bluuebunny/crossref_metadata_2025 huggingface dataset:
SEXUAL DIFFERENTIATION OF AVIAN BRAIN AND BEHAVIOR: Current Views on Gonadal Hormone-Dependent and Independent Mechanisms
Authors: Schlinger Barney A.
Published: July 2002

▪ Abstract  Gonadal hormones are known to act during development to establish permanent sex differences in the anatomy and function of the vertebrate brain. They also act on the adult brain to activate reproductive behaviors. However, there are wide gaps in our understanding of how sexually dimorphic neural circuits translate into sex differences in behavior and other CNS functions. Moreover, not all sexually dimorphic properties of the adult brain can be attributed to known effects of gonadal hormones during development or adulthood, and factors other than gonadal steroids may contribute to these sex differences. This paper reviews sexual differentiation and the role of gonadal steroids and non-gonadal factors on sexually dimorphic development of the avian brain.
Branching Morphogenesis During Kidney Development
Authors: Pohl M. , Stuart R. O. , Sakurai H. , Nigam S. K.
Published: July 2002

▪ Abstract  Epithelial tissues such as kidney, lung, and breast arise through branching morphogenesis of a pre-existing epithelial structure. They share common morphological stages and a need for regulation of a similar set of developmental decisions—where to start; when, where, and in which direction to branch; and how many times to branch—decisions requiring regulation of cell proliferation, apoptosis, invasiveness, and cell motility. It is likely that similar molecular mechanisms exist for the epithelial branching program. Here we focus on the development of the collecting system of the kidney, where, from recent data using embryonic organ culture, cell culture models of branching morphogenesis, and targeted gene deletion experiments, the outlines of a working model for branching morphogenesis begin to emerge. Key branching morphogenetic molecules in this model include growth factors, transcription factors, distal effector molecules (such as extracellular matrix proteins, integrins, proteinases and their inhibitors), and genes regulating apoptosis and cell proliferation.
Mechanisms in Political Processes
Authors: Tilly Charles
Published: July 2002

Ostensibly theoretical disputes in political science often involve competing approaches to explanation, including skepticism, covering law arguments, reconstructions of propensities, system models, and explanations featuring causal mechanisms. Mechanism- and process-based accounts, including cognitive, environmental, and relational effects, deserve more attention than they have received in recent political science. Analyses of democratization illustrate these points.
COGNITIVE SKILL ACQUISITION
Authors: VanLehn Kurt
Published: July 2002

▪ Abstract  Cognitive skill acquisition is acquiring the ability to solve problems in intellectual tasks, where success is determined more by subjects' knowledge than by their physical prowess. This review considers research conducted in the past ten years on cognitive skill acquisition. It covers the initial stages of acquiring a single principle or rule, the initial stages of acquiring a collection of interacting pieces of knowledge, and the final stages of acquiring a skill, wherein practice causes increases in speed and accuracy.
PSYCHOLOGY AND THE STUDY OF MARITAL PROCESSES
Authors: Gottman John Mordechai
Published: July 2002

▪ Abstract  The divorce rate in the United States is extremely high. It is estimated that between 50% and 67% of first marriages end in divorce. For second marriages, failure rates are even higher. There are strong negative consequences to separation and divorce on the mental and physical health of both spouses, including increased risk for psychopathology, increased rates of automobile accidents, and increased incidence of physical illness, suicide, violence, homicide, significant immunosuppression, and mortality from diseases. In children, marital distress, conflict, and disruption are associated with depression, withdrawal, poor social competence, health problems, poor academic performance, and a variety of conduct-related difficulties. Though intervention techniques might be expected to reduce these grim statistics, our best scholars have concluded that marital therapy is at a practical and theoretical impasse. This article discusses the progress of research on the study of marriage.
INTERVENTIONS FOR COUPLES
Authors: Christensen A. , Heavey C. L.
Published: July 2002

▪ Abstract  A substantial body of empirical research has documented both the promise and the shortcomings of psychological interventions for preventing or ameliorating marital distress. Couple therapy reduces relationship distress and may affect individual psychopathology, such as depression. However, some couples are unresponsive and others improve but relapse later. Interventions to prevent marital distress usually produce short-term changes in behavior and relationship satisfaction, but little evidence exists demonstrating a longer-term prevention effect. Furthermore, these interventions have yet to be examined on a diverse population of couples or with a diverse set of outcome criteria (e.g. effects on children). Concern about the negative impact of marital discord and divorce will continue to provide the impetus for research on more effective means of intervening with couples. Future research could benefit from a focus on a more diverse population of couples, treatment in natural settings, the development of more powerful interventions, and the examination of those interventions over longer periods of time and with more comprehensive outcome measures.
SINGLE-GENE INFLUENCES ON BRAIN AND BEHAVIOR
Authors: Wahlsten D.
Published: July 2002

