bluuebunny/crossref_metadata_2025 huggingface dataset:
Neural Representations for Sensorimotor Control. III. Learning a Body-Centered Representation of a Three-Dimensional Target Position
Authors: Guenther Frank H. , Bullock Daniel , Greve Douglas , Grossberg Stephen
Published: February 2008

A neural model is described of how the brain may autonomously learn a body-centered representation of a three-dimensional (3-D) target position by combining information about retinal target position, eye position, and head position in real time. Such a body-centered spatial representation enables accurate movement commands to the limbs to be generated despite changes in the spatial relationships between the eyes, head, body, and limbs through time. The model learns a vector representation—otherwise known as a parcellated distributed representation—of target vergence with respect to the two eyes, and of the horizontal and vertical spherical angles of the target with respect to a cyclopean egocenter. Such a vergence-spherical representation has been reported in the caudal midbrain and medulla of the frog, as well as in psychophysical movement studies in humans. A head-centered vergence-spherical representation of foveated target position can be generated by two stages of opponent processing that combine corollary discharges of outflow movement signals to the two eyes. Sums and differences of opponent signals define angular and vergence coordinates, respectively. The head-centered representation interacts with a binocular visual representation of nonfoveated target position to learn a visuomotor representation of both foveated and nonfoveated target position that is capable of commanding yoked eye movements. This head-centered vector representation also interacts with representations of neck movement commands to learn a body-centered estimate of target position that is capable of Commanding coordinated arm movements. Learning occurs during head movements made while gaze remains fixed on a foveated target. An initial estimate is stored and a VOR-mediated gating signal prevents the stored estimate from being reset during a gaze-maintaining head movement. As the head moves, new estimates are compared with the stored estimate to compute difference vectors which act as error signals that drive the learning process, as well as control the on-line merging of multimodal information.
Do Rats Have Prefrontal Cortex? The Rose-Woolsey-Akert Program Reconsidered
Authors: Preuss Todd M.
Published: February 2008

Primates are unique among mammals in possessing a region of dorsolateral prefrontal cortex with a well-developed internal granular layer. This region is commonly implicated in higher cognitive functions. Despite the histological distinctiveness of primate dorsolateral prefrontal cortex, the work of Rose, Woolsey, and Akert produced a broad consensus among neuroscientists that homologues of primate granular frontal cortex exist in nonprimates and can be recognized by their dense innervation from the mediodorsal thalamic nucleus (MD). Additional characteristics have come to be identified with dorsolateral prefrontal cortex, including rich dopaminergic innervation and involvement in spatial delayed-reaction tasks. However, recent studies reveal that these characteristics are not distinctive of the dorsolateral prefrontal region in primates: MD and dopaminergic projections are widespread in the frontal lobe, and medial and orbital frontal areas may play a role in delay tasks. A reevaluation of rat frontal cortex suggests that the medial frontal cortex, usually considered to be homologous to the dorsolateral prefrontal cortex of primates, actually consists of cortex homologous to primate premotor and anterior cin-date cortex. The lateral MD-projection cortex of rats resembles portions of primate orbital cortex. If prefrontal cortex is construed broadly enough to include orbital and cingulate cortex, rats can be said to have prefrontal cortex. However, they evidently lack homologues of the dorsolateral prefrontal areas of primates. This assessment suggests that rats probably do not provide useful models of human dorsolateral frontal lobe function and dysfunction, although they might prove valuable for understanding other regions of frontal cortex.
Distinct Cortical Activation Patterns during Long-Term Memory Retrieval of Verbal, Spatial, and Color Information
Authors: Rösler Frank , Heil Martin , Hennighausen Erwin
Published: February 2008

Slow, DC-like event-related brain potentials (ERPs) were recorded from the scalp of 30 healthy young adults to test the hypothesis that distinct cortical areas are activated when different types of information are retrieved from long-term memory. Three groups of 10 subjects each were first trained with associations between either pictures and spatial positions (spatial condition), pictures and color patches (color condition), or nouns and nouns (verbal condition). All three experimental conditions were completely analogous with respect to the established associative structure, the learning procedure, the performance criterion, and the retrieval test that followed 1 day after learning. Slow event-related brain potentials being recorded during retrieval had a significantly distinct topography. The maximum of a DC-like negative wave was found in the verbal condition over the left frontal, in the spatial condition over the parietal, and in the color condition over the right occipital to temporal cortex. These results are consistent with the idea that memory representations are either “down-loaded” into or directly reactivated within those cortical processing modules in which the same material was handled during perception. Response times, on the other hand, revealed no difference between the three retrieval conditions. In each case RT increased monotonically, if more items had to be scanned. Thus, while the ERPs suggest the involvement of different cortical processors during memory search the response times suggest that a sequentially operating scanning mechanism applies to all of them.
Separate Representation of Stimulus Frequency, Intensity, and Duration in Auditory Sensory Memory: An Event-Related Potential and Dipole-Model Analysis
Authors: Giard M. H. , Lavikahen J. , Reinikainen K. , Perrin F. , Bertrand O. , Pernier J. , Näätänen R
Published: February 2008

