bluuebunny/crossref_metadata_2025 huggingface dataset:
Glu298Asp Endothelial Nitric Oxide Synthase Gene Polymorphism Interacts With Environmental and Dietary Factors to Influence Endothelial Function
Authors: Leeson C.P.M. , Hingorani A.D. , Mullen M.J. , Jeerooburkhan N. , Kattenhorn M. , Cole T.J. , Muller D.P.R. , Lucas A. , Humphries S.E. , Deanfield J.E.
Published: July 2002

An endothelial nitric oxide synthase (eNOS) gene polymorphism (Glu298Asp) has been associated with cardiovascular disease. We investigated whether carriage of the polymorphism was associated with functional changes in the endothelium, and how genotype altered the harmful and beneficial impact of environmental influences on the endothelium. Endothelium-dependent, flow-mediated brachial artery dilatation (FMD) and endothelium-independent dilatation response to glyceryl trinitrate were measured using high-resolution ultrasound in 248 subjects (131 female, 117 male, aged 20 to 28) genotyped for the Glu298Asp polymorphism. Vascular function was compared between genotype groups and interactions with the proatherogenic risk factor, smoking, and the antiatherogenic influence of n-3 fatty acids (n-3FA) were investigated. Vascular function was not related to genotype in the group as a whole or within sexes. However, among males, smoking was associated with lower FMD in Asp298 carriers (nonsmokers 0.125±0.085 mm versus smokers 0.070±0.060 mm,
P
=0.006) but not in Glu298 homozygotes (nonsmokers 0.103±0.090 mm versus smokers 0.124±0.106,
P
=0.5). In the whole group, n-3FA levels were positively related to FMD in Asp298 carriers (reg coeff=0.023 mm/%,
P
=0.04,
r
=0.20) but not in Glu298 homozygotes (reg coeff=−0.019 mm/%,
P
=0.1). These differences between genotype groups were significant in interaction models. The Glu298Asp polymorphism is associated with differences in endothelial responses to both smoking and n-3 FA in healthy young subjects. These findings raise the possibility of genotype-specific prevention strategies in cardiovascular disease.
Social Stress Exacerbates Focal Cerebral Ischemia in Mice
Authors: Sugo Nobuo , Hurn Patricia D. , Morahan M. Brigid , Hattori Kimihiko , Traystman Richard J. , DeVries A. Courtney
Published: July 2002

Background and Purpose

—

The purpose of the present study was to determine whether exposure to stress or elevated corticosterone concentrations in the days preceding cerebral ischemia exacerbates ischemic injury as assessed by histological and behavioral outcomes.

Methods

—

For 7 consecutive days, male C57/BL6 mice were exposed to social stress for 45 minutes or injected with 1 mg/kg corticosterone or vehicle. The animals exposed to social stress were injected with either 1 mg/kg mifepristone, a glucocorticoid receptor antagonist, or the vehicle 30 minutes before stress. On the seventh day, all animals were trained in a passive avoidance task. Twenty-four hours after training, the animals were subjected to 60 minutes of intraluminal middle cerebral artery occlusion (MCAO) or sham surgery. At 72 hours of reperfusion, the animals were tested for retention of the passive avoidance task, and infarction size was determined.

Results

—

Animals subjected to chronic social stress or treated with exogenous corticosterone before MCAO exhibited larger infarcts and reduced retention of passive avoidance compared with the nonstressed MCAO control. The effects of social stress on infarct volume and passive avoidance were reversed by pretreatment with mifepristone. There was no difference between stressed and control groups in physiological parameters or reduction of laser-Doppler flow signal during MCAO or reperfusion.

Conclusions

—

Prior exposure to social stress increases infarction volume and exacerbates cognitive deficits associated with transient cerebral ischemia. The mechanism underlying the effects of stress on stroke outcome likely involves corticosterone acting through glucocorticoid receptors to increase subsequent ischemia-induced neuronal death.
The European Union's Legal System and Domestic Policy: Spillover or Backlash?
Authors: Alter Karen J.
Published: July 2002

Under what conditions do domestic actors use international legal mechanisms to influence domestic policy? Drawing on the European case, where legalization has progressed the furthest, I develop a generalizable framework for explaining variation in the use of the European Union's legal system by domestic actors to influence national policy. Four steps are involved in using the European legal process to pressure for policy change: (1) there must be a point of European law that creates legal standing and promotes the litigant's objectives; (2) litigants must embrace this law, adopting a litigation strategy; (3) a national court must refer the case to the European Court of Justice or apply ECJ jurisprudence; and (4) domestic actors must follow through on the legal victory to pressure national governments. Different factors influence each step, creating cross-national and cross-issue variation in the influence of EU law on national policy. Raising a significant challenge to neofunctionalist theory, I argue that negative interactive effects across the four steps and backlash created by the success of integration can stop or even reverse the expansionary dynamic of the legal process. I conclude by exploring the generalizability of this framework to other international contexts.
Situation Structure and Institutional Design: Reciprocity, Coercion, and Exchange
Authors: Mitchell Ronald B. , Keilbach Patricia M.
Published: July 2002

