bluuebunny/crossref_metadata_2025 huggingface dataset:
Cancer Gene Therapy: Scientific Basis
Authors: Wadhwa Punit D. , Zielske Steven P. , Roth Justin C. , Ballas Christopher B. , Bowman Janice E. , Gerson Stanton L.
Published: July 2002

▪ Abstract  Gene therapy of cancer has been one of the most exciting and elusive areas of therapeutic research in the past decade. Critical developments have occurred in gene therapy targeting cancer cells, cancer vasculature, the immune system, and the bone marrow, itself often the target for severe toxicity from therapeutic agents. We review some recent developments in the field. In each instance, clear preclinical models validated the therapeutic approach and efforts have been made to evaluate the target impact in both preclinical and early clinical trials. Although no cures can consistently be expected from today's cancer gene therapy, the rapid progress may imply that such cures are a few short years away.
LANTIBIOTICS: Biosynthesis and Biological Activities of Uniquely Modified Peptides from Gram-Positive Bacteria
Authors: Sahl Hans-Georg , Bierbaum Gabriele
Published: July 2002

▪ Abstract  A plethora of novel gene-encoded antimicrobial peptides from animals, plants and bacteria has been described during the last decade. Many of the bacterial peptides possess modified building blocks such as thioethers and thiazoles or unsaturated and stereoinverted amino acids, which are unique among ribosomally made peptides. Genetic and biochemical studies of many of these peptides, mostly the so-called lantibiotics, have revealed the degree to which cells are capable of transforming peptides by posttranslational modification. The biosynthesis follows a general scheme: Precursor peptides are first modified and then proteolytically activated; the latter may occur prior to, concomitantly with or after export from the cell. The genes for the biosynthetic machinery are organized in clusters and include information for the antibiotic prepeptide, the modification enzymes and accessory functions such as dedicated proteases and ABC transporters as well as immunity factors and regulatory proteins. These fundamental aspects are discussed along with the biotechnological potential of the peptides and of the biosynthesis enzymes, which could be used for construction of novel, peptide-based biomedical effector molecules.
The Induction of Apoptosis by Bacterial Pathogens
Authors: Weinrauch Yvette , Zychlinsky Arturo
Published: July 2002

▪ Abstract  Apoptosis is a highly regulated process of cell death that is required for the development and homeostasis of multicellular organisms. In contrast to necrosis, apoptosis eliminates individual cells without inducing an inflammatory response. Activation or prevention of cell death could be a critical factor in the outcome of an infection. Programmed cell death has been observed as a response to infection by a wide range of animal and plant pathogens and is mediated by an array of pathogen-encoded virulence determinants. Pathogen-induced modulation of the host cell-death pathway may serve to eliminate key immune cells or evade host defenses that can act to limit the infection. Alternatively, suppression of the death pathway may facilitate the proliferation of intracellular pathogens.
Giant Viruses Infecting Algae
Authors: Van Etten James L. , Meints Russel H.
Published: July 2002

▪ Abstract  Paramecium bursaria chlorella virus (PBCV-1) is the prototype of a family of large, icosahedral, plaque-forming, double-stranded–DNA-containing viruses that replicate in certain unicellular, eukaryotic chlorella-like green algae. DNA sequence analysis of its 330, 742-bp genome leads to the prediction that this phycodnavirus has 376 protein-encoding genes and 10 transfer RNA genes. The predicted gene products of ∼40% of these genes resemble proteins of known function. The chlorella viruses have other features that distinguish them from most viruses, in addition to their large genome size. These features include the following: (a) The viruses encode multiple DNA methyltransferases and DNA site-specific endonucleases; (b) PBCV-1 encodes at least part, if not the entire machinery to glycosylate its proteins; (c) PBCV-1 has at least two types of introns—a self-splicing intron in a transcription factor–like gene and a splicesomal processed type of intron in its DNA polymerase gene. Unlike the chlorella viruses, large double-stranded–DNA-containing viruses that infect marine, filamentous brown algae have a circular genome and a lysogenic phase in their life cycle.
Adaptation in Hair Cells
Authors: Eatock Ruth Anne
Published: July 2002

Hair cells adapt to sustained deflections of the hair bundle via Ca2+dependent negative feedback on the open probability of the mechanosensitive transduction channels. A model posits that adaptation relieves the input to the transduction channels—force applied by elastic tip links between stereocilia—by repositioning the insertions of the links in the stereocilium. The tip link insertion and transduction channel are dragged by myosins moving on the stereocilium’s actin core. This model accounts for many aspects of adaptation in hair cells of the frog saccule, where adaptation time constants are tens of milliseconds. Adaptation in hair cells of the turtle cochlea is much faster, possibly reflecting a more direct mechanism such as Ca2+ binding to the transduction channel. Adaptation mechanisms attenuate the transduction current at low frequencies and may be tuned to different corner frequencies according to the stimulus demands of the inner ear organ. Other sites of adaptation in the inner ear include accessory structures, voltage-dependent properties of hair cells, and afferent transmitter release. A remaining challenge is to understand how these processes work together to shape the output of the inner ear to natural stimuli.
INSIGHTS INTO PROTEIN FOLDING FROM NMR
Authors: Dyson H. Jane , Wright Peter E.
Published: July 2002