▪ Abstract  As traditional behavioral genetics analysis merges with neurogenetics, the field of neurobehavioral genetics, focusing on single-gene effects, comes into being. New biotechnology has greatly accelerated gene discovery and the study of gene function in relation to brain and behavior. More than 7,000 genes in mice and 10,000 in humans have now been documented, and extensive information about the genetics of several species is readily available on the World Wide Web. Based on knowledge of the DNA sequence of a gene, a targeted mutation with the capacity to disable it can be created. These knockouts— also called null mutants— are employed in the study of a wide range of phenotypes, including learning and memory, appetite and obesity, and circadian rhythms. The era of examining single-gene effects from a reductionistic perspective is waning, and research with interacting arrays of genes in various environmental contexts is demonstrating a need for systems-oriented theory.
NEUROETHOLOGY OF SPATIAL LEARNING: The Birds and the Bees
Authors: Capaldi E. A. , Robinson G. E. , Fahrbach S. E.
Published: July 2002

▪ Abstract  The discipline of neuroethology integrates perspectives from neuroscience, ethology, and evolutionary biology to investigate the mechanisms underlying the behavior of animals performing ecologically relevant tasks. One goal is to determine if common organizational principles are shared between nervous systems in diverse taxa. This chapter selectively reviews the evidence that particular brain regions subserve behaviors that require spatial learning in nature. Recent evidence suggests that the insect brain regions known as the mushroom bodies may function similarly to the avian and mammalian hippocampus. Volume changes in these brain regions during the life of an individual may reflect both developmental and phylogenetic trends. These patterns may reveal important structure-function relationships in the nervous system.
Empirically Supported Psychological Interventions: Controversies and Evidence
Authors: Chambless Dianne L. , Ollendick Thomas H.
Published: July 2002

▪ Abstract  Efforts to increase the practice of evidence-based psychotherapy in the United States have led to the formation of task forces to define, identify, and disseminate information about empirically supported psychological interventions. The work of several such task forces and other groups reviewing empirically supported treatments (ESTs) in the United States, United Kingdom, and elsewhere is summarized here, along with the lists of treatments that have been identified as ESTs. Also reviewed is the controversy surrounding EST identification and dissemination, including concerns abou research methodology, external validity, and utility of EST research, as well as the reliability and transparency of the EST review process.
Child Clinical/Pediatric Neuropsychology: Some Recent Advances
Authors: Rourke B. P. , Ahmad S. A. , Collins D. W. , Hayman-Abello B. A. , Hayman-Abello S. E. , Warriner E. M.
Published: July 2002

▪ Abstract  The neuropsychological assets and deficits of several types of pediatric neurological disease, disorder, and dysfunction are described. These are examined from the perspective of the syndrome of nonverbal learning disabilities (NLD) and the “white matter model” designed to explain its complex manifestations. It is concluded that children with some of these diseases exhibit the NLD phenotype, whereas others do not. For the most part, the diseases in which the NLD phenotype is particularly evident are those wherein it has been demonstrated that perturbations of white matter (long myelinated fibers) are particularly prominent.
MEDICARE AND MANAGED CARE
Authors: Luft Harold S.
Published: July 2002

▪ Abstract  Medicare offers nearly universal, but limited, coverage for the elderly. The vast majority of beneficiaries therefore obtain supplemental coverage, or they enroll in HMOs to gain extra benefits at substantially lower or zero cost. This is possible because of reduced utilization and costs, as well as favorable selection of lower-risk enrollees into HMOs. Competition from HMOs may lower local fee-for-service costs as well. Quality and satisfaction measures are quite balanced, with some results showing better HMO performance and some worse. The absence of adequate risk-adjusted payments to HMOs, however, gives them little incentive to develop high-quality programs for the sickest enrollees.
ERADICATION OF VACCINE-PREVENTABLE DISEASES
Authors: Hinman A.
Published: July 2002

▪ Abstract  Eradication is the permanent reduction to zero of the worldwide incidence of infection caused by a specific agent as a result of deliberate efforts; intervention measures are no longer needed. To date, the only infectious disease that has been eradicated is smallpox. Poliomyelitis is targeted for eradication by the year 2000, and the eradication initiative is well under way, with the Western Hemisphere certified as being polio-free and more than one year having passed since polio cases occurred in the Western Pacific Region of the World Health Organization. A review of the technical feasibility of eradicating other diseases preventable by vaccines currently licensed for civilian use in the United States indicates that measles, hepatitis B, mumps, rubella, and possibly disease caused by Haemophilus influenzae type b are potential candidates. From a practical point of view, measles seems most likely to be the next target. Global capacity to undertake eradication is limited, and care must be taken to ensure that a potential measles eradication effort does not impede achievement of polio eradication. Even in the absence of eradication, major improvements in control are both feasible and necessary with existing vaccines. New and improved vaccines may give further possibilities of eradication in the future. Eradication represents the ultimate in sustainability and social justice.
Design Issues for Conducting Cost-Effectiveness Analyses Alongside Clinical Trials
Authors: Ramsey Scott D , McIntosh Martin , Sullivan Sean D
Published: July 2002

