bluuebunny/crossref_metadata_2025 huggingface dataset:
Institutions and Investors: The Politics of the Economic Crisis in Southeast Asia
Authors: MacIntyre Andrew
Published: July 2002

I develop a systematic argument about the politics of the 1997–98 Asian economic crisis. I focus on institutions—specifically, the connection linking the institutional framework of national politics, the policy environment, and investment. I seek to resolve the tension between the literatures on credible policy commitment and policy flexibility, arguing that if either is severely undersupplied, the risk associated with the policy environment rises rapidly for investors. Building on a veto player framework, I develop a simple model of a U-shaped relationship between the number of veto players in a political system and policy risk to investors. Institutional vetoes on executive authority lower policy risk for investors but only up to a point, after which additional veto players promote unwelcome policy rigidity. I illustrate this using four cases: Thailand, the Philippines, Malaysia, and Indonesia, the four main Southeast Asian countries involved in the financial crisis. I argue that the institutional framework of national politics had a powerful and predictable influence on policy responses and investor reactions.
National structures and multinational corporate behavior: enduring differences in the age of globalization
Authors: Pauly Louis W. , Reich Simon
Published: July 2002

Liberal and critical theorists alike claim that the world political economy is becoming globalized. If they are right, leading corporations should gradually be losing their national characters and converging in their fundamental strategies and operations. Multinational corporations (MNCs) should be the harbingers of deep global integration. In fact, recent evidence shows little blurring or convergence at the cores of firms based in Germany, Japan, or the United States.
American identity and neutral rights from independence to the War of 1812
Authors: Bukovansky Mlada
Published: July 2002

In recent international relations theory debates, constructivists have argued that explanations based primarily on interests and the material distribution of power cannot fully account for important international phenomena and that analysis of the social construction of state identities ought to precede, and may even explain, the genesis of state interests. This claim has proved difficult to operationalize empirically, though some persuasive results are now emerging. This article analyzes the relationship between state identity and state interest in the development of American neutral rights policy from U.S. independence to the War of 1812.
International and Domestic Constraints on Political Business Cycles in OECD Economies
Authors: Clark William Roberts , Reichert Usha Nair , Lomas Sandra Lynn , Parker Kevin L.
Published: July 2002

The effect of increased capital mobility on the national control of macroeconomic policy continues to be a topic of debate. Empirical contributions to this debate share the assumption that domestic macroeconomic policy is driven by either partisan or countercyclical motivations, and that the effects of international financial flows have roughly similar effects in all countries. This article reevaluates the integration hypothesis in a framework in which manipulations of the macroeconomy derive from opportunistic motivations. The article emphasizes the ways in which prior institutional choices effect the way these motivations are translated into actions. Evidence from individual country and pooled time-series tests suggests that opportunistic cycles are less likely to occur when (1) a government maintains a fixed exchange rate in the presence of highly mobile capital or (2) when the central bank enjoys above-average independence.
Theories and Empirical Studies of International Institutions
Authors: Martin Lisa L. , Simmons Beth A.
Published: July 2002

Studies of international institutions, organizations, and regimes have consistently appeared in the pages of International Organization. We review the theoretical and empirical work on international institutions and identify promising directions for the institutionalist research program. Early studies of international institutions were rich with empirical insights and often influenced by theoretical developments in other fields of political science, but lacking an overarching analytical framework they failed to produce a coherent body of scholarship. Current efforts to reinvigorate the study of international institutions draw on a new body of theory about domestic institutions. We argue that the assumptions of this new approach to institutions are more appropriate to international studies than those of earlier attempts to transfer theories across levels of analysis. We suggest that the most productive questions for future research will focus on specifying alternative mechanisms by which institutions can influence outcomes and identify particular sets of questions within this agenda that are especially promising.
The Origins of Central Banking: Solutions to the Free-Rider Problem
Authors: Broz J. Lawrence
Published: July 2002

This article explains (1) the origins of central banking and (2) variations in the spread and durability of central banks across nations. Early central banks helped bind governments to honor their debts and thereby furthered governments' capacities to efficiently finance military expenditures. The origins of central banking are problematic because government credit-worthiness and efficient wartime fiscal policy are public goods, subject to the free-rider problem. Applying a variant of the joint-products model, I argue that governments offered private benefits (monopoly privileges) to select creditors to induce participation in central banks. To explain cross-national differences, I argue that the level of domestic political decentralization negatively affected the incidence and durability of central banking. Countries with decentralized political systems faced regulatory competition from strong local authorities as licensers of banking monopolies, making it difficult to adopt or sustain central banking. Qualitative and statistical evidence from Europe and the United States to about 1850 support the arguments.
Tariffs and Trade Fluctuations: Does Protectionism Matter as Much as We Think?
Authors: Thompson William R. , Reuveny Rafael
Published: July 2002