States experiencing negative externalities caused by other states' behaviors have incentives to devise international institutions to change those behaviors. The institutions states create to counter incentives to defect vary in whether and how they expand institutional scope to accomplish that goal. When facing symmetric externalities, states tend to devise narrow institutions based on issue-specific reciprocity. When facing asymmetric externalities, or upstream/downstream problems, states tend to broaden institutional scope using linkage strategies. When victims of an externality are stronger than its perpetrators, the resulting institutions, if any are devised, are likely to incorporate the negative linkage of sanctions or coercion. When victims are weaker, exchange institutions relying on the positive linkage of rewards are more likely. We illustrate the influence of situation structure on institutional design with three cases: international whaling, ozone-layer depletion, and Rhine River pollution.
Private Justice in a Global Economy: From Litigation to Arbitration
Authors: Mattli Walter
Published: July 2002

Drawing on the analytical framework developed by Barbara Koremenos, Charles Lipson, and Duncan Snidal in the Rational Design project, I seek to shed light on the striking institutional differences among the various methods of international commercial dispute resolution for private parties. These methods include recourse to public courts and more frequently to private international courts, such as the International Court of Arbitration of the International Chamber of Commerce or the London Court of International Arbitration, as well as recourse to so-called ad hoc arbitration and alternative dispute-resolution techniques, such as conciliation and mediation. The key institutional dimensions along which these methods of international dispute resolution vary are (1) procedural and adaptive flexibility, and (2) centralization of procedural safeguards and information collection. I explain why different methods of international commercial dispute resolution are selected. I argue that these methods respond to the varying institutional needs of different types of disputes and disputants. Such needs can be explained in terms of the severity of the enforcement problem, uncertainty about the preferences or behavior of contractual partners, and uncertainty about the state of the world.
The Constitutional Structure of International Society and the Nature of Fundamental Institutions
Authors: Reus-Smit Christian
Published: July 2002

Modern states have constructed a multiplicity of issue-specific regimes to facilitate collective action. The majority of these institutions are specific instances of the deeper institutional practices that structure modern international society, notably the fundamental institutions of contractual international law and multilateralism. Two observations can be made about fundamental institutions. First, they are “generic” structural elements of international societies. That is, their practice transcends changes in the balance of power and the configuration of interests, even if their density and efficacy vary. The modern practices of contractual international law and multilateralism intensified after 1945, but postwar developments built on institutional principles that were first endorsed by states during the nineteenth century and structured international relations long before the advent of American hegemony. Second, fundamental institutions differ from one society of states to another. While the governance of modern international society rests on the institutions of contractual international law and multilateralism, no such institutions evolved in ancient Greece. Instead, the city-states developed a sophisticated and successful system of third-party arbitration to facilitate ordered interstate relations. This institution, which operated in the absence of a body of codified interstate law, is best characterized as “authoritative trilateralism.”
Integrating Text Planning and Linguistic Choice Without Abandoning Modularity: The IGEN Generator
Authors: Rubinoff Robert
Published: July 2002

Natural language generation is usually divided into separate text planning and linguistic components. This division, though, assumes that the two components can operate independently, which is not always true. The IGEN generator eliminates the need for this assumption; it handles interactions between the components without sacrificing the advantages of modularity. IGEN accomplishes this by means of annotations that its linguistic component places on the structures it builds; these annotations provide an abstract description of the effects of particular linguistic choices, allowing the planner to evaluate these choices without needing any linguistic knowledge. This approach allows IGEN to vary the work done by each component independently, even in cases where the final output depends on interactions between them. In addition, since IGEN explicitly models the effects of linguistic choices, it can gracefully handle situations where the available time or linguistic resources are limited.
Models of Translational Equivalence among Words
Authors: Melamed I. Dan
Published: July 2002

Parallel texts (bitexts) have properties that distinguish them from other kinds of parallel data. First, most words translate to only one other word. Second, bitext correspondence is typically only partial—many words in each text have no clear equivalent in the other text. This article presents methods for biasing statistical translation models to reflect these properties. Evaluation with respect to independent human judgments has confirmed that translation models biased in this fashion are significantly more accurate than a baseline knowledge-free model. This article also shows how a statistical translation model can take advantage of preexisting knowledge that might be available about particular language pairs. Even the simplest kinds of language-specific knowledge, such as the distinction between content words and function words, are shown to reliably boost translation model performance on some tasks. Statistical models that reflect knowledge about the model domain combine the best of both the rationalist and empiricist paradigms.
Using Suffix Arrays to Compute Term Frequency and Document Frequency for All Substrings in a Corpus
Authors: Yamamoto Mikio , Church Kenneth W.
Published: July 2002