▪ Abstract  In response to rising demands for timely economic data on new medical technologies, cost-effectiveness studies are increasingly being conducted alongside clinical trials. Because of the historical differences in perspective and methods between cost-effectiveness studies and clinical trials, the design phase of these hybrid trials requires special consideration. Cost-effectiveness studies require more comprehensive evaluations of outcomes than the endpoints typically measured in clinical trials. Often, these comprehensive outcome measures (such as quality of life) prove useful for interpreting the other endpoints measured in the trial, as well as for estimating the cost-effectiveness of the intervention. In this manuscript, we discuss several aspects related to the design of joint clinical/economic trials, including study perspective, hypothesis testing, sample size estimation, and methods for collecting cost and outcome data. We also discuss issues that may limit the external validity of the cost-effectiveness results of these trials. Many potential threats to external validity can be successfully addressed if they are identified and accounted for in the design phase of the study.
Network Forms of Organization
Authors: Podolny Joel M. , Page Karen L.
Published: July 2002

Initial sociological interest in network forms of organization was motivated in part by a critique of economic views of organization. Sociologists sought to highlight the prevalence and functionality of organizational forms that could not be classified as markets or hierarchies. As a result of this work, we now know that network forms of organization foster learning, represent a mechanism for the attainment of status or legitimacy, provide a variety of economic benefits, facilitate the management of resource dependencies, and provide considerable autonomy for employees. However, as sociologists move away from critiquing what are now somewhat outdated economic views, they need to balance the exclusive focus on prevalence and functionality with attention to constraint and dysfunctionality. The authors review work that has laid a foundation for this broader focus and suggest analytical concerns that should guide this literature as it moves forward.
RECENT DEVELOPMENTS AND CURRENT CONTROVERSIES IN THE SOCIOLOGY OF RELIGION
Authors: Sherkat Darren E. , Ellison Christopher G.
Published: July 2002

▪ Abstract  The sociology of religion is experiencing a period of substantial organizational and intellectual growth. Recent theoretical and empirical papers on the sociology of religion appearing in top journals in sociology have generated both interest and controversy. We begin with a selective overview of research on religious beliefs and commitments. Second, we investigate the influence of religion on politics, the family, health and well-being, and on free space and social capital. Finally, we review rational choice theories in the sociology of religion and the controversies surrounding applications of these perspectives.
Social Implications of the Internet
Authors: DiMaggio Paul , Hargittai Eszter , Neuman W. Russell , Robinson John P.
Published: July 2002

The Internet is a critically important research site for sociologists testing theories of technology diffusion and media effects, particularly because it is a medium uniquely capable of integrating modes of communication and forms of content. Current research tends to focus on the Internet's implications in five domains: 1) inequality (the “digital divide”); 2) community and social capital; 3) political participation; 4) organizations and other economic institutions; and 5) cultural participation and cultural diversity. A recurrent theme across domains is that the Internet tends to complement rather than displace existing media and patterns of behavior. Thus in each domain, utopian claims and dystopic warnings based on extrapolations from technical possibilities have given way to more nuanced and circumscribed understandings of how Internet use adapts to existing patterns, permits certain innovations, and reinforces particular kinds of change. Moreover, in each domain the ultimate social implications of this new technology depend on economic, legal, and policy decisions that are shaping the Internet as it becomes institutionalized. Sociologists need to study the Internet more actively and, particularly, to synthesize research findings on individual user behavior with macroscopic analyses of institutional and political-economic factors that constrain that behavior.
Tea Consumption and Mortality After Acute Myocardial Infarction
Authors: Mukamal Kenneth J. , Maclure Malcolm , Muller James E. , Sherwood Jane B. , Mittleman Murray A.
Published: July 2002

Background

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Some studies have suggested that tea consumption may be associated with lower mortality among individuals with cardiovascular disease, but the effects of tea consumption on mortality after acute myocardial infarction are unknown.