Despite the widespread assumption that tariffs reduce trade volume in the short term, it is conceivable that long-term expansion and contractions in trade actually drive tariff levels. A Granger causality analysis performed on British, U.S., French, German, Japanese, and a systematic aggregate data on GDP-tariff levels encompassing the 1854–1990 period finds mixed support for both the short- and long-term interpretations. In general, the antecedence of trade on protectionism predominates over the antecedence of protectionism on trade. One implication is that the long-term context should not be ignored in analyzing short-term dynamics.
The Concept of Political Culture
Authors: Formisano Ronald P.
Published: July 2002

Although historians have frequently employed political culture in their writings, they often seem unaware of the long-standing controversy that has engaged social scientists regarding its theoretical grounding, its methods, and its substantive findings. Moreover, cultural historians who have pioneered new ways of looking at symbolic and expressive forms of power have tended to slight the more traditional dimensions of power—such as persisting elite hegemony and control of material resources—that ought not be excluded from the concept's domain. Historians would do well to attend more fully to the implications of political culture, especially its inherently comparative logic.
The Mental Representation of Semitic Words
Authors: Prunet Jean-François , Béland Renée , Idrissi Ali
Published: July 2002

This article is concerned with external evidence bearing on the nature of the units stored in the mental lexicons of speakers of Semitic languages. On the basis of aphasic metathesis errors we collected in a single case study, we suggest that roots can be accessed as independent morphological units. We review documented language games and slips of the tongue that lead to the same conclusion. We also discuss evidence for the morphemic status of templates from aphasic errors, language games, and slips of the tongue. We conclude that the available external evidence is best accounted for within a morpheme-based theory of morphology that forms words by combining roots and templates.
Specialized Neural Systems Underlying Representations of Sequential Movements
Authors: Harrington Deborah L. , Rao Stephen M. , Haaland Kathleen Y. , Bobholz Julie A. , Mayer Andrew R. , Binder Jeffrey R. , Cox Robert W.
Published: July 2002

The ease by which movements are combined into skilled actions depends on many factors, including the complexity of movement sequences. Complexity can be defined by the surface structure of a sequence, including motoric properties such as the types of effectors, and by the abstract or sequence-specific structure, which is apparent in the relations amongst movements, such as repetitions. It is not known whether different neural systems support the cognitive and the sensorimotor processes underlying different structural properties of sequential actions. We investigated this question using whole-brain functional magnetic resonance imaging (fMRI) in healthy adults as they performed sequences of five key presses involving up to three fingers. The structure of sequences was defined by two factors that independently lengthen the time to plan sequences before movement: the number of different fingers (1-3; surface structure) and the number of finger transitions (0-4; sequence-specific structure). The results showed that systems involved in visual processing (extrastriate cortex) and the preparation of sensory aspects of movement (rostral inferior parietal and ventral premotor cortex (PMv)) correlated with both properties of sequence structure. The number of different fingers positively correlated with activation intensity in the cerebellum and superior parietal cortex (anterior), systems associated with sensorimotor, and kinematic representations of movement, respectively. The number of finger transitions correlated with activation in systems previously associated with sequence-specific processing, including the inferior parietal and the dorsal premotor cortex (PMd), and in interconnecting superior temporal-middle frontal gyrus networks. Different patterns of activation in the left and right inferior parietal cortex were associated with different sequences, consistent with the speculation that sequences are encoded using different mnemonics, depending on the sequence-specific structure. In contrast, PMd activation correlated positively with increases in the number of transitions, consistent with the role of this area in the retrieval or preparation of abstract action plans. These findings suggest that the surface and the sequence-specific structure of sequential movements can be distinguished by distinct distributed systems that support their underlying mental operations.
Age Differences in Behavior and PET Activation Reveal Differences in Interference Resolution in Verbal Working Memory
Authors: Jonides John , Marshuetz Christina , Smith Edward E. , Reuter-Lorenz Patricia A. , Koeppe Robert A. , Hartley Alan
Published: July 2002

Older adults were tested on a verbal working memory task that used the item-recognition paradigm. On some trials of this task, response-conflict was created by presenting test-items that were familiar but were not members of a current set of items stored in memory. These items required a negative response, but their familiarity biased subjects toward a positive response. Younger subjects show an interference effect on such trials, and this interference is accompanied by activation of a region of left lateral prefrontal cortex. However, there has been no evidence that the activation in this region is causally related to the interference that the subjects exhibit. In the present study, we demonstrate that older adults show more behavioral interference than younger subjects on this task, and they also show no reliable activation at the same lateral prefrontal site. This leads to the conclusion that this prefrontal site is functionally involved in mediating resolution among conflicting responses or among conflicting representations in working memory.
Visual Discrimination Task Improvement: A Multi-Step Process Occurring During Sleep
Authors: Stickgold Robert , Whidbee Dana , Schirmer Beth , Patel Vipul , Hobson J. Allan
Published: July 2002

