bluuebunny/crossref_metadata_2025 huggingface dataset:
Clathrate Hydrates
Authors: Buffett Bruce A.
Published: July 2002

Substantial volumes of methane gas are trapped below the seafloor and in permafrost by an ice-like solid called clathrate hydrate. Global estimates of the methane in clathrate hydrate may exceed 1016 kg, which represents one of the largest sources of hydrocarbon on Earth. Speculations about large releases of methane from clathrate hydrate have raised serious but unresolved questions about its possible role in climate change. Progress in our understanding of clathrate hydrate has been made through integrated geophysical and geochemical surveys of known clathrate occurrences. Details from these surveys have motivated new investigations of the physical, chemical, and biological processes that contribute to growth and breakdown of clathrate hydrate in natural settings. In this article, I give an overview of recent advances and future challenges.
NUTRITION AND CULTURE OF ENTOMOPHAGOUS INSECTS
Authors: Thompson S. N.
Published: July 2002

▪ Abstract  This article reviews the current state of knowledge concerning the nutrition of entomophagous insects and other arthropods. Early nutritional investigations focused principally on the basic dietary and nutritional requirements for beneficial insects. Based on these findings, the first attempts were made to develop mass culture methods and to formulate artificial diets that would allow rearing of parasitoids and predators in the absence of host or prey, as well as the latter's food sources. Although limited success was achieved, these studies established the nutritional foundation for later advances. Recently, attention has focused on the interaction between nutrition, physiology, behavior, and ecology of the different life stages of entomophagous species within a unified concept of nutritional ecology. This approach has resulted in more comprehensive understanding of nutrition, which in turn has facilitated the continuous artificial culture of several parasites and predators. Additional studies have confirmed the importance of supplemental feeding of the adult stages of beneficial insects for maximizing reproduction and longevity. Applications of nutritional ecology to biological control are discussed.
Molecular Mechanism of Class Switch Recombination: Linkage with Somatic Hypermutation
Authors: Honjo Tasuku , Kinoshita Kazuo , Muramatsu Masamichi
Published: July 2002

Class switch recombination (CSR) and somatic hypermutation (SHM) have been considered to be mediated by different molecular mechanisms because both target DNAs and DNA modification products are quite distinct. However, involvement of activation-induced cytidine deaminase (AID) in both CSR and SHM has revealed that the two genetic alteration mechanisms are surprisingly similar. Accumulating data led us to propose the following scenario: AID is likely to be an RNA editing enzyme that modifies an unknown pre-mRNA to generate mRNA encoding a nicking endonuclease specific to the stem-loop structure. Transcription of the S and V regions, which contain palindromic sequences, leads to transient denaturation, forming the stem-loop structure that is cleaved by the AID-regulated endonuclease. Cleaved single-strand tails will be processed by error-prone DNA polymerase-mediated gap-filling or exonuclease-mediated resection. Mismatched bases will be corrected or fixed by mismatch repair enzymes. CSR ends are then ligated by the NHEJ system while SHM nicks are repaired by another ligation system.
JAHN-TELLER PHENOMENA IN SOLIDS
Authors: Goodenough J. B.
Published: July 2002

▪ Abstract  Jahn-Teller phenomena encountered in oxides are reviewed briefly. High-spin Mn(III) in an octahedral site illustrates an ion with twofold orbitally degenerate σ-bonding orbitals having a quenched orbital angular momentum; octahedral V(III) and high-spin Co(II), as well as tetrahedral high-spin Ni(II), are examples of ions with threefold orbitally degenerate π-bonding orbitals that retain orbital angular momentum. Cooperative local deformations that are static give rise, below a transition temperature Tt, to a lowering of the lattice symmetry, anisotropic interactions, and the possibility of a ferromagnetism that is oriented in opposition to a magnetic field applied on cooling through the transition. Dynamic local deformations can influence the physical properties of a solid in a variety of ways. Of special interest is the influence of dynamic deformations at a cross-over from localized to itinerant electronic behavior in a mixed-valent system.
MYOCARDIAL PRECONDITIONING PROMISES TO BE A NOVEL APPROACH TO THE TREATMENT OF ISCHEMIC HEART DISEASE
Authors: Cohen, M.D Michael V. , Downey, Ph.D James M.
Published: July 2002

▪ Abstract  In the phenomenon termed "ischemic preconditioning," a brief period of ischemia prior to a more prolonged one improves myocardial function (after reperfusion) and diminishes infarction. This phenomenon has been described extensively in experimental animals and now in humans. It is triggered by several agents released by ischemic cells and can be reproduced by infusion of agonists coupled to protein kinase C (PKC), e.g. adenosine, angiotensin, phenylephrine, bradykinin, and endothelin. The intracellular signaling pathway involves a phospholipase, either C or D, which metabolizes membrane phospholipids to produce diacylglycerol, a necessary endogenous cofactor for PKC activation. Which protein(s) is phosphorylated by PKC is not yet known, nor is the identity of the end-effector that actually mediates protection of the ischemic cell. Identification of the end-effector may make it possible in the routine treatment of patients with ischemic heart disease to precondition and thereby salvage ischemic myocardium and improve survival.
Clostridium difficile Infection
Authors: Kelly Ciarán P. , LaMont J. Thomas
Published: July 2002

