Representations underlying skill in the discrete sequence production task: effect of hand used and hand position

Various studies suggest that movement sequences are initially learned predominantly in effector-independent spatial coordinates and only after extended practice in effector-dependent coordinates. The present study examined this notion for the discrete sequence production (DSP) task by manipulating the hand used and the position of the hand relative to the body. During sequence learning in Experiment 1, in which sequences were executed by reacting to key-specific cues, hand position appeared important for execution with the practiced but not with the unpracticed hand. In Experiment 2 entire sequences were executed by reacting to one cue. This produced similar results as in Experiment 1. These experiments support the notion that robustness of sequencing skill is based on several codes, one being a representation that is both effector and position dependent

Numerical simulation of unsteady flow in hydraulic turbomachines

Turbines and pumps dealing with incompressible flow are examples of hydraulic turbomachines. In most cases the flow is highly turbulent and time-dependent, caused by the rotation of the impeller in a stationary casing. The geometry, with doubly curved surfaces, adds even more to the complexity. It all leads to a flow which is difficult to model. Yet, to optimize turbomachines it is necessary to analyze the flow in detail. Flow simulations using Computational Fluid Dynamics (CFD) can be a very helpful tool. The software solves the discretized partial differential equations for mass and momentum conservation on a grid that covers the flow domain. Two basic discretization schemes can be distinguished: collocated and staggered. When a collocated scheme is used, the solution suffers from odd-even decoupling. In practice this is suppressed with artificial measures which either decrease the accuracy of the simulation or increase the calculation time for an unsteady incompressible flow. Using a staggered scheme, accurate discretization is more difficult, but odd-even decoupling is avoided. In this thesis a CFD code is developed which is based on a staggered, blockstructured grid scheme. It is suited for the calculation of time-dependent fluid motion in turbomachines. The CFD code, named DEFT, is originally developed by the group ofWesseling at Delft University of Technology. The first extension in the current work was an interpolation procedure implemented to handle non-matching grids for more flexibility in grid generation. Furthermore, a sliding interface to connect the rotating grid in the impeller and the stationary grid was developed. Coriolis and centrifugal forces for calculations in the rotating frame of reference, were mplemented in two ways: using a conservative formulation and using source terms. An adaptation of the pressure equation proved necessary to reduce calculation time for computations involving a sliding interface. Although the conceptual ideas behind these extensions are applicable in 3D, they have been implemented in 2D and verified with the simulation of a number of relatively simple flows. DeFT was validated with the simulation of the flow through a cascade of blades which is a model of an axial-flow pump. The blade surface pressure and the total force on the blade are calculated. There is good agreement between values calculated with DeFT, Fluent, values from experiments, and other CFD calculations obtained from literature. The flow through a centrifugal pump with a vaned diffusor is simulated using the staggered discretization in DeFT and the collocated discretization in Fluent. The calculated time-averaged pressure and velocity along the pitch of a rotor channel show good correspondence. The agreement with results from experiments and other CFD calculations obtained from literature is more qualitative. The calculation time needed by DeFT and Fluent is approximately equal, despite the use of a large number of blocks in DeFT and its lack of a convergence enhancing multi-grid method which is used by Fluent

Cognitive control of sequential behavior

Movement can be considered as a crucial aspect of any living being, and has sometimes been considered as the main reason for the actual coming into existence of cognition. Most actions we perform in everyday life consist of series (sequences) of simple movements, by which we are able to attain fluent execution of more complex movement patterns. In this thesis, the mechanisms underlying motor sequence learning, as studied with the discrete sequence production (DSP) task, were investigated by focusing on response times, error rates and measures derived from the electroencephalogram (EEG). Results show that sequence learning in the DSP task is initially based on stimulus-response learning, but with practice sequence learning in the DSP task becomes based on multiple representations, which develop with practice. These representations can be effector dependent and effector independent. Measured derived from the EEG suggest the involvement of a general motor representation during the preparation of sequences, which is effector independent. The activity of this general motor representation decreases with practice, which suggests that with unfamiliar sequences response specifications are unknown and have to be filled in, whereas with familiar and mirrored sequences more response specifications are fixed in the general motor representation. Finally, to learn more about sequence learning we studied the differences in sequence learning in people with dyslexia. Dyslexics are thought to have difficulties with skill automatization, such as motor sequence learning. In this thesis it was shown for the first time that dyslexics were slowed in discrete sequence learning, as compared with controls. This agrees with the automatization deficit in dyslexics suggested by the cerebellar-deficit hypothesis

Is Bevacizumab (Avastin) Safe and Effective as Adjuvant Chemotherapy for Adult Patients With Stage IIIb or IV Non-Small Cell Lung Carcinoma (NSCLC)?

