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Objective assessment of chromatic and achromatic pattern adaptation reveals the temporal response properties of different visual pathways
- ANTHONY G. ROBSON, JANUS J. KULIKOWSKI
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- Journal:
- Visual Neuroscience / Volume 29 / Issue 6 / November 2012
- Published online by Cambridge University Press:
- 04 December 2012, pp. 301-313
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The aim was to investigate the temporal response properties of magnocellular, parvocellular, and koniocellular visual pathways using increment/decrement changes in contrast to elicit visual evoked potentials (VEPs). Static achromatic and isoluminant chromatic gratings were generated on a monitor. Chromatic gratings were modulated along red/green (R/G) or subject-specific tritanopic confusion axes, established using a minimum distinct border criterion. Isoluminance was determined using minimum flicker photometry. Achromatic and chromatic VEPs were recorded to contrast increments and decrements of 0.1 or 0.2 superimposed on the static gratings (masking contrast 0–0.6). Achromatic increment/decrement changes in contrast evoked a percept of apparent motion when the spatial frequency was low; VEPs to such stimuli were positive in polarity and largely unaffected by high levels of static contrast, consistent with transient response mechanisms. VEPs to finer achromatic gratings showed marked attenuation as static contrast was increased. Chromatic VEPs to R/G or tritan chromatic contrast increments were of negative polarity and showed progressive attenuation as static contrast was increased, in keeping with increasing desensitization of the sustained responses of the color-opponent visual pathways. Chromatic contrast decrement VEPs were of positive polarity and less sensitive to pattern adaptation. The relative contribution of sustained/transient mechanisms to achromatic processing is spatial frequency dependent. Chromatic contrast increment VEPs reflect the sustained temporal response properties of parvocellular and koniocellular pathways. Cortical VEPs can provide an objective measure of pattern adaptation and can be used to probe the temporal response characteristics of different visual pathways.
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- By Rose Teteki Abbey, K. C. Abraham, David Tuesday Adamo, LeRoy H. Aden, Efrain Agosto, Victor Aguilan, Gillian T. W. Ahlgren, Charanjit Kaur AjitSingh, Dorothy B E A Akoto, Giuseppe Alberigo, Daniel E. Albrecht, Ruth Albrecht, Daniel O. Aleshire, Urs Altermatt, Anand Amaladass, Michael Amaladoss, James N. Amanze, Lesley G. Anderson, Thomas C. Anderson, Victor Anderson, Hope S. Antone, María Pilar Aquino, Paula Arai, Victorio Araya Guillén, S. Wesley Ariarajah, Ellen T. Armour, Brett Gregory Armstrong, Atsuhiro Asano, Naim Stifan Ateek, Mahmoud Ayoub, John Alembillah Azumah, Mercedes L. García Bachmann, Irena Backus, J. Wayne Baker, Mieke Bal, Lewis V. Baldwin, William Barbieri, António Barbosa da Silva, David Basinger, Bolaji Olukemi Bateye, Oswald Bayer, Daniel H. Bays, Rosalie Beck, Nancy Elizabeth Bedford, Guy-Thomas Bedouelle, Chorbishop Seely Beggiani, Wolfgang Behringer, Christopher M. Bellitto, Byard Bennett, Harold V. Bennett, Teresa Berger, Miguel A. Bernad, Henley Bernard, Alan E. Bernstein, Jon L. Berquist, Johannes Beutler, Ana María Bidegain, Matthew P. Binkewicz, Jennifer Bird, Joseph Blenkinsopp, Dmytro Bondarenko, Paulo Bonfatti, Riet en Pim Bons-Storm, Jessica A. Boon, Marcus J. Borg, Mark Bosco, Peter C. Bouteneff, François Bovon, William D. Bowman, Paul S. Boyer, David Brakke, Richard E. Brantley, Marcus Braybrooke, Ian Breward, Ênio José da Costa Brito, Jewel Spears Brooker, Johannes Brosseder, Nicholas Canfield Read Brown, Robert F. Brown, Pamela K. Brubaker, Walter Brueggemann, Bishop Colin O. Buchanan, Stanley M. Burgess, Amy Nelson Burnett, J. Patout Burns, David B. Burrell, David Buttrick, James P. Byrd, Lavinia Byrne, Gerado Caetano, Marcos Caldas, Alkiviadis Calivas, William J. Callahan, Salvatore Calomino, Euan K. Cameron, William S. Campbell, Marcelo Ayres Camurça, Daniel F. Caner, Paul E. Capetz, Carlos F. Cardoza-Orlandi, Patrick W. Carey, Barbara Carvill, Hal Cauthron, Subhadra Mitra Channa, Mark D. Chapman, James H. Charlesworth, Kenneth R. Chase, Chen Zemin, Luciano Chianeque, Philip Chia Phin Yin, Francisca H. Chimhanda, Daniel Chiquete, John T. Chirban, Soobin Choi, Robert Choquette, Mita Choudhury, Gerald Christianson, John Chryssavgis, Sejong Chun, Esther Chung-Kim, Charles M. A. Clark, Elizabeth A. Clark, Sathianathan Clarke, Fred Cloud, John B. Cobb, W. Owen Cole, John A Coleman, John J. Collins, Sylvia Collins-Mayo, Paul K. Conkin, Beth A. Conklin, Sean Connolly, Demetrios J. Constantelos, Michael A. Conway, Paula M. Cooey, Austin Cooper, Michael L. Cooper-White, Pamela Cooper-White, L. William Countryman, Sérgio Coutinho, Pamela Couture, Shannon Craigo-Snell, James L. Crenshaw, David Crowner, Humberto Horacio Cucchetti, Lawrence S. Cunningham, Elizabeth Mason Currier, Emmanuel Cutrone, Mary L. Daniel, David D. Daniels, Robert Darden, Rolf Darge, Isaiah Dau, Jeffry C. Davis, Jane Dawson, Valentin Dedji, John W. de Gruchy, Paul DeHart, Wendy J. 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Yee, Viktor Yelensky, Yeo Khiok-Khng, Gustav K. K. Yeung, Angela Yiu, Amos Yong, Yong Ting Jin, You Bin, Youhanna Nessim Youssef, Eliana Yunes, Robert Michael Zaller, Valarie H. Ziegler, Barbara Brown Zikmund, Joyce Ann Zimmerman, Aurora Zlotnik, Zhuo Xinping