Performance on a visual discrimination task shows longterm improvement after a single training session. When tested within 24 hr of training, improvement, was not observed unless subjects obtained at least 6 hr of postraining sleep prior to retesting, in which case improvement was proportional to the amount of sleep in excess of 6 hr. For subjects averaging 8 hr of sleep, overnight improvement was proportional to the amount of slow wave sleep (SWS) in the first quarter of the night, as well as the amount of rapid eye movement sleep (REM) in the last quarter. REM during the intervening 4 hr did not appear to contribute to improvement. A two-step process, modeling throughput as the product of the amount of early SWS and late REM, accounts for 80 percent of intersubject variance. These results suggest that, in the case of this visual discrimination task, both SWS and REM are required to consolidate experience-dependent neuronal changes into a form that supports improved task performance.
Anterior Cingulate and the Monitoring of Response Conflict: Evidence from an fMRI Study of Overt Verb Generation
Authors: Barch Deanna M. , Braver Todd S. , Sabb Fred W. , Noll Douglas C.
Published: July 2002

Studies of a range of higher cognitive functions consistently activate a region of anterior cingulate cortex (ACC), typically posterior to the genu and superior to the corpus collosum. In particular, this ACC region appears to be active in task situations where there is a need to override a prepotent response tendency, when responding is underdetermined, and when errors are made. We have hypothesized that the function of this ACC region is to monitor for the presence of “crosstalk” or competition between incompatible responses. In prior work, we provided initial support for this hypothesis, demonstrating ACC activity in the same region both during error trials and during correct trials in task conditions designed to elicit greater response competition. In the present study, we extend our testing of this hypothesis to task situations involving underdetermined responding. Specifically, 14 healthy control subjects performed a verb-generation task during event-related functional magnetic resonance imaging (fMRI), with the on-line acquisition of overt verbal responses. The results demonstrated that the ACC, and only the ACC, was more active in a series of task conditions that elicited competition among alternative responses. These conditions included a greater ACC response to: (1) Nouns categorized as low vs. high constraint (i.e., during a norming study, multiple verbs were produced with equal frequency vs. a single verb that produced much more frequently than any other); (2) the production of verbs that were weak associates, rather than, strong associates of particular nouns; and (3) the production of verbs that were weak associates for nouns categorized as high constraint. We discuss the implication of these results for understanding the role that the ACC plays in human cognition.
Motor Area Activity During Mental Rotation Studied by Time-Resolved Single-Trial fMRI
Authors: Richter Wolfgang , Somorjai Ray , Summers Randy , Jarmasz Mark , Menon Ravi S. , Gati Joseph S. , Georgopoulos Apostolos P. , Tegeler Carola , Ugurbil Kamil , Kim Seong-Gi
Published: July 2002

The functional equivalence of overt movements and dynamic imagery is of fundamental importance in neuroscience. Here, we investigated the participation of the neocortical motor areas in a classic task of dynamic imagery, Shepard and Metzler's mental rotation task, by time-resolved single-trial functional Magnetic Resonance Imaging (fMRI). The subjects performed the mental-rotation task 16 times, each time with different object pairs. Functional images were acquired for each pair separately, and the onset times and widths of the activation peaks in each area of interest were compared to the response times. We found a bilateral involvement of the superior parietal lobule, lateral premotor area, and supplementary motor area in all subjects; we found, furthermore, that those areas likely participate in the very act of mental rotation. We also found an activation in the left primary motor cortex, which seemed to be associated with the right-hand button press at the end of the task period.
Deficits in Visual Feature Binding Under Isoluminant Conditions
Authors: Lehky Sidney R.
Published: July 2002

The contribution of the magnocellular stream to visual feature binding was examined psychophysically through the use of isoluminant stimuli. Subjects were presented with three briefly flashed colored letters arranged in an array and asked to identify the shape and color of the center letter. The rate of illusory conjunctions was much higher when the letters were isoluminant with a gray background, compared to when the letters were either brighter or dimmer. Over 90% of conjunction errors involved pairing the wrong shape with the correct color, rather than vice versa. Directing attention to the target location with a nonisoluminant cue did not reduce illusory conjunctions. High rates of binding errors under isoluminance are interpreted here in terms of abnormalities in visual form processing rather than an attentional effect. In another experiment designed to examine the role of synchrony in feature binding, the rate of illusory conjunctions was highest when flanking letters were presented before the central target letter and not synchronously.
The Strategic Control of Gaze Direction in the Tower of London Task
Authors: Hodgson Timothy L. , Bajwa Adnan , Owen Adrian M. , Kennard Christopher
Published: July 2002