The present study analyzed the neural correlates of acoustic stimulus representation in echoic sensory memory. The neural traces of auditory sensory memory were indirectly studied by using the mismatch negativity (MMN), an event-related potential component elicited by a change in a repetitive sound. The MMN is assumed to reflect change detection in a comparison process between the sensory input from a deviant stimulus and the neural representation of repetitive stimuli in echoic memory. The scalp topographies of the MMNs elicited by pure tones deviating from standard tones by either frequency, intensity, or duration varied according to the type of stimulus deviance, indicating that the MMNs for different attributes originate, at least in part, from distinct neural populations in the auditory cortex. This result was supported by dipole-model analysis. If the MMN generator process occurs where the stimulus information is stored, these findings strongly suggest that the frequency, intensity, and duration of acoustic stimuli have a separate neural representation in sensory memory.
Agrammatism: Behavioral Description and Neurobiological Explanation
Authors: Pulvermüller Friedemann
Published: February 2008

Subjects with brain damage resulting in agrammatic aphasia frequently omit or substitute function items (function words and inflectional affixes). However, they show only mild deficits in using meaningful content words. Agrammatics' performance on comprehension tests reveals a rather complex pattern. They usually understand active sentences correctly, but perform on chance level on passives. The same contrast is observed for more complex sentence types, such as subject vs. object clefts or relatives. This complex comprehension pattern suggests that agrammatism is a syntactic disturbance that selectively affects particular sentence structures. Nevertheless, it is possible that both the production and comprehension patterns go back to an access problem for grammatical morphemes. If an agrammatic aphasic comprehends only 50% of these morphemes, she or he may well be problem-free in understanding the resulting “pruned” active sentences in which some of the grammatical morphemes are missing. In contrast, she or he is likely to arrive at the wrong meaning when confronted with “pruned” passives. This hypothesis raises the question of how fully competent speakers interpret ungrammatical “pruned” strings derived from well-formed sentences by systematically deleting function items. Experimental data demonstrate that competent speakers approximate the agrammatic comprehension pattern when being presented with “pruned” strings. This argues that agrammatism can, indeed, be viewed as a deficit in processing function words and inflectional affixes, which may manifest itself in production and/or comprehension tasks. Assuming that cortical cell assemblies with distinct topographies correspond to content words and grammatical morphemes, it is possible to explain agrammatism in terms of lesions to these neuronal networks. This neurobiological model can explain additional aspects of agrammatics' performance.
Recognition of CVC Syllables from LVF, RVF, and Central Locations: Hemispheric Differences and Interhemispheric Interaction
Authors: Hellige Joseph B. , Cowin Elizabeth L. , Eng Tami L.
Published: February 2008

In each of two experiments, subjects were required to identify consonant-vowel-consonant nonsense syllables projected to the left visual fiel/right hemisphere (LVF/RH), right visual field/left hemisphere (RVF/LH), or to the CENTER of the visual field. There were fewer errors on RVF/LH than on LVF/RH trials and the pattern of errors was qualitatively different on RVF/LH and LVF/RH trials. The pattern of errors was consistent with the hypothesis that attention is distributed across the three letters in a relatively slow serial fashion on LVF/RH trials whereas attention is distributed more rapidly and evenly across the three letters on RVF/LH trials. Despite the large RVF/LH advantage, the qualitative pattern of errors on CENTER trials (when viewing conditions do not favor one hemisphere or the other) was very similar to the pattern obtained on LW/RH trials. Implications of this counterintuitive finding are considered for the nature of interhemispheric interaction.
Double Dissociation between Overt and Covert Face Recognition
Authors: Tranel Daniel , Damasio Hanna , Damasio Antonio R.
Published: February 2008

Some patients with face agnosia (prosopagnosia) caused by occipitotemporal damage produce discriminatory covert responses to the familiar faces that they fail to identify overtly. For example, their average skin conductance responses (SCRs) to familiar faces are significantly larger than average SCRs to unfamiliar faces. In this study we describe the opposite dissociation in four patients with bilateral ventromedial frontal damage: The patients recognized the identity of familiar faces normally, yet failed to generate discriminatory SCRs to those same familiar faces. Taken together, the two sets of results constitute a double dissociation: bilateral occipitotemporal damage impairs recognition but allows SCR discrimination, whereas bilateral ventromedial damage causes the opposite. The findings suggest that the neural systems that process the somatic-based valence of stimuli are separate from and parallel to the neural systems that process the factual, nonsomatic information associated with the same stimuli.
A Positron Emission Tomography Study of Visual and Mental Spatial Exploration
Authors: Mellet E. , Tzourio N. , Denis M. , Mazoyer B.
Published: February 2008

