bluuebunny/crossref_metadata_2025 huggingface dataset:
Population pharmacokinetics of dapsone in children with human immunodeficiency virus infection
Authors: Mirochnick Mark , Cooper Ellen , Capparelli Edmund , McIntosh Ken , Lindsey Jane , Xu Jing , Jacobus David , Mofenson Lynne , Bonagura Vincent R. , Nachman Sharon , Yogev Ram , Sullivan John L. , Spector Stephen A.
Published: August 2002

Background

Previous studies of dapsone pharmacokinetics in children have been too small to allow assessment of the relationships between dapsone pharmacokinetic parameters and patient characteristics or markers of efficacy and toxicity.

Methods

We used population analysis to estimate dapsone pharmacokinetic parameters in children participating in a phase I/II study of daily and weekly dapsone in children with human immunodeficiency virus (HIV) infection. With use of the program NONMEM and a 1‐compartment open model, the influence of demographic and clinical characteristics on oral clearance (CL/F) and oral volume of distribution (V/F) were examined. Measures of drug exposure (area under the concentration–time curve [AUC] and predicted concentrations just before and 2 hours after administration) were estimated for each patient and correlated with markers of efficacy and toxicity.

Results

Sixty children (median age, 3 years; age range, 2 months to 12 years) contributed 412 dapsone concentrations collected after 175 study doses. Final parameter estimates were 1.40 L/kg for V/F, 0.0283 L/kg/h for CL/F, and 2.66 for the absorption rate constant. Of the clinical characteristics evaluated, dapsone CL/F was significantly increased by 50% in children taking rifabutin, by 39% in black children, and by 38% in children younger than 2 years old. Although no significant correlations were found between any dapsone exposure parameter and markers of toxicity, increased AUC was associated with a decreased risk of Pneumocystis carinii pneumonia (PCP).

Conclusion

Ethnicity, age, and concomitant rifabutin use were associated with dapsone CL/F, with more rapid clearance observed in black children, children younger than 2 years old, and children receiving rifabutin. Dapsone pharmacokinetic parameters were not associated with toxicity, but higher dapsone AUC was associated with decreased risk of PCP. Monitoring of serum dapsone levels may be needed for optimal management of dapsone for PCP prophylaxis in children.

Clinical Pharmacology & Therapeutics (2001) 70, 24–32; doi: 10.1067/mcp.2001.115891
Median effect analysis of efficacy versus adverse effects of immunosuppressants
Authors: Kahan Barry D. , Kramer William G.
Published: August 2002

Background

A rigorous model to describe concentration‐effect relations—the median effect analysis—was applied to quantitate immunosuppressive versus adverse effects in human renal transplantation.

Methods

The median effect equation was used to analyze data collected from three clinical studies, including the two phase III blinded, placebo‐controlled trials (n = 1295 patients) of sirolimus versus azathioprine or placebo treatment added to a cyclosporine (INN, ciclosporin)/prednisone regimen and a sirolimus/azathioprine/prednisone (in the absence of cyclosporine) phase II cohort (n = 41 patients).

Results

The clinical effects correlated with drug concentrations as expressed by the median effect equation. Sirolimus or cyclosporine alone permitted drug concentrations that were 5‐fold and 2.2‐fold lower, respectively, to render 90% of patients rejection‐free, suggesting a synergistic interaction between the two drugs. Further, the sirolimus concentrations to render 50% of patients rejection‐free were about 200‐fold and 60‐fold less, respectively, than the concentration that caused 50% of patients to experience thrombocytopenia or hypertriglyceridemia. The correlation coefficient of the median effect analysis for the occurrence of hypercholesterolemia was more robust for sirolimus than for cyclosporine. Although the concentrations for 50% of patients rendered rejection‐free versus 50% affected by hypercholesterolemia were similar, a 7‐fold difference was calculated between the concentrations at which 90% of patients were free of rejection versus patients who were affected by hypercholesterolemia.

Conclusion

The median effect analysis proffers a useful tool to assess both drug interactions and the windows between therapeutic versus toxic effects of immunosuppressive agents. The current analysis suggests a synergistic interaction between sirolimus and cyclosporine.

Clinical Pharmacology & Therapeutics (2001) 70, 74–81; doi: 10.1067/mcp.2001.116309
The influence of efavirenz on the pharmacokinetics of a twice‐daily combination of indinavir and low‐dose ritonavir in healthy Volunteers
Authors: Aarnoutse Rob E. , Grintjes Karin J. T. , Telgt Denise S. C. , Stek Michael , Hugen Patricia W. H. , Reiss Peter , Koopmans Peter P. , Hekster Yechiel A. , Burger David M.
Published: August 2002

Objective

This study evaluated the effect of multiple‐dose efavirenz on the steady‐state pharmacokinetics of the combination of indinavir (800 mg) and low‐dose ritonavir (100 mg) twice a day, in which ritonavir is used to increase indinavir plasma concentrations.

Methods

Eighteen healthy male volunteers participated in this multiple‐dose, 1‐arm, 2‐period interaction study. They took a combination of 800 mg indinavir and 100 mg ritonavir with food for 15 days. From days 15 to 29, a once‐daily administration of 600 mg efavirenz was added to the combination. Pharmacokinetics of indinavir and ritonavir on days 15 and 29 were compared.