Bigrams and trigrams are commonly used in statistical natural language processing; this paper will describe techniques for working with much longer n-grams. Suffix arrays (Manber and Myers 1990) were first introduced to compute the frequency and location of a substring (n-gram) in a sequence (corpus) of length N. To compute frequencies over all N(N+1)/2 substrings in a corpus, the substrings are grouped into a manageable number of equivalence classes. In this way, a prohibitive computation over substrings is reduced to a manageable computation over classes. This paper presents both the algorithms and the code that were used to compute term frequency (tf) and document frequency (df) for all n-grams in two large corpora, an English corpus of 50 million words of Wall Street Journal and a Japanese corpus of 216 million characters of Mainichi Shimbun.

The second half of the paper uses these frequencies to find “interesting” substrings. Lexicographers have been interested in n-grams with high mutual information (MI) where the joint term frequency is higher than what would be expected by chance, assuming that the parts of the n-gram combine independently. Residual inverse document frequency (RIDF) compares document frequency to another model of chance where terms with a particular term frequency are distributed randomly throughout the collection. MI tends to pick out phrases with noncompositional semantics (which often violate the independence assumption) whereas RIDF tends to highlight technical terminology, names, and good keywords for information retrieval (which tend to exhibit nonrandom distributions over documents). The combination of both MI and RIDF is better than either by itself in a Japanese word extraction task.
Contrasting Cortical and Subcortical Activations Produced by Attentional-Set Shifting and Reversal Learning in Humans
Authors: Rogers R. D. , Andrews T. C. , Grasby P. M. , Brooks D. J. , Robbins T. W.
Published: July 2002

Much evidence suggests that lesions of the prefrontal cortex (PFC) produce marked impairments in the ability of subjects to shift cognitive set, as exemplified by performance of the Wisconsin Card Sorting Test (WCST). However, studies with humans and experimental primates have suggested that damage to different regions of PFC induce dissociable impairments in two forms of shift learning implicit in the WCST (that is, extradimensional (ED) shift learning and reversal shift learning), with similar deficits also being apparent after damage to basal ganglia structures, especially the caudate nucleus. In this study, we used the same visual discrimination learning paradigm over multidimensional stimuli, and the H2 15O positron emission tomography (PET) technique, to examine regional cerebral blood flow (rCBF) changes associated with these subcomponent processes of the WCST. In three conditions, subjects were scanned while acquiring visual discriminations involving either (i) the same stimulus dimension as preceding discriminations (intradimensional (ID) shifts); (ii) different stimulus dimensions from previous discriminations (ED shifts) or (iii) reversed stimulus-reward contingencies (reversal shifts). Additionally, subjects were scanned while responding to already learnt discriminations (‘performance baseline’). ED shift learning, relative to ID shift learning, produced activations in prefrontal regions, including, left anterior PFC and right dorsolateral PFC (BA 10 and 9/46). By contrast, reversal learning, relative to ID shift learning, produced activations of the left caudate nucleus. Additionally, compared to reversal and ID shift learning, ED shift learning was associated with relative deactivations in occipito-temporal pathways (for example, BA 17 and 37). These results confirm that, in the context of visual discrimination learning over multidimensional stimuli, the control of an acquired attentional bias or 'set', and the control of previously acquired stimulus-reinforcement associations, activate distinct cortical and subcortical neural stations. Moreover, we propose that the PFC may contribute to the control of attentional-set by modulating attentional processes mediated by occipito-temporal pathways.
Hemispheric Asymmetries for Whole-Based and Part-Based Face Processing in the Human Fusiform Gyrus
Authors: Rossion Bruno , Dricot Laurence , Devolder Anne , Bodart Jean-Michel , Crommelinck Marc , Gelder Beatrice de , Zoontjes Richard
Published: July 2002

Behavioral studies indicate a right hemisphere advantage for processing a face as a whole and a left hemisphere superiority for processing based on face features. The present PET study identifies the anatomical localization of these effects in well-defined regions of the middle fusiform gyri of both hemispheres. The right middle fusiform gyrus, previously described as a face-specific region, was found to be more activated when matching whole faces than face parts whereas this pattern of activity was reversed in the left homologous region. These lateralized differences appeared to be specific to faces since control objects processed either as wholes or parts did not induce any change of activity within these regions. This double dissociation between two modes of face processing brings new evidence regarding the lateralized localization of face individualization mechanisms in the human brain.
A Double Dissociation in the Affective Modulation of Startle in Humans: Effects of Unilateral Temporal Lobectomy
Authors: Funayama E. Sumie , Grillon Christian , Davis Michael , Phelps Elizabeth A.
Published: July 2002