In this paper, we describe a novel approach to the study of problem solving involving the detailed analysis of natural scanning eye movements during the “one-touch” Tower-of-London (TOL) task. We showed subjects a series of pictures depicting two arrangements of colored balls in pockets within the uper and lower halves of a computer display. The task was to plan (but not to execute)the shortest movement sequence required to rearrange the balls in one half of the display (the workspace)to match the arrangement in the opposite half (the Goalspace)and indicate the minimum number of moves required for problem solution. We report that subjects are more likely to look towards the Goalspace in the initial period after picture presentation, but bias gaze towards the Workspace during the middle of trials. Towards the end of a trial, subjects are once again more likely to fixate the Goalspace. This pattern is found regardless of whether the subjects solve problems by rearranging the balls in the lower or uper visual fields, demonstrating that this strategy correlates with discreate phases in problem solving. A second experiment showed that efficient planners direct their gaze selectively towards the problem critical balls in the workspace. In contrast, Individuals who make errors spend more time looking at irrelevant items and are strongly influenced by the movement strategy needed to solve the preceding problem. We conclude that efficient solution of the TOL requires the capacity to generate and flexibly shift between control sets, including those underlying ocular scanning. The role of working memory and the prefrontal cerebral cortex in the task are discussed.
The Effects of Divided Attention on Encoding- and Retrieval-Related Brain Activity: A PET Study of Younger and Older Adults
Authors: Anderson Nicole D. , Iidaka Tetsuya , Cabeza Roberto , Kapur Shitij , McIntosh Anthony R. , Craik Fergus I. M.
Published: July 2002

Divided attention (DA) disrupts episodic encoding, but has little effect on episodic retrieval. Furthermore, normal aging is associated with episodic memory impairments, and when young adults are made to encode information under DA conditions, their memory performance is reduced and resembles that of old adults working under full attention (FA) conditions. Together, these results suggest a common neurocognitive mechanism by which aging and DA during encoding disrupt memory performance. In the current study, we used PET to investigate younger and older adults' brain activity during encoding and retrieval under FA and DA conditions. In FA conditions, the old adults showed reduced activity in prefrontal regions that younger adults activated preferentially during encoding or retrieval, as well as increased activity in prefrontal regions young adults did not activate. These results indicate that prefrontal functional specificity of episodic memory is reduced by aging. During encoding, DA reduced memory performance, and reduced brain activity in left-prefrontal and medial-temporal lobe regions for both age groups, indicating that DA during encoding interferes with encoding processes that lead to better memory performance. During retrieval, memory performance and retrieval-related brain activity were relatively immune to DA for both age groups, suggesting that DA during retrieval does not interfere with the brain systems necessary for successful retrieval. Finally, left inferior prefrontal activity was reduced similarly by aging and by DA during encoding, suggesting that the behavioral correspondence between these effects is the result of a reduced ability to engage in elaborate encoding operations.
The Representation of Objects in the Human Occipital and Temporal Cortex
Authors: Ishai Alumit , Ungerleider Leslie G. , Martin Alex , Haxby James V.
Published: July 2002

Recently, we identified, using fMRI, three bilateral regions in the ventral temporal cortex that responded preferentially to faces, houses, and chairs [Ishai, A., Ungerleider, L. G., Martin, A., Schouten, J. L., & Haxby, J. Y. (1999). Distributed representation of objects in the human ventral visual pathway. Proceedings of the National Academy of Sciences, U.S.A., 96, 9379-9384]. Here, we report differential patterns of activation, similar to those seen in the ventral temporal cortex, in bilateral regions of the ventral occipital cortex. We also found category-related responses in the dorsal occipital cortex and in the superior temporal sulcus. Moreover, rather than activating discrete, segregated areas, each category was associated with its own differential pattern of response across a broad expanse of cortex. The distributed patterns of response were similar across tasks (passive viewing, delayed matching) and presentation formats (photographs, line drawings). We propose that the representation of objects in the ventral visual pathway, including both occipital and temporal regions, is not restricted to small, highly selective patches of cortex but, instead, is a distributed representation of information about object form. Within this distributed system, the representation of faces appears to be less extensive as compared to the representations of nonface objects.
Object Orientation Agnosia: A Failure to Find the Axis?
Authors: Harris Irina M. , Harris Justin A. , Caine Diana
Published: July 2002