We measured normalized regional cerebral blood flow (NrCBF) using positron emission tomography (PET) and oxygen-15-labeled water in eight young right-handed healthy volunteers selected as high-imagers. during 2 runs of 3 different conditions: 1, rest in total darkness 2; visual exploration of a map 3; mental exploration of the same map in total darkness. NrCBF images were aligned with individual magnetic resonance images (MRI), and NrCBF variations between pairs of measurements (N = 15) were computed in regions of interest having anatomical boundaries that were defined using a three-dimensional (3-D) reconstruction of each subject MRI. During visual exploration, we found bilateral activations of primary visual areas, superior and inferior occipital gyri, fusiform and lingual gyri, cuneus and precuneus, bilateral superior parietal, and angular gyri. The right lateral premotor area was also activated during this task while superior temporal gyri and Broca's area were deactivated. By contrast, mental exploration activated the right superior occipital cortex, the supplementary motor area, and the cerebellar vermis. No activation was observed in the primary visual area. These results argue for a specific participation of the superior occipital cortex in the generation and maintenance of visual mental images.
Rapid Changes of Optical Parameters in the Human Brain During a Tapping Task
Authors: Gratton Gabriele , Fabiani Monica , Friedman David , Franceschini Maria Angela , Fantini Sergio , Corballis Paul , Gratton Enrico
Published: February 2008

Measures of parameters of the migration of near-infrared photons through the head (attenuation, or intensity, and time-of-flight, or delay) have been proposed as a way of assessing noninvasively and in a quasicontinuous fashion changes in the scattering and absorption properties of brain tissue. These, in turn, may reflect functional changes associated with behavioral tasks. To test this hypothesis, we measured changes of photon migration parameters from scalp locations proximal to the motor cortex from four human subjects, tapping at a rate of 0.8 Hz with their left or right hand, or with their left or right foot. Tapping produced both slow effects (requiring several seconds) and fast effects (tracking the tapping frequency). Slow effects were characterized by increase and delay of the light passing through the hemisphere contralateral to the tapping hand. Fast effects consisted of changes in the light delay during hand tapping. Monte Carlo simulations based on layer models of the brain indicated that fast effects are consistent with changes in deep layers of the head (presumably in the cortex), and that slow effects are consistent with either a shift of absorbing material toward deeper layers or a reduction in scattering. These results suggest that optical parameters can monitor rapid changes of brain activity, matching the contralateral organization of the motor cortex.
Neural Representations: Some Old Problems Revisited
Authors: Milner Peter M.
Published: February 2008

Hebb's (1949) cell assembly, originally conceived as an explanation for stimulus equivalence, also serves as a neural representation of stimuli. Association between cell assemblies was a major theme of Hebb's book, but the state of physiological knowledge at the time was such that no satisfactory basis for it could he devised. Subsequent theory has been more concerned with the recognition and “attractor” features of the cell assembly than its capacity to represent and associate concepts. This is unfortunate because while generalization is important, so is discrimination, which is not well served by an attractor model. This dilemma is avoided by postulating that stimulus representation and stimulus equivalence involve different neural circuits. Human beings can instantly form and use associations between many more concepts than there are synapses on the average cortical neuron, indicating that the associative links between engrams are sparse. The connections within an engram, on the other hand. must be dense to ensure that a weak input can activate all its neurons. It would appear that two processes are anatomically and physiologically different, which may account for the fact that engrams remain distinct in spite of being associated with each other. The fact that a single concept may have very many associations puts a heavy demand on the process of selective attention to avert complete chaos. I propose that attention is a manifestation of motivation. Motivation facilitates responses, which in turn facilitate engrams of associated stimuli. The enhanced engram activity is fed back through centrifugal paths to intensify sensory input that has previously played a part in executing the planned responses. Attention may also contribute to a mechanism that prevents the engrams of component parts of an object from being assimilated into the engram of the whole.
Development of Schemata during Event Parsing: Neisser's Perceptual Cycle as a Recurrent Connectionist Network
Authors: Hanson Catherine , Hanson Stephen José
Published: February 2008

Neural net simulations of human event parsing are described. A recurrent net was used to simulate data collected from human subjects watching short videotaped event sequences. In one simulation, the net was trained on one-half of a taped sequence with the other half of the sequence being used to test transfer performance. In another simulation, the net was trained on one complete event sequence and transfer to a different event sequence was tested. Neural net simulations provide a unique means of observing the interrelation of top-down and bottom-up processing in a basic cognitive task. Examination of computational patterns of the net and cluster analysis of the hidden units revealed two factors that may be central to event perception: (1) similarity between a current input and an activated schema and (2) expected duration of a given event. Although the importance of similarity between input and activated schemata during event perception has been acknowledged previously (e.g., Neisser, 1976; Schank, 1982), the present study provides specific instantiation of how similarity judgments can be made using both top-down and bottom-up processing. Moreover, unlike other work on event perception, this approach provides a potential mechanism for how schemata develop.
Progressive Nonfluent Aphasia: Language, Cognitive, and PET Measures Contrasted with Probable Alzheimer's Disease
Authors: Grossman Murray , Mickanin Jenifer , Onishi Kris , Hughes Elizabeth , D'Esposito Mark , Ding Xin-Sheng , Alavi Abass , Reivich Martin
Published: February 2008