Methods and Results

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As part of the Determinants of Myocardial Infarction Onset Study, we performed a prospective cohort study of 1900 patients hospitalized with a confirmed acute myocardial infarction between 1989 and 1994, with a median follow-up of 3.8 years. Trained interviewers assessed self-reported usual weekly caffeinated tea consumption during the year before infarction with a standardized questionnaire. We compared long-term mortality according to tea consumption using Cox proportional hazards regression. Of the 1900 patients, 1019 consumed no tea (nondrinkers), 615 consumed <14 cups per week (moderate tea drinkers), and 266 consumed 14 or more cups per week (heavy tea drinkers). Compared with nondrinkers, age- and sex-adjusted mortality was lower among moderate tea drinkers (hazard ratio, 0.69; 95% CI, 0.53 to 0.89) and heavy tea drinkers (hazard ratio, 0.61; 95% CI, 0.42 to 0.86). Additional adjustment for clinical and sociodemographic characteristics did not appreciably alter this association (hazard ratio, 0.72; 95% CI, 0.55 to 0.94 for moderate tea drinkers; hazard ratio, 0.56; 95% CI, 0.37 to 0.84 for heavy tea drinkers). The association of tea and mortality was similar for total and cardiovascular mortality.

Conclusions

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Self-reported tea consumption in the year before acute myocardial infarction is associated with lower mortality after infarction.
Calcium Modulation of Adherens and Tight Junction Function
Authors: Brown Rachel C. , Davis Thomas P.
Published: July 2002

Background

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This review deals with the role of calcium in endothelial cell junctions of the blood-brain barrier (BBB). Calcium is critical for adherens junction function, but it appears that calcium is also important in regulating tight junction function necessary for the barrier characteristics of cerebral microvessels.

Summary of Review

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The BBB is critical for brain homeostasis and is located at the cerebral microvessel endothelial cells. These endothelial cells maintain their barrier characteristics via cell-cell contacts made up of adherens and tight junctions. Adherens junctions are calcium dependent; recent evidence suggests that calcium also affects tight junctions. After stroke, there is a disruption of the BBB. Interfering with calcium flux under hypoxic conditions can prevent BBB breakdown. Calcium may alter BBB junction integrity by a number of different signal transduction cascades, as well as via direct interaction of calcium ions with junction proteins. It remains to be determined whether clinical use of calcium channel antagonists is a viable means to reduce BBB disruption after stroke.

Conclusions

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With the widespread use of calcium channel blockers as clinical treatments for hypertension, which is a risk factor for stroke, the exact role of calcium in modulating BBB integrity needs to be elucidated.
Democratic Institutions and Exchange-rate Commitments
Authors: Bernhard William , Leblang David
Published: July 2002

Since the collapse of the Bretton Woods system, countries have been able to choose from a variety of exchange-rate arrangements. We argue that politicians' incentives condition the choice of an exchange-rate arrangement. These incentives reflect the configuration of domestic political institutions, particularly electoral and legislative institutions. In systems where the cost of electoral defeat is high and electoral timing is exogenous, politicians will be less willing to forgo their discretion over monetary policy with a fixed exchange rate. In systems where the costs of electoral defeat are low and electoral timing is endogenous, politicians are more likely to adopt a fixed exchange-rate regime. Consequently, differences in domestic political systems can help account for variations in the choice of exchange-rate arrangements. We test this argument using constrained multinomial logit and binomial logit on a sample of twenty democracies over the period 1974–95. Domestic political institutions have a significant effect on exchange-rate regime choice, even after controlling for systemic, macroeconomic, and other political variables.
The Fruitful Error: Reconsidering Millennial Enthusiasm
Authors: Landes Richard
Published: July 2002

Apocalyptic hopes for an imminent millenial “new age” have taken a wide variety of forms in European history, from the earlier religious manifestations to the more secular and, hence, more activist ones of the modern world. Although none of these apocalyptic expectations has been accurate, and many have had disastrous immediate consequences for those involved, they have set in motion powerful social dynamics. Western science and technology, revolutionary politics, dreams of global peace, and the realities of world wars all derive peculiar inspiration from the terrible hopes of the millennial vision.
Ritual, Space, and Authority in Seventeenth-Century English Cathedral Cities
Authors: Estabrook Carl B.
Published: July 2002

In seventeenth-century English cathedral cities, civic authorities and cathedral clergy vied vigorously for control over the ritual use of urban space. A close examination of this contest in its spatial context is essential to a thorough understanding of serious disputes linking the struggle for civic autonomy to religious culture. Moreover, it provides a window onto the role of public space in the devotional, communal, and political experience of English dwellers during a turbulent and transitional period.
Data Culture Generation: After Content, Process as Aesthetic
Authors: Riddell Alistair
Published: July 2002

The concepts of process and data, inherent in the technology of contemporary music, are contributing to a new musical practice and aesthetic. The role of technology in musical production has cast music into data (a tangible entity, commodity or product) and thus made data a kind of cultural object itself in certain contexts (LPs, CDs, MP3 files). This condition suggests that a rethinking/transformation of contemporary audio arts based on process is taking place. Increasingly, sound may be only one of several simultaneous and expressive components constituting a cultural experience. Here process can suggest and define a set of possibilities as an artistic statement irrespective of whether something or anything is manifest by any artist. With the environment saturated with music, the creative design of musical processes might become an art in itself.
Digital Ontologies: The Ideality of Form in/and Code Storage—or— Can Graphesis Challenge Mathesis?
Authors: Drucker Johanna
Published: July 2002