▪ Abstract  NMR has emerged as an important tool for studies of protein folding because of the unique structural insights it can provide into many aspects of the folding process. Applications include measurements of kinetic folding events and structural characterization of folding intermediates, partly folded states, and unfolded states. Kinetic information on a time scale of milliseconds or longer can be obtained by real-time NMR experiments and by quench-flow hydrogen-exchange pulse labeling. Although NMR cannot provide direct information on the very rapid processes occurring during the earliest stages of protein folding, studies of isolated peptide fragments provide insights into likely protein folding initiation events. Multidimensional NMR techniques are providing new information on the structure and dynamics of protein folding intermediates and both partly folded and unfolded states.
OH-H2ENTRANCE CHANNEL COMPLEXES
Authors: Loomis Richard A. , Lester Marsha I.
Published: July 2002

▪ Abstract  The entrance channel to the OH + H2→ H2O + H hydrogen abstraction reaction has been investigated from several different experimental approaches and complementary theoretical calculations. Weakly bound complexes between the hydroxyl radical and molecular hydrogen have been stabilized within a shallow well in the entrance channel and characterized via electronic spectroscopy on the OH A2Σ+− X2Π transition. Laser-induced fluorescence and fluorescence depletion experiments have revealed the binding energy of H2/D2with ground state OH X2Π radicals, the intermolecular energy levels supported by the OH A2Σ+(v′ = 0,1) + H2/D2potential, and the OH-H2/D2excited state dissociation limit. The OH X2Π + H2potentials have also been examined through inelastic scattering measurements on Λ-doublet state–selected OH with normal or para-H2. Finally, photodetachment of an electron from the H3O−anion enabled the neutral reaction to be probed in conformations sampled by the two isomeric forms of the anion.
TIME-DEPENDENTQUANTUMMETHODS FORLARGESYSTEMS
Authors: Makri Nancy
Published: July 2002

▪ Abstract  This review focuses on time-dependent methods suitable for simulating the quantum dynamics of processes in large clusters and condensed-phase environments. A number of mean field, quantum-classical, and quantum statistical approximations that avoid the conventional exponential scaling with the number of degrees of freedom are reviewed. In addition, rigorous semiclassical and path integral approaches are described that are feasible in certain physical situations. Select chemical applications illustrating the capabilities of these methods are discussed.
Large-Scale Shape Changes in Proteins and Macromolecular Complexes
Authors: Wall Michael E. , Gallagher Stephen C. , Trewhella Jill
Published: July 2002

Proteins and RNA undergo intricate motions as they carry out functions in biological systems. These motions frequently entail large-scale conformational changes that induce changes in the surface structure, or shape, of a molecule. This review describes the experimental characterization of large-scale shape changes in proteins and macromolecular complexes and the effects of such changes on macromolecular behavior. We describe several important results that have been obtained by using small-angle scattering, which is emerging as a powerful technique for determining macromolecular shapes and elucidating the quaternary structure of macromolecular assemblies.
Mechanisms Underlying the Cost of Living in Animals
Authors: Hulbert A. J. , Else Paul Lewis
Published: July 2002

▪ Abstract  The cost of living can be measured as an animal’s metabolic rate. Basal metabolic rate (BMR) is factorially related to other metabolic rates. Analysis of BMR variation suggests that metabolism is a series of linked processes varying in unison. Membrane processes, such as maintenance of ion gradients, are important costs and components of BMR. Membrane bilayers in metabolically active systems are more polyunsaturated and less monounsaturated than metabolically less-active systems. Such polyunsaturated membranes have been proposed to result in an increased molecular activity of membrane proteins, and in this manner the amount of membrane and its composition can act as a pacemaker for metabolism. The potential importance of membrane acyl composition in metabolic depression, hormonal control of metabolism, the evolution of endothermy, as well as its implications for lifespan and human health, are briefly discussed.
Psychology and International Relations Theory
Authors: Goldgeier J. M. , Tetlock P. E.
Published: July 2002

Organized around several major theoretical traditions in international relations, this essay suggests which literature in psychology should be of greatest interest to different kinds of international relations scholars. New work in cognitive social psychology and behavioral decision theory simultaneously expands on and qualifies earlier error-and-bias portraits of the foreign policy maker, thereby enriching our understanding of internal divisions within the realist camp. Work on bounded rationality in competitive markets and mixed-motive games, as well as the literature on the power of human emotions to shape judgments of what represents an equitable allocation of scarce resources or a just resolution of conflicts of interest, can inform neo-institutionalist and constructivist theories. Developments in cross-cultural social psychology shed light on constructivist arguments about the creation and maintenance of international social order that typically rest on assumptions about decision making that are qualitatively different from realist and institutionalist approaches to world politics.
ORGANIZATIONAL BEHAVIOR IN THE NEW ORGANIZATIONAL ERA
Authors: Rousseau Denise M.
Published: July 2002

