Visuospatial deficits, walking dynamics and effects of visual cues on gait regulation in Parkinson's disease (PD)

Individuals with Parkinson’s disease (PD) present with motor and non-motor symptoms, including in the visuospatial domain. Correction of walking abnormalities through application of visual cues in the environment has been reported in PD, but the mechanisms of action are poorly understood. The present project examined competing explanations of the effects of visual guidance on multiple aspects of gait in PD. Comfortable over-ground walking was performed by 9 participants with left-side motor onset (LPD), 11 with right-side motor onset (RPD), and 13 age-matched normal control participants (NC). Study 1 examined whether veering in PD is predominantly induced by asymmetrical perception of the visual environment or by motor asymmetry between relatively affected and relatively non-affected body side. Walking conditions were eyes-open, vision-occluded, and egocentric reference point (walk toward the perceived center of a distant target). The visual hypothesis predicted that LPD, with a known tendency toward left spatial hemineglect, would veer rightward, whereas RPD would veer leftward. The motor hypothesis predicted the opposite pattern of results because the more affected body side has shorter step length. The results supported the visual hypothesis. In Study 2, visually-cued gait was examined to establish whether the key variable to improvement is attention to pattern rhythmicity, or instead if improvement may arise from perception of dynamic flow. Floor patterns included transverse lines (attention; 3 frequencies) and randomly-placed squares (dynamic; 3 densities). Relative to baseline, both transverse lines and random squares, especially at higher frequency/density, resulted in gait improvements and induced more stable interlimb coordination, especially for LPD, the subgroup known to have greater visual dependence. Effects lasted after the cues were removed. The success of the random-squares cuing indicates that the mechanism of improvement may be dynamic flow of visual texture rather than attention, and further suggests that vision-based interventions need not be restricted to transverse lines. Taken together, the studies lay the foundation for the development of treatments for walking disturbances in PD by addressing critical issues that could influence the outcomes of therapeutic interventions, including the role of visual input and the differential effects on PD subgroups.2017-07-01T00:00:00

Synthesis and characterisation of metal oxides and fluorinated perovskite-related oxides

Perovskite-related materials of composition LaFe1-xCoxO3 prepared by conventional calcination methods and mechanical milling are shown by temperature programmed reduction to be more susceptible to reduction in a flowing mixture of hydrogen and nitrogen by the incorporation of cobalt. X-ray powder diffraction and Mossbauer spectroscopy show that in iron-rich systems the limited reduction of iron and cobalt leads to the segregation of discrete metallic phases without destruction of the perovskite structure. In cobalt-rich systems, the reduction of Co3+ to Coo precedes complete reduction of Fe3+ and the segregation of alloy and metal phases is accompanied by destruction of the perovskite structure. Phases made by milling techniques were of smaller particle size and are more susceptible to hydrogen reduction than their counterparts made by conventional techniques. Materials of the type La0.5Sr0.5MO3 (M= Fe, Co) made by calcination methods are more susceptible to reduction when the transition metal M is cobalt as compared to iron. Perovskite-related oxides of composition La1-xSrxFe1-yCoyO3 have been fluorinated by reaction with poly(vinylidene fluoride). The materials have been characterised by X-ray powder diffraction and Mossbauer spectroscopy. Fluorination induces a reduction in the oxidation state of iron from Fe4+ to Fe3+. The fluorinated materials were magnetically ordered at 298 K. Compounds of the type SrFe1-xSnxO3 were found to contain Fe5+ and Fe3+. Fluorination resulted in reduction of the transition metal to Fe3+ and, in iron-rich systems, magnetic order. The compound Ba2SnO4 which adopts the K2NiF4-type structure has also been fluorinated by reaction with zinc fluoride. X-ray powder diffraction shows an enlargement of the unit cell of the fluorinated phase along the c-axis. Small particle iron- and vanadium- antimonate have been prepared by mechanical milling methods. The phases have been examined by M6ssbauer spectroscopy and can be formulated M3+Sb5+O4 (M = Fe, V). Thermal analysis suggests that the vanadium animonate formed by milling V2O5 and Sb2O3 in an inert atmosphere may be oxygen deficient. X-ray powder diffraction shows that milling also induces the phase transformation of the cubic senarmontite Sb2O3 form to the orthorhombic valentinite Sb2O3 form and of a-Sb2O4 to B-Sb2O4

Optimal Taxation of Externalities Interacting through Markets: A Theoretical General Equilibrium Analysis

This study develops a theoretical general equilibrium model to examine optimal externality tax policy in the presence of externalities linked to one another through markets rather than technical production relationships. Analytical results reveal that the second-best externality tax rate may be greater or less than the first-best rate, depending largely on the elasticity of substitution between the two externality-generating products. These results are explored empirically for the case of greenhouse gas from fossil fuel and nitrogen emissions associated with biofuels.second-best tax, multiple externalities, biofuel, GHG emissions, nitrogen leaching

NNSplitter: An Active Defense Solution for DNN Model via Automated Weight Obfuscation