Digital media gain their cultural authority in part because of the perception that they function on mathematical principles. The relationship between digital images and their encoded files, and in other cases, between digital images and the algorithms that generate them as display, lends itself to a conviction that the image and the file are mutually interchangeable. This relationship posits a connection of identicality between the file and the image according to which the mathematical basis and the image seem to share similar claims to truth. Since the history of images within Western culture is fraught with charges of deception and illusion, the question arises whether the ontological condition of the digital image, its very existence and identity, challenges this tradition. Or, by contrast, does the material instantiation of images, in their display or output, challenge the truth claims of the mathematically based digital file?
Probabilistic Learning Algorithms and Optimality Theory
Authors: Keller Frank , Asudeh Ash
Published: July 2002

This article provides a critical assessment of the Gradual Learning Algorithm (GLA) for probabilistic optimality-theoretic (OT) grammars proposed by Boersma and Hayes (2001). We discuss the limitations of a standard algorithm for OT learning and outline how the GLA attempts to overcome these limitations. We point out a number of serious shortcomings with the GLA: (a) A methodological problem is that the GLA has not been tested on unseen data, which is standard practice in computational language learning. (b) We provide counterexamples, that is, attested data sets that the GLA is not able to learn. (c) Essential algorithmic properties of the GLA (correctness and convergence) have not been proven formally. (d) By modeling frequency distributions in the grammar, the GLA conflates the notions of competence and performance. This leads to serious conceptual problems, as OT crucially relies on the competence/performance distinction.
The Directionality of Emphasis Spread in Arabic
Authors: Watson Janet C. E.
Published: July 2002

Many modern Arabic dialects exhibit asymmetries in the direction of emphasis (for most dialects, pharyngealization) spread. In a dialect of Yemeni Arabic, emphasis has two articulatory correlates, pharyngealization and labialization: within the phonological word, pharyngealization spreads predominantly leftward, and labialization spreads rightward, targeting short high vowels. Since asymmetries in the directionality of spread of a secondary feature are phonetically motivated and depend on whether the feature is anchored to the onset or the release phase of the primary articulation, it is argued that the unmarked directionality of spread should be encoded in the phonology as a markedness statement on that feature.
Neural Activation During Response Competition
Authors: Hazeltine Eliot , Poldrack Russell , Gabrieli John D. E.
Published: July 2002

The flanker task, introduced by Eriksen and Eriksen [Eriksen, B. A., & Eriksen, C. W. (1974). Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception & Psychophysics, 16, 143-149], provides a means to selectively manipulate the presence or absence of response competition while keeping other task demands constant. We measured brain activity using functional magnetic resonance imaging (fMRI) during performance of the flanker task. In accordance with previous behavioral studies, trials in which the flanking stimuli indicated a different response than the central stimulus were performed significantly more slowly than trials in which all the stimuli indicated the same response. This reaction time effect was accompanied by increases in activity in four regions: the right ventrolateral prefrontal cortex, the supplementary motor area, the left superior parietal lobe, and the left anterior parietal cortex. The increases were not due to changes in stimulus complexity or the need to overcome previously learned associations between stimuli and responses. Correspondences between this study and other experiments manipulating response interference suggest that the frontal foci may be related to response inhibition processes whereas the posterior foci may be related to the activation of representations of the inappropriate responses.
Activity in Human Frontal Cortex Associated with Spatial Working Memory and Saccadic Behavior
Authors: Postle Bradley R. , Berger Jeffrey S. , Taich Alexander M. , D'Esposito Mark
Published: July 2002