▪ Abstract  Changes in contemporary firms and their competitive environments translate into a new focus in organizational research. This chapter reviews organizational behavior research reflecting the shift from corporatist organizations to organizing. Key research themes include emerging employment relations, managing the performance paradox, goal setting and self-management, discontinuous information processing, organization learning, organizational change and individual transitions, and the implications of change for work-nonwork relations. Research into organizing is building upon and extending many of the field's traditional concepts. This chapter suggests that some assumptions of organizational behavior research are being superseded by those more responsive to the new organizational era.
LIFESPAN PSYCHOLOGY: Theory and Application to Intellectual Functioning
Authors: Baltes Paul B. , Staudinger Ursula M. , Lindenberger Ulman
Published: July 2002

▪ Abstract  The focus of this review is on theory and research of lifespan (lifespan developmental) psychology. The theoretical analysis integrates evolutionary and ontogenetic perspectives on cultural and human development across several levels of analysis. Specific predictions are advanced dealing with the general architecture of lifespan ontogeny, including its directionality and age-differential allocation of developmental resources into the three major goals of developmental adaptation: growth, maintenance, and regulation of loss. Consistent with this general lifespan architecture, a meta-theory of development is outlined that is based on the orchestrated and adaptive interplay between three processes of behavioral regulation: selection, optimization, and compensation. Finally, these propositions and predictions about the general nature of lifespan development are examined and supported by empirical evidence on the development of cognition and intelligence across the life span.
Sleep-Wake as a Biological Rhythm
Authors: Lavie P.
Published: July 2002

▪ Abstract  Evidence that the sleep-wake rhythm is generated endogenously has been provided by studies employing a variety of experimental paradigms such as sleep deprivation, sleep displacement, isolating subjects in environments free of time cues, or imposing on subjects sleep-wake schedules widely deviating from 24 hours. The initial observations obtained in isolated subjects revealed that the period of the endogenous circadian pacemaker regulating sleep is of approximately 25 hours. More recent studies, however, in which a more rigorous control of subjects' behavior was exerted, particularly over lighting conditions, have shown that the true periodicity of the endogenous pacemaker deviates from 24 hours by a few minutes only. Besides sleep propensity, the circadian pacemaker has been shown to regulate sleep consolidation, sleep stage structure, and electroencephalographic activities. The pattern of light exposure throughout the 24 hours appears to participate in the entrainment of the circadian pacemaker to the geophysical day-night cycle. Melatonin, the pineal hormone produced during the dark hours, participates in communicating both between the environmental light-dark cycle and the circadian pacemaker, and between the circadian pacemaker and the sleep-wake-generating mechanism. In contrast to prevailing views that have placed great emphasis on homeostatic sleep drive, recent data have revealed a potent circadian cycle in the drive for wakefulness, which is generated by the suprachiasmatic nucleus. This drive reaches a peak during the evening hours just before habitual bedtime.
Water Reclamation and Unrestricted Nonpotable Reuse: A New Tool in Urban Water Management
Authors: Okun Daniel A.
Published: July 2002

▪ Abstract  Growing urbanization accompanying growing population is increasing the demand for water supply in communities throughout the world. Water resources for many cities are already proving inadequate. Additional water resources are inherently more costly and are often not available because other communities and/or land owners have the water rights. Although conservation, particularly through demand management, may delay the need for additional sources for a short period, the need is inevitable. One approach that has been found to provide substantial additional water for communities is the reclamation of wastewaters produced by the communities themselves for unrestricted nonpotable purposes, such as for landscape and market crop irrigation, industry, cooling towers, air conditioning, toilet flushing, construction, vehicle washing, and environmental enhancement. This is done by providing dual distribution systems.

Nonpotable reuse is already widely practiced despite the fact that the reclaimed water distribution systems needed to be installed in existing communities. Inasmuch as additional water is needed for growing populations, the costs would be substantially reduced if the two systems were to be built at the same time in the newly developing areas. Reuse of reclaimed water for potable purposes may be feasible, but it imposes added public health risks that need to be accepted only as a last resort.
The Future of Benefit-Cost Analyses of the Clean Air Act
Authors: Krupnick Alan , Morgenstern Richard
Published: July 2002

