Human prehension movements have been studied with regard to the parallel processing of motor control and sensorimotor coordination. Temporal aspects of the movement (e.g., onset time and duration) have been studied extensively, while spatial aspects have not been studied systematically. Thus, the purpose of this study was to examine spatiotemporal variability of the transport (wrist trajectory) and grasp (grip aperture between the index finger and the thumb) components. In this experiment, the extrinsic (e.g., distance) and intrinsic object properties (e.g., object size) were manipulated. Subjects were required to pick up an aluminum cylinder as quickly and accurately as possible using the index finger and the thumb. It was found that object size significantly affected both transport and grasp components. Distance mainly affected the transport component. These kinematic results were consistent with the findings of earlier studies. Furthermore, the distribution of mean within-subject variability across normalized movement time for the transport component was not the same as that of the grasp component, suggesting that the different motor control processes exist. The peak amplitudes in variability of the wrist trajectory and the grip aperture were obtained at similar points throughout movement time. Furthermore, the peak of wrist variability depended on distance not object size, while that of aperture variability depended on both distance and object size. These results strongly support the hypothesis that the grasp component is adjusted using dynamic information provided from the transport component as the wrist moves toward the object. We also found that wrist variability converged to the target point, while aperture variability was biphasic: it converged, at least, around the point of maximum aperture in the first phase and then remained constant in the second phase. This result suggests that the two components are under different control processes. We hypothesize that the transport component can be modeled as a single feedforward system, while the grasp component can be divided into two separate mechanisms.

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In order to investigate the local symmetry at the Si(4e)-site above and below hidden order temperature T O = 17.5 K in URu 2 Si 2 , we have carried out 73 Ge-nuclear magnetic resonance (NMR) measurement on 10%73 Ge-substituted sample URu 2 (Si 0.9 Ge 0.1 ) 2 . The specific heat measurement on the present sample shows a clear second-order transition, indicating that the hidden order is still a bulk property. Besides, equally split 73 Ge-NMR lines due to the nuclear quadrupole interaction gives evidence for fairly uniform electric-field gradient at the Ge-substituted sites, Although this is the first attempt to investigate the local symmetry at the 4e-site by proving electric interactions, no evidence for symmetry lowering below T O has been obtained at present.The mysterious order at T O = 17.5 K in URu 2 Si 2 , so called the "hidden order", has been a topic of interest and controversy for more than two decades. Recently a new aspect from the space group analysis has been presented, 1) in which the authors indicated symmetry lowing of the system below T O is characterized by changes in local charge distribution without causing any kind of lattice distortion. From experimental point of view, in order to examine theoretical predictions, one needs information about how symmetry of the system changes at the second-order phase transition. As for detecting modifications of the local charge distributions, measurements of the nuclear quadrupole interaction is useful, because the nuclear spin I (restricted to I ≥ 1) interacts with the electricfield gradient (EFG) that surrounding charges cause at the observing nuclear position. This approach has been successfully employed in the determination of an ordered structure in the filled Skutterudite compound SmRu 4 P 12 . Namely 101 Runuclear quadrupole resonance (NQR) line shape is clearly split into two peaks below the second-order phase transition, implying the crystal structure changes to one of the maximal subgroups (R3) of the filled Skutterudite structure. 2)In this paper, we present the first results of 73 Ge-nuclear magnetic resonance (NMR) measurements on 10%73 Gesubstituted sample URu 2 (Si 0.9 Ge 0.1 ) 2 . Here, motivated by the above-mentioned space group analysis, the local symmetry at the Si(4e)-site will be discussed. There are actually many reports of NMR study on URu 2 Si 2 so far (see Ref. [3][4][5] and references therein). However, none of them studied the nuclear quadrupole interactions at the 4e-site, because 29 Si nuclear spin I = 1/2 does not couple to the EFG. In this context, the NMR experiment of isotope 73 Ge (I = 9/2) on the Si-site opens a way to obtain more detailed information about the local symmetry at this site. Note that, according to the prediction of Ref. [1], the possible symmetry lowering at T O in URu 2 Si 2 does not accompanied with any splitting of the three sites, but does with just breakdown of 4-fold symmetry at the U(2a)-and 4e-sites. This might be more difficult to observe * E-mail address: mito@sci.u-hyogo.ac.jp directly, compare...