- Edited by Daniel Patte, Vanderbilt University, Tennessee
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- The Cambridge Dictionary of Christianity
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- 05 August 2012
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- 20 September 2010, pp xi-xliv
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Measurement of macular pigment optical density and distribution using the steady-state visual evoked potential
- ANTHONY G. ROBSON, NEIL R.A. PARRY
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- Journal:
- Visual Neuroscience / Volume 25 / Issue 4 / July 2008
- Published online by Cambridge University Press:
- 01 July 2008, pp. 575-583
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The purpose of this study was to specify isoluminance at different retinal eccentricities and to characterize macular pigment optical density (MPOD) and distribution using the steady-state visual evoked potential (VEP). Red–green (R/G) and blue–green (B/G) gratings were generated within two circular stimulus fields (radius = 0.55 or 1.1 deg) and within four annular fields (maximum mean radius = 6.0 deg) on a color monitor. Temporal frequency was 15 Hz. Isoluminance was determined for each stimulus using minimum flicker photometry. Steady-state onset–offset VEPs were recorded to the same annular stimuli as the luminance ratio between adjacent chromatic components was changed from 0.25 to 0.85 in 11 automated steps (0.5 representing photometric isoluminance). Fourier analysis showed that the power of the first harmonic was minimized at the isoluminant ratio specific to each subject. Relative OD was computed by comparing the isoluminant ratio at any location with that for the most eccentric annulus. To compensate for the broadband characteristics of the monitor, OD values were corrected according to minimum flicker measurements made through known concentrations of carotenoid solution. MPOD was additionally measured using minimum motion photometry.
There was high correlation between the isoluminant ratios determined by minimum flicker and VEPs for both R/G and B/G stimulation (r = 0.91, P < 0.005, slope = 1). Calibrated OD values computed from VEP estimates of B/G isoluminance correlated with those derived from minimum flicker (r = 0.96, P < 0.0005, slope = 0.85) and motion photometry (r = 0.94, P < 0.0005, slope = 0.88). OD values derived from B/G VEPs increased toward the fovea and corresponded closely with minimum flicker and minimum motion assessment of MP distribution profiles. The steady-state VEP can be used to determine isoluminance at different retinal eccentricities. MPOD and distribution can be measured by steady-state VEPs to B/G stimuli.
Fungal siderophores: structures, functions and applications
- Joanna C. RENSHAW, Geoff D. ROBSON, Anthony P. J. TRINCI, Marilyn G. WIEBE, Francis R. LIVENS, David COLLISON, Robin J. TAYLOR
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- Journal:
- Mycological Research / Volume 106 / Issue 10 / October 2002
- Published online by Cambridge University Press:
- 03 December 2002, pp. 1123-1142
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- October 2002
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Siderophores are low molecular weight, iron-chelating ligands produced by nearly all microorganisms. Fungi synthesize a wide range of hydroxamate siderophores. This review considers the chemical and biological aspects of these siderophores, their distribution amongst fungal genera and their possible applications. Siderophores function primarily as iron transport compounds. Expression of siderophore biosynthesis and the uptake systems is regulated by internal iron concentrations. Transport of siderophores is an energy-dependent process and is stereoselective, depending on recognition of the metal ion coordination geometry. In addition to transporting iron, siderophores have other functions and effects, including enhancing pathogenicity, acting as intracellular iron storage compounds and suppressing growth of other microorganisms. Siderophores can complex other metals apart from iron, in particular the actinides. Because of their metal-binding ability there are potential applications for siderophores in medicine, reprocessing of nuclear fuel, remediation of metal-contaminated sites and the treatment of industrial waste.