We examined, with event-related fMRI, two hypotheses about the organization of human working memory function in frontal cortex: (1) that a region immediately anterior to the frontal eye fields (FEF) (superior frontal cortex, SFC) is specialized for spatial working memory (Courtney, et al., 1998); and (2) that dorsolateral prefrontal cortex (PFC) plays a privileged role in the manipulation of spatial stimuli held in working memory (Owen, et al., 1996; Petrides 1994). Our delayed-response task featured 2-D arrays of irregularly arranged squares that were highlighted serially in a random sequence. The Forward Memory condition required maintenance of the spatio-temporal sequence, the Manipulate Memory condition required reordering this sequence into a new spatially defined order, the Guided Saccade condition required saccades to highlighted squares in the array, but no memory, and the Free Saccade condition required self-paced, horizontal saccades. The comparison of fMRI signal intensity associated with 2-D saccade generation (Guided Saccades) versus fMRI signal intensity associated with the delay period of the working memorials condition revealed no evidence for greater working memory-related activity than saccade-related activity in SFC in any individual subject, nor at the level of the group, and greater 2-D saccade than delay-period activity in three of five subjects. These results fail to support the hypothesis that spatial working memory-related activity is represented preferentially in a region of SFC anterior to the FEF (Courtney, et al., 1998). The comparison of maintenance versus manipulation of spatio-temporal information in working memory revealed significantly greater activity associated with the latter in dorsolateral PFC, but not in ventrolateral PFC or in SFC. These results suggest that the delay-related function of SFC is limited to the maintenance of spatial information, and that this region does not support the nonmnemonic executive control functions supported by dorsolateral PFC. These results also indicate that the preferential recruitment of dorsolateral PFC for the manipulation of information held in working memory applies to tasks employing spatial stimuli, as well as to tasks employing verbal stimuli (D'Esposito, et al., 1999); Petrides et al., 1993; Postle et al., 1999).
Dynamic Diaschisis: Anatomically Remote and Context-Sensitive Human Brain Lesions
Authors: Price C. J. , Warburton E. A. , Moore C. J. , Frackowiak R. S. J. , Friston K. J.
Published: July 2002

Functional neuroimaging was used to investigate how lesions to the Broca's area impair neuronal responses in remote undamaged cortical regions. Four patients with speech output problems, but relatively preserved comprehension, were scanned while viewing words relative to consonant letter strings. In normal subjects, this results in left lateralized activation in the posterior inferior frontal, middle temporal, and posterior inferior temporal cortices. Each patient activated normally in the middle temporal region but abnormally in the damaged posterior inferior frontal cortex and the undamaged posterior inferior temporal cortex. In the damaged frontal region, activity was insensitive to the presence of words but in the undamaged posterior inferior temporal region, activity decreased in the presence of words rather than increasing as it did in the normal individuals. The reversal of responses in the left posterior inferior temporal region illustrate the context-sensitive nature of the abnormality and that failure to activate the left posterior temporal region could not simply be accounted for by insufficient demands on the underlying function. We propose that, in normal individuals, visual word presentation changes the effective connectivity among reading areas and, in patients, posterior temporal responses are abnormal when they depend upon inputs from the damaged inferior frontal cortex. Our results serve to introduce the concept of dynamic diaschisis; the anatomically remote and context-sensitive effects of focal brain lesions. Dynamic diaschisis reveals abnormalities of functional integration that may have profound implications for neuropsychological inference, functional anatomy and, vicariously, cognitive rehabilitation.
Vase or Face? A Neural Correlate of Shape-Selective Grouping Processes in the Human Brain
Authors: Hasson Uri , Hendler Talma , Bashat Dafna Ben , Malach Rafael
Published: July 2002

Recent neuroimaging studies have described a differential activation pattern associated with specific object images (e.g., face-related and building-related activation) in human occipito-temporal cortex. However, it is as yet unclear to what extent this selectivity is due to differences in the statistics of local object features present in the different object categories, and to what extent it reflects holistic grouping processes operating across the entire object image. To resolve this question it is essential to use images in which identical sets of local features elicit the perception of different object categories. The classic Rubin vase-face illusion provides an excellent experimental set to test this question. In the illusion, the same local contours lead to the perception of different objects (vase or face). Here we employed a modified Rubin vase-face illusion to explore to what extent the activation in face-related regions is attributable to the presence of local face features, or is due to a more holistic grouping process that involves the entire face figure. Biasing cues (gratings and color) were used to control the perceptual state of the observer. We found enhanced activation in face-related regions during the “face profile” perceptual state compared to the “vase” perceptual state. Control images ruled out the involvement of the biasing cues in the effect. Thus, object-selective activation in human face-related regions entails global grouping processes that go beyond the local processing of stimulus features.
Motor Learning of Compatible and Incompatible Visuomotor Maps
Authors: Grafton Scott T. , Salidis Joanna , Willingham Daniel B.
Published: July 2002

Brain imaging studies demonstrate increasing activity in limb motor areas during early motor skill learning, consistent with functional reorganization occurring at the motor output level. Nevertheless, behavioral studies reveal that visually guided skills can also be learned with respect to target location or possibly eye movements. The current experiments examined motor learning under compatible and incompatible perceptual/motor conditions to identify brain areas involved in different perceptual-motor transformations. Subjects tracked a continuously moving target with a joystick-controlled cursor. The target moved in a repeating sequence embedded within random movements to block sequence awareness. Psychophysical studies of behavioral transfer from incompatible (joystick and cursor moving in opposite directions) to compatible tracking established that incompatible learning was occurring with respect to target location. Positron emission tomography (PET) functional imaging of compatible learning identified increasing activity throughout the precentral gyrus, maximal in the arm area. Incompatible learning also led to increasing activity in the precentral gyrus, maximal in the putative frontal eye fields. When the incompatible task was switched to a compatible response and the previously learned sequence was reintroduced, there was an increase in arm motor cortex. The results show that learning-related increases of brain activity are dynamic, with recruitment of multiple motor output areas, contingent on task demands. Visually guided motor sequences can be linked to either oculomotor or arm motor areas. Rather than identifying changes of motor output maps, the data from imaging experiments may better reflect modulation of inputs to multiple motor areas.
The Attentional Role of the Left Parietal Cortex: The Distinct Lateralization and Localization of Motor Attention in the Human Brain
Authors: Rushworth Matthew F. S. , Krams Michael , Passingham Richard E.
Published: July 2002

