The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
H M Van Driel - One of the best experts on this subject based on the ideXlab platform.
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temporally and spatially resolved Ballistic pure spin transport
Physical Review B, 2007Co-Authors: Hui Zhao, Arthur L Smirl, H M Van DrielAbstract:The Ballistic Movement of spin-polarized electrons in a semiconductor is spatially and temporally resolved. Pure spin currents are injected into GaAs quantum wells at 80 K by optical quantum interference processes, and the subsequent Ballistic transport is measured by pump-probe techniques having 200 fs temporal and 1 nm spatial resolution. An average injection velocity of 50 nm/ps and spin momentum relaxation times ranging from 1.2 to 0.6 ps are extracted for carrier densities varying from 1.5 to 12 1016 cm−3 when the electrons are excited into the conduction band with excess energy 25 meV, less than that of one optical phonon.
Rolf Ulrich - One of the best experts on this subject based on the ideXlab platform.
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Late backward effects in the refractory period paradigm: effects of Task 2 execution on Task 1 performance
Psychological Research PRPF, 2010Co-Authors: Susana Ruiz Fernández, Rolf UlrichAbstract:The central bottleneck model assumes that in the psychological refractory paradigm, Task 1 performance is independent of Task 2 demands. Previous studies, however, have reported backward crosstalk effects of motor demands in Task 2 on Task 1 performance. These effects have been attributed to interference at the central level. The present study aimed to isolate more directly potential backward effects at the motor level. Therefore, in three experiments, Movement distance in Task 2 was manipulated using a guided Ballistic Movement. The results showed that Movement distance in Task 2 affected reaction time as well as response duration in Task 1. It is argued that the backward effect observed in this study is due to response coupling at motor rather than central levels.
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Motor Limitation in Dual-Task Processing Under Ballistic Movement Conditions
Psychological science, 2006Co-Authors: Rolf Ulrich, Susana Ruiz Fernández, Ines Jentzsch, Bettina Rolke, Hannes Schröter, Hartmut LeutholdAbstract:The standard bottleneck model of the psychological refractory period (PRP) assumes that the selection of the second response is postponed until the first response has been selected. Accordingly, dual-task interference is attributed to a single central-processing bottleneck involving decision and response selection, but not the execution of the response itself. In order to critically examine the assumption that response execution is not part of this bottleneck, we systematically manipulated the temporal demand for executing the first response in a classical PRP paradigm. Contrary to the assumption of the standard bottleneck model, this manipulation affected the reaction time for Task 2. Specifically, reaction time for Task 2 increased with execution time for Task 1. This carryover effect from Task 1 to Task 2 provides evidence for the notion that response execution can be part of the processing bottleneck.
Eric J Perreault - One of the best experts on this subject based on the ideXlab platform.
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planning of Ballistic Movement following stroke insights from the startle reflex
PLOS ONE, 2012Co-Authors: Claire F Honeycutt, Eric J PerreaultAbstract:Following stroke, reaching Movements are slow, segmented, and variable. It is unclear if these deficits result from a poorly constructed Movement plan or an inability to voluntarily execute an appropriate plan. The acoustic startle reflex provides a means to initiate a motor plan involuntarily. In the presence of a Movement plan, startling acoustic stimulus triggers non-voluntary early execution of planned Movement, a phenomenon known as the startReact response. In unimpaired individuals, the startReact response is identical to a voluntarily initiated Movement, except that it is elicited 30–40 ms. As the startReact response is thought to be mediated by brainstem pathways, we hypothesized that the startReact response is intact in stroke subjects. If startReact is intact, it may be possible to elicit more task-appropriate patterns of muscle activation than can be elicited voluntarily. We found that startReact responses were intact following stroke. Responses were initiated as rapidly as those in unimpaired subjects, and with muscle coordination patterns resembling those seen during unimpaired volitional Movements. Results were striking for elbow flexion Movements, which demonstrated no significant differences between the startReact responses elicited in our stroke and unimpaired subject groups. The results during planned extension Movements were less straightforward for stroke subjects, since the startReact response exhibited task inappropriate activity in the flexors. This inappropriate activity diminished over time. This adaptation suggests that the inappropriate activity was transient in nature and not related to the underlying Movement plan. We hypothesize that the task-inappropriate flexor activity during extension results from an inability to suppress the classic startle reflex, which primarily influences flexor muscles and adapts rapidly with successive stimuli. These results indicate that stroke subjects are capable of planning Ballistic elbow Movements, and that when these planned Movements are involuntarily executed they can be as rapid and appropriate as those in unimpaired individuals.
Satoshi Suzuki - One of the best experts on this subject based on the ideXlab platform.
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The possibility of determination of accuracy of performance just before the onset of a reaching task using Movement-related cortical potentials
Medical & Biological Engineering & Computing, 2010Co-Authors: Satoshi Suzuki, Takemi Matsui, Yusuke Sakaguchi, Kazuhiro Ando, Nobuyuki Nishiuchi, Masayuki IshiharaAbstract:This study aimed to examine the relationships among electroencephalogram parameters as physiological indices, Ballistic Movement as an index of operation, and accuracy of task performance. Experiments were conducted using a “reaching” task, in which subjects touched the target appearing 300 pixels away from a start point in a vertical direction on a touch-sensitive screen with the forefinger. During experiments, EEG, EMG as trigger, high-speed camera images, and task efficiency were acquired. Significant differences between the high- and low-performance groups were clearly confirmed on the slope of NS (negative slope) in Movement-related cortical potentials (MRCPs) acquired from Fz ( p
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The possibility of determination of accuracy of performance just before the onset of a reaching task using Movement-related cortical potentials
Medical & biological engineering & computing, 2010Co-Authors: Satoshi Suzuki, Takemi Matsui, Yusuke Sakaguchi, Kazuhiro Ando, Nobuyuki Nishiuchi, Masayuki IshiharaAbstract:This study aimed to examine the relationships among electroencephalogram parameters as physiological indices, Ballistic Movement as an index of operation, and accuracy of task performance. Experiments were conducted using a “reaching” task, in which subjects touched the target appearing 300 pixels away from a start point in a vertical direction on a touch-sensitive screen with the forefinger. During experiments, EEG, EMG as trigger, high-speed camera images, and task efficiency were acquired. Significant differences between the high- and low-performance groups were clearly confirmed on the slope of NS (negative slope) in Movement-related cortical potentials (MRCPs) acquired from Fz (p < 0.05) and Cz (p < 0.05). Furthermore, a difference between these groups was confirmed in duration of Ballistic Movement. Based on our findings, we discuss whether it is possible to extract MRCP rapidly and automatically without using signal averaging and also to estimate accuracy just before a motion is executed.