In the present study we report a double dissociation between right and left medial temporal lobe damage in the modulation of fear responses to different types of stimuli. We found that right unilateral temporal lobectomy (RTL) patients, in contrast to control subjects and left temporal lobectomy (LTL) patients, failed to show potentiated startle while viewing negative pictures. However, the opposite pattern of impairment was observed during a stimulus that patients had been told signaled the possibility of shock. Control subjects and RTL patients showed potentiated startle while LTL patients failed to show potentiated startle. We hypothesize that the right medial temporal lobe modulates fear responses while viewing emotional pictures, which involves exposure to (emotional) visual information and is consistent with the emotional processing traditionally ascribed to the right hemisphere. In contrast, the left medial temporal lobe modulates fear responses when those responses are the result of a linguistic/cognitive representation acquired through language, which, like other verbally mediated material, generally involves the left hemisphere. Additional evidence from case studies suggests that, within the medial temporal lobe, the amygdala is responsible for this modulation.
The Constraints Functional Neuroimaging Places on Classical Models of Auditory Word Processing
Authors: Giraud A. L. , Price C. J.
Published: July 2002

Several previous functional imaging experiments have demonstrated that auditory presentation of speech, relative to tones or scrambled speech, activate the superior temporal sulci (STS) bilaterally. In this study, we attempted to segregate the neural responses to phonological, lexical, and semantic input by contrasting activation elicited by heard words, meaningless syllables, and environmental sounds. Inevitable differences between the duration and amplitude of each stimulus type were controlled with auditory noise bursts matched to each activation stimulus. Half the subjects were instructed to say “okay” in response to presentation of all stimuli. The other half repeated back the words and syllables, named the source of the sounds, and said “okay” to the control stimuli (noise bursts). We looked for stimulus effects that were consistent across task. The results revealed that central regions in the STS were equally responsive to speech (words and syllables) and familiar sounds, whereas the posterior and anterior regions of the left superior temporal gyrus were more active for speech. The effect of semantic input was small but revealed more activation in the inferior temporal cortex for words and familiar sounds than syllables and noise. In addition, words (relative to syllables, sounds, and noise) enhanced activation in the temporo-parietal areas that have previously been linked to modality independent semantic processing. Thus, in cognitive terms, we dissociate phono-logical (speech) and semantic responses and propose that word specificity arises from functional integration among shared phonological and semantic areas.
Detection of Sounds in the Auditory Stream: Event-Related fMRI Evidence for Differential Activation to Speech and Nonspeech
Authors: Vouloumanos Athena , Kiehl Kent A. , Werker Janet F. , Liddle Peter F.
Published: July 2002

The detection of speech in an auditory stream is a requisite first step in processing spoken language. In this study, we used event-related fMRI to investigate the neural substrates mediating detection of speech compared with that of nonspeech auditory stimuli. Unlike previous studies addressing this issue, we contrasted speech with nonspeech analogues that were matched along key temporal and spectral dimensions. In an oddball detection task, listeners heard nonsense speech sounds, matched sine wave analogues (complex nonspeech), or single tones (simple nonspeech). Speech stimuli elicited significantly greater activation than both complex and simple nonspeech stimuli in classic receptive language areas, namely the middle temporal gyri bilaterally and in a locus lateralized to the left posterior superior temporal gyrus. In addition, speech activated a small cluster of the right inferior frontal gyrus. The activation of these areas in a simple detection task, which requires neither identification nor linguistic analysis, suggests they play a fundamental role in speech processing.
Hemispheric Processing of Categorical and Coordinate Spatial Relations in the Absence of Low Spatial Frequencies
Authors: Okubo Matia , Michimata Chikashi
Published: July 2002

Right-handed participants performed the categorical and coordinate spatial relation judgments on stimuli presented to either the left visual field—right hemisphere (LVF-RH) or the right visual field—left hemisphere (RVF-LH). The stimulus patterns were formulated either by bright dots or by contrast-balanced dots. When the stimuli were bright, an RVF-LH advantage was observed for the categorical task, whereas an LVF-RH advantage was observed for the coordinate task. When the stimuli were contrast balanced, the RVF-LH advantage was observed for the categorical task, but the LVF-RH advantage was eliminated for the coordinate task. Because the contrast-balanced dots are largely devoid of low spatial frequency content, these results suggest that processing of low spatial frequency is responsible for the right hemisphere advantage for the coordinate spatial processing.
Neural Site of the Redundant Target Effect: Electrophysiological Evidence
Authors: Miniussi C. , Girelli M. , Marzi C. A.
Published: July 2002