Clostridium difficile infection is associated with broad-spectrum antibiotic therapy and is the most common cause of infectious diarrhea in hospital patients. Pathogenic strains of C. difficile produce two protein exotoxins, toxin A and toxin B, which cause colonic mucosal injury and inflammation. Infection may be asymptomatic, cause mild diarrhea, or result in severe pseudomembranous colitis. Diagnosis depends on the demonstration of C. difficile toxins in the stool. The first step in management is to discontinue the antibiotic that caused diarrhea. If diarrhea and colitis are severe or persistent, oral metronidazole is the treatment of choice. Oral vancomycin is also effective, but it is more expensive than metronidazole and its widespread use may encourage the proliferation of vancomycin-resistant nosocomial bacteria. Diarrhea and colitis usually improve within three days after a patient starts taking metronidazole or vancomycin, but 20% suffer a relapse of diarrhea when these agents are discontinued.
The Ubiquitin-Proteasome Pathway and Pathogenesis of Human Diseases
Authors: Schwartz, PhD, MD Alan L. , Ciechanover, MD, PhD Aaron
Published: July 2002

The ubiquitin-proteasome pathway plays a pivotal role in the degradation of short-lived and regulatory proteins important in a variety of basic cellular processes, including regulation of the cell cycle, modulation of cell surface receptors and ion channels, and antigen presentation. The pathway involves an enzymatic cascade through which multiple ubiquitin molecules are covalently attached to the protein substrate, which is then degraded by the 26S proteasome complex. The pathway has been implicated in several forms of malignancy, in the pathogenesis of several genetic diseases (including cystic fibrosis, Angelman's syndroome, and Liddle syndrome), in immune surveillance/viral pathogenesis, and in the pathology of muscle wasting. The molecular mechanisms that underlie these processes are being unraveled at present.
The Development of Genetic Tools for Dissecting the Biology of Malaria Parasites
Authors: de Koning-Ward Tania F. , Janse Chris J. , Waters Andrew P.
Published: July 2002

▪ Abstract  Plasmodium parasites are haploid unicellular organisms that cause malaria. In the last decade, transfection systems have been developed for both human and animal model species of Plasmodium, providing a broad range of genetic tools for the study of malaria parasite biology. Transient transfection has been used to provide insight into the regulation of gene expression by Plasmodium spp. The development of stable transfection technologies has provided the opportunity to express transgenes in Plasmodium spp., as well as elucidate the function of proteins by disrupting, modifying, or replacing the genes encoding them. These genetic tools represent an important breakthrough for malaria research and will significantly contribute to our understanding of the biology of the parasite. However, further developments in this technology are still required, especially because the full genome sequence of the major human malaria parasite Plasmodium falciparum will shortly be available. Ultimately, the biological information obtained through genetic manipulation of Plasmodium spp. will facilitate a more rational approach to vaccine and drug design.
CARRIER-MEDIATED MEMBRANE TRANSPORT OF FOLATES IN MAMMALIAN CELLS
Authors: Sirotnak F. M. , Tolner Berend
Published: July 2002

▪ Abstract  Mediated internalization of folates is required for cellular macromolecular biosynthesis. Multiple carrier-mediated mechanisms have been identified that can fulfill this role in a variety of mammalian cell types, including neoplastic cells, with and without proliferative potential. The absorption of dietary folates also relies on the function of a carrier-mediated system in mature luminal epithelium of small intestine. The various carrier-mediated systems can be distinguished by their preferences for various folate compounds as permeants as well as by differences in temperature and pH dependence. The widely studied one-carbon, reduced-folate transport system is mediated by a transporter encoded by the newly discovered RFC-1 (reduced-folate carrier) gene. The characteristics of this gene in rodent and human cells are similar, consistent with the close similarity between these species of folate transport mediated by this transporter. However, differences occur in the form of tissue-specific expression, alternate splicing, and 5′ end mRNA heterogeneity, as well as in promoter utilization regulating transcription. RFC-1 gene expression also appears to regulate luminal epithelial cell folate absorption in small intestine. However, the properties of RFC-1–mediated folate transport in these cells is anomalous when compared with that seen in nonabsorptive cell types. Detailed mechanisms as to the regulation of RFC-1 transcription are now emerging along with other information on structure and function of the transporter and its alteration following mutation.
CANNABINOID RECEPTORS AND THEIR ENDOGENOUS AGONISTS
Authors: Felder Christian C. , Glass Michelle
Published: July 2002