A dissociation between the ability to recognize misoriented objects and to determine their orientation has been reported in a small number of patients with vascular lesions. In this article, we describe a 57-year-old man with probable Alzheimer's disease who shows the same dissociation. Neuro-imaging findings indicated marked hypometabolism in the posterior cortical regions, particularly the postero-superior parietal lobes. Clinically, the patient had good object recognition accompanied by severely impaired spatial abilities. The experimental investigations comprised a variety of tasks in which he identified misoriented objects, evaluated the orientation of single objects, or discriminated the orientation of simultaneously presented items. Results revealed that his object recognition was independent of orientation and was largely mediated by salient features. With respect to orientation judgements, the patient displayed a profound inability to judge the orientation of nonupright objects, but remarkably intact (though largely implicit) knowledge of the upright orientation. Strikingly, his orientation judgements were also more accurate for upside-down objects than for other orientations (i.e., 90°). We interpret these results as evidence that judgements about object orientation are facilitated when the orientation of the principal axis of the object matches that of an internal representation. We propose that the inability to determine other orientations may be due to the failure of an “axis-finding” mechanism implemented in the posterior parietal lobes, that translates between object-centered and eye-centered coordinates appropriate for guiding visual scanning.
Visual Representation in the Wild: How Rhesus Monkeys Parse Objects
Authors: Munakata Yuko , Santos Laurie R. , Spelke Elizabeth S. , Hauser Marc D. , O'Reilly Randall C.
Published: July 2002

Visual object representation was studied in free-ranging rhesus monkeys. To facilitate comparison with humans, and to provide a new tool for neurophysiologists, we used a looking time procedure originally developed for studies of human infants. Monkeys' looking times were measured to displays with one or two distinct objects, separated or together, stationary or moving. Results indicate that rhesus monkeys used featural information to parse the displays into distinct objects, and they found events in which distinct objects moved together more novel or unnatural than events in which distinct objects moved separately. These findings show both common-alities and contrasts with those obtained from human infants. We discuss their implications for the development and neural mechanisms of higher-level vision.
The Role of Large-Scale Memory Organization in the Mismatch Negativity Event-Related Brain Potential
Authors: Winkler István , Schröger Erich , Cowan Nelson
Published: July 2002

The mismatch negativity (MMN) component of event-related brain potentials is elicited by infrequent changes in regular acoustic sequences even if the participant is not actively listening to the sound sequence. Therefore, the MMN is assumed to result from a preattentive process in which an incoming sound is checked against the automatically detected regularities of the auditory sequence and is found to violate them. For example, presenting a discriminably different (deviant) sound within the sequence of a repetitive (standard) sound elicits the MMN. In the present article, we tested whether the memory organization of the auditory sequence can affect the preattentive change detection indexed by the MMN. In Experiment 1, trains of six standard tones were presented with a short, 0.5-sec stimulus onset asynchrony (SOA) between tones in the train. This was followed by a variable SOA between the last standard and the deviant tone (the “irregular presentation” condition). Of 12 participants displaying an MMN at the 0.5-sec predeviant SOA, it was elicited by 11 with the 2-sec predeviant SOA, in 5 participants with the 7-sec SOA, and in none with the 10-sec SOA. In Experiment 2, we repeated the 7-sec irregular predeviant SOA condition, along with a “regular presentation” condition in which the SOA between any two tones was 7 sec. MMN was elicited in about half of the participants (9 out of 16) in the irregular presentation condition, whereas in the regular presentation condition, MMN was elicited in all participants. These results cannot be explained on the basis of memory-strength decay but can be interpreted in terms of automatic, auditory preperceptual grouping principles. In the irregular presentation condition, the close grouping of standards may cause them to become irrelevant to the mismatch process when the deviant tone is presented after a long silent break. Because the MMN indexes preattentive auditory processing, the present results provide evidence that large-scale preperceptual organization of auditory events occurs despite attention being directed away from the auditory stimuli.
Electrophysiological Correlates of Emotion-Induced Recognition Bias
Authors: Windmann Sabine , Kutas Marta
Published: July 2002

The question of how emotions influence recognition memory is of interest not only within basic cognitive neuro-science but from clinical and forensic perspectives as well. Emotional stimuli can induce at “recognition bias” such that individuals are more likely to respond “old” to a negative item than to an emotionally neutral item, whether the item is actually old or new. We investigated this bias using event-related brain potential (ERP) measures by comparing the processing of words given “old” responses with accurate recognition of old/new differences. For correctly recognized items, the ERP difference between old items (hits) and new items (correct rejections, CR) was largely unaffected by emotional violence. That is, regardless of emotional valence, the ERP associated with hits was characterized by a widespread positivity between 300 and 700 msec relative to that for CRs. By contrast, the analysis of ERPs to old and new items that were judged “old” (hits and false alarms [FAs], respectively) revealed a differential effect of valence by 300 msec: Neutral items showed a large old/new difference over prefrontal sites, whereas negative items did not. These results are the first clear demonstration of response bias effects on ERPs linked to recognition memory. They are consistent with the idea that frontal cortex areas may be responsible for relaxing the retrieval criterion for negative stimuli so as to ensure that emotional events are not as easily “missed” or forgotten as neutral events.
The Number of Synaptic Inputs and the Synchrony of Large, Sparse Neuronal Networks
Authors: Golomb D. , Hansel D.
Published: July 2002