The present study represents an attempt to find an electrophysiological correlate of the redundant targets effect, or RTE (i.e., the speeding up of reaction time, or RT, for redundant vs. single targets). Subjects made a speeded response either to one small checkerboard presented to the left or right of fixation or to a pair of identical checkerboards presented simultaneously to both hemifields. Both single and double targets could appear either in the upper or lower visual hemifield. The task required detection but not discrimination of the stimuli. During task performance, we recorded the event-related potentials (ERPs) elicited by the checkerboard targets. As in previous studies, we found that manual RTs to bilateral stimuli were faster than those to unilateral stimuli. This effect was more marked for lower-than for upper-field stimuli and could not be ascribed to probability summation. In addition, we found that the P1 and N1 components of the visual ERP had a shorter latency for bilateral than for summed unilateral stimuli presented to the two hemifields. In parallel with the behavioral findings, the latency values for the above components showed a larger RTE for lower-field stimuli. These findings indicate that the RTE occurs at the level of early visual processing, probably in the extrastriate visual cortex, rather than at late decisional or pre-motor stages.
The Neurology of Empty Categories: Aphasics' Failure to Detect Ungrammaticality
Authors: Grodzinsky Yosef , Finkel Lisa
Published: July 2002

A direct investigation into the grammatical abilities of Broca's and Wernicke's aphasics sought to obtain critical evidence for a revised model of the functional neuroanatomy of language. We examined aphasics' ability to make grammaticality judgments on a set of theoretically selected, highly complex syntactic structures that involve, most prominently, fine violations of constraints on syntactic movement. Although both groups have been thought to possess intact abilities in this domain, we discovered severe deficits: Broca's and Wernicke's aphasics (whose performances differed) exhibited clear, delineated, and grammatically characterizable deficits—they follow from the Trace-Deletion Hypothesis, which is motivated by independent comprehension results. These conclusions have both linguistic and neurological implications: Linguistically, they show that the aphasic deficit interacts with more than one module of the grammar. Namely, it manifests not only when the thematic module is called for in interpretive tasks but also when constraints on syntactic movement are tapped in a study of judgment. Neurologically, the results support a view of receptive grammatical mechanisms in the left cortex, which is functionally more restrictive than currently assumed; neuroanatomically, however, it is more distributed.
The Neurophysiology of Backward Visual Masking: Information Analysis
Authors: Rolls Edmund T. , Tovée Martin J. , Panzeri Stefano
Published: July 2002

Backward masking can potentially provide evidence of the time needed for visual processing, a fundamental constraint that must be incorporated into computational models of vision. Although backward masking has been extensively used psychophysically, there is little direct evidence for the effects of visual masking on neuronal responses. To investigate the effects of a backward masking paradigm on the responses of neurons in the temporal visual cortex, we have shown that the response of the neurons is interrupted by the mask. Under conditions when humans can just identify the stimulus, with stimulus onset asynchronies (SOA) of 20 msec, neurons in macaques respond to their best stimulus for approximately 30 msec. We now quantify the information that is available from the responses of single neurons under backward masking conditions when two to six faces were shown. We show that the information available is greatly decreased as the mask is brought closer to the stimulus. The decrease is more marked than the decrease in firing rate because it is the selective part of the firing that is especially attenuated by the mask, not the spontaneous firing, and also because the neuronal response is more variable at short SOAs. However, even at the shortest SOA of 20 msec, the information available is on average 0.1 bits. This compares to 0.3 bits with only the 16-msec target stimulus shown and a typical value for such neurons of 0.4 to 0.5 bits with a 500-msec stimulus. The results thus show that considerable information is available from neuronal responses even under backward masking conditions that allow the neurons to have their main response in 30 msec. This provides evidence for how rapid the processing of visual information is in a cortical area and provides a fundamental constraint for understanding how cortical information processing operates.
Relationships Between the A Priori and A Posteriori Errors in Nonlinear Adaptive Neural Filters
Authors: Mandic Danilo P. , Chambers Jonathon A.
Published: July 2002

The lower bounds for the a posteriori prediction error of a nonlinear predictor realized as a neural network are provided. These are obtained for a priori adaptation and a posteriori error networks with sigmoid nonlinearities trained by gradient-descent learning algorithms. A contractivity condition is imposed on a nonlinear activation function of a neuron so that the a posteriori prediction error is smaller in magnitude than the corresponding a priori one. Furthermore, an upper bound is imposed on the learning rate η so that the approach is feasible. The analysis is undertaken for both feedforward and recurrent nonlinear predictors realized as neural networks.
No Free Lunch for Noise Prediction
Authors: Magdon-Ismail Malik
Published: July 2002

No-free-lunch theorems have shown that learning algorithms cannot be universally good. We show that no free funch exists for noise prediction as well. We show that when the noise is additive and the prior over target functions is uniform, a prior on the noise distribution cannot be updated, in the Bayesian sense, from any finite data set. We emphasize the importance of a prior over the target function in order to justify superior performance for learning systems.
Relationship Between Phase and Energy Methods for Disparity Computation
Authors: Qian Ning , Mikaelian Samuel
Published: July 2002