The purpose of this study was to compare the language and cognitive profiles of four progressive nonfluent aphasia (PNFA) patients with 25 probable Alzheimer's disease (pAD) patients, and to identify the distinct cortical defects associated with cognitive deficits in PNFA using positron emission tomography (PET). Longitudinal observations of PNFA patients revealed progressively telegraphic speech and writing and a gradual deterioration of sentence comprehension, but memory and visual functioning were relatively preserved. Direct contrast with PAD patients revealed that PNFA patients are significantly impaired on grammatical phrase structure aspects of sentence comprehension and expression, phonemic judgments, repetition, and digit span, but not on other cognitive measures. PET studies of PNFA revealed reduced cortical activity throughout the left hemisphere. In addition, there was a prominent defect in left superior and middle temporal and inferior frontal regions of PNFA patients that differed significantly from the distribution of regional cerebral dysfunction in pAD. We conclude that PNFA is associated with a distinct profile of language and cognitive difficulty, and that this pattern of impairment is related to cortical dysfunction in a specific distribution of the left hemisphere.
The Search for “Common Sense”: An Electrophysiological Study of the Comprehension of Words and Pictures in Reading
Authors: Ganis Giorgio , Kutas Marta , Sereno Martin I.
Published: February 2008

Event-related brain potentials (ERPs) from 26 scalp sites were used to investigate whether or not and, if so, the extent to which the brain processes subserving the understanding of imageable written words and line drawings are identical. Sentences were presented one word at a time to 28 undergraduates for comprehension. Each sentence ended with either a written word (regular sentences) or with a line drawing (rebus sentences) that rendered it semantically congruous or semantically incongruous. For half of the subjects regular and rebus sentences were randomly intermixed whereas for the remaining half the regular and rebus sentences were presented in separate blocks (affording within-subject comparisons in both cases). In both presentation formats, words and line drawings generated greater negativity between 325 and 475 msec post-stimulus in ERPs to incongruous relative to congruous sentence endings (i.e., an N400-like effect). While the time course of this negativity was remarkably similar for words and pictures, there were notable differences in their scalp distributions; specifically, the classic N400 effect for words was larger posteriorly than it was for pictures. The congruity effect for pictures but not for words was also associated with a longer duration (lower frequency) negativity over frontal sites. In addition, under the mixed presentation mode, the N400 effect peaked about 30 msec earlier for pictures than for words. All in all, the data suggest that written words and pictures when they terminate sentences are processed similarly, but by at least partially nonoverlapping brain areas.
Dual Population Coding in the Neocortex: A Model of Interaction between Representation and Attention in the Visual Cortex
Authors: Koechlin Etienne , Burnod Yves
Published: February 2008

The text describes a model that extends the population coding principles to any multidimensional attribute. The model distinguishes between the distribution of cell activity and the overall activity of a population. The distribution of cell activity is assumed to encode attribute information, while overall activity is assumed to reflect the significance or pertinence of the encoded attribute in the cerebral cortex, according to the dual coding principle. Three basic mechanisms of interaction between the representation of attribute and pertinence are defined and are applied to the motion (MT-MST) cortical pathway in the visual cortex. This framework determines three sources of pertinence that model cognitive processing, including preattentive processing, spatial-selective attention, and object-selective attention. The model accommodates most of the published psychophysical, neurophysiological, and neuroanatomical data and makes several testable predictions about the representations of attribute and enhanced effects in these areas.
Implicit and Explicit Conceptual Memory Following Frontal Lobe Damage
Authors: Gershberg Felicia B.
Published: February 2008

In two experiments, the performance of patients with frontal lobe lesions was examined on implicit and explicit tests of conceptual memory for organized lists of words. Frontal patients exhibited normal levels of conceptual priming on implicit category production and free association tests, but they exhibited impaired memory performance on explicit category- and associate-cued recall tests. The findings of normal performance on implicit conceptual tests suggest that frontal patients do not have a basic deficit in semantic processing of individual items. Impaired performance on explicit cued recall tests may be related to deficits in the use of organizational encoding and strategic retrieval processes.
The End of the Line for a Brain-Damaged Model of Unilateral Neglect
Authors: Mozer Michael C. , Halligan Peter W. , Marshall John C.
Published: February 2008