The prevalence of coherent oscillations in various frequency ranges in the central nervous system raises the question of the mechanisms that synchronize large populations of neurons. We study synchronization in models of large networks of spiking neurons with random sparse connectivity. Synchrony occurs only when the average number of synapses, M, that a cell receives is larger than a critical value, Mc. Below Mc, the system is in an asynchronous state. In the limit of weak coupling, assuming identical neurons, we reduce the model to a system of phase oscillators that are coupled via an effective interaction, Γ. In this framework, we develop an approximate theory for sparse networks of identical neurons to estimate Mc analytically from the Fourier coefficients of Γ. Our approach relies on the assumption that the dynamics of a neuron depend mainly on the number of cells that are presynaptic to it. We apply this theory to compute Mc for a model of inhibitory networks of integrate-and-fire (I&F) neurons as a function of the intrinsic neuronal properties (e.g., the refractory period Tr), the synaptic time constants, and the strength of the external stimulus, Iext. The number Mc is found to be nonmonotonous with the strength of Iext. For Tr = 0, we estimate the minimum value of Mc over all the parameters of the model to be 363.8. Above Mc, the neurons tend to fire in smeared one-cluster states at high firing rates and smeared two-or-more-cluster states at low firing rates. Refractoriness decreases Mc at intermediate and high firing rates. These results are compared to numerical simulations. We show numerically that systems with different sizes, N, behave in the same way provided the connectivity, M, is such that 1/Meff = 1/M — 1/N remains constant when N varies. This allows extrapolating the large N behavior of a network from numerical simulations of networks of relatively small sizes (N = 800 in our case). We find that our theory predicts with remarkable accuracy the value of Mc and the patterns of synchrony above Mc, provided the synaptic coupling is not too large. We also study the strong coupling regime of inhibitory sparse networks. All of our simulations demonstrate that increasing the coupling strength reduces the level of synchrony of the neuronal activity. Above a critical coupling strength, the network activity is asynchronous. We point out a fundamental limitation for the mechanisms of synchrony relying on inhibition alone, if heterogeneities in the intrinsic properties of the neurons and spatial fluctuations in the external input are also taken into account.
Architecture-Independent Approximation of Functions
Authors: Angulo Vicente Ruiz de , Torras Carme
Published: July 2002

We show that minimizing the expected error of a feedforward network over a distribution of weights results in an approximation that tends to be independent of network size as the number of hidden units grows. This minimization can be easily performed, and the complexity of the resulting function implemented by the network is regulated by the variance of the weight distribution. For a fixed variance, there is a number of hidden units above which either the implemented function does not change or the change is slight and tends to zero as the size of the network grows. In sum, the control of the complexity depends on only the variance, not the architecture, provided it is large enough.
A Proposed Function for Hippocampal Theta Rhythm: Separate Phases of Encoding and Retrieval Enhance Reversal of Prior Learning
Authors: Hasselmo Michael E. , Bodelón Clara , Wyble Bradley P.
Published: July 2002

The theta rhythm appears in the rat hippocampal electroencephalogram during exploration and shows phase locking to stimulus acquisition. Lesions that block theta rhythm impair performance in tasks requiring reversalofpriorlearning, includingreversalinaT-maze, whereassociations between one arm location and food reward need to be extinguished in favor of associations between the opposite arm location and food reward. Here, a hippocampal model shows how theta rhythm could be important for reversal in this task by providing separate functional phases during each 100-300 msec cycle, consistent with physiological data. In the model, effective encoding of new associations occurs in the phase when synaptic input from entorhinal cortex is strong and long-term potentiation (LTP) of excitatory connections arising from hippocampal region CA3 is strong, but synaptic currents arising from region CA3 input are weak (to prevent interference from prior learned associations). Retrieval of old associations occurs in the phase when entorhinal input is weak and synaptic input from region CA3 is strong, but when depotentiation occurs at synapses from CA3 (to allow extinction of prior learned associations that do not match current input). These phasic changes require that LTP at synapses arising from region CA3 should be strongest at the phase when synaptic transmission at these synapses is weakest. Consistent with these requirements, our recent data show that synaptic transmission in stratum radiatum is weakest at the positive peak of local theta, which is when previous data show that induction of LTP is strongest in this layer.
Population Coding and Decoding in a Neural Field: A Computational Study
Authors: Wu Si , Amari Shun-ichi , Nakahara Hiroyuki
Published: July 2002