▪ Abstract  This review examines the first two studies conducted pursuant to a Congressional mandate that the U.S. Environmental Protection Agency analyze the effects of the Clean Air Act on the “public health, economy, and the environment of the United States.” While these studies indicate that overall, the nation received good value for the resources it invested in improving air quality over the past three decades, we don't know if even higher value could have been obtained by changing or eliminating certain potentially inefficient elements. The review focuses on the critical policy and technical choices made in the analyses, including the selection of the appropriate baseline and the level of disaggregation for the studies. It is proposed that a potential third analysis focus on potential new policies not yet mandated by law or regulation. It is also proposed that the next study fill in key information gaps, expand the benefit categories, and incorporate new research on topics such as mortality and morbidity benefits, cost uncertainties, and others.
Breakdown Theories of Collective Action
Authors: Useem Bert
Published: July 2002

Historically, breakdown theory dominated the sociological study of collective action. In the 1970s, this theory was found to be increasingly unable to account for contemporaneous events and newly discovered historical facts. Resource mobilization theory displaced breakdown theory as the dominant paradigm. Yet the evidence against breakdown theory is weak once a distinction is made between routine and nonroutine collective action. Several recent contributions affirm the explanatory power of breakdown theory for nonroutine collective action. Breakdown theory also contributes to an understanding of the use of governmental force against protest and of the moral features of collective action. Breakdown and resource mobilization theories explain different types of phenomena, and both are needed to help account for the full range of forms of collective action.
Race and Race Theory
Authors: Winant Howard
Published: July 2002

Race has always been a significant sociological theme, from the founding of the field and the formulation of classical theoretical statements to the present. Since the nineteenth century, sociological perspectives on race have developed and changed, always reflecting shifts in large-scale political processes. In the classical period, colonialism and biologistic racism held sway. As the twentieth century dawned, sociology came to be dominated by US-based figures. DuBois and the Chicago School presented the first notable challenges to the field's racist assumptions. In the aftermath of World War II, with the destruction of European colonialism, the rise of the civil rights movement, and the surge in migration on a world scale, the sociology of race became a central topic. The field moved toward a more critical, more egalitarian awareness of race, focused particularly on the overcoming of prejudice and discrimination. Although the recognition of these problems increased and political reforms made some headway in combatting them, racial injustice and inequality were not surmounted. As the global and domestic politics of race entered a new period of crisis and uncertainty, so too has the field of sociology. To tackle the themes of race and racism once again in the new millennium, sociology must develop more effective racial theory. Racial formation approaches can offer a starting point here. The key tasks will be the formulation of a more adequate comparative historical sociology of race, the development of a deeper understanding of the micro-macro linkages that shape racial issues, and the recognition of the pervasiveness of racial politics in contemporary society. This is a challenging but also exciting agenda. The field must not shrink from addressing it.
Family, State, and Child Well-Being
Authors: McLanahan Sara
Published: July 2002

Sociologists have long recognized the importance of the family in social mobility and in the reproduction of poverty (Featherman & Hauser 1978, McLanahan & Sandefur 1994). More recently, they have begun to study the role of the state in these processes (Skocpol 1992, O’Connor et al 1999). Children depend on their parents to provide them with the resources they need to develop into healthy and successful adults. Parents, in turn, depend on their communities and on government to share the costs of raising children. Changes that undermine children’s claims on parental resources or parents’ claims on public resources are likely to have long-term negative consequences for society. As we enter the twenty-first century, two such changes are underway—an increase in nonmarital childbearing and a restructuring of the welfare state. Nonmarital childbearing, a trend that now affects one of three children born in the United States, undermines children’s claims on fathers’ resources (time and money). Welfare reform, which curtails welfare benefits and strengthens child support enforcement, undermines the claims of poor parents on public resources. These changes disproportionately affect families at the lower end of the income distribution, who have the highest rates of nonmarital childbearing and welfare receipt.

In order to assess the full impact of these changes in the family and the state, sociologists need answers to several questions. First, they need to know more about the capabilities of the men and women who bear children outside marriage, especially the fathers. Second, they need a better understanding of the relationship between unwed parents and between parents and children. And third, they need to understand how welfare and child support policies affect parents’ relationships
Dosimetric Measurements in Isolated Human Coronary Arteries
Authors: Hanefeld Christoph , Amirie Schgofa , Borchardt Dieter , Grewe Peter , Müller K.-M. , Kissler Maria , Mügge Andreas
Published: July 2002

Background

—

Intravascular brachytherapy is being applied more and more in patients with coronary artery disease for the prevention of restenosis subsequent to balloon angioplasty, in particular after stent implantation. Several radiation sources (β- and γ-emitters) are available in clinical routine. It was the purpose of this study to compare the radiation doses at the level of the adventitia in diseased and stented human coronary arteries for
192
Ir and
90
Sr/Y emitters in routine use. In contrast to previously published work, we performed dosimetry instead of calculating depth-dose distribution by use of the Monte Carlo system.