Results

Fourteen volunteers completed the study. The addition of efavirenz resulted in significant reductions (P < .01) in indinavir area under the curve (AUC, −25%), trough concentration (Cmin, −50%), and maximum concentration (Cmax, −17%). All indinavir Cmin levels on day 29 remained equivalent to or above the mean Cmin value described for the regimen of 800 mg indinavir three times a day, without ritonavir (0.15 mg/L). Changes in ritonavir AUC, Cmin, and Cmax were −36%, −39%, and −34%, respectively. Pharmacokinetics of efavirenz on day 29 were comparable with published data.

Conclusions

The addition of efavirenz to a combination of 800 mg indinavir and 100 mg ritonavir twice daily results in significant decreases in AUC, Cmax, and especially Cmin of indinavir. The dose of indinavir or ritonavir should be increased to maintain similar indinavir drug levels after addition of efavirenz to the indinavir‐ritonavir combination. Dose modifications may not be needed in antiretroviral‐naive human immunodeficiency virus–infected patients if the reference Cmin of the regimen of 800 mg indinavir 3 times a day is considered to be adequate.

Clinical Pharmacology & Therapeutics (2002) 71, 57–67; doi: 10.1067/mcp.2002.121424
Amplitude and Phase in the MüLler-Lyer Illusion
Authors: Skottun Bernt C
Published: August 2002

It has previously been claimed that the Müller-Lyer illusion is the result of low-pass spatial filtering. One way to understand this would be that the distribution of amplitudes is what generates this illusion. This possibility was investigated by computing the 2-D Fourier transforms of the two Müller-Lyer stimuli and extracting their phase and amplitude spectra. These spectra were combined to create hybrid spectra having the phase of one Müller-Lyer figure and the amplitudes of the other. Images were then created by computing the inverse Fourier transform of the hybrid spectra. Except in cases where the analysis was performed patchwise on very small patches, the figures generated with the phase spectrum of the stimuli having outward-pointing fins appear the longer. This was also the case when stimuli were generated with flat amplitude spectra. Because they show that the Müller-Lyer illusion does not depend on any particular distribution of amplitudes, these demonstrations do not support the theory that the Müller-Lyer illusion is the result of low-frequency filtering.
Last but Not Least
Authors: Kitaoka Akiyoshi , Gyoba Jiro , Sakurai Kenzo , Kawabata Hideaki
Published: August 2002

Here we draw attention to similarity between Petter's effect and the visual phantom illusion. Phantoms are visible when the spatial frequency of the inducing grating is low or the occluder is thin, whereas phantoms are invisible when the spatial frequency of the inducing grating is high or the occluder is thick. Moreover, phantoms are perceived in front of the occluder when they are visible, whereas the occluder is seen in front of the inducing gratings when phantoms are invisible. These characteristics correspond to Petter's effect, in which the thicker region tends to be perceived in front of the thinner region when two regions of the same lightness and of different sizes overlap, since ‘thick’ corresponds to low spatial frequency of the inducing grating or a thick occluder while ‘thin’ corresponds to high spatial frequency of the inducing grating or a thin occluder.
Depth Capture by Kinetic Depth and by Stereopsis
Authors: Kham Keetaek , Blake Randolph
Published: August 2002

The perceived depth of regions within a stereogram lacking explicit disparity information can be captured by the surface structure of regions where disparity is explicit: stereo capture. In two experiments, observers estimated surface curvature/depth of an untextured object (a ‘ribbon’) superimposed on a cylinder textured with dots, the cylinder curvature being defined by disparity (stereo depth) or by motion parallax (kinetic depth: KD). With the stereo-defined cylinder, depth capture was obtained under conditions where the disparity of the ribbon was ambiguous; with the KD, cylinder depth capture was obtained under conditions where the motion flow of the cylinder was in a direction parallel to that of the ribbon. These results demonstrate yet another similarity between KD and stereopsis.
Imposed Vibration Influences Perceived Tactile Smoothness
Authors: Hollins Mark , Fox Aaron , Bishop Carianne
Published: August 2002

According to the duplex theory of tactile texture perception, detection of cutaneous vibrations produced when the exploring finger moves across a surface contributes importantly to the perception of fine textures. If this is true, a vibrating surface should feel different from a stationary one. To test this prediction, experiments were conducted in which subjects examined two identical surfaces, one of which was surreptitiously made to vibrate, and judged which of the two was smoother. In experiment 1, the vibrating surface was less and less often judged smoother as the amplitude of (150 Hz) vibration increased. The effect was comparable in subjects who realized the surface was vibrating and those who did not. Experiment 2 showed that different frequencies (150–400 Hz) were equally effective in eliciting the effect when equated in sensation level (dB SL). The results suggest that vibrotaction contributes to texture perception, and that, at least within the Pacinian channel, it does so by means of an intensity code.
Mental Imagery of Visual Motion Modifies the Perception of Roll-Vection Stimulation
Authors: Mast Fred W , Berthoz Alain , Kosslyn Stephen M
Published: August 2002