▪ Abstract  Marijuana has been in use for over 4000 years as a therapeutic and as a recreational drug. Within the past decade, two cannabinoid receptor types have been identified, their signal transduction characterized, and an endogenous lipid agonist isolated from mammalian tissues. The CB1 cannabinoid receptor is widely distributed in mammalian tissues, with the highest concentrations found in brain neurons. CB1 receptors are coupled to modulation of adenylate cyclase and ion channels. The CB2 receptor is found in cells of the immune system and is coupled to inhibition of adenylate cyclase. Both receptor types selectively bind Δ9-THC, the active principle in marijuana, and anandamide (arachidonylethanolamide), an endogenous cannabimimetic eicosanoid. Progress is being made in the development of novel agonists and antagonists with receptor subtype selectivity, mice with genetic deletion of the cannabinoid receptors, and receptor-specific antibodies, which should help in providing a better understanding of the physiological role of the cannabinoid receptors.
THEPHOTOPHYSICS OFSILVERHALIDEIMAGINGMATERIALS
Authors: Eachus Raymond S. , Marchetti Alfred P. , Muenter Annabel A.
Published: July 2002

▪ Abstract  Experimental and computational studies of photophysical processes in silver halide imaging materials are presented. Recent investigations that have refined our understanding of carrier recombination paths, exciton behavior, quantum confinement effects, and the structure and function of small surface silver clusters are detailed. The theory and mechanism of electron and hole injection from photoexcited surface-adsorbed dye molecules are outlined. The carrier trapping properties and subsequent photophysics of transition-metal dopant complexes are presented. Particular emphasis is given to the role of relaxation processes in electron and hole trapping events.
SPATIAL RELATIONSHIPS IN EARLY SIGNALING EVENTS OF FLOW-MEDIATED ENDOTHELIAL MECHANOTRANSDUCTION
Authors: Davies Peter F. , Barbee Kenneth A. , Volin Michael V. , Robotewskyj Andre , Chen Jai , Joseph Loren , Griem Melvin L. , Wernick Miles N. , Jacobs Elizabeth , Polacek Denise C. , DePaola Natacha , Barakat Abdul I.
Published: July 2002

▪ Abstract  Blood flow interactions with the vascular endothelium represent a specialized example of mechanical regulation of cell function that has important physiological and pathological cardiovascular consequences. The endothelial monolayer in vivo acts as a signal transduction interface for forces associated with flowing blood (hemodynamic forces) in the acute regulation of artery tone and chronic structural remodeling of arteries, including the pathology of atherosclerosis. Mechanisms related to spatial relationships at the cell surfaces and throughout the cell that influence flow-mediated endothelial mechanotransduction are discussed. In particular, flow-mediated ion channel activation and cytoskeletal dynamics are considered in relation to topographic analyses of the luminal and abluminal surfaces of living endothelial cells.
ELECTRICAL AND CALCIUM SIGNALING IN DENDRITES OF HIPPOCAMPAL PYRAMIDAL NEURONS
Authors: Magee Jeffrey , Hoffman Dax , Colbert Costa , Johnston Daniel
Published: July 2002

▪ Abstract  This review discusses recent data regarding the different types of voltage-gated Na+, Ca2+, and K+ channels in dendrites of CA1 pyramidal neurons and their function for synaptic integration and plasticity. Na+ and Ca2+ channels are uniformly distributed throughout the dendrites, although Na+ channels in the soma and proximal dendrites differ in their inactivation properties from Na+ channels in more distal regions. Also, different regions of the neuron express different subtypes of Ca2+ channels. K+ channels are unevenly distributed, with the distal dendrites expressing a more than fivefold greater density of a transient A-type K+ channel than proximal regions. These K+ channels exert profound control over the excitability of the pyramidal neurons and the spread of synaptic potentials throughout the dendrites. The ways in which the active properties of dendrites may contribute toward the induction and maintenance of long-term synaptic plasticity are discussed.
MICROBIAL ELICITORS AND THEIR RECEPTORS IN PLANTS
Authors: Hahn Michael G.
Published: July 2002

▪ Abstract  Elicitors are molecules that stimulate any of a number of defense responses in plants. Research over the past decade has focused on the mechanisms by which plant cells perceive and transduce these biological signals to activate defense responses. Of particular interest has been the identification of specific elicitor-binding proteins that might function as physiological receptors in the signal transduction cascade. The existence of specific high-affinity binding sites has been demonstrated for oligosaccharide, glycopeptide, and peptide elicitors, and candidate elicitor-binding proteins have been identified for several of them. The properties of these binding sites/proteins are consistent with those expected of physiologically important receptors, although experimental verification of the role of these binding proteins as receptors has not yet been obtained. The purification and characterization of specific elicitor-binding proteins is essential for a detailed understanding of the molecular basis for the signal exchange between plant hosts and microbial pathogens that leads to activation of host defenses.
CHANGING OPTIONS FOR THE CONTROL OF DECIDUOUS FRUIT TREE DISEASES
Authors: Sutton Turner B.
Published: July 2002

