The "mirror box" illusion: effect of visual information on bimanual coordination in children with spastic hemiparetic cerebral palsy

The study examined symmetrical bimanual coordination of children with spastic hemiparetic cerebral palsy (SHCP) and a typically developing (TD) control group under conditions of visual feedback created by placing a glass screen, opaque screen or a mirror (“mirror box”) between the arms. The “mirror box” creates a visual illusion, which gives rise to a visual perception of a zero lag, symmetric movement between the two arms. Children with SHCP exhibited a similar mean coordination pattern as the TD control group, but had greater movement variability between the arms. Furthermore, movement variability in children with SHCP was significantly greater in the screen condition compared with the glass and mirror condition, which were similar to each other. The effects of the availability of visual feedback in individuals with hemiparesis are discussed with reference to central and peripheral mechanisms

Effects of experience on the coordination of internally and externally timed soccer kicks

The authors investigated differences in the soccer kick between 8 experienced and 10 less experienced participants in 2 different task conditions (kicking a stationary ball or a moving ball at a target). The experienced participants were more accurate than their less experienced counterparts, whereas there were no differences in maximum foot velocity between groups or between conditions. When compared with their performance in the stationary condition, participants kicked the moving ball with a smaller range of movement at the knee of the kicking leg, maintaining a proximodistal coordination pattern. Because of their significantly shorter knee-flexion phase, the participants in the experienced group displayed a significantly shorter time between initiation of the forward swing of the kick and ball contact than that of those in the less experienced group. The rapid knee flexion may have been a strategy of exploiting passive dynamics to increase accuracy rather than velocity. Members of both groups showed a proximodistal initiation sequence in the kicking leg, which suggests that players can acquire that coordination pattern with relatively little structured practice and that further practice leads to improvement possibly through the increased exploitation of passive dynamics. Copyright © 2007 Heldref Publications

Deficits in the coordination of agonist and antagonist muscles in stroke patients: implications for normal motor control

Movement impairments about a single joint in stroke patients may be related to deficits in the central regulation of stretch reflex (SR) thresholds of agonist and antagonist muscles. One boundary of the SR threshold range for elbow flexor and extensor muscles was measured in hemiparetic subjects by analysing electromyographic activity during stretching of relaxed muscles at seven different velocities. For each velocity, dynamic SR thresholds were measured as angles at which electromyographic activity appeared. These data were used to determine the sensitivity of the threshold to velocity and the static SR thresholds for flexors and extensors. In contrast to relaxed muscles in healthy subjects, static flexor and extensor thresholds lay within the physiological range in 11/12 and 4/12 subjects, respectively. This implies that, in the range between the static SR threshold and one of the physiological joint limits, relaxation of the muscle was impossible. Subjects then made slow movements against different loads to determine their ranges of active movement. Maximal flexor and extensor torques were lower in hemiparetic subjects throughout the angular range. In some subjects, ranges were found in which no active torque could be produced in either extensor or both muscle groups. These ranges were related to the boundary values of SR thresholds found during passive muscle stretch. The range in which reciprocally organized agonist and antagonist muscle activity could be generated was limited in all but one subject. When attempting to produce torque from positions outside their measured range of movement, excessive muscle coactivation occurred, typically producing no or paradoxical motion in the opposite direction. Results suggest a relationship between spasticity measured at rest and the movement deficit in stroke by demonstrating a link between motor deficits and control deficits in the central regulation of individual SR thresholds. Copyright (C) 2000 Elsevier Science B.V

Importance of Systematic Diagnostic Testing in Idiopathic Ventricular Fibrillation: Results From the Dutch iVF Registry.

BACKGROUND: Idiopathic ventricular fibrillation (iVF) is a diagnosis of exclusion. Systematic diagnostic testing is important to exclude alternative causes for VF. The early use of "high yield" testing, including cardiac magnetic resonance (CMR), exercise testing, and sodium channel blocker provocation, has been increasingly recognized. OBJECTIVES: The purpose of this study was to investigate the importance and consistency of systematic diagnostic testing in iVF. METHODS: This study included 423 iVF patients from 11 large secondary and tertiary hospitals in the Netherlands. Clinical characteristics and diagnostic testing data were ascertained. RESULTS: IVF patients experienced the index event at a median age of 40 years (IQR: 28-52 years), and 61% were men. The median follow-up time was 6 years (IQR: 2-12 years). Over the years, "high yield" diagnostic tests were increasingly performed (mean 68% in 2000-2010 vs 75% in 2011-2021; P < 0.001). During follow-up, 38 patients (9%) originally labeled as iVF received an alternative diagnosis. Patients in whom "high-yield" diagnostic tests were consistently performed during the initial work-up received an alternative diagnosis less frequently during follow-up (HR: 0.439; 95% CI: 0.219-0.878; P = 0.020). Patients who received an alternative diagnosis during follow-up had a worse prognosis in terms of cardiac death (P = 0.012) with a trend toward more implantable cardioverter-defibrillator therapy (P = 0.055). CONCLUSIONS: Although adherence to (near) complete diagnostic testing in this population of iVF patients increased over the years, patients with iVF still undergo varying levels of diagnostic evaluation. The latter leads to initial underdiagnosis of alternative conditions and is associated with a worse prognosis. Our results underscore the importance of early systematic diagnostic assessment in patients with apparent iVF

Concepts and Languages for Privacy-Preserving Attribute-Based Authentication

Part 3: Session 2 - Anonymous CredentialsInternational audienceExisting cryptographic realizations of privacy-friendly authentication mechanisms such as anonymous credentials, minimal disclosure tokens, selfblindable credentials, and group signatures vary largely in the features they offer and in how these features are realized. Some features such as revocation or de-anonymization even require the combination of several cryptographic protocols. These differences and the complexity of the cryptographic protocols hinder the deployment of these mechanisms for practical applications and also make it almost impossible to switch the underlying cryptographic algorithms once the application has been designed. In this paper, we aim to overcome this issue and simplify both the design and deployment of privacy-friendly authentication mechanisms. We define and unify the concepts and features of privacy-preserving attribute-based credentials (Privacy-ABCs) and provide a language framework in XML schema. Our language framework enables application developers to use Privacy-ABCs with all their features without having to consider the specifics of the underlying cryptographic algorithms—similar to as they do today for digital signatures, where they do not need to worry about the particulars of the RSA and DSA algorithms either