When viewing a wide-angle visual display, which rotates in the frontoparallel plane around the line of sight, observers experience an illusory shift of the direction of gravity; this shift leads to an apparent tilt of the body and displaces allocentric space coordinates. In this study, subjects adjusted an indicator to the apparent horizontal while viewing a rotating display. To determine whether top–down processes could affect the illusion, the subjects were asked to visualize a rotating configuration of dots onto a blank central portion of the moving visual field. Visualizing dots and actually viewing the dots deflected the spatial judgment in very similar ways. These results demonstrate that top–down processing can affect allocentric space coordinates.
The Backward Inclination of a Surface Defined by Empirical Corresponding Points
Authors: Grove Philip M , Kaneko Hirohiko , Ono Hiroshi
Published: August 2002

Three experiments were conducted to investigate whether a locus of binocular correspondence extends eccentrically from the vertical horopter. In experiment 1, we investigated whether the backward inclination of the vertical horopter was manifested in the angle at which readers prefer to orient the page. All observers preferred a page inclined backwards to any other orientation. This backward inclination was less than predicted from previous psychophysical reports, however. In experiment 2, we investigated the extent of binocular correspondence, defined by minimal apparent interocular horizontal motion, in the central 24 deg of the binocular field. Our data define a planar surface inclined top-away from the observer as a locus from which psychophysical corresponding points are stimulated. In experiment 3, we measured vertical adjustments required to eliminate apparent vertical motion. Together, the pattern of results from experiments 2 and 3 is most consistent with a planar surface, inclined top-away from the observer. This is consistent with Helmholtz's account of the backward inclination of the vertical horopter and expands the locus of zero horizontal disparity from a single line in the median plane to eccentric loci extending at least ±12 deg in the central binocular field.
Effect of Photographic Negation on Matching the Expressions and Identities of Faces
Authors: White Murray
Published: August 2002

In four experiments, participants made speeded same – different responses to pairs of face photographs showing the same woman or different women with the same expression or different expressions. Compared with responses to positive pairs, negative pairs were matched more slowly on identity than on expression. A secondary finding showed that face expressions (same, different) influenced identity responses, and identities influenced expression responses, equally for positive and negative pairs. The independence of this irrelevant-dimension effect from the contrast effect supports the conclusion required by the main finding—that negation slows perceptual encoding of surface-based information used for identification more than it does encoding of edge-based information used for expression recognition.
Biodiversity and ecology of Australasian yeasts (fungi)
Authors: Fleet Graham H. , Fleet Graham H.
Published: August 2002

The biodiversity and ecology of yeasts associated with natural habitats have
attracted little systematic research in Australasia. Most isolations concern
yeasts associated with foods and beverages such as wine, fruit juices, soft
drinks, dairy products, high-sugar products and processed meats. Although
these yeasts have interesting physiological and biochemical properties (e.g.
xerotolerance, preservative resistance, protease and lipase activity), they
are similar to species found in products in other countries. Ecological
studies of yeasts associated with cactus, hibiscus, morning glory plants and
associated insects of New South Wales and Queensland have revealed new species
including Pichia opuntiae,
Clavispora opuntiae, and
Wickerhamiella australiensis,
Kodamaea anthophila,
Kodamaea kakaduensis,
Metschnikowia hibisciand a unique predacious species of
Candida. New species of
Cryptococcus and Rhodotorula were
isolated from soils and pasture grasses in New Zealand. Clinical isolates in
the genera Candida and
Cryptococcus are similar to those found overseas but
Cryptococcus neoformans var.
gattii is uniquely associated with the red gum tree,
Eucalyptus camaldulensis.
The lichen genus Graphis (Graphidaceae) in Australia
Authors: Archer Alan W.
Published: August 2002

An account of the lichen genus Graphis Adans.
(Graphidaceae) in Australia is given. Of the 48 taxa recognised, 10 are
described as new and nine are new reports of the genus in Australia.
Graphis desquamescens (Fée) Zahlbr.,
G. endoxantha Nyl., G. inamoena
Zahlbr., G. leptocarpa Fée,
G. leptoclada MÜll.Arg.,
G. silicicola Redinger,
G. stenotera Vainio, G. treubii
Zahlbr. and G. turgidula MÜll.Arg. are reported as
new to Australia and the following new taxa are described:
Graphis apertella A.W.Archer,
G. catherinae A.W.Archer,
G. howeana A.W.Archer,
G. immersicans A.W.Archer,
G. kakaduensis A.W.Archer,
G. nigririmis var. deficiens
A.W.Archer, G. streimannii A.W.Archer,
G. subregularis A.W.Archer,
G. supracola A.W.Archer and
G. turgidula var. norstictica
A.W.Archer. Graphis malacodes Nyl. is reported as an
earlier synonym of G. argopholis C.Knight ex
MÜll.Arg. A lectotype is chosen for
Graphis leptoclada MÜll.Arg. A key to the species
of Graphis in Australia is given.
Analysis of genetic diversity in Cassia brewsteri with randomly amplified DNA fingerprints (RAFs)
Authors: Cunningham David C. , Walsh Kerry B. , Anderson Eric R. , Harrison Dion K. , Carroll Bernie J.
Published: August 2002