Evolution of Aspergillus niger and A. nidulans in glucose-limited chemostat cultures, as indicated by oscillations in the frequency of cycloheximide resistant and morphological mutants
- Richard J. SWIFT, Sally H. CRAIG, Marilyn G. Wiebe, Geoffrey D. ROBSON, Anthony P. J. TRINCI
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- Journal:
- Mycological Research / Volume 104 / Issue 3 / March 2000
- Published online by Cambridge University Press:
- 01 March 2000, pp. 333-337
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- March 2000
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Aspergillus niger and A. nidulans were grown separately in glucose-limited chemostat cultures on modified Vogel's medium. Periodic selection (the appearance of new mutant populations) in A. niger was determined by monitoring oscillations in the concentration of cycloheximide-resistant mycelial fragments in samples from the fermenter vessel. Using these data, the interval between the periodic selection of each new mutant population was 32±6 generations (mean±S.E.M.). Periodic selection in cycloheximide resistance in three morphologically distinct sub-populations of the A. niger culture averaged 36±2, 31±11 and 28±5 generations and these values were not significantly different from that of the whole population (32±6 generations). Also, it was possible to estimate the rate of evolution taking place in these cultures by monitoring oscillations in the frequency of morphological mutants. The intervals between the periodic selection of morphological mutant populations in A. niger and A. nidulans were 28±3 and 22±2 generations respectively.
Mutants with general growth rate advantages are the predominant morphological mutants to be isolated from the Quorn® production plant
- DUNCAN R. SIMPSON, JULIE M. WITHERS, MARILYN G. WIEBE, GEOFFREY D. ROBSON, ANTHONY P. J. TRINCI
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- Journal:
- Mycological Research / Volume 102 / Issue 2 / February 1998
- Published online by Cambridge University Press:
- 01 February 1998, pp. 221-227
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- February 1998
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Sixteen highly branched (colonial) mutants of Fusarium graminearum A3/5 were isolated at the end of 11 Quorn® myco-protein production fermentations. These ranged from the highly branched C134-3 to the sparsely branched C145, which was similar to A3/5 in liquid culture. Although allelic complementation was observed to occur between some of the mutants, heterokaryon analysis revealed that all the highly branched mutants belonged to a single complementation group. Mixed cultures of A3/5 and six of the colonial mutants were grown in glucose-, ammonium-, magnesium- and sulphate-limited chemostat culture. One mutant (C153) had a selective advantage over A3/5 in all nutrient limitations tested; four mutants (C134-1, C134-3, C137-1, and C135) had a selective advantage over A3/5 in all except one nutrient limitation; and one mutant (C139) had a selective advantage over A3/5 in magnesium-limited chemostat culture only. Four mutants (C134-3, C139-1, C153 and C135) had a selective advantage over A3/5 when the dilution rate was increased above the critical dilution rate (0·22 h−1) and nutrients were present in excess. These results suggest that the growth conditions in the Quorn® production plant (which is operated as a glucose-stat) favour mutations that confer general growth rate advantages, but these mutations may result in growth disadvantages when nutrient limitations are imposed. As all of the mutations appear to occur in one gene or gene cluster, the differing patterns of selective advantage/disadvantage for the six mutants studied suggests that regulatory genes may also be involved or that different sites of mutation can lead to a variety of pleiotropic effects.
Protoplast production and transformation of morphological mutants of the Quorn® myco-protein fungus, Fusarium graminearum A3/5, using the hygromycin B resistance plasmid pAN7-1
- MARILYN G. WIEBE, MICHAELA NOVÁKOVA, LAURIE MILLER, MARGARET L. BLAKEBROUGH, GEOFFREY D. ROBSON, PETER J. PUNT, ANTHONY P. J. TRINCI
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- Journal:
- Mycological Research / Volume 101 / Issue 7 / July 1997
- Published online by Cambridge University Press:
- 01 July 1997, pp. 871-877
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- July 1997
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A protocol for the generation of high yields of viable protoplasts has been developed for several highly branched (colonial) strains of the Quorn® myco-protein fungus, Fusarium graminearum A3/5. Driselase was found to produce higher protoplast yields (ca 109 g−1 wet weight) than the other lytic enzymes tested (Glucanex, Novozyme, β-glucuronidase, Sigma lytic enzyme, or ICN lytic enzyme), although yields differed for the various strains. Protoplast regeneration frequencies of 25–50% were observed when glucose (1·0 M) or sucrose (1·0 M) was used as the osmotic stabilizer. A highly branched strain of F. graminearum CC1-5, which grows better in submerged culture than the more sparsely branched wild-type strain (A3/5) was transformed using the hygromycin B resistance plasmid pAN7-1.