▪ Abstract  The evolution of disease management programs for deciduous fruit trees in the United States over the past 50 years has been influenced by factors that include public concern over pesticide residues on fruit and in the environment, the development of resistance of many important tree pathogens to fungicides and bactericides, the loss of fungicide registrations and restrictions on their use due to concern for human health and the environment and/or marketing decisions by the manufacturers, and changes in cultural practices and marketing objectives. These factors have led to wider use of forecasting models and cultural controls, the development of resistance management strategies, and the introduction of new equipment and methods for pesticide application. These same factors will most likely continue to drive the fruit industry to adopt disease management programs that rely less on pesticides in the future.
THE EVOLUTIONARY BIOLOGY OFFUSARIUM OXYSPORUM
Authors: Gordon T. R. , Martyn R. D.
Published: July 2002

▪ Abstract  Fusarium oxysporum is an anamorphic species that includes both pathogenic and nonpathogenic strains. Plant pathogenic forms cause a wilt disease and are grouped into formae speciales based on their host range; some are further subdivided into pathogenic races. Many formae speciales are comprised of multiple clonal lineages and, in some cases, a pathogenic race is associated with more than one clonal lineage, suggesting independent origins. Although some evidence suggests one pathogenic race may give rise to another, recent derivation of a pathogen from a nonpathogen has not been documented. Most new occurrences of Fusarium wilt appear to be the result of a recent introduction rather than an independent local origin of the pathotype. Asexual propagation is the dominant influence on population structure in F. oxysporum and the absence of sexual reproduction is not likely to prevent this pathogen from continuing to inflict significant damage on susceptible crop hosts.
MUSIC PERFORMANCE
Authors: Palmer Caroline
Published: July 2002

▪ Abstract  Music performance provides a rich domain for study of both cognitive and motor skills. Empirical research in music performance is summarized, with particular emphasis on factors that contribute to the formation of conceptual interpretations, retrieval from memory of musical structures, and transformation into appropriate motor actions. For example, structural and emotional factors that contribute to performers' conceptual interpretations are considered. Research on the planning of musical sequences for production is reviewed, including hierarchical and associative retrieval influences, style-specific syntactic influences, and constraints on the range of planning. The fine motor control evidenced in music performance is discussed in terms of internal timekeeper models, motor programs, and kinematic models. The perceptual consequences of music performance are highlighted, including the successful communication of interpretations, resolution of structural ambiguities, and concordance with listeners' expectations. Parallels with other domains support the conclusion that music performance is not unique in its underlying cognitive mechanisms.
THE SUGGESTIBILITY OF CHILDREN'S MEMORY
Authors: Bruck Maggie , Ceci Stephen J.
Published: July 2002

▪ Abstract  In this review, we describe a shift that has taken place in the area of developmental suggestibility. Formerly, studies in this area indicated that there were pronounced age-related differences in suggestibility, with preschool children being particularly susceptible to misleading suggestions. The studies on which this conclusion was based were criticized on several grounds (e.g. unrealistic scenarios, truncated age range). Newer studies that have addressed these criticisms, however, have largely confirmed the earlier conclusions. These studies indicate that preschool children are disproportionately vulnerable to a variety of suggestive influences. There do not appear to any strict boundary conditions to this conclusion, and preschool children will sometimes succumb to suggestions about bodily touching, emotional events, and participatory events. The evidence for this assertion is presented in this review.
Emotions, Morbidity, and Mortality: New Perspectives from Psychoneuroimmunology
Authors: Kiecolt-Glaser Janice K. , McGuire Lynanne , Robles Theodore F. , Glaser Ronald
Published: July 2002

▪ Abstract  Negative emotions can intensify a variety of health threats. We provide a broad framework relating negative emotions to a range of diseases whose onset and course may be influenced by the immune system; inflammation has been linked to a spectrum of conditions associated with aging, including cardiovascular disease, osteoporosis, arthritis, type 2 diabetes, certain cancers, Alzheimer's disease, frailty and functional decline, and periodontal disease. Production of proinflammatory cytokines that influence these and other conditions can be directly stimulated by negative emotions and stressful experiences. Additionally, negative emotions also contribute to prolonged infection and delayed wound healing, processes that fuel sustained proinflammatory cytokine production. Accordingly, we argue that distress-related immune dysregulation may be one core mechanism behind a large and diverse set of health risks associated with negative emotions. Resources such as close personal relationships that diminish negative emotions enhance health in part through their positive impact on immune and endocrine regulation.
CHEMOPREVENTION OF LUNG CANCER: The Rise and Demise of Beta-Carotene
Authors: Omenn Gilbert S.
Published: July 2002

▪ Abstract  Beta-carotene and retinoids were the most promising agents against common cancers when the National Cancer Institute mounted a substantial program of population-based trials in the early 1980s. Both major lung cancer chemoprevention trials not only showed no benefit, but had significant increases in lung cancer incidence and in cardiovascular and total mortality. A new generation of laboratory research has been stimulated.