Genetic diversity in Cassia brewsteri (F.Muell.)
F.Muell. ex Benth. was assessed with Randomly Amplified DNA Fingerprints
(RAFs). Thirty accessions of C. brewsteri collected from
throughout its natural distribution were analysed with three random decamer
primers, along with three accessions of C. tomentella
(Benth.) Domin and a single accession of each of
C. queenslandica C.T.White and
C. marksiana (F.M.Bailey) Domin. The three primers
yielded a reproducible amplification profile of 265 scorable polymorphic
fragments for the 35 accessions. These molecular markers were used to
calculate Nei and Li similarity coefficients between each pair of individuals.
A matrix of dissimilarity of each pair of individuals was examined by
multidimensional scaling (MDS). The analysis supports the division of
C. brewsteri into two subspecies and the suggestion that
intergradation ofC. brewsteri and
C. tomentella can occur where the distributions of these
species meet.
RECURSION FORMULAS FOR SOME ABELIAN KNOT INVARIANTS
Authors: STEVENS WAYNE H.
Published: August 2002

Let K be a tame knot in S3. We show that the sequence of cyclic resultants of the Alexander polynomial of K satisfies a linear recursion formula with integral coefficients. This means that the orders of the first homology groups of the branched cyclic covers of K can be computed recursively. We further establish the existence of a recursion formula that generates sequences which contain the square roots of the orders for the odd-fold covers that contain the square roots of the orders for the even-fold covers quotiented by the order for the two-fold cover. (That these square roots are all integers follows from a theorem of Plans.)
HAND AND DISTAL FOREARM REPLANTATION — IMMEDIATE AND LONG-TERM FOLLOW-UP
Authors: Hegazi Mohammed M.
Published: August 2002

Six cases of traumatic amputation of hand and/or forearm were treated by replantation over the last 20 years at this hospital. Reattachment was successful in all of the cases. Success was largely due to proper selection of cases, meticulous technique and availability of skilled manpower and technological help. Although survival of replanted part was achieved in all cases, functional success was not uniform as revealed by subjective and objective criteria used during evaluation and follow-up. Tamai method of scoring the functional aspect of a replanted part not only indicates the functional ability of a replanted part but also creates uniformity in data collection for easier comparison with other reported series.
OPTIMAL ORIENTATIONS OF ANNULAR NETWORKS
Authors: BERMOND JEAN-CLAUDE , BOND JOHNY , MARTIN CAROLE , PEKEČ ALEKSANDAR , ROBERTS FRED S.
Published: August 2002

Annular Network AN (c, s) is a graph representing a c × s grid in polar coordinates. We give bounds for the diameter of orientations of AN (c, s) and provide orientations which show that bounds are tight in most cases.
Effects of oral administration of ibutamoren mesylate, a nonpeptide growth hormone secretagogue, on the growth hormone–insulin‐like growth factor I axis in growth hormone–deficient children
Authors: Codner Ethel , Cassorla Fernando , Tiulpakov Anatoly N. , Mericq M. Verónica , Avila Alejandra , Pescovitz Ora H. , Svensson Johan , Cerchio Kristine , Krupa David , Gertz Barry J. , Murphy Gail
Published: August 2002

Ibutamoren mesylate (MK‐0677), an orally active nonpeptide growth hormone (GH) secretagogue, stimulates GH release through a pituitary and hypothalamic receptor that is different from the GH–releasing hormone receptor. We evaluated the safety and tolerability and the GH–insulin‐like growth factor (IGF) responses to two dosages of oral ibutamoren mesylate given to children with GH deficiency for 7 to 8 days. The patients, 18 prepubertal children (15 male, 3 female) with idiopathic GH deficiency, had a chronologic age of 10.6 ± 0.8 years (mean ± SD), bone age of 7.4 ± 0.7 years, growth velocity <10th percentile for age, height <10th percentile for age, and a maximum GH response of ≤10 μg/L to two different GH stimulation tests. The children were assigned as follows to one of three treatment groups with ibutamoren mesylate: 0.2 mg/kg per day for 7 days (days 1–7 or 8–14) and matching placebo for the alternate 7 days (groups I and II, respectively) or 0.8 mg/kg per day for 7 days (days 8–14, group III). On day 15 all patients received an 0.8‐mg/kg dose of ibutamoren mesylate. Patients in groups I and II were studied first to assess safety at the low dose before advancement to the high dose. Hormonal profiles were evaluated on day −1 (baseline) and day 15, and the results were expressed as the change from baseline within each group. After administration of ibutamoren mesylate 0.8 mg/kg for 8 days (group III), the median increases (on day 15) from baseline were as follows: 3.8 μg/L (range, 0 to 34.3) for serum GH peak concentration (P = .001), 4.3 μg · h/L (range, 1.3 to 35.6) for the GH area under the concentration‐time curve from time zero to 8 hours (AUC0–8) (P < .001), 12 μg/L (range, −4 to 116) for serum IGF‐I (P = .01), and 0.4 μg/L (range, −0.9 to 1.5) for serum IGF‐binding protein 3 (IGFBP‐3) (P = .01). There was no change in serum prolactin, glucose, triiodothyronine, thyroxine, thyrotropin, peak serum cortisol, and insulin concentrations or 24‐hour urinary free cortisol after administration of 0.8 mg/kg per day of ibutamoren mesylate for 8 days. We conclude that short‐term administration of ibutamoren mesylate can increase GH, IGF‐I, and IGFBP‐3 levels in some children with GH deficiency. Thus this compound is applicable for testing its effect on growth velocity.