For more than a century, it has been known that damage to the right hemisphere of the brain can cause patients to be unaware of the contralesional side of space. This condition, known as unilateral neglect, represents a collection of clinically related spatial disorders characterized by the failure in free vision to respond, explore, or orient to stimuli predominantly located on the side of space opposite the damaged hemisphere. Recent studies using the simple task of line bisection, a conventional diagnostic test, have proven surprisingly revealing with respect to the spatial and attentional impairments involved in neglect. In line bisection, the patient is asked to mark the midpoint of a thin horizontal lie on a sheet of paper. Neglect patients generally transect far to the right of the center. Extensive studies of line bisection have been conducted, manipulating-among other factors-line length, orientation, and position. We have simulated the pattern of results using an existing computational model of visual perception and selective attention called MORSEL (Mozer, 1991). MORSEL has already been used to model data in a related disorder, neglect dyslexia (Mozer & Behrmann, 1990). In this earlier work, MORSEL was “lesioned” in accordance with the damage we suppose to have occurred in the brains of neglect patients. The same model and lesion can simulate the detailed pattern of performance on line bisection, including the following observations: (1) no consistent across-subject bias is found in normals; (2) transection displacements are proportional to line length in neglect patients; (3) variability of displacements is proportional to line length, in both normals and patients; (4) position of the lines with respect to the body or the page on which they are drawn has little effect; and (5) for lines drawn at different orientations, displacements are proportional to the cosine of the orientation angle. MORSEL fails to account for one observation: across patients, the variability of displacements for a particular line length is roughly proportional to mean displacement. Nonetheless, the overall fit of the model is sufficiently good that we believe MORSEL can be used as a diagnostic tool to characterize the specific nature of a patient's deficit, and thereby has potential down the line in therapy.
Islands of Residual Vision in Hemianopic Patients
Authors: Wessinger C. Mark , Fendrich Robert , Gazzaniga Michael S.
Published: February 2008

Following damage to primary visual cortex, some patients our initial findings. The data reveal a patchy distribution of redemonstrate a limited ability to respond to stimuli they do not sidual visual abilities in the absence of acknowledged awareness. acknowledge seeing. This residual vision, which has been referred to as “blindsight,” has been attributed to secondary visual pathways. We previously reported an isolated island of blindsight in one patient and argued it was a likely consequence of cortical sparing in V1. We now report an extension of our initial findings. The data reveal a patchy distribution of residual visual abilities in the absence of acknowledged awareness. Variable patterns of cortical sparing appear to be the most parsimonious way to account for this outcome, suggesting that blindsight is generally mediated by the primary visual pathway.
Functional Neuroimaging of Cortical Dysfunction in Alcoholic Korsakoff's Syndrome
Authors: Paller Ken A. , Acharya Ananth , Richardson Brian C. , Plaisant Odile , Shimamura Arthur P. , Reed Bruce R. , Jagust William J.
Published: February 2008

Many neuropsychological investigations of human memory have focused on the amnesic deficits of alcoholic Korsakoff's syndrome. Structural neuroimaging suggests that the syndrome results from midline diencephalic damage, but functional neuroimaging has the potential to reveal additional neuropathology that may be responsible for cognitive dysfunction. Accordingly, high-resolution positron emission tomography (PET) was used to measure regional cerebral metabolic rates for glucose utilization in five alcoholic Korsakoff patients and nine alcoholic control subjects. Results from a continuous recognition test administered during the radiotracer uptake period indicated that all subjects performed normally with respect to immediate memory, whereas Korsakoff patients demonstrated a marked memory impairment in delayed recognition. PET results from the Korsakoff group showed a widespread decline in glucose metabolism in frontal, parietal, and cingulate regions, suggesting that these functional abnormalities in the cerebral cortex contribute to the memory impairment. Hippocampal glucose metabolism did not differ between the groups. Thus, the evidence did not support the hypothesis that parallel brain dysfunctions are responsible for the similar amnesic symptomatology after hippocampal and diencephalic damage. We hypothesize that the amnesic dysfunction of Korsakoff's syndrome depends on a disruption of thalamocortical interactions that mediate a function critical for normal memory storage.
Egocentric and Allocentric Constraints in the Expression of Patterns of Interlimb Coordination
Authors: Swinnen Stephan P. , Jardin Kris , Meulenbroek Ruud , Dounskaia Natalia , Den Brandt Myriam Hofkens-Van
Published: February 2008

Tasks that are easy when performed in isolation become difficult when performed simultaneously in the upper and/or lower limbs. This observation points to basic CNS constraints in the organization of patterns of interlimb coordination. The present studies provide evidence for the existence of two basic coordinative constraints whose effects may be additive under certain conditions. On one hand, the egocentric constraint denotes a general preference for moving the limbs toward or away from the longitudinal axis of the body in a symmetrical fashion and is of primary importance during the coordination of homologous limbs. On the other hand, the allocentric constraint refers to a general preference to move the limbs in the same direction in extrinsic space and pertains to the coordination of nonhomologous limbs (eg., various combinations of the upper and lower limbs). In the present context, constraints are considered as expressions of basic features of CNS operation that give way to preferred coordination patterns to which the system is naturally drawn or biased. The identification and description of these constraints is considered of critical importance to obtain a better understanding of the control of coordination patterns.
Time-Related Changes in Neural Systems Underlying Attention and Arousal During the Performance of an Auditory Vigilance Task
Authors: Paus Tomáš , Zatorre Robert J. , Hofle Nina , Caramanos Zografos , Gotman Jean , Petrides Michael , Evans Alan C.
Published: February 2008