OBJECTIVE: The objective of this selective EBM review is to determine whether or not bevacizumab (avastin) is safe and effective as adjuvant chemotherapy for adult patients with stage IIIb or IV non-small cell lung carcinoma (NSCLC). STUDY DESIGN: Review of three randomized controlled trials (RCT) published in 2006, 2009, and 2011, all English language. DATA SOURCES: Two randomized, double-blind, controlled clinical trials comparing bevacizumab to placebo as adjunctive chemotherapy, and one RCT comparing bevacizumab as adjunctive chemotherapy versus the use of no adjunctive chemotherapy. All articles were found using PubMed, Medline, and OVID. OUTCOMES MEASURED: Overall survival (OS) and progression-free survival (PFS) were measured. OS was defined as time from randomization to death from any cause. PFS was defined as time from randomization to first documented disease progression or death on study treatment, whichever occurred first. Event-time distributions were estimated using the Kaplan-Meier method. RESULTS: Herbst et al2 and Reck et al6 compared traditional chemotherapy plus bevacizumab to traditional chemotherapy plus placebo, and Sandler et al3 compared traditional chemotherapy plus bevacizumab to traditional chemotherapy alone. Herbst et al2 failed to find a significant difference in OS or PFS between subjects using adjuvant bevacizumab and those using traditional chemotherapy. Reck et al6 was unable to assess OS; however, the investigators reported that PFS was significantly improved with the addition of bevacizumab to traditional chemotherapy. Sandler et al3 established that the addition of bevacizumab to traditional chemotherapy has statistically significant survival benefits in patients with NSCLC. CONCLUSIONS: From the research performed and results obtained, the evidence is inconclusive and conflicting to support the use of bevacizumab as adjuvant chemotherapy for stage IIIb or IV NSCLC. With inconsistencies and differing results among the three RCTs, further research would be helpful to confirm or negate the question of whether bevacizumab is actually beneficial as adjuvant therapy. In addition to researching the efficacy and safety of bevacizumab as adjuvant chemotherapy, it would be advantageous to study the efficacy and safety of bevacizumab as monotherapy. Further research is warranted to obtain more conclusive data

Why does positive mental health buffer against psychopathology?:An exploratory study on self compassion as a resilience mechanism and adaptive emotion regulation strategy

Growing evidence suggests that positive mental health or wellbeing protects against psychopathology. How and why those who flourish derive these resilient outcomes is, however, unknown. This exploratory study investigated if self-compassion, as it continuously provides a friendly, accepting and situational context for negative experiences, functions as a resilience mechanism and adaptive emotion regulation strategy that protects against psychopathology for those with high levels of positive mental health. Participants from the general population (n = 349) provided measures at one time-point on positive mental health (MHC-SF), self-compassion (SCS-SF), psychopathology (HADS) and negative affect (mDES). Self-compassion significantly mediated the negative relationship between positive mental health and psychopathology. Furthermore, higher levels of self-compassion attenuated the relationship between state negative affect and psychopathology. Findings suggest that especially individuals with high levels of positive mental health possess self-compassion skills that promote resilience against psychopathology. These might function as an adaptive emotion regulation strategy and protect against the activation of schema related to psychopathology following state negative affective experiences. Enhancing self-compassion is a promising positive intervention for clinical practice. It will not only impact psychopathology through reducing factors like rumination and self-criticism, but also improve positive mental health by enhancing factors such as kindness and positive emotions. This may reduce the future risk of psychopatholog

Context-dependent motor skill and the role of practice

Research has shown that retrieval of learned information is better when the original learning context is reinstated during testing than when this context is changed. Recently, such contextual dependencies have also been found for perceptual-motor behavior. The current study investigated the nature of context-dependent learning in the discrete sequence production task, and in addition examined whether the amount of practice affects the extent to which sequences are sensitive to contextual alterations. It was found that changing contextual cues—but not the removal of such cues—had a detrimental effect on performance. Moreover, this effect was observed only after limited practice, but not after extensive practice. Our findings support the notion of a novel type of context-dependent learning during initial motor skill acquisition and demonstrate that this context-dependence reduces with practice. It is proposed that a gradual development with practice from stimulus-driven to representation-driven sequence execution underlies this practice effect

The Effect of Static Ear Canal Pressure on Human Spontaneous Otoacoustic Emissions: Spectral Width as a Measure of the Intra-cochlear Oscillation Amplitude

Spontaneous otoacoustic emissions can be detected as peaks in the Fourier spectrum of a microphone signal recorded from the ear canal. The height, center frequency, and spectral width of SOAE peaks changed when a static pressure was applied to the ear canal. Most commonly, with either increasing or decreasing static pressure, the frequency increased, the amplitude decreased, and the width increased. These changes are believed to result from changes in the middle ear properties. Specifically, reduced middle ear transmission is assumed to attenuate the amplitude of emissions. We reconsidered this explanation by investigating the relation between peak height and width. We showed that the spectral width of SOAE peaks is approximately proportional to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1/\sqrt {{{\hbox{peak}}\;{\hbox{height}}}}$$\end{document}. This is consistent with a (Rayleigh) oscillator model in which broadening of the SOAE peak is caused by broadband intra-cochlear noise, which is assumed to be independent of static ear canal pressure. The relation between emission peak height and width implicates that the intra-cochlear oscillation amplitude attentuates relative to the intra-cochlear noise level when a static ear canal pressure is applied. Apparently, ear canal static pressure directly affects the active mechanics in the inner ear

Cognitive Processing in New and Practiced Discrete Keying Sequences

This study addresses the role of cognitive control in the initiation and execution of familiar and unfamiliar movement sequences. To become familiar with two movement sequences participants first practiced two discrete key press sequences by responding to two fixed series of 6-key specific stimuli. In the ensuing test phase they executed these two familiar and also two unfamiliar keying sequences while there was a two-third chance a tone was presented together with one randomly selected key specific stimulus in each sequence. In the counting condition of the test phase participants counted the low pitched (i.e., target) tones. By and large the results support the dual processor model in which the prime role of the cognitive processor shifts from executing to initiating sequences while the gradual development of motor chunks allows a motor processor to execute the sequences. Yet, the results extend this simple model by suggesting that with little practice sequence execution is based also on some non-cognitive (perhaps associative) learning mechanism and, for some participants, on the use of explicit sequence knowledge. Also, after extensive practice the cognitive processor appears to still contribute to slower responses. The occurrence of long interkey intervals was replicated suggesting that fixed 6-key sequences include several motor chunks. Yet, no indication was found that the cognitive processor is responsible for concatenating these chunks