Clinical Pharmacology & Therapeutics (2001) 70, 91–98; doi: 10.1067/mcp.2001.116514
Clopidogrel, but not abciximab, reduces platelet leukocyte conjugates and P‐selectin expression in a human ex vivo in vitro model
Authors: Klinkhardt Ute , Graff Jochen , Harder Sebastian
Published: August 2002

Formation of platelet‐leukocyte aggregates (PLA) through the CD62 ligand is an important mechanism by which leukocytes contribute to thrombosis and inflammation. We investigated the formation of PLA in human subjects after stimulation with thrombin receptor activating peptide and adenosine diphosphate (ADP) after treatment with clopidogrel and after in vitro application of the platelet glycoprotein IIb/IIIa complex antagonist abciximab. Expression of CD62 was significantly reduced 30% to 50% with clopidogrel, depending on the type and concentration of the inducer, but addition of abciximab led to a significant approximately 30% increase in CD62 expression whenplatelets were stimulated by ADP. Formation of PLA decreased significantly with clopidogrel to 55% to 75% of the baseline value, whereas addition of abciximab caused a significant increase in PLA in ADP‐stimulated samples before but not after administration of clopidogrel. The increase in formation of PLA after in vitro addition of abciximab was not paralleled by a decrease in platelet microaggregates and is therefore presumed not caused by enhanced availability of platelets. To our knowledge, this is the first report showing that clopidogrel reduces formation of PLA. The findings also suggest intersection between an “outside‐in” signal generated by abciximab and stimulation of platelet P2T12 purinergic receptors that augments degranulation and increases formation of PLA but is inhibited by clopidogrel.

Clinical Pharmacology & Therapeutics (2002) 71, 176–185; doi: 10.1067/mcp.2002.122018
Rebuilding Bridges: A Critical Geopolitics of Iberian Transfrontier Cooperation in a European Context
Authors: Sidaway James Derrick
Published: August 2002

In the context of approaches to understanding the European Union (EU) and ‘critical geopolitics’ which traces the construction of geopolitical narratives, the author writes about the imaginations of European society and space as harmonised and networked which are associated with visions of governance for ‘an ever closer union’. This is done through a critical examination of the European Commission's project of sponsoring cross-border cooperation. Drawing on a case study from the Portuguese — Spanish frontier, he examines contradictions that have arisen and are mediated through an unresolved dispute concerning the demarcation of a short section of what is the longest, poorest (in terms of material underdevelopment), and oldest (in terms of relative stability) border between two EU member states. Focusing on the EU-funded (re)construction of a ruined bridge across the border, he examines the way in which the boundary dispute (and attendant Portuguese irredentism) has become enfolded within and disrupts the strategic visions of the EU Working with a mixture of historical and contemporary documents, media accounts, archival records, and interviews relating to this case study, the author reflects on and elaborates broader understandings of the spatiality of power in the EU.
Metaphors of Meltdown: Political Representations of Economic Space in the Asian Financial Crisis
Authors: Kelly Philip F
Published: August 2002

Economic geographers have increasingly acknowledged the importance of discursive constructions and metaphorical representations of economic space. The representational has been recognized as more than just colourful rhetoric, being also a construction of reality that contains implicit understandings of how economic processes work and the corollaries of such processes in terms of government policy. Furthermore, the connections between understanding processes, making policy, and retaining legitimacy mean that such metaphors are highly political. The author explores some of the metaphors that have been employed by political leaders in understanding the Asian financial crisis of 1997–99. Two sets of contrasting metaphors are highlighted in the rhetoric of leaders in Malaysia and Singapore, respectively: in Malaysia, metaphors of colonial domination and militaristic aggression dominate; in Singapore, ‘natural’ metaphors of typhoon damage and tectonic shifts tend to prevail. These representational strategies can be linked to discourses of political power and the construction of economic policy in each context.
Narrating Interracial Relations and the Negotiation of Public Spaces
Authors: Tyner James A
Published: August 2002

Although interracial (hetero)sexual relations are no longer illegal, and the number of visible, consensual interracial partnerships has increased, there still remains a discourse against these social arrangements circulating in the United States that continues to bear the traces of the history of antimiscegenation. The purpose of this paper is to examine the everyday negotiation of public spaces of an African-American man as he participates in interracial (heterosexual relations. With a theoretical debt to both Lefebvre and de Certeau, and employing a narrative approach, I highlight the complex interactions of race, gender, and sexuality, and how these are manifest spatially. Through this narrative, moreover, I demonstrate how resistance to one form of hegemony (racism) may simultaneously contribute to the augmentation of other forms of dominance (patriarchy).
Spatially Parallel Processing of Within-Dimension Conjunctions
Authors: Linnell Karina J , Humphreys Glyn W
Published: August 2002