Methods and Results

—

Postmortem calcified human coronary artery segments were stented and placed in an organ bath. Commercially available γ-emitters (
192
Ir; Cordis Checkmate) and β-emitters (
90
Sr/Y; Novoste Beta-Cath) were used. Relative dose distributions along the adventitia were measured by a specially designed scintillation detector system. Whereas dose perturbations caused by stents and calcified plaque were negligible for the
192
Ir source, radiation from the beta source was significantly impaired (as much as 40%) at the level of the adventitia (3.0-mm vessel diameter). Dose perturbation was clearly dependent on the extent and severity of calcification, less affected by stent material.

Conclusions

—

Dose perturbation caused by calcified plaque and metallic stents is significant for β-sources. This dosimetric difference between β- and γ-emitters in diseased coronary arteries should be considered when calculating doses in intravascular brachytherapy.
Five-Year Clinical Follow-Up After Intracoronary Radiation
Authors: Grise Mark A. , Massullo Vincent , Jani Shirish , Popma Jeffrey J. , Russo Robert J. , Schatz Richard A. , Guarneri Erminia M. , Steuterman Stephen , Cloutier David A. , Leon Martin B. , Tripuraneni Prabhakar , Teirstein Paul S.
Published: July 2002

Background

—

Several clinical trials indicate that intracoronary radiation is safe and effective for treatment of restenotic coronary arteries. We previously reported 6-month and 3-year clinical and angiographic follow-up demonstrating significant decreases in target lesion revascularization (TLR) and angiographic restenosis after γ radiation of restenotic lesions. The objective of this study was to document the clinical outcome 5 years after treatment of restenotic coronary arteries with catheter-based iridium-192 (
192
Ir).

Methods and Results

—

A double-blind, randomized trail compared
192
Ir to placebo sources in patients with restenosis after coronary angioplasty. Over a 9-month period, 55 patients were enrolled; 26 were randomized to
192
Ir and 29 to placebo. At 5-year follow-up, TLR was significantly lower in the
192
Ir group (23.1% versus 48.3%;
P
=0.05). There were 2 TLRs between years 3 and 5 in patients in the
192
Ir group and none in patients in the placebo group. The 5-year event-free survival rate (freedom from death, myocardial infarction, or TLR) was greater in
192
Ir-treated patients (61.5% versus 34.5%;
P
=0.02).

Conclusions

—

Despite apparent mitigation of efficacy over time, there remains a significant reduction in TLR at 5 years and an improvement in event-free survival in patients treated with intracoronary
192
Ir. The early clinical benefits after intracoronary γ radiation with
192
Ir seem durable at 5-year clinical follow-up.
Legalization, Trade Liberalization, and Domestic Politics: A Cautionary Note
Authors: Goldstein Judith , Martin Lisa L.
Published: July 2002

If the purpose of legalization is to enhance international cooperation, more may not always be better. Achieving the optimal level of legalization requires finding a balance between reducing the risks of opportunism and reducing the potential negative effects of legalization on domestic political processes. The global trade regime, which aims to liberalize trade, has become increasingly legalized over time. Increased legalization has changed the information environment and the nature of government obligations, which in turn have affected the pattern of mobilization of domestic interest groups on trade. From the perspective of encouraging the future expansion of liberal trade, we suggest some possible negative consequences of legalization, arguing that these consequences must be weighed against the positive effects of legalization on increasing national compliance. Since the weakly legalized GATT institution proved sufficient to sustain widespread liberalization, the case for further legalization must be strong to justify far-reaching change in the global trade regime.
The Absence of Middle Eastern Great Powers: Political “Backwardness” in Historical Perspective
Authors: Lustick Ian S.
Published: July 2002

Propelled by the oil boom of the mid-1970s the Middle East emerged as the world's fastest growing region. Hopes and expectations were high for Arab political consolidation, economic advancement, and cultural efflorescence. With falling oil prices and a devastating war between Iran and Iraq, these hopes had dimmed somewhat by the early 1980s. In 1985, however, the spectacular image of an Arab great power was still tantalizing. A Pan-Arab state, wrote two experts on the region, would include a total area of 13.7 million square kilometers,

second only to the Soviet Union and considerably larger than Europe, Canada, China, or the United States. … By 2000 it would have more people than either of the two superpowers. This state would contain almost two-thirds of the world's proven oil reserves. It would also have enough capital to finance its own economic and social development. Conceivably, it could feed itself.… Access to a huge market could stimulate rapid industrial growth. Present regional inequalities could ultimately be lessened and the mismatch between labor-surplus and labor-short areas corrected. The aggregate military strength and political influence of this strategically located state would be formidable.… It is easy to comprehend why this dream has long intoxicated Arab nationalists.
The Language of Iconica
Authors: Innocent Troy
Published: July 2002