As a type of valuable intellectual property (IP), deep neural network (DNN) models have been protected by techniques like watermarking. However, such passive model protection cannot fully prevent model abuse. In this work, we propose an active model IP protection scheme, namely NNSplitter, which actively protects the model by splitting it into two parts: the obfuscated model that performs poorly due to weight obfuscation, and the model secrets consisting of the indexes and original values of the obfuscated weights, which can only be accessed by authorized users with the support of the trusted execution environment. Experimental results demonstrate the effectiveness of NNSplitter, e.g., by only modifying 275 out of over 11 million (i.e., 0.002%) weights, the accuracy of the obfuscated ResNet-18 model on CIFAR-10 can drop to 10%. Moreover, NNSplitter is stealthy and resilient against norm clipping and fine-tuning attacks, making it an appealing solution for DNN model protection. The code is available at: https://github.com/Tongzhou0101/NNSplitter.Comment: To appear at ICML 202

Effects of Parkinson’s disease on optic flow perception for heading direction during navigation

Visuoperceptual disorders have been identified in individuals with Parkinson’s disease (PD) and may affect the perception of optic flow for heading direction during navigation. Studies in healthy subjects have confirmed that heading direction can be determined by equalizing the optic flow speed (OS) between visual fields. The present study investigated the effects of PD on the use of optic flow for heading direction, walking parameters, and interlimb coordination during navigation, examining the contributions of OS and spatial frequency (dot density). Twelve individuals with PD without dementia, 18 age-matched normal control adults (NC), and 23 young control adults (YC) walked through a virtual hallway at about 0.8 m/s. The hallway was created by random dots on side walls. Three levels of OS (0.8, 1.2, and 1.8 m/s) and dot density (1, 2, and 3 dots/m2) were presented on one wall while on the other wall, OS and dot density were fixed at 0.8 m/s and 3 dots/m2, respectively. Three-dimensional kinematic data were collected, and lateral drift, walking speed, stride frequency and length, and frequency, and phase relations between arms and legs were calculated. A significant linear effect was observed on lateral drift to the wall with lower OS for YC and NC, but not for PD. Compared to YC and NC, PD veered more to the left under OS and dot density conditions. The results suggest that healthy adults perceive optic flow for heading direction. Heading direction in PD may be more affected by the asymmetry of dopamine levels between the hemispheres and by motor lateralization as indexed by handedness.Published versio

Dual tasking in Parkinson's disease: cognitive consequences while walking

Published in final edited form as: Neuropsychology. 2017 September; 31(6): 613–623. doi:10.1037/neu0000331.OBJECTIVE: Cognitive deficits are common in Parkinson's disease (PD) and exacerbate the functional limitations imposed by PD's hallmark motor symptoms, including impairments in walking. Though much research has addressed the effect of dual cognitive-locomotor tasks on walking, less is known about their effect on cognition. The purpose of this study was to investigate the relation between gait and executive function, with the hypothesis that dual tasking would exacerbate cognitive vulnerabilities in PD as well as being associated with gait disturbances. METHOD: Nineteen individuals with mild-moderate PD without dementia and 13 age- and education-matched normal control adults (NC) participated. Executive function (set-shifting) and walking were assessed singly and during dual tasking. RESULTS: Dual tasking had a significant effect on cognition (reduced set-shifting) and on walking (speed, stride length) for both PD and NC, and also on stride frequency for PD only. The impact of dual tasking on walking speed and stride frequency was significantly greater for PD than NC. Though the group by condition interaction was not significant, PD had fewer set-shifts than NC on dual task. Further, relative to NC, PD showed significantly greater variability in cognitive performance under dual tasking, whereas variability in motor performance remained unaffected by dual tasking. CONCLUSIONS: Dual tasking had a significantly greater effect in PD than in NC on cognition as well as on walking. The results suggest that assessment and treatment of PD should consider the cognitive as well as the gait components of PD-related deficits under dual-task conditions. (PsycINFO Database Record)

CDA: A clustering degree based influential spreader identification algorithm in weighted complex network

Identifying the most influential spreaders in a weighted complex network is vital for optimizing utilization of the network structure and promoting the information propagation. Most existing algorithms focus on node centrality, which consider more connectivity than clustering. In this paper, a novel algorithm based on clustering degree algorithm (CDA) is proposed to identify the most influential spreaders in a weighted network. First, the weighted degree of a node is defined according to the node degree and strength. Then, based on the node weighted degree, the clustering degree of a node is calculated in respect to the network topological structure. Finally, the propagation capability of a node is achieved by accounting the clustering degree of the node and the contribution from its neighbors. In order to evaluate the performance of the proposed CDA algorithm, the susceptible-infected-recovered model is adopted to simulate the propagation process in real-world networks. The experiment results have showed that CDA is the most effective algorithm in terms of Kendall's tau coefficient and with the highest accuracy in influential spreader identification compared with other algorithms such as weighted degree centrality, weighted closeness centrality, evidential centrality, and evidential semilocal centrality