Rational public health recommendations at this time include: 1. Five-A-Day servings of fruits and vegetables, a doubling of current mean intake; 2. systematic investigation of the covariates of extremes of fruit and vegetable intake; 3. discouragement of beta-carotene supplement use, due to adverse effects in smokers and no evidence of benefit in non-smokers; 4. multilevel research to develop and evaluate candidate chemoprevention agents to prevent lung and other common cancers; and 5. continued priority for smoking prevention, smoking cessation, and avoidance of known carcinogens in the environment.
Pharmacy Benefit Management Companies: Dimensions of Performance
Authors: Lipton Helene L. , Kreling David H. , Collins Ted , Hertz Karen C.
Published: July 2002

▪ Abstract  Research on pharmacy benefit management companies focuses on descriptive accounts of the organizations and the scope of their services. This review provides a critical analysis of publicly available research on contemporary issues surrounding the operations and effects of pharmacy benefit management companies. There has been very little systematic, empirical research on these issues; major questions concerning the impact of pharmacy benefit management companies on quality, costs, and patient outcomes remain unanswered. We analyze what is known and what needs to be known, and we explore major research challenges that lie ahead in the assessment of the pharmacy benefit management company's role in the health care system and in improving the public's health.
CULTURAL CRIMINOLOGY
Authors: Ferrell Jeff
Published: July 2002

▪ Abstract  As an emergent orientation in sociology, criminology, and criminal justice, cultural criminology explores the convergence of cultural and criminal processes in contemporary social life. Drawing on perspectives from cultural studies, postmodern theory, critical theory, and interactionist sociology, and on ethnographic methodologies and media/textual analysis, this orientation highlights issues of image, meaning, and representation in the interplay of crime and crime control. Specifically, cultural criminology investigates the stylized frameworks and experiential dynamics of illicit subcultures; the symbolic criminalization of popular culture forms; and the mediated construction of crime and crime control issues. In addition, emerging areas of inquiry within cultural criminology include the development of situated media and situated audiences for crime; the media and culture of policing; the links between crime, crime control, and cultural space; and the collectively embodied emotions that shape the meaning of crime.
Celiac Disease Associated With Autoimmune Myocarditis
Authors: Frustaci Andrea , Cuoco Lucio , Chimenti Cristina , Pieroni Maurizio , Fioravanti Giuseppina , Gentiloni Nicola , Maseri Attilio , Gasbarrini Giovanni
Published: July 2002

Background
—

Both celiac disease (CD) and myocarditis can be associated with systemic autoimmune disorders; however, the coexistence of the 2 entities has never been investigated, although its identification may have a clinical impact.

Methods and Results
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We screened the serum of 187 consecutive patients with myocarditis (118 males and 69 females, mean age 41.7±14.3 years) for the presence of cardiac autoantibodies, anti–tissue transglutaminase (IgA-tTG), and anti-endomysial antibodies (AEAs). IgA-tTG–positive and AEA-positive patients underwent duodenal endoscopy and biopsy and HLA analysis. Thirteen of the 187 patients were positive for IgA-tTG, and 9 (4.4%) of them were positive for AEA. These 9 patients had iron-deficient anemia and exhibited duodenal endoscopic and histological evidence of CD. CD was observed in 1 (0.3%) of 306 normal controls (
P
<0.003). In CD patients, myocarditis was associated with heart failure in 5 patients and with ventricular arrhythmias (Lown class III-IVa) in 4 patients. From histological examination, a lymphocytic infiltrate was determined to be present in 8 patients, and giant cell myocarditis was found in 1 patient; circulating cardiac autoantibodies were positive and myocardial viral genomes were negative in all patients. HLA of the patients with CD and myocarditis was DQ2-DR3 in 8 patients and DQ2-DR5(11)/DR7 in 1 patient. The 5 patients with myocarditis and heart failure received immunosuppression and a gluten-free diet, which elicited recovery of cardiac volumes and function. The 4 patients with arrhythmia, after being put on a gluten-free diet alone, showed improvement in the arrhythmia (Lown class I).

Conclusions
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A common autoimmune process toward antigenic components of the myocardium and small bowel can be found in >4% of the patients with myocarditis. In these patients, immunosuppression and a gluten-free diet can be effective therapeutic options.
Urban Identity in Medieval English Towns
Authors: Attreed Lorraine
Published: July 2002

Throughout the later Middle Ages, English towns continued to augment both their legal privileges and the physical spaces in which they exercised them. Urban officials struggled to define civic identity as distinct from the rural, noble, and ecclesiastical power that surrounded them. Four case studies from Exeter, Shrewsbury, Norwich, and York allow in-depth explorations to be made of the ways in which towns defined physical and juridical space through lawsuits. The disputes and their pursuit before the law show clearly how urban space impacted territorial, legal, and ethnic identity in late medieval society.
Information Structure and the Syntax-Phonology Interface
Authors: Steedman Mark
Published: July 2002

The article proposes a theory of grammar relating syntax, discourse semantics, and intonational prosody. The full range of English intonational tunes distinguished by Beckman and Pierrehumbert (1986) and their semantic interpretation in terms of focus and information structure are discussed, including “discontinuous” themes and rhemes. The theory extends an earlier account based on Combinatory Categorial Grammar, which directly pairs phonological and logical forms without intermediary representational levels.
A Neural Model of Smooth Pursuit Control and Motion Perception by Cortical Area MST
Authors: Pack Christopher , Grossberg Stephen , Mingolla Ennio
Published: July 2002