Visual languages play an important role in electronically mediated communication. In particular, iconography has developed as an important component of user interface design. Interactivity makes an icon an active agent in communication, rather than a passive communicator. The author's interactive work Iconica uses icons to represent the function and structure of an artificial-life model. In this work, iconic elements are the basic building blocks of a world literally made of language. This world has the capacity to evolve, change and mutate through human interaction and its own evolutionary process. Communication with the resident life forms occurs via the iconic language that defines the world, including its elements, forms, entities, spaces and behaviors.
Movement Operations after Syntax
Authors: Embick David , Noyer Rolf
Published: July 2002

We develop a theory of movement operations that occur after the syntactic derivation, in the PF component, within the framework of Distributed Morphology.The theory is an extension of what was called Morphological Merger in Marantz 1984 and subsequent work.A primary result is that the locality properties of a Merger operation are determined by the stage in the derivation at which the operation takes place: specifically, Merger that takes place before Vocabulary Insertion, on hierarchical structures, differs from Merger that takes place post—Vocabulary Insertion/linearization.Specific predictions of the model are tested in numerous case studies.Analyses showing the interaction of syntactic movement, PF movement, and rescue operations are provided as well, including a treatment of Englishdo-support.
Generativity and Explanation in Semantics: A Reply to Fodor and Lepore
Authors: Pustejovsky James
Published: July 2002

In this article I address the remarks made in Fodor and Lepore's article, “The Emptiness of the Lexicon: Reflections on James Pustejovsky's The Generative Lexicon,” regarding the research program outlined in Pustejovsky 1995. My response focuses on two themes, FL's misreadings and misinterpretations of the substance as well as the details of the theory, and the generally negative and unconstructive view of the study of semantics and natural language meaning inherent in their approach.
Multitiered Nonlinear Morphology Using Multitape Finite Automata: A Case Study on Syriac and Arabic
Authors: Kiraz George Anton
Published: July 2002

This paper presents a computational model for nonlinear morphology with illustrations from Syriac and Arabic. The model is a multitiered one in that it allows for multiple lexical representations corresponding to the multiple tiers of autosegmental phonology. The model consists of three main components: (i) a lexicon, which is made of sublexica, with each sublexicon representing lexical material from a specific tier, (ii) a rewrite rules component that maps multiple lexical representations into one surface form and vice versa, and (iii) a morphotactic component that employs regular grammars. The system is finite-state in that lexica and rules can be represented by multitape finite-state machines.
An Electrophysiological Test of Directed Forgetting: The Role of Retrieval Inhibition
Authors: Ullsperger Markus , Mecklinger Axel , Müller Ulrich
Published: July 2002

A central issue in the research of directed forgetting is whether the differential memory performance for to-be-remembered (TBR) and to-be-forgotten (TBF) items is solely due to differential encoding or whether retrieval inhibition of TBF items plays an additional role. In this study, recognition-related event-related brain potentials (ERPs) were used to examine this issue. The spatio-temporal distributions of the old/new ERP effects obtained in Experiment 1 that employed a directed forgetting paradigm were compared with those recorded in Experiment 2 in which the level of processing was manipulated. In Experiment 1, participants were instructed to remember or to forget words by means of a cue presented after each word. ERPs recorded in the recognition test revealed early phasic frontal and parietal old/new effects for TBR items, whereas TBF items elicited only a frontal old/new effect. Moreover, a late right-frontal positive slow wave was more pronounced for TBF items, suggesting that those items were associated with a larger amount of post-retrieval processing. In Experiment 2, the same cueing method and the same stimulus materials were used, and memory encoding was manipulated by cueing participants to process the words either deeply or shallowly. Both deeply and shallowly encoded items elicited phasic frontal and parietal old/new effects followed by a late right-frontal positive slow wave. However, in contrast to TBR and TBF items, these effects differed only quantitatively. The results suggest that differential encoding alone cannot account for the effects of directed forgetting. They are more consistent with the view that items followed by an instruction to forget become inhibited and less accessible, and, therefore, more difficult to retrieve.
II. Hypersociability in Williams Syndrome
Authors: Jones Wendy , Bellugi Ursula , Lai Zona , Chiles Michael , Reilly Judy , Lincoln Alan , Adolphs Ralph
Published: July 2002

Studies of abnormal populations provide a rare opportunity for examining relationships between cognition, genotype and brain neurobiology, permitting comparisons across these different levels of analysis. In our studies, we investigate individuals with a rare, genetically based disorder called Williams syndrome (WMS) to draw links among these levels. A critical component of such a cross-domain undertaking is the clear delineation of the phenotype of the disorder in question. Of special interest in this paper is a relatively unexplored unusual social phenotype in WMS that includes an overfriendly and engaging personality. Four studies measuring distinct aspects of hypersocial behavior in WMS are presented, each probing specific aspects in WMS infants, toddlers, school age children, and adults. The abnormal profile of excessively social behavior represents an important component of the phenotype that may distinguish WMS from other developmental disorders. Furthermore, the studies show that the profile is observed across a wide range of ages, and emerges consistently across multiple experimental paradigms. These studies of hypersocial behavior in WMS promise to provide the ground-work for crossdisciplinary analyses of gene-brain-behavior relationships.
Activation Timecourse of Ventral Visual Stream Object-recognition Areas: High Density Electrical Mapping of Perceptual Closure Processes
Authors: Doniger Glen M. , Foxe John J. , Murray Micah M. , Higgins Beth A. , Snodgrass Joan Gay , Schroeder Charles E. , Javitt Daniel C.
Published: July 2002