It is widely agreed that visuospatial orienting attention depends on a network of frontal and parietal areas in the right hemisphere. It is thought that the visuospatial orienting role of the right parietal lobe is related to its role in the production of overt eye movements. The experiments reported here test the possibility that other parietal regions may be important for directing attention in relation to response modalities other than eye movement. Specifically, we used positron emission tomography (PET) to test the hypothesis that a ‘left’ parietal area, the supramarginal gyrus, is important for attention in relation to limb movements (Rushworth et al., 1997; Rushworth, Ellison, & Walsh, in press). We have referred to this process as ‘motor attention’ to distinguish it from orienting attention. In one condition subjects spent most of the scanning period covertly attending to ‘left’ hand movements that they were about to make. Activity in this first condition was compared with a second condition with identical stimuli and movement responses but lacking motor attention periods. Comparison of the conditions revealed that motor attention related activity was almost exclusively restricted to the ‘left’ hemisphere despite the fact that subjects only ever made ipsilateral, left-hand responses. Left parietal activity was prominent in this comparison, within the parietal lobe the critical region for motor attention was the supramarginal gyrus and the adjacent anterior intraparietal sulcus (AIP), a region anterior to the posterior parietal cortex identified with orienting attention. In a second part of the experiment we compared a condition in which subjects covertly rehearsed verbal responses with a condition in which they made verbal responses immediately without rehearsal. A comparison of the two conditions revealed verbal rehearsal-related activity in several anterior left hemisphere areas including Broca's area. The lack of verbal rehearsal-related activity in the left supra-marginal gyrus confirms that this area plays a direct role in motor attention that cannot be attributed to any strategy of verbal mediation. The results also provide evidence concerning the importance of ventral premotor (PMv) and Broca's area in motor attention and language processes.
Synaesthetic Photisms Influence Visual Perception
Authors: Smilek Daniel , Dixon Mike J. , Cudahy Cera , Merikle Philip M.
Published: July 2002

When C, a digit-color synaesthete, views black digits, she reports that each digit elicits a highly specific color (a photism), which is experienced as though the color was externally projected onto the digit. We evaluated this claim by assessing whether C's photisms influenced her ability to perceive visually presented digits. C identified and localized target digits presented against backgrounds that were either congruent or incongruent with the color of her photism for the digits. The results showed that C was poorer at identifying and localizing digits on congruent than incongruent trials. Such differences in performance between congruent and incongruent trials were not found with nonsynaesthete control participants. These results suggest that C's colored photisms influence her perception of black digits. We propose a model in which color information influences the perception of digits through reentrant pathways in the visual system.
Knowing Where Things Are: Parahippocampal Involvement in Encoding Object Locations in Virtual Large-Scale Space
Authors: Maguire E. A. , Frith C. D. , Burgess N. , Donnett J. G. , O'Keefe J.
Published: July 2002

The involvement of the medial temporal-lobe region in allocentric mapping of the environment has been observed in human lesion and functional imaging work. Cognitive models of environmental learning ascribe a key role to salient landmarks in representing large-scale space. In the present experiments we examined the neural substrates of the topographical memory acquisition process when environmental landmarks were more specifically identifiable. Using positron emission tomography (PET), we measured regional cerebral blood flow changes while normal subjects explored and learned in a virtual reality environment. One experiment involved an environment containing salient objects and textures that could be used to discriminate different rooms. Another experiment involved a plain empty environment in which rooms were distinguishable only by their shape. Learning in both cases activated a network of bilateral occipital, medial parietal, and occipito-temporal regions. The presence of salient objects and textures in an environment additionally resulted in increased activity in the right parahippocampal gyrus. This region was not activated during exploration of the empty environment. These findings suggest that encoding of salient objects into a representation of large-scale space is a critical factor in instigating parahippocampal involvement in topographical memory formation in humans and accords with previous studies implicating parahippocampal areas in the encoding of object location.
Sleep-Induced Changes in Associative Memory
Authors: Stickgold Robert , Scott Laurie , Rittenhouse Cynthia , Hobson J. Allan
Published: July 2002

The notion that dreaming might alter the strength of associative links in memory was first proposed almost 200 years ago. But no strong evidence of such altered associative links has been obtained. Semantic priming can be used to quantify the strength of associative links between pairs of words; it is thought to measure the automatic spread of activation from a “node” representing one word to nodes representing semantically related words. Semantic priming could thus be used to test for global alterations in the strengths of associative links across the wake-sleep cycle.