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An approach for the task performance estimation using biological signals just before and after the onset of voluntary motion
2009Co-Authors: Satoshi Suzuki, Takemi Matsui, Yusuke Sakaguchi, Kazuhiro Ando, Kentaro Mikajiri, Nobuyuki NishiuchiAbstract:In order to predict of accuracy of Movement just before the onset of Movement using biological signals, the relationships between MRCP measured as a physiological index and the accuracy of task performance were investigated. As experiments, subjects touched the target appearing 300 pixels away from a start point in a vertical direction on a touch-sensitive screen with the forefinger. During experiments, EEG, EMG as trigger, high-speed camera images, and task efficiency were acquired. As a result, significant differences between the high- and low-performance groups were clearly confirmed on the slope of NS in MRCPs. Furthermore, a difference between these groups was confirmed in duration of Ballistic Movement.
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HCI (1) - On the Possibility about Performance Estimation Just before Beginning a Voluntary Motion Using Movement Related Cortical Potential
Human-Computer Interaction. New Trends, 2009Co-Authors: Satoshi Suzuki, Takemi Matsui, Yusuke Sakaguchi, Kazuhiro Ando, Nobuyuki Nishiuchi, Toshimasa Yamazaki, Shin'ichi FukuzumiAbstract:The present study aimed to investigate this tripartite relationship, regarding MRCP as a physiological index, Ballistic Movement as an index of operation and accuracy of the task performance. Experiments were conducted 'reaching' task; the subject touches the target appears 300 pixels away from the start point in a vertical direction on the touch sensitive screen with the forefinger. During experiments, EEG, EMG as trigger, image by high-speed camera and the efficiency of task were acquired. As a result, significant differences between the high and poor performance groups were clear on the NS in MRCP acquired from Fz(p < 0.05), Cz (p < 0.05) and Pz (p < 0.05). Furthermore, the difference was confirmed on the duration of Ballistic Movement. Based on our findings, we attempted to extract MRCP rapidly and automatically without using signal averaging and discuss whether it is possible to estimate accuracy just before the motion is executed.
Josep Valls-solé - One of the best experts on this subject based on the ideXlab platform.
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Excitability of the pathways mediating the startle reaction before execution of a voluntary Movement
Experimental brain research, 2005Co-Authors: Hatice Kumru, Josep Valls-soléAbstract:Studies with transcranial electrical or magnetic stimulation have shown a progressive increase of motor cortex excitability beginning at about 80 ms before the onset of electromyographic (EMG) activity in a voluntary Movement. We studied whether a similar increase in excitability occurs in subcortical motor tracts before execution of a Ballistic Movement. In ten healthy volunteers, we examined the effects of a startling auditory stimulus (SAS) applied at various intervals following the imperative signal (IS) in a reaction time task experiment. We hypothesized that, if the excitability of the reticulospinal tract increases before onset of muscle activity, there would be a corresponding change in the size of the startle response elicited either in muscles responding to the SAS, the orbicularis oculi (OOc) and sternocleidomastoid (SCM), or in the agonist muscle for the reaction. A SAS was applied at intervals of 0, 20, 40, 60, 80, and 100 ms after IS in a reaction time task paradigm in which subjects had to perform a Ballistic Movement of wrist flexion. We measured the size of the EMG bursts recorded in the OOc and the SCM, as well as the size of the first EMG burst in the wrist flexors (WF). Comparisons were done with data obtained in baseline trials, in which unexpected SAS of the same intensity were delivered without preparation, and control trials, in which subjects performed the same motor task with no SAS. The size of the averaged OOc, SCM, and WF were larger in trials with SAS than in baseline or control trials, with significant differences in the SCM and in the WF (p 0.05). These results indicate that, in the execution of a Ballistic Movement, the excitability of the subcortical motor tracts activated by a SAS is similarly enhanced at the time of the IS and 100 ms afterwards, just before the onset of EMG activity. We conclude that, in contrast with the reported progressive increase of excitability in the corticospinal tract, the excitability of the tracts activated by a SAS do not change between the IS and the onset of EMG activity.
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The effects of a startle on awareness of action.
Experimental brain research, 2004Co-Authors: M. T. Sanegre, Juan M. Castellote, Patrick Haggard, Josep Valls-soléAbstract:The execution of a Ballistic Movement within a reaction time task paradigm is significantly speeded up when an unexpected startling auditory stimulus (SAS) is delivered together with the imperative signal. Using Libet's clock, we investigated whether acceleration involves also the subjective appraisal of the time of task execution. In trials containing the SAS, reaction time shortened to 68.7% of control values. However, subjective judgment of task execution remained a similar time with respect to the imperative signal as in control trials. The dissociation between task execution and its subjective perception indicates the existence of separate circuits for action execution and action awareness.