Object recognition is achieved even in circumstances when only partial information is available to the observer. Perceptual closure processes are essential in enabling such recognitions to occur. We presented successively less fragmented images while recording high-density event-related potentials (ERPs), which permitted us to monitor brain activity during the perceptual closure processes leading up to object recognition. We reveal a bilateral ERP component (Ncl) that tracks these processes (onsets ∼ 230 msec, maximal at ∼290 msec). Scalp-current density mapping of the Ncl revealed bilateral occipito-temporal scalp foci, which are consistent with generators in the human ventral visual stream, and specifically the lateral-occipital or LO complex as defined by hemodynamic studies of object recognition.
Electrophysiological Correlates of the Retrieval of Emotional and Non-emotional Context
Authors: Maratos Elizabeth J. , Rugg Michael D.
Published: July 2002

In two experiments, words were presented in negatively or neutrally valenced sentences. At test, subjects made old/new recognition judgments to these words. In Experiment 2 only, for words judged old, subjects also indicated whether the words had been studied in a neutral or a negative context. In Experiment 1, left parietal old/new event-related brain potential (ERP) effects were larger and more sustained when elicited by words that had been studied in negative sentences, and a right frontal old/new effect was elicited by these words exclusively. In Experiment 2, the left parietal and right frontal effects elicited by old words correctly assigned to their study context were equivalent in size regardless of the nature of the context; a third ERP old/new effect, maximal over posterior scalp regions, was seen only for words from negative contexts. The findings indicate that incidental retrieval of emotional context gives rise to greater activation in neural systems supporting conscious recollection than does retrieval of nonemotional context. When contextual retrieval is intentional, recollection of emotional and non-emotional information are associated with equivalent engagement of these systems. The findings from Experiment 2 suggest that additional neural circuitry may be activated selectively by emotionally valenced episodic information.
An fMRI Study on the Time-Limited Role of the Medial Temporal Lobe in Long-Term Topographical Autobiographic Memory
Authors: Niki Kazuhisa , Luo Jing
Published: July 2002

The time-limited role of the medial temporal lobe (MTL) in human long-term memory is well known. However, there is still no direct neuroimaging evidence to confirm it. In this fMRI study, nine subjects were scanned while asked to recall the places they visited more than seven years ago (remote memories); and the places they visited recently (recent memories). We observed robust and dominant MTL activity peaking in the left parahippocampal gyrus when recent memories were contrasted with remote memories. This result provided direct evidence for the time-limited role of the MTL in long-term topographical autobiographic memory. Further analysis revealed that this MTL activity was not due to the fact that the retrieval of recent memories was accompanied by more details. When detailed recent memories were contrasted with detailed remote memories, there was still MTL activity peaking in the left parahippocampal gyrus. The effects of details in remote memories are also discussed.
Binocular Rivalry and Motion Perception
Authors: Blake Randolph , Yu Karen , Lokey Michelle , Norman Hideko
Published: July 2002

In a series of experiments psychophysical techniques were used to study the relation between binocular rivalry and motion perception. An initial series of experiments confirmed that motion enhances the predominance of an eye during rivalry, although the direction of motion does not matter. The presence of an annulus of motion immediately surrounding one eye's rival target greatly enhances dominance of that target, but the influence of the annulus progressively decreases as the separation between disk and annulus increased. Opponent directions of motion in disk and annulus yield greater dominance than when dots in the disk and annulus moved in identical directions. In a second experiment the two eyes were adapted to orthogonal directions of motion, generating strong, distinctively different monocular motion aftereffects (MAEs). Even though the two eyes view physically identical random-motion displays following differential adaptation, binocular rivalry of the discrepant MAEs can occur. Finally, using a stimulus replacement technique to measure detectability of translational and rotational motion, it was found that both types of motion were readily detected during periods of dominance but went undetected during periods of suppression. Taken together, these results bear on the process responsible for rivalry and its neural locus relative to the analysis of different types of motion.
A Phase Model of Temperature-Dependent Mammalian Cold Receptors
Authors: Roper Peter , Bressloff Paul C. , Longtin André
Published: July 2002