Vigilance behavior, or watch keeping, involves the focusing of attention on the detection of subtle changes in the environment that occur over a long period of time. We investigated the time course of changes in brain activity during the continuous performance of a 60-min auditory vigilance task. The task required the detection of an intensity drop that occurred in 5% of the auditory stimuli. Six 1-min samples of cerebral blood flow (CBF) and electroencephalographic (EEG) activity were obtained at l0-min intervals during the vigilance performance. Changes in CBF were measured by means of positron emission tomography (PET). Performance data (hits, false alarms, reaction time) were analyzed across six 10-min blocks. Eight healthy male volunteers participated in the study. During the 60-min test, the number of correct detections (hits) did not change, but both the reaction time and EEG activity in the theta (4 to 7 Hz) range progressively increased across testing. CBF in several subcortical structures (thalamus, substantia innominata, and putamen) and cortical areas (ventrolateral, dorsolateral, and orbital frontal cortex; parietal cortex; and temporal cortex) decreased as a function of time-on-task; changes in the cortical regions were limited to the right hemisphere. Blood flow also decreased in the temporalis muscles. At the same time, CBF increased in several visual cortical areas including the left and right fusiform gyri. Furthermore, the thalamic blood-flow response co-varied with that in the substantia innominata, the ponto-mesencephalic tegmentum, and the anterior cingulate cortex. The right ventrolateral-frontal blood-flow response covaried with that in the right parietal, orbitofrontal, and dorsolateral frontal cortex. 'Iko main conclusions are drawn from the obtained data. First, we suggest that the observed time-related changes in reaction time, EEG activity, and blood flow in the temporalis muscles are related to changes in the level of arousal (alertness) and that CBF changes in the thalamus-related neural circuitry represent a brain correlate of such changes. Second, we speculate that time-related CBF decreases in cortical regions of the right hemisphere underlie a shift from controlled to automatic attentional processing of the auditory stimuli.
Localizing Arithmetic Processes in the Brain: Evidence from a Transient Deficit During Cortical Stimulation
Authors: Whalen John , McCloskey Michael , Lesser Ronald P. , Gordon Barry
Published: February 2008

Although substantial progress has been made in characterizing the cognitive processes involved in simple arithmetic, the localization of these processes in the brain is not yet well understood. In this article we consider the localization of a specific arithmetic process, the retrieval of arithmetic table facts from memory. We report a single-patient study in which cortical stimulation was used to create transient disruption of brain activity in localized regions of the cortex. We show that stimulation at a left parietal site impaired performance on simple multiplication problems and further that the impairment reflected stimulation-induced disruption of arithmetic fact retrieval. Our findings support the hypothesis (e.g., Warrington, 1982) that the left parietal lobe is implicated in the arithmetic fact retrieval process.
Visual Imagery: Effects of Short- and Long-Term Memory
Authors: Ishai Alumit , Sagi Dov
Published: February 2008

Visual imagery and perception share several functional properties and apparently share common underlying brain structures. A main approach to the scientific study of visual imagery is exploring the effects of mental imagery on perceptual processes. Previous studies have shown that visual imagery interferes with perception (Perky effect). Recently we have shown a direct facilitatory effect of visual imagery on visual perception. In an attempt to differentiate the conditions under which visual imagery interferes or facilitates visual perception, we designed new experimental paradigms, using detection tasks of a Gabor target. We found that imagery-induced interference and facilitation are memorydependent: Visual recall of common objects from long-term memory can interfere with perception, while on short-term memory tasks facilitation can be obtained. These results support the distinction between low-level and structural representations in visual memory.
Global Rise Of Neoliberal State And Its Impact On Citizenship: Experiences In Developing Nations
Authors: Haque Shamsul
Published: February 2008

In general, the realization of major principles and dimensions of citizenship, especially with regard to people's rights, entitlements, and obligations, is largely determined by the nature of the state, which varies depending on its socio-historical context. It is argued in this article that the recent decades have witnessed a fundamental shift in the nature of the state worldwide, based on neoliberal assumptions, policies, and programs. Focusing mainly on developing countries, the article examines the major tenets of such a neoliberal state, especially with regard to its policy preferences and reorientations, and evaluates its implications for democratic citizenship in these countries. It concludes by exploring some policy alternatives for the revival of such a citizenship.
Politics of Identities and Resources in Chittagong Hill Tracts, Bangladesh: Ethnonationalism and/or Indigenous Identity
Authors: Chowdhury Khairul
Published: February 2008

