Browsing by Subject "Transitivity"

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    Disrupted network topology in patients with stable and progressive mild cognitive impairment and alzheimer's disease
    (Oxford University Press, 2016) Pereira, J. B.; Mijalkov, M.; Kakaei, E.; Mecocci, P.; Vellas, B.; Tsolaki, M.; Kłoszewska, I.; Soininen, H.; Spenger, C.; Lovestone, S.; Simmons, A.; Wahlund, L.-O.; Volpe, G.; Westman, E.
    Recent findings suggest that Alzheimer's disease (AD) is a disconnection syndrome characterized by abnormalities in large-scale networks. However, the alterations that occur in network topology during the prodromal stages of AD, particularly in patients with stable mild cognitive impairment (MCI) and those that show a slow or faster progression to dementia, are still poorly understood. In this study, we used graph theory to assess the organization of structural MRI networks in stable MCI (sMCI) subjects, late MCI converters (lMCIc), early MCI converters (eMCIc), and AD patients from 2 large multicenter cohorts: ADNI and AddNeuroMed. Our findings showed an abnormal global network organization in all patient groups, as reflected by an increased path length, reduced transitivity, and increased modularity compared with controls. In addition, lMCIc, eMCIc, and AD patients showed a decreased path length and mean clustering compared with the sMCI group. At the local level, there were nodal clustering decreases mostly in AD patients, while the nodal closeness centrality detected abnormalities across all patient groups, showing overlapping changes in the hippocampi and amygdala and nonoverlapping changes in parietal, entorhinal, and orbitofrontal regions. These findings suggest that the prodromal and clinical stages of AD are associated with an abnormal network topology.
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    Estimating the glossiness transfer function induced by illumination change and testing its transitivity
    (Association for Research in Vision and Ophthalmology, 2010) Doerschner, K.; Boyacı, Hüseyin; Maloney, Laurence T.
    The light reflected from a glossy surface depends on the reflectance properties of that surface as well as the flow of light in the scene, the light field. We asked four observers to compare the glossiness of pairs of surfaces under two different realword light fields, and used this data to estimate a transfer function that captures how perceived glossiness is remapped in changing from one real-world light field to a second. We wished to determine the form of the transfer function and to test whether for any set of three light fields the transfer function from light field 1 to light field 2 and the transfer function from light field 2 to light field 3 could be used to predict the glossiness transfer function from light field 1 to light field 3. Observers' estimated glossiness transfer functions for three sets of light fields were best described by a linear model. The estimated transfer functions exhibited the expected transitivity pattern for three out of four observers. The failure of transitivity for one observer, while significant, was less than 12.5% of the gloss range.