Cortical and cerebellar activation induced by reflexive and voluntary saccades

Reflexive saccades are driven by visual stimulation whereas voluntary saccades require volitional control. Behavioral and lesional studies suggest that there are two separate mechanisms involved in the generation of these two types of saccades. This study investigated differences in cerebral and cerebellar activation between reflexive and self-paced voluntary saccadic eye movements using functional magnetic resonance imaging. In two experiments (whole brain and cerebellum) using the same paradigm, differences in brain activations induced by reflexive and self-paced voluntary saccades were assessed. Direct comparison of the activation patterns showed that the frontal eye fields, parietal eye field, the motion-sensitive area (MT/V5), the precuneus (V6), and the angular and the cingulate gyri were more activated in reflexive saccades than in voluntary saccades. No significant difference in activation was found in the cerebellum. Our results suggest that the alleged separate mechanisms for saccadic control of reflexive and self-paced voluntary are mainly observed in cerebral rather than cerebellar areas

Credit Rationing with Symmetric Information

Without denying the importance of asymmetric information, this article purports the view that credit rationing may also originate from a lender's inability to classify loan applicants in proper risk categories. This effect is particularly strong when novel technologies are involved. Furthermore, its relevance may increase with the importance assigned to internal rating systems by the Basel accord. This article presents a measure of the inadequacy of a lender's classification criteria to the qualitative features of prospective borrowers. Even without information asymmetries, credit rationing may occur if this quantity reaches too high a value. Furthermore, some general principles are outlined, that may be used by lenders in order to change their classification criteria

PRETRANSITION PHENOMENA

Quatre types de fluctuations — 1) classiques, 2) anti-phasés, 3) hétéro-phasées et 4) critiques — sont décrits et sont utilisés pour passer en revue plusieurs larges aspects des phénomènes de pré-transmission qui ont été signalés près des transitions de premier et de second ordre dans des systèmes réels aussi bien que dans des systèmes modèles. Des observations directes des phénomènes de pré-transition faites au microscope électronique ont révélé des fluctuations critiques dans un alliage de Fe-26,5 at. % Al et des fluctuations hétéro-phasées dans un alliage de Cu-Au. Ces dernières semblent interagir d'une manière forte avec des dislocations et avec la surface libre de la feuille de métal. La mise en évidence des fluctuations hétéro-phasées de Cu3Au a été aussi récemment rapportée, sur la base d'une dépendance de l'ordre à courte distance en fonction de la température près de la température critique. Des expériences sur les pics centraux observés pendant les transitions de phase structurelle suggèrent qu'ils ont une double origine intrinsèque-extrinsèque résultant d'un mélange d'ondes de groupes dynamiques et de groupes statiques, issues des localisations d'impuretés et de défauts. Des expériences par ordinateur sur des systèmes modèles sont passées en revue car elles donnent un aperçu des transitions de phase et permettent un essai précis des formulations théoriques sans les nombreux effets perturbateurs qui se rencontrent dans des systèmes réels.Four types of fluctuations — 1) classical, 2) antiphase, 3) heterophase and 4) critical — are described and used to review several broad aspects of pretransition phenomena that have been reported near second- and first-order transitions in both real and model systems. Direct observations of pretransition phenomena in the electron microscope have revealed critical fluctuations in an Fe-26.5 a/o Al alloy and heterophase fluctuations in a CuAu alloy. The latter appear to be interacting strongly with dislocations and the free surface of the foil. Evidence for heterophase fluctuations in Cu3Au has also recently been reported based on the temperature dependence of the short range order intensity near the transformation temperature. Experiments on the central peaks observed at structural phase transitions suggest that they have a dual intrinsic-extrinsic origin resulting from a mix of dynamical cluster waves and static clusters formed at impurities and defects. Computer experiments on model systems are reviewed as they give an insight into phase transitions and allow an exacting test of theoretical formulations without the many complicating effects found in real systems

Pretransition Phenomena(Metallurgy)

Four types of fluctuations-1) classical, 2) antiphase, 3) heterophase and 4) critical-are described and used to review several broad aspects of pretransition phenomena that have been reported near second- and first-order transitions in both real and model systems. Direct observations of pretransition phenomena in the electron microscope have revealed critical fluctuations in an Fe-26.5 a/o Al alloy and heterophase fluctuations in a CuAu alloy. The latter appear to be interacting strongly with dislocations and the free surface of the foil. Evidence for heterophase fluctuations in Cu_3Au has also recently been reported based on the temperature dependence of the short range order intensity near the transformation temperature. Experiments on the central peaks observed at structural phase transitions suggest that they have a dual intrinsic-extrinsic origin resulting from a mix of dynamical cluster waves and static clusters formed at impurities and defects. Computer experiments on model systems are reviewed as they give an insight into phase transitions and allow an exacting test of theoretical formulations without the many complicating effects found in real systems