In recent years, representation of indigenous communities and their relation to resources has been highly contested. Rather than offering critique to the representation of indigenous communities, this paper examines Jumma and indigenous identity formation among the hill peoples of the Chittagong Hill Tracts, their historical contingency and dynamics. I show that groups' identities are products of agencies emerging from a particular pattern of struggle between the group and other political forces of their given circumstance, and are informed by their particular history, place and practices. I also show that claims over resources based on indigenous identity is a recent positioning in comparison to claims based on Jumma identity. Difference and convergence between Jumma and indigenous identities are contingent upon specific historical contexts and groups' relation with the state and its legal provision, and ideological settings.
Globalization and State Autonomy in Singapore
Authors: Khondker Habibul Haque
Published: February 2008

This paper revisits the concept of state autonomy in the context of globalization. Earlier literature either considered state autonomy from the social forces in broad institutional and cultural terms or from the dominant classes in a restrictive sense. However, in either case the focus remained on domestic/national society, not the global society. The discussion of relative autonomy of the state began among the Marxists in the 1970s and then graduated into the mainstream social sciences in the 1980s and 1990s. In the upshot, the notions of developmental state and the embedded autonomy have significantly added to our knowledge of the role of the state. This paper broadens the idea of embedded autonomy by locating the sources of embeddedness in both local as well global institutions and norms. The paper uses the Singapore case to illustrate some of the possibilities and limitations of the reconfigured role of the state in the face of globalization.
Global DNA: Genomics, the Nation-State and Globalisation
Authors: Baber Zaheer
Published: February 2008

Globalization has influenced the conduct of scientific research in a number of expected and unexpected ways. At the same time the emergence of specific scientific fields has also influenced the texture and trajectory of globalization. In this paper the relationship between globalization and genomics is analyzed. Much like the globalization of traditional manufacturing, genomics research represents a phase of global bio-capitalism. With specific reference to Singapore, the possible social, economic and political effects of the rapid global circulation of scientists, knowledge, capital and DNA are examined in this paper.
The First Judgement of the Special Court for Sierra Leone: A Missed Opportunity?
Authors: Guibert Nolwenn , Blumenstock Tilman
Published: February 2008

On 29 June 2007, the Special Court for Sierra Leone – a criminal tribunal created by an agreement between the United Nations and Sierra Leone – rendered its first judgement. The three accused, all senior members of a military junta which had ousted the elected government, were amongst other things found guilty of "new" international crimes, such as using child soldiers and collectively punishing the civilian population. This note critically analyses the achievements and shortcomings of what can be seen as a landmark ruling in international criminal law. It discusses the court's rejection of a separate crime of "forced marriages" as well as the application of "effective control" in terms of responsibility of a superior in the context of an "African conflict". Finally, this note examines the treatment of defective pleadings in the indictment in relation to particulars, crimes committed by the accused in person, and the existence of a joint criminal enterprise. It will be demonstrated that the judgement is of significance not only for assessing the success of the Special Court for Sierra Leone, but also for future criminal trials dealing with similar charges.
New Observations of Precipitation Initiation in Warm Cumulus Clouds
Authors: Small Jennifer D. , Chuang Patrick Y.
Published: February 2008

The mechanism responsible for formation of rain in warm clouds has been debated for over six decades. Here, the authors analyze new measurements of shallow cumulus made with a phase Doppler interferometer during the Rain in Cumulus over the Ocean (RICO) experiment. These observations show that drops sufficiently large (>55-μm diameter) to initiate precipitation (termed collision–coalescence initiators or CCIs) are found preferentially at cloud top, tend to cluster with each other, and are found in environments that are thermodynamically, dynamically, and microphysically distinct from those of smaller drops. The CCI environments exhibit cloud spectra that are shifted to larger sizes, with enhanced broadening toward larger drop sizes. Increased entrainment is also associated with CCIs, suggesting that it is an important process in CCI production. A simple model combining inhomogeneous mixing and condensation is inadequate to explain these observations. It is hypothesized that CCIs are produced in cloud-top regions where turbulence generated by entrainment mixing locally enhances collision–coalescence rates.
The Spectral Ice Habit Prediction System (SHIPS). Part II: Simulation of Nucleation and Depositional Growth of Polycrystals
Authors: Hashino Tempei , Tripoli Gregory J.
Published: February 2008

This paper proposes a framework to predict polycrystals along with hexagonal monocrystals in a cloud-resolving model and discusses validity of the scheme and physical processes important for habit distribution by implementing 2D cloud-resolving simulations of an orographic winter storm. The vapor depositional growth is simulated based on a habit frequency map constructed in the laboratory and based on a predicted growth history under evolving atmospheric conditions. Differences brought by predicting polycrystals in spatial distribution were apparent, and sedimentation of polycrystals from middle and upper levels was significant. The immersion freezing process appeared to be a key process resulting in the creation of planar polycrystals, while the homogeneous freezing process was found important for columnar and irregular polycrystals. The ice nuclei (IN) concentration was shown to affect habit distribution by changing the supersaturation, tendency of the freezing nucleation processes, and sedimentation. Preliminary comparison of simulated habit distributions and frequencies with observations indicates usefulness of the framework for polycrystals. Implications of these modeling studies on the needs of future observational campaigns are discussed.
A Study of the Probability of Clear Line of Sight through Single-Layer Cumulus Cloud Fields in the Tropical Western Pacific
Authors: Taylor Patrick C. , Ellingson Robert G.
Published: February 2008