This study uses a neural field model to investigate computational aspects of population coding and decoding when the stimulus is a single variable. A general prototype model for the encoding process is proposed, in which neural responses are correlated, with strength specified by a gaussian function of their difference in preferred stimuli. Based on the model, we study the effect of correlation on the Fisher information, compare the performances of three decoding methods that differ in the amount of encoding information being used, and investigate the implementation of the three methods by using a recurrent network. This study not only re-discovers main results in existing literatures in a unified way, but also reveals important new features, especially when the neural correlation is strong. As the neural correlation of firing becomes larger, the Fisher information decreases drastically. We confirm that as the width of correlation increases, the Fisher information saturates and no longer increases in proportion to the number of neurons. However, we prove that as the width increases further—wider than p2 times the effective width of the turning function—the Fisher information increases again, and it increases without limit in proportion to the number of neurons. Furthermore, we clarify the asymptotic efficiency of the maximum likelihood inference (MLI) type of decoding methods for correlated neural signals. It shows that when the correlation covers a nonlocal range of population (excepting the uniform correlation and when the noise is extremely small), the MLI type of method, whose decoding error satisfies the Cauchy-type distribution, is not asymptotically efficient. This implies that the variance is no longer adequate to measure decoding accuracy.
A Neural Model of Contour Integration in the Primary Visual Cortex
Authors: Li Zhaoping
Published: July 2002

Experimental observations suggest that contour integration may take place in V1. However, there has yet to be a model of contour integration that uses only known V1 elements, operations, and connection patterns.This article introduces such a model, using orient ation selective cells, local cortical circuits, and horizontal intracortical connections. The model is composed of recurrently connected excitatory neurons and inhibitory interneurons, receiving visual input via oriented receptive fields resembling those found in primary visual cortex. Intracortical interactions modify initial activity patterns from input, selectively amplifying the activities of edges that form smooth contours in the image. The neural activities produced by such interactions are oscillatory and edge segments within a contour oscillate in synchrony. It is shown analytically and empirically that the extent of contour enhancement and neural synchrony increases with the smoothness, length, and closure of contours, as observed in experiments on some of these phenomena. In addition, the model incorporates a feedback mechanism that allows higher visual centers selectively to enhance or suppress sensitivities to given contours, effectively segmenting one from another. The model makes the testable prediction that the horizontal cortical connections are more likely to target excitatory (or inhibitory) cells when the two linked cells have their preferred orientation aligned with (or orthogonal to) their relative receptive field center displacements.
High-Order Contrasts for Independent Component Analysis
Authors: Cardoso Jean-François
Published: July 2002

This article considers high-order measures of independence for the independent component analysis problem and discusses the class of Jacobi algorithms for their optimization. Several implementations are discussed. We compare the proposed approaches with gradient-based techniques from the algorithmic point of view and also on a set of biomedical data.
Rave New World: Trance-Mission, Trance-Nationalism, and Trance-scendence in the “New” South Africa
Authors: Marlin-Curiel Stephanie
Published: July 2002

In the “new South Africa” some young Afrikaners are using raves to explore ways for finding a constructive place for themselves, their language, and their culture. This is the winning entry in TDR's 2000 Student Essay Contest.
Evaluation of Rate-Based, Force-Reflecting Teleoperation in Free Motion and Contact
Authors: Williams Robert L. , Henry Jason M. , Repperger Daniel W.
Published: July 2002

This research focuses on improved control for force-reflecting teleoperation systems in free motion and contact tasks. Specifically, the Naturally Transitioning Rate-to-Force Controller (NTRFC) is implemented in an Air Force experimental force-reflecting teleoperation system to achieve a unified controller with no mode switches from free motion to contact, and to reduce the wrench exerted on the environment by the slave manipulator during remote teleoperation tasks. In an effectiveness evaluation experiment, the experimental hypothesis is validated: the NTRFC with force reflection performs the best amongst four teleoperation control modes with respect to minimal wrench exertion on the environment. A negligible difference was found in total task-completion times amongst the four modes. The NTRFC with force reflection has the potential to improve task performance in remote, hazardous, teleoperation tasks in which minimal exerted wrench is desirable.
Virtual Reality-Based Simulation of Endoscopic Surgery
Authors: Székely G. , Brechbühler Ch. , Dual J. , Enzler R. , Hug J. , Hutter R. , Ironmonger N. , Kauer M. , Meier V. , Niederer P. , Rhomberg A. , Schmid P. , Schweitzer G. , Thaler M. , Vuskovic V. , Tröster G. , Haller U. , Bajka M.
Published: July 2002

Virtual reality (VR)-based surgical simulator systems offer a very elegant approach to enriching and enhancing traditional training in endoscopic surgery. However, while a number of VR simulator systems have been proposed and realized in the past few years, most of these systems are far from being able to provide a reasonably realistic surgical environment. We explore the current limits for realism and the approaches to reaching and surpassing those limits by describing and analyzing the most important components of VR-based endoscopic simulators. The feasibility of the proposed techniques is demonstrated on a modular prototype system that implements the basic algorithms for VR training in gynaecologic laparoscopy.
Duration and Exposure to Virtual Environments: Sickness Curves During and Across Sessions
Authors: Kennedy Robert S. , Stanney Kay M. , Dunlap William P.
Published: July 2002