Within-dimension conjunction search for red–green targets amongst red–blue, and blue – green, nontargets is extremely inefficient (Wolfe et al, 1990 Journal of Experimental Psychology: Human Perception and Performance16 879–892). We tested whether pairs of red – green conjunction targets can nevertheless be processed spatially in parallel. Participants made speeded detection responses whenever a red–green target was present. Across trials where a second identical target was present, the distribution of detection times was compatible with the assumption that targets were processed in parallel (Miller, 1982 Cognitive Psychology14 247–279). We show that this was not an artifact of response-competition or feature-based processing. We suggest that within-dimension conjunctions can be processed spatially in parallel. Visual search for such items may be inefficient owing to within-dimension grouping between items.
Thatcher Illusion: Dependence on Angle of Rotation
Authors: Stürzel Frank , Spillmann Lothar
Published: August 2002

The expression of a face with its eyes and mouth inverted changes from ‘pleasant’ to ‘grotesque’ as the stimulus is rotated from 180° to 0° (Thatcher illusion). We determined the angular orientation at which this change occurred for three manipulated faces. Mean thresholds for eighteen observers were found to lie between 94° and 100° relative to the vertical with an average overlap of about 15° between an observer's ascending and descending thresholds. The sudden nature and relatively narrow zone of the changeover suggest a neuronal step-tuning of hypothetical face cells in the human brain, underlying the holistic (‘grotesque’) versus componential (‘pleasant’) processing of upright versus upside-down faces. Findings are discussed within the framework of cognitive, neuroimaging, and single-cell studies.
Bottom–Up Clues in Target Finding: Why a Dalmatian May Be Mistaken for an Elephant
Authors: van Tonder Gert J , Ejima Yoshimichi
Published: August 2002

We provide informal psychophysical support for a strategy where bottom–up features guide attention toward a target, and the top–down path interprets hypothetical shapes at the target location—as opposed to a dominant top–down approach. In our survey, for which we used the familiar picture of a Dalmatian dog against a dappled background, (i) 75% of subjects initially found a bulging body which overlaps that of the dog, but final ‘top–down’ percepts were unexpected: nearly all subjects assigned an incorrect head and limbs to the body; (ii) after random rotation of texture elements overlapping computed features only 45% of subjects reported a bulging body, with a few adding limbs etc. The picture of the Dalmatian dog must therefore contain many bottom–up features—a top–down strategy may find ‘incorrect’ targets at correct target locations. Computational support for these claims is more easily constructed than one may expect. We could compute at least two bottom–up features, both useful in 3-D surface interpolation from 2-D scenes, which yielded significant values at the location of the Dalmatian dog: anisotropic texture compression and affine texture distortion cues. We therefore conclude that the role of top–down processing is overstated in a traditional example such as the Dalmatian dog picture.
Raised Line Drawings are Spontaneously Explored with a Single Finger
Authors: Symmons Mark , Richardson Barry
Published: August 2002

In this study we examine the strategies used by blindfolded subjects asked to freely explore raised line drawings and identify what is depicted in them. We were particularly interested in how often a single finger is spontaneously used because in several studies subjects are forced to use only one fingertip and the extent to which this restriction may depress haptic perception is unclear. The results suggest that despite a variety of strategies, people ‘naturally’ use single fingertips sufficiently often to allow confidence in conclusions that are based on studies imposing this restriction.
The Colors Seen behind Transparent Filters
Authors: D'Zmura Michael , Rinner Oliver , Gegenfurtner Karl R
Published: August 2002

How do the colors and lightnesses of surfaces seen to lie behind a transparent filter depend on the chromatic properties of the filter? A convergence model developed in prior work (D'Zmura et al, 1997 Perception26 471–492; Chen and D'Zmura, 1998 Perception27 595–608) suggests that the visual system interprets a filter's transformation of color in terms of a convergence in color space. Such a convergence is described by a color shift and a change in contrast. We tested the model using an asymmetric matching task. Observers adjusted, in computer graphic simulation, the color of a surface seen behind a transparent filter in order to match the color of a surface seen in plain view. The convergence model fits the color-matching results nearly as well as a more general affine-transformation model, even though the latter has many more parameters. Other models, including von Kries scaling, did not perform as well. These results suggest that the color constancy revealed in this task is described best by a model that takes into account both color shifts and changes in contrast.
Color Appearance of Surfaces Viewed through Fog
Authors: Hagedorn John , D'Zmura Michael
Published: August 2002

How do the colors of surfaces seen through fog depend on the chromatic properties of the fog? Prior work (eg Chen and D'Zmura, 1998 Perception27 595–608) shows that the colors of surfaces seen through a transparent filter can be described by a convergence model. The convergence model takes into account color shift and change in contrast. Whether the convergence model can also be applied to fog was tested experimentally with an asymmetric matching task. In computer graphic simulation, observers adjusted the color of a surface seen through fog in order to match the color of a surface seen in the absence of fog. The convergence model fits the data well. The results suggest that the color constancy revealed in this task with fog is described best by a model that takes into account both shift in color and change in contrast.
A Neuro-Cognitive Visual System for Object Recognition Based on Testing of Interactive Attentional Top – down Hypotheses
Authors: Deco Gustavo , Schürmann Bernd
Published: August 2002