The plane-parallel horizontal (PPH) hypothesis used to approximate clouds in GCMs neglects three-dimensional cloud effects. Such effects can amount to as much as 20 W m−2 in longwave radiation. Several investigators have proposed accounting for longwave three-dimensional cloud effects by using information on the probability of clear line of sight (PCLoS) to modify the PPH approximation. This study investigates the PCLoS at the Atmosphere Radiation Measurement (ARM) Program’s Tropical Western Pacific (TWP) site. PCLoS is estimated for single-layer tropical marine cumulus cases for 2-h intervals using the Whole Sky Imager (WSI) observations at the Manus and Nauru sites. PCLoS estimates are compared to calculations from a set of simple PCLoS models using measured cloud field statistics as input. A summary of the PCLoS at the TWP site is presented in addition to a statistical summary of retrieved cloud field characteristics. The results are used to investigate the spatial variability of the PCLoS and to test the usefulness of the parameterization of effective cloud fraction.
Long-Term Changes in Ice Phenology of the Yellow River in the Past Decades
Authors: Jiang Yundi , Dong Wenjie , Yang Song , Ma Jun
Published: February 2008

The authors quantitatively describe the changes in the characteristics of ice phenology including the flow rate and freeze/breakup dates of the Yellow River based on observations of the past 50 yr. In both the upper and lower reaches of the Yellow River, increasing temperature delays the freeze date and advances the breakup date, thus decreasing the number of freeze days and the expanse of river freeze. From 1968 to 2001, the freeze duration has shortened significantly by 38 days at Bayangaole and 25 days at Sanhuhe, respectively. From the early 1950s to the early 2000s, the changes in freeze and breakup dates have shortened the freeze duration in the lower reach of the Yellow River by 12 days. The flow rate has reduced from 500 to 260 m3 s−1, and the expanse of river freeze has also decreased significantly by about 310 km. In addition, in the lower reach of the river, the location of earliest ice breakup has shifted downstream significantly in the last 50 yr, although the location of earliest freeze exhibits little change.
Toward Climate Prediction: Interannual Potential Predictability due to an Increase in CO2 Concentration as Diagnosed from an Ensemble of AO GCM Integrations
Authors: von Storch Jin-Song
Published: February 2008

Predictability studies of the second kind are often carried out to address the potential in predicting atmospheric variables based on knowledge of changes in sea surface temperature (SST). Here a predictability study of the second kind is performed for the coupled atmosphere–ocean system based on knowledge of changes in CO2 concentration. The focus is on potential predictabilities obtained after imposing a CO2 forcing over a short time period (i.e., a few years), which are less sensitive to the exact future time evolution of the CO2 forcing. Potential predictability is measured by the ensemble mean difference resulting from the CO2 forcing relative to the ensemble spread subjected to the same forcing. The measure is calculated from a 50-member prediction ensemble obtained from an atmosphere–ocean GCM forced by a 3% increase in CO2 concentration per year and a reference ensemble obtained under a constant CO2 concentration.

The largest potential predictabilities are found in and over the Southern Ocean. The origin of these predictabilities is a positive feedback involving interactions between the atmosphere and the upper ocean. An increase in the meridional gradient of SST resulting from a large SST increase in the southern subtropics leads to a strengthening of atmospheric circulation, and from that increases in surface zonal wind stress result. The latter enhances the northward Ekman transport over the southern high latitudes, which transports polar water equatorward, whereby maintaining the meridional temperature gradient. Potential predictability is also found in the deep ocean, characterized by the downward propagation of the surface warming within a few years through two “corridors,” located at 40°S and 40°N and extending from the near surface to about 3000–3500 m. The warming in the atmosphere and the upper ocean is reduced by half because of this downward heat propagation.
The Impact of Analysis Error on Medium-Range Weather Forecasts
Authors: Swanson Kyle L. , Roebber Paul J.
Published: February 2008

All meteorological analyzed fields contain errors, the magnitude of which ultimately determines the point at which a given forecast will fail. Here, the authors explore the extent to which analysis difference fields capture certain aspects of the actual but unknowable flow-dependent analysis error. The analysis difference fields considered here are obtained by subtracting the NCEP and ECMWF reanalysis 500-hPa height fields. It is shown that the magnitude of this 500-hPa analysis difference averaged over the North Pacific Ocean has a statistically significant impact on forecast skill over the continental United States well into the medium range (5 days). Further, it is shown that the impact of this analysis difference on forecast skill is similar to that of ensemble spread well into the medium range, a measure of forecast uncertainty currently used in the operational setting. Finally, the analysis difference and ensemble spread are shown to be independent; hence, the impact of these two quantities upon forecast skill is additive.