The phase and energy methods for computing binocular disparity maps from stereograms are motivated differently, have different physiological relevances, and involve different computational steps. Nevertheless, we demonstrate that at the final stages where disparity values are made explicit, the simplest versions of the two methods are exactly equivalent. The equivalence also holds when the quadrature-pair construction in the energy method is replaced with a more physiologically plausible phase-averaging step. The equivalence fails, however, when the phase-difference receptive field model is replaced by the position-shift model. Additionally, intermediate results from the two methods are always quite distinct. In particular, the energy method generates a distributed disparity representation similar to that found in the visual cortex, while the phase method does not. Finally, more elaborate versions of the two methods are in general not equivalent. We also briefly compare these two methods with some other stereo models in the literature.
Population Coding with Correlation and an Unfaithful Model
Authors: Wu Si , Nakahara Hiroyuki , Amari Shun-ichi
Published: July 2002

This study investigates a population decoding paradigm in which the maximum likelihood inference is based on an unfaithful decoding model (UMLI). This is usually the case for neural population decoding because the encoding process of the brain is not exactly known or because a simplified decoding model is preferred for saving computational cost. We consider an unfaithful decoding model that neglects the pair-wise correlation between neuronal activities and prove that UMLI is asymptotically efficient when the neuronal correlation is uniform or of limited range. The performance of UMLI is compared with that of the maximum likelihood inference based on the faithful model and that of the center-of-mass decoding method. It turns out that UMLI has advantages of decreasing the computational complexity remarkably and maintaining high-leveldecoding accuracy. Moreover, it can be implemented by a biologically feasible recurrent network (Pouget, Zhang, Deneve, & Latham, 1998). The effect of correlation on the decoding accuracy is also discussed.
Spike Frequency Adaptation Affects the Synchronization Properties of Networks of Cortical Oscillators
Authors: Crook Sharon M. , Ermentrout G. Bard , Bower James M.
Published: July 2002

Oscillations in many regions of the cortex have common temporal characteristics with dominant frequencies centered around the 40 Hz (gamma) frequency range and the 5–10 Hz (theta) frequency range. Experimental results also reveal spatially synchronous oscillations, which are stimulus dependent (Gray&Singer, 1987;Gray, König, Engel, & Singer, 1989; Engel, König, Kreiter, Schillen, & Singer, 1992). This rhythmic activity suggests that the coherence of neural populations is a crucial feature of cortical dynamics (Gray, 1994). Using both simulations and a theoretical coupled oscillator approach, we demonstrate that the spike frequency adaptation seen in many pyramidal cells plays a subtle but important role in the dynamics of cortical networks. Without adaptation, excitatory connections among model pyramidal cells are desynchronizing. However, the slow processes associated with adaptation encourage stable synchronous behavior.
Axon Guidance: Stretching Gradients to the Limit
Authors: Goodhill Geoffrey J. , Baier Herwig
Published: July 2002

Neuronal growth cones, the sensory-motile structures at the tips of developing axons, navigate to their targets over distances that can be many times greater than their diameter. They may accomplish this impressive task by following spatial gradients of axon guidance molecules in their environment (Bonhoeffer & Gierer, 1984; Tessier-Lavigne & Placzek, 1991; Baier & Bonhoeffer, 1994). We calculate the optimal shape of a gradient and the distance over which it can be detected by a growth cone for two competing mechanistic models of axon guidance. The results are surprisingly simple: Regardless of the mechanism, the maximum distance is about 1 cm. Since gradients and growth cones have coevolved, we suggest that the shape of the gradient in situ will predict the mechanism of gradient detection. In addition, we show that the experimentally determined dissociation constants for receptor-ligand complexes implicated in axon guidance are about optimal with respect to maximizing guidance distance. The relevance of these results to the retinotectal system is discussed.
Modeling the Combination of Motion, Stereo, and Vergence Angle Cues to Visual Depth
Authors: Fine I. , Jacobs Robert A.
Published: July 2002

Three models of visual cue combination were simulated: a weak fusion model, a modified weak model, and a strong model. Their relative strengths and weaknesses are evaluated on the basis of their performances on the tasks of judging the depth and shape of an ellipse. The models differ in the amount of interaction that they permit among the cues of stereo, motion, and vergence angle. Results suggest that the constrained nonlinear interaction of the modified weak model allows better performance than either the linear interaction of the weak model or the unconstrained nonlinear interaction of the strong model. Further examination of the modified weak model revealed that its weighting of motion and stereo cues was dependent on the task, the viewing distance, and, to a lesser degree, the noise model. Although the dependencies were sensible from a computational viewpoint, they were sometimes inconsistent with psychophysical experimental data. In a second set of experiments, the modified weak model was given contradictory motion and stereo information. One cue was informative in the sense that it indicated an ellipse, while the other cue indicated a flat surface. The modified weak model rapidly reweighted its use of stereo and motion cues as a function of each cue's informativeness. Overall, the simulation results suggest that relative to the weak and strong models, the modified weak fusion model is a good candidate model of the combination of motion, stereo, and vergence angle cues, although the results also highlight areas in which this model needs modification or further elaboration.
Analog VLSI-Based Modeling of the Primate Oculomotor System
Authors: Horiuchi Timothy K. , Koch Christof
Published: July 2002

