The integration of sequential aiming movements: Switching hand and direction at the first target

Movement times to a single target are typically shorter compared to when movement to a second target is required. This one target movement time advantage has been shown to emerge when participants use a single hand throughout the target sequence and when there is a switch between hands at the first target. Our goal was to investigate the lacuna in the movement integration literature surrounding the interactive effects between switching hands and changing movement direction at the first target. Participants performed rapid hand movements in five conditions; movements to a single target; two target movements with a single hand in which the second target required an extension or reversal in direction; and movements to two targets where the hands were switched at the first target and the second target required an extension or reversal in direction. The significance of including these latter two (multiple hand-multiple direction) movements meant that for the first time research could differentiate between peripheral and central processes within movement integration strategies. Reaction times were significantly shorter in the single task compared to the two target tasks. More importantly, movement times to the first target were significantly shorter in the single target task compared to all two target tasks (reflecting the so-called one target advantage), except when the second movement was a reversal movement with the same hand. These findings demonstrate for the first time the contrasting effects of movement integration at central and peripheral levels

Sequential aiming movements and the one-target advantage in individuals with Down syndrome

Research has revealed that individuals with Down syndrome (DS) have elevated reaction times, longer movement times, and greater movement errors during single-target single-limb actions compared to their typically developing (TD) peers. These perceptual-motor impairments have been attributed to both central processes and the physical phenotype associated with DS. The purpose of the present study was to directly investigate these possible central and peripheral deficits by examining how individuals with DS plan and execute more complex movements. Three groups (DS, TD, and individuals with an undifferentiated intellectual disability; UID) of 8 participants completed a single target movement, a two-target movement performed by a single arm, and a two-target movement where the first movement was performed with one arm and the second movement performed with the other arm. For all groups and all conditions, movement times revealed a one-target advantage (OTA). Specifically, times to the first target were longer in the two-target responses compared to the single-target response. In general, the OTA finding reveals that persons with DS utilise planning strategies similar to their TD peers when performing sequential actions involving two targets and two arms. Furthermore, because the OTA was observed in both the single- and two-arm two-target responses the interference in movement one associated with having to make a subsequent movement is not due to peripheral processes associated with single limb constraints. Rather, individuals with DS treat movements within a sequence as functionally dependent. Thus, the central processes associated with timing the implementation of the second element of the movement appear to be responsible for the interference that leads to the OTA

Sequential aiming with one and two limbs: Effects of target size

It is well reported that movement times to the first target in a two-target sequence are slower than when a single target response is required. This one-target advantage has been shown to emerge when the two-target sequence is performed with the same limb and when the first and second segments within the sequence are performed with different limbs (i.e., when there is a switch between limbs at the first target). The present study examined the functional dependency between response segments in both single and two limb sequential aiming by varying the accuracy demands at the first and second target. Results revealed that, for both one and two limb conditions, the one-target advantage was present with large first targets but not with small first targets. Additionally, when the first target was large and the second target was small, spatial variability at the first target was significantly less (or constrained more) in both one and two limb conditions compared to conditions requiring only a single target response. These findings suggest that similar principles underlie the one-target advantage in both single and two limb sequential movements

Two-Stream Instability Model With Electrons Trapped in Quadrupoles

We formulate the theory of the two-stream instability (e-cloud instability) with electrons trapped in quadrupole magnets. We show that a linear instability theory can be sensibly formulated and analyzed. The growth rates are considerably smaller than the linear growth rates for the two-stream instability in drift spaces and are close to those actually observed

Watch me if you can: imagery ability moderates observational learning effectiveness

Recent research has revealed similarities in brain activity during observational learning and motor execution. However, whilst action develops visual, motor and afferent representations during acquisition, action-observation has been proposed to only develop visual-spatial learning via visual representation. In addition, it has been suggested that the vividness of visual representations are determined by imagery ability. Thus, the purpose of the current investigation was to explore the possible moderating role of imagery ability in the effectiveness of observational learning. Participants (n=40) were assessed on their imagery ability via the VMIQ-2 and then assigned to one of four groups; high imagery ability and observational learning (HIA-OL), low imagery ability and observational learning (LIA-OL), high imagery ability control (HIA-C) and low imagery ability control (LIA-C). Following group allocation all participants performed a pre-test consisting of 5 actual practice trials of a novel gymnastics routine. The HIA-OL and LIA-OL groups then participated in a 14 day observational learning intervention whilst the HIA-C & LIA-C groups acted as controls. Following this, participants performed a post test, which was identical in nature to the pre-test, before finally completing the VMIQ-2 again. Performance on both the pre-test and post test was evaluated by two qualified gymnastics judges. Results revealed that gymnastics performance increased from pre-test to post test for both the HIA-OL and LIA-OL groups. However, this effect was greater in the HIA-OL group suggesting that the relationship between observational learning and successful imitation performance is moderated by imagery ability

Practice with anxiety improves performance, but only when anxious: evidence for the specificity of practice hypothesis

We investigated for the first time whether the principles of specificity could be extended to the psychological construct of anxiety and whether any benefits of practicing with anxiety are dependent on the amount of exposure and timing of that exposure in relation to where in learning the exposure occurs. In Experiment 1, novices practiced a discrete golf-putting task in one of four groups: all practice trials under anxiety (anxiety), non-anxiety (control), or a combination of these two (i.e., the first half of practice under anxiety before changing to non-anxiety conditions, anxiety-control, or the reverse of this, control-anxiety). Following acquisition, all groups were transferred to an anxiety condition. Results revealed a significant acquisition-to-transfer decrement in performance between acquisition and transfer for the control group only. In Experiment 2, novices practiced a complex rock climbing task in one of the four groups detailed above, before being transferred to both a high-anxiety condition and a low-anxiety condition (the ordering of these was counterbalanced across participants). Performance in anxiety transfer was greater following practice with anxiety compared to practice without anxiety. However, these benefits were influenced by the timing of anxiety exposure since performance was greatest when exposure to anxiety occurred in the latter half of acquisition. In the low-anxiety transfer test, performance was lowest for those who had practiced with anxiety only, thus providing support for the specificity of practice hypothesis. Results demonstrate that the specificity of learning principle can be extended to include the psychological construct of anxiety. Furthermore, the specificity advantage appears dependent on its timing in the learning process

Tsallis non-extensive statistics, intermittent turbulence, SOC and chaos in the solar plasma. Part one: Sunspot dynamics

In this study, the nonlinear analysis of the sunspot index is embedded in the non-extensive statistical theory of Tsallis. The triplet of Tsallis, as well as the correlation dimension and the Lyapunov exponent spectrum were estimated for the SVD components of the sunspot index timeseries. Also the multifractal scaling exponent spectrum, the generalized Renyi dimension spectrum and the spectrum of the structure function exponents were estimated experimentally and theoretically by using the entropy principle included in Tsallis non extensive statistical theory, following Arimitsu and Arimitsu. Our analysis showed clearly the following: a) a phase transition process in the solar dynamics from high dimensional non Gaussian SOC state to a low dimensional non Gaussian chaotic state, b) strong intermittent solar turbulence and anomalous (multifractal) diffusion solar process, which is strengthened as the solar dynamics makes phase transition to low dimensional chaos in accordance to Ruzmaikin, Zeleny and Milovanov studies c) faithful agreement of Tsallis non equilibrium statistical theory with the experimental estimations of i) non-Gaussian probability distribution function, ii) multifractal scaling exponent spectrum and generalized Renyi dimension spectrum, iii) exponent spectrum of the structure functions estimated for the sunspot index and its underlying non equilibrium solar dynamics.Comment: 40 pages, 11 figure