Hierarchy of spatial interactions in the processing of contrast-defined contours.

Both psychophysical and neurophysiological evidence suggest that there are two visual cortical processing streams, a linear stream that processes first-order stimuli and a nonlinear stream that also processes second-order stimuli. This evidence also suggests that before the extraction of the second-order signal, the nonlinear pathway broadly but not completely pools signals across initial linear filters that encode the orientation of the carrier of the second-order signal. The evidence suggests that such pooling does not occur across carrier spatial frequencies. We show that similar results are obtained with repulsion tilt illusions but not with attraction effects. Attraction effects exhibit complete orientation crossover (while retaining spatial frequency selectivity), perhaps indicating higher-level processing; an experiment on interocular transfer of the effects supported this conclusion.

Orthogonal adaptation improves orientation discrimination.

We investigated the effect of adaptation on orientation discrimination using two experienced observers, then replicated the main effects using a total of 50 naïve subjects. Orientation discrimination around vertical improved after adaptation to either horizontal or vertical gratings, but was impaired by adaptation at 7.5 or 15 degrees from vertical. Improvement was greatest when adapter and test were orthogonal. We show that the results can be understood in terms of a functional model of adaptation in cortical vision.

Informed strain improvement for lignin degradation by Phanerochaete chrysosporium.

The effect of breeding from the white rot fungus Phanerochaete chrysosporium ME446 on performance for lignin mineralization was examined. This model for informed strain improvement without mutagenesis is based on abundant restriction fragment length polymorphisms (RFLPs). Under optimized conditions for lignin mineralization, extracellular manganese peroxidase (MnP) but not lignin peroxidase (LiP) could be detected, so measurement of LiP activity is not a valid assay for lignin degradation. Mineralization of 14C-labelled synthetic lignin (14C-DHP) was used to compare the performance of the wild-type strain ME446 with those of sets of progeny strains. Meiotic progeny from strain ME446, heterokaryotic progeny of crosses between such strains, and meiotic progeny of one heterokaryotic strain were examined. In each case, a minority of strains performed more efficiently than the parental strain ME446. The greatest range of lignin-mineralization performance (70-fold) was found within the set of initial progeny of ME446 and the narrowest was within the set of secondary homokaryotic strains. This is consistent with the view that a moderate number of determinants contribute to lignin mineralization performance. However, performance did not correlate with the possession of any single allele of those for 38 previously defined RFLP markers. The results show that lignin mineralization performance can be improved by cycles of crosses and fruiting, without mutagenesis.

Selectivity to K+ and Na+ of protoplast fractions isolated from different regions of Aspergillus nidulans hyphae.

The selectivity to K+ and Na+ of protoplast samples representing cytoplasm isolated from different regions of the hyphal filament of Aspergillus nidulans was investigated. Concentrations of both ions contained in successive protoplast fractions were measured. During lytic digestion, protoplasts were released first from apical regions and subsequently from progressively older regions of hyphae. A low K+/Na+ ratio was found in protoplasts containing primarily apical cytoplasm and a high K+/Na+ ratio was found in protoplasts originating from older regions of hyphae. The ratios were the same whether MgSO4 or mannitol was used as stabilizer. Absolute concentrations of both ions were higher in protoplasts of apical origin. Protoplasts stabilized in mannitol lost more ions than those stabilized in MgSO4 over an 8 h incubation period. Na+ losses were higher from apical protoplasts whereas K+ losses were higher from protoplasts liberated from older regions of hyphae. The addition of divalent metal cations (1.5 mM-Mn2+ or Mg2+) reduced losses of Na+ from protoplasts but did not affect loss of K+. Data obtained using protoplast samples were related to those obtained for intact mycelium. Absolute losses of both ions from mycelium were lower than for protoplasts but when compared on a protein basis the data suggested that protoplasts possess properties similar to those of intact mycelium in terms of K+ and Na+ selectivity.