We present a tractable stochastic phase model of the temperature sensitivity of a mammalian cold receptor. Using simple linear dependencies of the amplitude, frequency, and bias on temperature, the model reproduces the experimentally observed transitions between bursting, beating, and stochastically phase-locked firing patterns. We analyze the model in the deterministic limit and predict, using a Strutt map, the number of spikes per burst for a given temperature. The inclusion of noise produces a variable number of spikes per burst and also extends the dynamic range of the neuron, both of which are analyzed in terms of the Strutt map. Our analysis can be readily applied to other receptors that display various bursting patterns following temperature changes.
Blind Source Separation by Sparse Decomposition in a Signal Dictionary
Authors: Zibulevsky Michael , Pearlmutter Barak A.
Published: July 2002

The blind source separation problem is to extract the underlying source signals from a set of linear mixtures, where the mixing matrix is unknown. This situation is common in acoustics, radio, medical signal and image processing, hyperspectral imaging, and other areas. We suggest a two-stage separation process: a priori selection of a possibly overcomplete signal dictionary (for instance, a wavelet frame or a learned dictionary) in which the sources are assumed to be sparsely representable, followed by unmixing the sources by exploiting the their sparse representability. We consider the general case of more sources than mixtures, but also derive a more efficient algorithm in the case of a nonovercomplete dictionary and an equal numbers of sources and mixtures. Experiments with artificial signals and musical sounds demonstrate significantly better separation than other known techniques.
A Competitive-Layer Model for Feature Binding and Sensory Segmentation
Authors: Wersing Heiko , Steil Jochen J. , Ritter Helge
Published: July 2002

We present a recurrent neural network for feature binding and sensory segmentation: the competitive-layer model (CLM). The CLM uses topo-graphically structured competitive and cooperative interactions in a layered network to partition a set of input features into salient groups. The dynamics is formulated within a standard additive recurrent network with linear threshold neurons. Contextual relations among features are coded by pairwise compatibilities, which define an energy function to be minimized by the neural dynamics. Due to the usage of dynamical winner-take-all circuits, the model gains more flexible response properties than spin models of segmentation by exploiting amplitude information in the grouping process. We prove analytic results on the convergence and stable attractors of the CLM, which generalize earlier results on winner-take-all networks, and incorporate deterministic annealing for robustness against local minima. The piecewise linear dynamics of the CLM allows a linear eigensubspace analysis, which we use to analyze the dynamics of binding in conjunction with annealing. For the example of contour detection, we show how the CLM can integrate figure-ground segmentation and grouping into a unified model.
Memory Maintenance via Neuronal Regulation
Authors: Horn David , Levy Nir , Ruppin Eytan
Published: July 2002

Since their conception half a century ago, Hebbian cell assemblies have become a basic term in the neurosciences, and the idea that learning takes place through synaptic modifications has been accepted as a fundamental paradigm. As synapses undergo continuous metabolic turnover, adopting the stance that memories are engraved in the synaptic matrix raises a fundamental problem: How can memories be maintained for very long time periods? We present a novel solution to this long-standing question, based on biological evidence of neuronal regulation mechanisms that act to maintain neuronal activity. Our mechanism is developed within the framework of a neural model of associative memory. It is operative in conjunction with random activation of the memory system and is able to counterbalance degradation of synaptic weights and normalize the basins of attraction of all memories. Over long time periods, when the variance of the degradation process becomes important, the memory system stabilizes if its synapses are appropriately bounded. Thus, the remnant memory system is obtained by a dynamic process of synaptic selection and growth driven by neuronal regulatory mechanisms. Our model is a specific realization of dynamic stabilization of neural circuitry, which is often assumed to take place during sleep.
Detecting and Estimating Signals in Noisy Cable Structures, II: Information Theoretical Analysis
Authors: Manwani Amit , Koch Christof
Published: July 2002

This is the second in a series of articles that seek to recast classical single-neuron biophysics in information-theoretical terms. Classical cable theory focuses on analyzing the voltage or current attenuation of a synaptic signal as it propagates from its dendritic input location to the spike initiation zone. On the other hand, we are interested in analyzing the amount of information lost about the signal in this process due to the presence of various noise sources distributed throughout the neuronal membrane. We use a stochastic version of the linear one-dimensional cable equation to derive closed-form expressions for the second-order moments of the fluctuations of the membrane potential associated with different membrane current noise sources: thermal noise, noise due to the random opening and closing of sodium and potassium channels, and noise due to the presence of “spontaneous” synaptic input.

We consider two different scenarios. In the signal estimation paradigm, the time course of the membrane potential at a location on the cable is used to reconstruct the detailed time course of a random, band-limited current injected some distance away. Estimation performance is characterized in terms of the coding fraction and the mutual information. In the signal detection paradigm, the membrane potential is used to determine whether a distant synaptic event occurred within a given observation interval. In the light of our analytical results, we speculate that the length of weakly active apical dendrites might be limited by the information loss due to the accumulated noise between distal synaptic input sites and the soma and that the presence of dendritic nonlinearities probably serves to increase dendritic information transfer.