We propose an extension of a systemic model for object recognition formulated by Rybak et al (1998 Vision Research38 2387–2400) which is based on the functional organisation of the visual systems in primate brains. In contrast to the learning and recognition scheme of Rybak et al we do not assume a behavioural paradigm, ie a visuomotor programmed scanpath that determines the sequence of foveation on the different parts of the object. As in the basis architecture of Rybak et al, the system modules are separated into ‘what’-like subsystems corresponding to the ventral occipito-inferotemporal visual path and ‘where’-like complexes analogous to the dorsal occipito-parietal visual path. The ‘what’ system analyses local features in the actual foveation as in Rybak et al. But, in our case, the ‘where’ memory, instead of programming a behavioural scanpath, scores the spatial relationship between successive fixation and the spatial relationship between the associated main edges. The recognition is based on the identification of parts and their spatial relationship. This gives the learning and recognition mechanisms more flexibility in the sense that, for recognising an object, several different fixation sequences may be accepted.
Speed Perception is Affected by the Ebbinghaus–Titchener Illusion
Authors: Pavlova Marina , Sokolov Alexander
Published: August 2002

We examined whether the apparent extent of motion affects speed perception. On the first presentation of each trial, a light dot travelled horizontally across a central circle of one of the Ebbinghaus configurations (with either small or large inducing elements). On the second presentation, observers adjusted the speed of a dot moving within the central circle alone so as to match the speed perceived in the first presentation. For all stimulus speeds (1.3, 2.1, and 5.5 deg s−1), the matched speed with small inducing circles was systematically less than that with large inducing circles. The findings indicate that the perceived speed depends on the apparent extent of motion: the larger the apparent size of a frame, the slower the apparent speed. These results are consistent with the predictions of transposition effects in visual motion.
Curvature Biases in Stereoscopic Vision: A Nasotemporal Asymmetry
Authors: Ninio Jacques
Published: August 2002

The reliability of curvature judgments for linear elements was studied, with stereograms that contained a binocular arc with curvature in depth, and either a binocular frontoparallel arc or a monocular one, on a background representing a hemiellipsoid. The subjects made about 15% errors on binocular arcs with curvature in depth, and 60%–80% of these occurred when both the hemiellipsoid and the arc were convex, the arc being perceived as concave, by transparency through the hemiellipsoid. There were also about 15%–30% errors on frontoparallel arcs, but spread among all situations, with a small prevalence of concave judgments. Curvature in depth was assigned to the monocular stimuli in more than 60% of the cases. There was a curvature bias when the monocular arcs were on the nasal side, and were viewed against a concave background. Assuming parallel viewing, nasal ingoing arcs were usually perceived as concave, and nasal outgoing arcs usually perceived as convex, in agreement with geometrical likelihood. Nasal-side elements captured by one eye are, in general, those with the highest likelihood of having matching elements in the other eye. Then the observed nasal bias effect suggests that the matching process in stereopsis could be driven from the nasal sides of the projections in the two cerebral hemispheres.
Simultaneous Lightness Contrast with Double Increments
Authors: Bressan Paola , Actis-Grosso Rossana
Published: August 2002

In this paper we demonstrate the existence of simultaneous lightness contrast in displays in which the target patches are both more luminant than their surrounds. These effects are not predicted by theories of lightness that assume that the highest luminance in a scene is perceived as white, and anchors all the other luminances. We show that the strength of double-increment illusions depends crucially on the luminance of both the surrounds and the target patches. Such luminance prerequisites were not met in previous studies, which explains why simultaneous contrast with incremental targets has so far been regarded as extremely weak or nonexistent.
Explaining Lightness Illusions
Authors: Bressan Paola
Published: August 2002

Grey looks darker when set against white than when set against black. In some complex figures this illusion becomes startling, and can be shown to depend on the perceptual organisation of regions within the image. The most widely accepted explanations of such effects are based on the analysis of the junctions formed where the boundaries of nearby regions meet. Even theories where junctions are not the subject of special concern underline their importance as grouping cues. In this paper I present several new families of figures that challenge both views, and conclude that junctions do not play any crucial role in lightness estimation.
Features Derived from First-Order Motion Mechanisms Predict Anomalies in Motion Perception
Authors: Bowns Linda
Published: August 2002

Current dominant hypotheses of how humans detect the movement of patterns assume that the pattern is divided into one-dimensional sinusoidally varying luminance patterns, referred to as gratings (first-order components). The speed of these gratings is independently encoded from predominantly spatial and temporal frequency information, and their direction is encoded from orientation information. This paper addresses the problem of how the individually encoded grating information is combined to give perceived pattern direction, given that real moving objects are generally made up of more than one component. More specifically, further evidence is presented for a combination based on the use of a feature derived from first-order components—‘first-order feature hypothesis’. This hypothesis essentially implements a constraint on pattern direction called the intersection of constraints (IOC) proposed by Adelson and Movshon [1982, Nature300 523–525]. A simulation of the model is used to make three new predictions about a perceived motion reversal reported by Derrington et al (1992, Vision Research32 699–707); these predictions are tested and found to be consistent with the first-order feature hypothesis.
Reflexive Shifts of Covert Attention Operate in an Egocentric Coordinate Frame
Authors: Barrett Doug J K , Bradshaw Mark F , Rose David , Everatt John , Simpson Peter J
Published: August 2002