One way to understand a neurobiological system is by building a simulacrum that replicates its behavior in real time using similar constraints. Analog very large-scale integrated (VLSI) electronic circuit technology provides such an enabling technology. We here describe a neuromorphic system that is part of a long-term effort to understand the primate oculomotor system. It requires both fast sensory processing and fast motor control to interact with the world. A one-dimensional hardware model of the primate eye has been built that simulates the physical dynamics of the biological system. It is driven by two different analog VLSI chips, one mimicking cortical visual processing for target selection and tracking and another modeling brain stem circuits that drive the eye muscles. Our oculomotor plant demonstrates both smooth pursuit movements, driven by a retinal velocity error signal, and saccadic eye movements, controlled by retinal position error, and can reproduce several behavioral, stimulation, lesion, and adaptation experiments performed on primates.
Rasaesthetics
Authors: Schechner Richard
Published: July 2002

What happens when the Natyasastra, an ancient Sanskrit text about the “flavors of emotion”, meets the enteric nervous system? How do “gut feelings” affect performance, reception, actor training, and performance theory?
Zaju and Kabuki in English: Directing in the Classical Styles
Authors: Shen Grant Guangren
Published: July 2002

Zaju, a Chinese theatre genre, has not been staged for 500 years. Kabuki has never been performed in English in Asia. In Singapore, a vigorously multicultural city, Shen directed English-language productions of zaju and kabuki. Are such productions “authentic”? What does authentic mean these days?
Merce Cunningham and the Aesthetic of Collage
Authors: Copeland Roger
Published: July 2002

Collage has been central to Cunningham's work from the very beginning in the 1950s. Unlike Wagner's Gesamtkunstwerk, which exemplifies a hunger for wholeness, collage appeals to an age that has come to distrust claims of closure, “unity,” and fixed boundaries.
Control Design and Task Performance in Endoscopic Teleoperation
Authors: Ben-Porat Ori , Shoham Moshe , Meyer Joachim
Published: July 2002

Endoscopic surgery, while offering considerable gains for the patient, has created new difficulties for the surgeon. One problem is the fulcrum effect, which causes the movement of a surgical instrument, as seen on the monitor, to be in the opposite direction to the movement of the surgeon's hand. The problem has been shown to impede the acquisition of endoscopic skills. Teleoperated robotic arms may circumvent this problem by allowing different control-response relations. Four alternative control designs of a teleoperated device were compared in a simulated endoscopic task. A rigid teleoperated robotic arm with two degrees of freedom representing a surgical tool was coupled to a joystick in a position control mode. Feedback was provided through a video display. Participants without prior experience in endoscopy performed a target acquisition task, first by pointing the robotic arm at the targets, and later by maneuvering an object. Performance was measured under four different combinations of visual-motor mapping (normal/reversed), and the joystick's orientation (upwards/downwards). Task completion time under normal visual-motor mapping was found to be significantly shorter than under reversed visual-motor mapping, emphasizing the potential advantage of a teleoperated endoscopic system. The joystick's orientation affected the maneuvering of an object under only the reversed visual-motor mapping, implying that the positioning of a surgical tool and the manipulation of tissues or objects with the tool may be differentially affected by the control design.
The Virtual Lens
Authors: Neveu Charles F. , Stark Lawrence W.
Published: July 2002

We describe a new type of feedback display based upon ocular accommodation, called the virtual lens, that maintains a focused projection of a CRT image on the retina independent of changes in accommodation, and that replaces the optical image-processing action of the crystalline lens with an arbitrary computable image transform. We describe some applications of the virtual lens in visual psychophysics and virtual environments.
The Virtual Venue: User-Computer Interaction in Information-Rich Virtual Environments
Authors: Bowman Doug A. , Hodges Larry F. , Bolter Jay
Published: July 2002

We present a virtual environment application that allows users to access embedded information within an immersive virtual space. Due to the richness and complexity of this environment, efficient and easy-to-use interaction techniques are a crucial requirement. The “Virtual Venue” seamlessly combines both twoand three-dimensional interaction techniques into a single system and utilizes previously reported as well as novel techniques that fit the task of information access. We present tools for user control of the system, travel through the environment, and information retrieval, as well as authoring tools for the creation of information-rich virtual environments. A usability study and its results are also presented and discussed. The study indicates that the use of abstract information that is tightly coupled to the virtual environment can be quite successful in enhancing the relevance of both the environment and the information. Results also show that the set of well-constrained interaction techniques presented here are usable and efficient for information retrieval.
Implementation of Partial Surface Display
Authors: Hirota Koichi , Hirose Michitaka
Published: July 2002