Awakenings from REM and nonREM (NREM) sleep produce a period of state carry-over during which performance is altered as a result of the brain's slow transition to full wakefulness, and cognitive testing in this period can provide information about the functioning of the brain during the prior sleep period. When subjects were tested across the night—before and after a night's sleep as well as immediately following forced awakenings from REM and NREM sleep—weak priming (e.g., thief-wrong) was found to be state dependent (p = 0.016), whereas strong priming (e.g., hot-cold) was not (p = 0.89). Weak primes were most effective in the presleep and REM sleep conditions and least effective in NREM and postsleep conditions.

Most striking are analyses comparing weak and strong priming within each wake-sleep state. Contrary to the normal pattern of priming, subjects awakened from REM sleep showed greater priming by weak primes than by strong primes (p = 0.01). This result was seen in each of three protocols. In contrast, strong priming exceeded weak priming in NREM sleep.

The shift in weak priming seen after REM sleep awakenings suggests that cognition during REM sleep is qualitatively different from that of waking and NREM sleep and may reflect a shift in associative memory systems, a shift that we hypothesize underlies the bizarre and hyperassociative character of REM-sleep dreaming. Known changes in brainstem activity that control the transition into and maintenance of REM sleep provide a possible explanation of this shift.
Fields as Limit Functions of Stochastic Discrimination and Their Adaptability
Authors: Loocke Philip Van
Published: July 2002

For a particular type of elementary function, stochastic discrimination is shown to have an analytic limit function. Classifications can be performed directly by this limit function instead of by a sampling procedure. The limit function has an interpretation in terms of fields that originate from the training examples of a classification problem. Fields depend on the global configuration of the training points. The classification of a point in input space is known when the contributions of all fields are summed. Two modifications of the limit function are proposed. First, for nonlinear problems like high-dimensional parity problems, fields can be quantized. This leads to classification functions with perfect generalization for high-dimensional parity problems. Second, fields can be provided with adaptable amplitudes. The classification corresponding to a limit function is taken as an initialization; subsequently, amplitudes are adapted until an error function for the test set reaches minimal value. It is illustrated that this increases the performance of stochastic discrimination. Due to the nature of the fields, generalization improves even if the amplitude of every training example is adaptable.
Synaptic Pruning in Development: A Computational Account
Authors: Chechik Gal , Meilijson Isaac , Ruppin Eytan
Published: July 2002

Research with humans and primates shows that the developmental course of the brain involves synaptic overgrowth followed by marked selective pruning. Previous explanations have suggested that this intriguing, seemingly wasteful phenomenon is utilized to remove “erroneous” synapses. We prove that this interpretation is wrong if synapses are Hebbian. Under limited metabolic energy resources restricting the amount and strength of synapses, we show that memory performance is maximized if synapses are first overgrown and then pruned following optimal “minimal-value” deletion. This optimal strategy leads to interesting insights concerning childhood amnesia.
The Effect of Correlated Variability on the Accuracy of a Population Code
Authors: Abbott L. F. , Dayan Peter
Published: July 2002

We study the impact of correlated neuronal firing rate variability on the accuracy with which an encoded quantity can be extracted from a population of neurons. Contrary to widespread belief, correlations in the variabilities of neuronal firing rates do not, in general, limit the increase in coding accuracy provided by using large populations of encoding neurons. Furthermore, in some cases, but not all, correlations improve the accuracy of a population code.
Compositional Syntax From Cultural Transmission
Authors: Brighton Henry
Published: July 2002

A growing body of work demonstrates that syntactic structure can evolve in populations of genetically identical agents. Traditional explanations for the emergence of syntactic structure employ an argument based on genetic evolution: Syntactic structure is specified by an innate language acquisition device (LAD). Knowledge of language is complex, yet the data available to the language learner are sparse. This incongruous situation, termed the “poverty of the stimulus,” is accounted for by placing much of the specification of language in the LAD. The assumption is that the characteristic structure of language is somehow coded genetically. The effect of language evolution on the cultural substrate, in the absence of genetic change, is not addressed by this explanation. We show that the poverty of the stimulus introduces a pressure for compositional language structure when we consider language evolution resulting from iterated observational learning. We use a mathematical model to map the space of parameters that result in compositional syntax. Our hypothesis is that compositional syntax cannot be explained by understanding the LAD alone: Compositionality is an emergent property of the dynamics resulting from sparse language exposure.