resources modulate the gain mechanisms for color and luminance contrast.

We used an interference paradigm to investigate whether attention is attribute-specific at early levels of visual processing. We show that the peripheral increment thresholds for luminance contrast deteriorate when the observer is currently performing another luminance (form or contrast) discrimination task in central view, but not when he or she is performing a color discrimination task. Similar results were obtained for color increment thresholds, indicating that the interference is specific to contrast modality. The effects are strong and robust over primary task difficulties and perceptual learning levels. Modeling suggests that attention improves contrast sensitivity by modulating the gain of the neuronal response to contrast. These results suggest that attention is parceled in independent resources for luminance and color contrast.

Characterization of ewe's milk by capillary zone electrophoresis.

The purpose of the present work was to develop a procedure able to separate and identify the major protein components of ewe's milk by capillary zone electrophoresis (CZE). Thirty-five individual milk samples of Massese breed were analyzed using a coated capillary. The analyses were performed at pH 3.0 at a temperature of 40 degrees C in the presence of 6 M urea. The purification of casein fractions was carried out by preparative fast protein liquid chromatography and the CZE results were confirmed by polyacrylamide agarose gel electrophoresis (PAAGE). The identification of whey proteins was also carried out by comparison with high-performance liquid chromatography data. The present study permitted the identification of the major components of ewe's milk by high-resolution electropherograms and characteristic migration times (tM). it was also possible to detect the presence of genetic variants of beta-lactoglobulin. The tM of k-casein was determined after enzymatic action of chymosin by verifying the simultaneous formation of p-k-casein. In most of the samples a fast moving alpha-s2-casein variant was identified by comparison with PAAGE results. Minor genetic differences were found in other casein fractions for this pool of samples.