The sensations of touch and force have come to be recognized as essential factors in virtual reality, and many efforts have been made to develop display devices that reproduce these sensations. Such devices are divided into two categories: wearing and nonwearing. In this paper, a method is proposed for representing virtual objects of arbitrary shapes using a nonwearing device. Based on this method, a device was fabricated to describe our approach. Our prototype device was designed to approximately represent part of the surface of a virtual object as a tangential surface (i.e., partial surface) to the user's fingertip. The device was implemented as a mechanism with five degrees of freedom that are commonly used to measure the fingertip position and to present the partial surface to the fingertip. The mechanism was controlled through two calculation loops: a model loop that gives a tangential surface from the fingertip position and the shape of objects, and a servo loop that manages the mechanism to represent the given tangential surface by the partial surface. Also, a stereoscopic, head-tracking visual system was implemented to realize the combined presentation of visual information and the partial surface.

As an example of the applications of the environment, a task of writing characters was simulated. From the observation of the performance of the task, the presentation of the partial surface was proved to have an effect on decreasing blur and dragging in written characters.
A Macroscopic Analytical Model of Collaboration in Distributed Robotic Systems
Authors: Lerman Kristina , Galstyan Aram , Martinoli Alcherio , Ijspeert Auke
Published: July 2002

In this article, we present a macroscopic analytical model of collaboration in a group of reactive robots. The model consists of a series of coupled differential equations that describe the dynamics of group behavior. After presenting the general model, we analyze in detail a case study of collaboration, the stick-pulling experiment, studied experimentally and in simulation by Ijspeert et al. [Autonomous Robots, 11, 149–171]. The robots' task is to pull sticks out of their holes, and it can be successfully achieved only through the collaboration of two robots. There is no explicit communication or coordination between the robots. Unlike microscopic simulations (sensor-based or using a probabilistic numerical model), in which computational time scales with the robot group size, the macroscopic model is computationally efficient, because its solutions are independent of robot group size. Analysis reproduces several qualitative conclusions of Ijspeert et al.: namely, the different dynamical regimes for different values of the ratio of robots to sticks, the existence of optimal control parameters that maximize system performance as a function of group size, and the transition from superlinear to sublinear performance as the number of robots is increased.
On the Evolution of Multicellularity and Eusociality
Authors: Bull Larry
Published: July 2002

In this article versions of the abstract NKC model are used to examine the conditions under which two significant evolutionary phenomena—multicellularity and eusociality—are likely to occur and why. First, comparisons in evolutionary performance are made between simulations of unicellular organisms and very simple multicellular-like organisms, under varying conditions. The results show that such multicellularity without differentiation appears selectively neutral, but that differentiation to soma (nonreproductives) proves beneficial as the amount of epistasis in the fitness landscape increases. This is explained by considering mutations in the generation of daughter cells and their subsequent effect on the propagule's fitness. This is interpreted as a simple example of the Baldwin effect. Second, the correspondences between multicellularity and eusociality are highlighted, particularly that both contain individuals who do not reproduce. The same process is then used to explain the emergence of eusocial colonies.
The Political Stalinization of China: The Establishment of One-Party Constitutionalism, 1948–1954
Authors: Li Hua-yu
Published: July 2002

This article offers a fresh perspective on the establishment of a one-party constitutional structure in China from 1948 to 1954, using documents and first-hand accounts published in China over the past two decades. These documents suggest that the Stalinization of China cannot be understood outside the larger context of the political Stalinization of the rest of the Communist world. Stalin played a critical role in determining the pace of political reform in China, and he actively encouraged Mao to allow non-Communists to take part in the Chinese electoral process and in the writing of the Chinese constitution. Although Mao would have preferred to establish a Soviet-style one-party system right away, he readily yielded to Stalin's advice. Mao chose to obey Stalin's dictates for political reform so that he could gain greater independence in domestic economic policies.
It's Capacity, Stupid: International Assistance and National Implementation
Authors: VanDeveer Stacy D. , Dabelko Geoffrey D.
Published: July 2002

Issues associated with state inability (or incapacity) to meet international commitments—and how to build such capacity—are now ubiquitous in the theorizing, practice and research agendas of international environmental cooperation. Yet “capacity” and “capacity building” remain under-specified at the conceptual level. They are neglected areas of empirical research, and generally unreflective in practice. International and national level policy-makers are struggling with questions about how best to enhance state, local and NGO capacities to meet international commitments. To illustrate the need for more conceptual attention and empirical research around issues of public sector capacity, the article presents a multi-dimensional understanding of public sector capacity and highlights programs that appear to be successfully building capacity in recipient countries and programs that seem to be unsuccessful. The article draws examples from multilateral assistance programs within regional marine pollution control regimes and from bilateral assistance programs associated with cleaning up radioactive legacies of the Cold War in post-communist states.