Covert shifts of attention have been shown to improve detection and discrimination thresholds for a range of visual stimuli. Although there is some evidence to suggest that the allocation of attention to a particular region of interest occurs in a retinotopic frame of reference, the importance of an allocentric, or object-based, framework has gained widespread empirical support. The current experiment investigates the nature of the spatial representation in which covert shifts of attention occur in response to a reflexive prime. Primes and targets were presented in four conditions designed to vary systematically the validity of the spatial relationship between the prime and target in egocentric or allocentric coordinate frameworks. A significant advantage, in terms of reaction time and correct identification, was found for targets located in positions previously primed in an egocentric (but not allocentric) framework whereas there was no advantage for locations primed in an allocentric (but not egocentric) framework. These results suggest that the allocation of covert spatial attention within an egocentric framework may be more important than previously thought.
Visual Inter-Attribute Contour Completion
Authors: Poom Leo
Published: August 2002

A new visual phenomenon, inter-attribute illusory (completed) contours, is demonstrated. Contour completions are perceived between any combination of spatially separate pairs of inducing elements (Kanizsa-like ‘pacman’ figures) defined either by pictorial cues (luminance contrast or offset gratings), temporal contrast (motion, second-order-motion or ‘phantom’ contours), or binocular-disparity contrast. In a first experiment, observers reported the perceived occurrence of contour completion for all pair combinations of inducing elements. In a second experiment they rated the perceived clarity of the completed contours. Both methods generated similar results—contour completions were perceived even though the inducing elements were defined by different attributes. Ratings of inter-attribute clarity were no lower than in either of the two corresponding intra-attribute conditions and seem to be the average of these two ratings. The results provide evidence for the existence of attribute-invariant Gestalt processes, and on a mechanistic level indicate that the completion process operates on attribute-invariant contour detectors.
Perceptual Grouping in Two Visually Reliant Species: Humans (Homo Sapiens) and Australian Sea Lions (Neophoca Cinerea)
Authors: Burke Darren , Everingham Paul , Rogers Tracey , Hinton Melinda , Hall-Aspland Sophie
Published: August 2002

Kurylo, van Nest, and Knepper (1997 Journal of Comparative Psychology111 126–134) have recently shown that hooded rats are able to judge the global orientation of an array of elements if orientation is signalled by the perceptual-grouping principle of proximity, but not if it is signalled by element alignment. Using a procedure designed to overcome some potential problems with the experiment of Kurylo et al, we found the same distinction in the perceptual processing of Australian sea lions. The sea lions were able to judge the orientation of arrays containing strong proximity and similarity information, but performed at chance levels judging arrays in which element alignment signalled global orientation. Human subjects were able to judge all three pattern types quickly and accurately. This is strong evidence of a qualitative distinction in the way in which perceptual grouping operates in humans and the non-human species tested. Whether this distinction is a consequence of evolutionary or experiential factors is a question for future research, but the mere fact of a qualitative difference holds important implications for our understanding of perceptual grouping.
What does the Ternus Display Tell us about Motion Processing in Human Vision?
Authors: Scott-Samuel Nicholas E , Hess Robert F
Published: August 2002

The Ternus display is a moving visual stimulus which elicits two very different percepts, according to the length of the interstimulus interval (ISI) between each frame of the motion sequence. These two percepts, referred to as element motion and group motion, have previously been analysed in terms of the operation of a low-level, dedicated short-range motion process (in the case of element motion), and of a higher-level, attentional long-range motion process (in the case of group motion). We used a novel Ternus configuration to show that both element and group motion are, in fact, mediated solely by a process sensitive to changes in the spatial appearance of the Ternus elements. In light of this, it appears that Ternus displays tell us nothing about low-level motion processing, implying that previous studies using Ternus displays, for instance those dealing with dyslexia, require reinterpretation. Further manipulations of the Ternus display revealed that the orientation and spatial-frequency discrimination of the process underlying the analysis of Ternus displays is far worse than thresholds for spatial vision. We conclude that Ternus displays are analysed via a long-range motion, or feature-tracking, process, and that this process is distinct from spatial vision.
Pathogenicity of root and stolon-colonising fungi to white clover
Authors: Zahid M. I. , Gurr G. M. , Nikandrow A. , Fulkerson W. J. , Nicol H. I.
Published: August 2002

Fungi isolated from white clover plants growing in dairy pastures in northern
New South Wales and south-eastern Queensland were tested for their
pathogenicity to seedlings, excised stolons and mature white clover plants.
Thirty out of 65 isolates tested, including species of
Fusarium, Phytophthora,
Pythium, Rhizoctonia,
Phoma, Codinaea,
Gliocladium, Microsphaeropsis,
Trichoderma, Nectria and
Macrophomina, were pathogenic to white clover roots
in vitro. Ten of the fungi, including the genera
Alternaria, Colletotrichum,
Drechslera, Fusarium,
Phoma, Macrophomina,
Phomopsis and Rhizoctonia, caused
stolon rot symptoms. Of the 23 fungi tested on seedlings and mature white
clover plants Phytophthora megasperma,
Phoma nebulosa and
Pythium irregulare were the most pathogenic to both
seedlings and mature plants. Root rot and plant growth suppression was more
severe in pot tests using field soil compared with pasteurised potting mix.
Novel methods are described for testing pathogenicity to excised stolons.