Smooth pursuit eye movements (SPEMs) are eye rotations that are used to maintain fixation on a moving target. Such rotations complicate the interpretation of the retinal image, because they nullify the retinal motion of the target, while generating retinal motion of stationary objects in the background. This poses a problem for the oculomotor system, which must track the stabilized target image while suppressing the optokinetic reflex, which would move the eye in the direction of the retinal background motion (opposite to the direction in which the target is moving). Similarly, the perceptual system must estimate the actual direction and speed of moving objects in spite of the confounding effects of the eye rotation. This paper proposes a neural model to account for the ability of primates to accomplish these tasks. The model simulates the neurophysiological properties of cell types found in the superior temporal sulcus of the macaque monkey, specifically the medial superior temporal (MST) region. These cells process signals related to target motion, background motion, and receive an efference copy of eye velocity during pursuit movements. The model focuses on the interactions between cells in the ventral and dorsal subdivisions of MST, which are hypothesized to process target velocity and background motion, respectively. The model explains how these signals can be combined to explain behavioral data about pursuit maintenance and perceptual data from human studies, including the Aubert-Fleischl phenomenon and the Filehne Illusion, thereby clarifying the functional significance of neurophysiological data about these MST cell properties. It is suggested that the connectivity used in the model may represent a general strategy used by the brain in analyzing the visual world.
Interference with Performance of a Response Selection Task that has no Working Memory Component: An rTMS Comparison of the Dorsolateral Prefrontal and Medial Frontal Cortex
Authors: Hadland K. A. , Rushworth M. F. S. , Passingham R. E. , Jahanshahi M. , Rothwell J. C.
Published: July 2002

It has been suggested that the dorsolateral prefrontal cortex (DLPFC) is involved in free selection (FS), the process by which subjects themselves decide what action to perform. Evidence for this proposal has been provided by imaging studies showing activation of the DLPFC when subjects randomly generate responses. However, these response selection tasks have a hidden working memory element and it has been widely reported that the DLPFC is activated when subjects perform tasks which involve working memory. The primary aim of this experiment was to establish if the DLPFC is genuinely involved in response selection. We used repetitive transcranial magnetic stimulation (rTMS) to investigate whether temporary interference of the DLPFC could disrupt performance of a response selection task that had no working memory component. Subjects performed tasks in which they made bimanual sequences of eight nonrepeating finger movements. In the FS task, subjects chose their movements at random while a computer monitor displayed these moves. This visual feedback obviated the need for subjects to maintain their previous moves “on-line.” No selection was required for the two control tasks as responses were cued by the visual display. The attentional demands of the control tasks varied. In the high load (HL) version, subjects had to maintain their attention throughout the sequence, but this requirement was absent in the low load (LL) task. rTMS over the DLPFC slowed response times on the FS task and at the end of the sequence on the HL task, but had no effect on the LL task. rTMS over the medial frontal cortex (MFC) slowed response times on the FS task but had no effect on the HL task. This suggests that a response selection task without a working memory load will depend on the DLPFC and the MFC. The difference appears to be that the DLPFC is important when selecting between competing responses or when concentrating if there is a high attentional demand, but that the MFC is only important during the response selection task.
Emotion and Attention Interaction Studied through Event-Related Potentials
Authors: Carretié Luis , Martín-Loeches Manuel , Hinojosa José Antonio , Mercado Francisco
Published: July 2002

Several studies on hemodynamic brain activity indicate that emotional visual stimuli elicit greater activation than neutral stimuli in attention-related areas such as the anterior cingulate cortex (ACC) and the visual association cortex (VAC). In order to explore the temporo-spatial characteristics of the interaction between attention and emotion, two processes characterized by involving short and rapid phases, event-related potentials (ERPs) were measured in 29 subjects using a 60-electrode array and the LORETA source localization software. A cue/target paradigm was employed in order to investigate both expectancy-related and input processing related attention. Four categories of stimuli were presented to subjects: positive arousing, negative arousing, relaxing, and neutral. Three attention-related components were finally analyzed: N280pre (from pretarget ERPs), P200post and P340post (both from posttarget ERPs). N280pre had a prefrontal focus (ACC and/or medial prefrontal cortex) and presented significantly lower amplitudes in response to cues announcing negative targets. This result suggests a greater capacity of nonaversive stimuli to generate expectancy-related attention. P200post and P340post were both elicited in the VAC, and showed their highest amplitudes in response to negative- and to positive-arousing stimuli, respectively. The origin of P200post appears to be located dorsally with respect to the clear ventral-stream origin of P340post. The conjunction of temporal and spatial characteristics of P200post and P340post leads to the deduction that input processing-related attention associated with emotional visual stimulation involves an initial, rapid, and brief ‘early’ attentional response oriented to rapid motor action, being more prominent towards negative stimulation. This is followed by a slower but longer ‘late’ attentional response oriented to deeper processing, elicited to a greater extent by appetitive stimulation.
A Cortico-Spinal Model of Reaching and Proprioception under Multiple Task Constraints
Authors: Cisek Paul , Grossberg Stephen , Bullock Daniel
Published: July 2002