Although simulator sickness is known to increase with protracted exposure and to diminish with repeated sessions, limited systematic research has been performed in these areas. This study reviewed the few studies with sufficient information available to determine the effect that exposure duration and repeated exposure have on motion sickness. This evaluation confirmed that longer exposures produce more symptoms and that total sickness subsides over repeated exposures. Additional evaluation was performed to investigate the precise form of this relationship and to determine whether the same form was generalizable across varied simulator environments. The results indicated that exposure duration and repeated exposures are significantly linearly related to sickness outcomes (duration being positively related and repetition negatively related to total sickness). This was true over diverse systems and large subject pools. This result verified the generalizability of the relationships among sickness, exposure duration, and repeated exposures. Additional research is indicated to determine the optimal length of a single exposure and the optimal intersession interval to facilitate adaptation.
Haptic Representation of Elastic Objects
Authors: Hirota Koichi , Kaneko Toyohisa
Published: July 2002

In this paper, a method for visually and haptically representing elastic objects in a virtual environment is proposed. A linear FEM (finite-element method) model is employed to define the elasticity of an object. By computing the inverse stiffness matrix in advance, the force and the displacement according to the interaction are obtained in real time using the precomputed inverse stiffness matrix. Based on the fast-computation method of FEM, an approach for implementing an elastic virtual object is proposed. In this approach, a force interpolation method is introduced to realize a smooth change of the feedback force on the surface of objects. Moreover, the force update process and deformation process are executed asynchronously to attain a high update rate of force.
Note on Information Transfer Rates in Human Communication
Authors: Reed Charlotte M. , Durlach Nathaniel I.
Published: July 2002

Information-transfer (IT) rates in bits/sec were estimated for a variety of methods of human communication and modalities of reception. Using previously published data, a range of communication rates for which transmission is highly accurate was established for each method and modality. These communication rates were converted into a normalized unit of transmission (words/sec). The normalized units were then converted into estimates of IT rate (bits/sec) using Shannon's (1951) calculations of the information content of a single letter of the alphabet. Maximal estimates of IT rates of roughly 40 to 60 bits/sec are observed for speech (through audition) and for reading and sign language (through vision). Maximal rates roughly 50 percent lower are obtained for reading through the tactual sense. Estimates of IT rates for motor output tasks are also considered. A close correspondence is generally observed between IT rates for receiving a given display and IT rates for the motor output task required for producing the display. These results have implications for the design of synthetic-environment systems and the displays and controls to be used in these systems, by providing examples of communication rates that have been achieved by humans in the area of language communication.
Sensing and Displaying Spatially Distributed Fingertip Forces in Haptic Interfaces for Teleoperator and Virtual Environment Systems
Authors: Lederman Susan J. , Klatzky Roberta L.
Published: July 2002

This article reports a variety of sensory and perceptual consequences of eliminating, via a rigid fingertip sheath, the spatially distributed fingertip force information that is normally available during tactile and haptic sensing. Sensory measures included tactile spatial acuity, tactile force, and vibrotactile thresholds. Suprathreshold tasks included perception of roughness, perception of 2-D edge orientation, and detection of a simulated 3-D mass in simulated tissue via fingertip palpation. Of these performance measures, only vibrotactile thresholds and texture perception failed to show substantial impairment. The results are discussed in terms of their implications for the future design of haptic interfaces for teleoperator and virtual environment systems.
WYSIWYF Display: A Visual/Haptic Interface to Virtual Environment
Authors: Yokokohji Yasuyoshi , Hollis Ralph L. , Kanade Takeo
Published: July 2002

To build a VR training system for visuomotor skills, an image displayed by a visual interface should be correctly registered to a haptic interface so that the visual sensation and the haptic sensation are both spatially and temporally consistent. In other words, it is desirable that what you see is what you feel (WYSIWYF).

In this paper, we propose a method that can realize correct visual/haptic registration, namely WYSIWYF, by using a vision-based, object-tracking technique and a video-keying technique. Combining an encountered-type haptic device with a motion-command-type haptic rendering algorithm makes it possible to deal with two extreme cases (free motion and rigid constraint). This approach provides realistic haptic sensations, such as free-to-touch and move-and-collide. We describe a first prototype and illustrate its use with several demonstrations. The user encounters the haptic device exactly when his or her hand reaches a virtual object in the display. Although this prototype has some remaining technical problems to be solved, it serves well to show the validity of the proposed approach.
Open Problems in Artificial Life
Authors: Bedau Mark A. , McCaskill John S. , Packard Norman H. , Rasmussen Steen , Adami Chris , Green David G. , Ikegami Takashi , Kaneko Kunihiko , Ray Thomas S.
Published: July 2002

This article lists fourteen open problems in artificial life, each of which is a grand challenge requiring a major advance on a fundamental issue for its solution. Each problem is briefly explained, and, where deemed helpful, some promising paths to its solution are indicated.