A model of cortico-spinal trajectory generation for voluntary reaching movements is developed to functionally interpret a broad range of behavioral, physiological, and anatomical data. The model simulates how arm movements achieve their remarkable efficiency and accuracy in response to widely varying positional, speed, and force constraints. A key issue in arm movement control is how the brain copes with such a wide range of movement contexts. The model suggests how the brain may set automatic and volitional gating mechanisms to vary the balance of static and dynamic feedback information to guide the movement command and to compensate for external forces. For example, with increasing movement speed, the system shifts from a feedback position controller to a feedforward trajectory generator with superimposed dynamics compensation. Simulations of the model illustrate how it reproduces the effects of elastic loads on fast movements, endpoint errors in Coriolis fields, and several effects of muscle tendon vibration, including tonic and antagonist vibration reflexes, position and movement illusions, effects of obstructing the tonic vibration reflex, and reaching undershoots caused by antagonist vibration.
A Computational Model of How the Basal Ganglia Produce Sequences
Authors: Berns Gregory S. , Sejnowski Terrence J.
Published: July 2002

We propose a systems-level computational model of the basal ganglia based closely on known anatomy and physiology. First, we assume that the thalamic targets, which relay ascending information to cortical action and planning areas, are tonically inhibited by the basal ganglia. Second, we assume that the output stage of the basal ganglia, the internal segment of the globus pallidus (GPi), selects a single action from several competing actions via lateral interactions. Third, we propose that a form of local working memory exists in the form of reciprocal connections between the external globus pallidus (GPe) and the subthalamic nucleus (STN). As a test of the model, the system was trained to learn a sequence of states that required the context of previous actions. The striatum, which was assumed to represent a conjunction of cortical states, directly selected the action in the GP during training. The STN-to-GP connection strengths were modified by an associative learning rule and came to encode the sequence after 20 to 40 iterations through the sequence. Subsequently, the system automatically reproduced the sequence when cued to the first action. The behavior of the model was found to be sensitive to the ratio of the striatal-nigral learning rate to the STN-GP learning rate. Additionally, the degree of striatal inhibition of the globus pallidus had a significant influence on both learning and the ability to select an action. Low learning rates, which would be hypothesized to reflect low levels of dopamine, as in Parkinson's disease, led to slow acquisition of contextual information. However, this could be partially offset by modeling a lesion of the globus pallidus that resulted in an increase in the gain of the STN units. The parameter sensitivity of the model is discussed within the framework of existing behavioral and lesion data.
Blindsight in Subjects with Homonymous Visual Field Defects
Authors: Schärli Heinz , Harman Alison M. , Hogben John H.
Published: July 2002

Brain damage in the visual system can lead to apparently blind visual areas. However, more elaborate testing indicates that some visual ability may still exist for specific stimuli in the otherwise blind regions. This phenomenon is called “blindsight” if subjects report no conscious awareness of visual stimuli but when forced to guess, nevertheless perform better than chance. It has mainly been suggested that secondary visual pathways are responsible for this phenomenon. However, no published study has clearly shown the neural mechanism responsible for blindsight. Furthermore, experimental artifacts may have been responsible for the appearance of the phenomenon in some subjects. In the present study, the visual fields of nine subjects were mapped and residual visual performance was examined in many areas using three different experimental procedures. Artifacts such as stray light or eye movements were well controlled. In addition, confidence ratings were required after each trial in the forced-choice tests. The results show that only one subject with a lesion in the optic radiation had blindsight in two discrete areas of the affected visual field. Spared optic radiation fibers of the main (primary) geniculo-striate visual pathway were most likely to account for this finding.
“What”—Then—“Where” in Visual Working Memory: An Event-Related fMRI Study
Authors: Postle Bradley R. , D'Esposito Mark
Published: July 2002

Behavioral studies indicate that spatial and object working memory are computed by dissociable subsystems. We investigated the neural bases of this dissociation with a whole-brain fMRI design and analysis technique that permitted direct assessment of delay-period activity, uncontaminated by other components of the trial. The task employed a “what”-then-“where” design, with an object and a spatial delay period incorporated in each trial; within-trial order of delay conditions was balanced across each scan. Our experiment failed to find evidence, at the single-subject level and at the group level, for anatomical segregation of spatial and object working memory function in the frontal cortex. Delay-period activity in the caudate nucleus revealed a sensitivity to position in the trial in the spatial, but not the object, condition. In posterior regions, spatial delay-period activity was associated with preferential recruitment of extrastriate areas falling within Brodmann's area 19 and, less reliably, the superior parietal lobule. Object-specific delay-period activity was found predominantly in ventral regions of the posterior cortex and demonstrated more topographic variability across subjects than did spatial working memory activity.
National Erotica, The Politics of “Traditional” Dance in Tanzania
Authors: Edmondson Laura
Published: July 2002

In Tanzania, a tension exists between the persistence of the “primi-tive” and “erotic” stereotype of African performance and the emergent means of representing culture and gender on the dance stage. This tension leads to a complex process of inventing, counterinventing, and reinventing tradition.
Single-Point Active Alignment Method (SPAAM) for Optical See-Through HMD Calibration for Augmented Reality
Authors: Tuceryan Mihran , Genc Yakup , Navab Nassir
Published: July 2002

Augmented reality (AR) is a technology in which a user's view of the real world is enhanced or augmented with additional information generated from a computer model. To have a working AR system, the see-through display system must be calibrated so that the graphics are properly rendered. The optical see-through systems present an additional challenge because, unlike the video see-through systems, we do not have direct access to the image data to be used in various calibration procedures.

This paper reports on a calibration method we developed for optical see-through headmounted displays. We first introduce a method for calibrating monocular optical seethrough displays (that is, a display for one eye only) and then extend it to stereo optical see-through displays in which the displays for both eyes are calibrated in a single procedure. The method integrates the measurements for the camera and a six-degrees-offreedom tracker that is attached to the camera to do the calibration. We have used both an off-the-shelf magnetic tracker as well as a vision-based infrared tracker we have built. In the monocular case, the calibration is based on the alignment of image points with a single 3D point in the world coordinate system from various viewpoints. In this method, the user interaction to perform the calibration is extremely easy compared to prior methods, and there is no requirement for keeping the head immobile while performing the calibration. In the stereo calibration case, the user aligns a stereoscopically fused 2D marker, which is perceived in depth, with a single target point in the world whose coordinates are known. As in the monocular case, there is no requirement that the user keep his or her head fixed.
Implementation and Evaluation of “Just Follow Me”: An Immersive, VR-Based, Motion-Training System
Authors: Yang Ungyeon , Kim Gerard Jounghyun
Published: July 2002

Training is usually regarded as one of the most natural application areas of virtual reality (VR). To date, most VR-based training systems have been situation based, but this paper examines the utility of VR for a different class of training: learning to execute exact motions, which are often required in sports and the arts. In this paper, we propose an interaction method, called Just Follow Me (JFM), that uses an intuitive “ghost” metaphor and a first-person viewpoint for effective motion training. Using the ghost metaphor (GM), JFM visualizes the motion of the trainer in real time as a ghost (initially superimposed on the trainee) that emerges from one's own body. The trainee who observes the motion from the first-person viewpoint “follows” the ghostly master as closely as possible to learn the motion. Our basic hypothesis is that such a VR system can help a student learn motion effectively and quickly, comparably to the indirect real-world teaching methods. Our evaluation results show that JFM produces training and transfer effects as good as—and, in certain situations, better than—in the real world. We believe that this is due to the more direct and correct transfer of proprioceptive information from the trainer to the trainee.
Locus of User-Initiated Control in Virtual Environments: Influences on Cybersickness
Authors: Stanney Kay M. , Hash Phillip
Published: July 2002

Cybersickness is a pervasive and deleterious effect of human-virtual environment interaction. This paper applies motion-sickness adaptation theory to cybersickness in virtual environments to determine if the degree of user-initiated control can suppress sickness. It is suggested that if users are allowed some level of control over their movement within a virtual environment, cybersickness will not be as severe as that resulting from an enviornment in which users must follow a predetermined (i.e., scripted) path of movement. While past motion-sickness studies have examined control versus no control, the present study focuses on modifying the level of user-initiated control such that it matches the needs of the task characteristics while minimizing sickness. The degree of user sickness was tested under passive, active, and active-passive control scenarios. As measured by the Simulator Sickness Questionnaire, the active (i.e., complete control) condition reduced the severity of the symptoms experienced as compared to the passive (i.e., no control) condition, but did not do so as completely as the active-passive (i.e., coupled control) condition. The implication is that the level of user-initiated control can be manipulated to modify the deleterious effects of human-virtual environment interaction.
BEFORE THE IMF: THE ECONOMIC IMPLICATIONS OF UNINTENTIONAL STRUCTURAL ADJUSTMENT IN ANCIENT EGYPT
Authors: Warburton David
Published: July 2002

Debate about states and markets in the Bronze Age world has directed attention away from their roles and thus away from the way these economies functioned. The ancient Egyptian state assigned fields to its dependents and stimulated demand by spending and taxation. Markets and market forces were responsible for the allocation and distribution of materials in the ancient Near East from the end of the third millennium. Growth did not result from technological improvement or market competition so much as from demand stimulus, as in the modern world, suggesting that demand is more important than supply.
INDIC IMPETUS? INNOVATIONS IN TEXTILE USAGE IN ANGKORIAN PERIOD CAMBODIA
Authors: Green Gillian
Published: July 2002

Detailed analysis of Khmer costumes and textiles on sculpted images of the Angkorian period reveals a wealth of styles and usages. Vocabulary from contemporaneous inscriptions supplements this information. It is argued that Khmer costume and textile usage at this time was influenced principally by contact with India's culture, the stimulus not only of stylistic innovations and but also the main source of textiles with which to create them.