Planning and Control of Straight-Ahead and Angled Planar Movements in Adults and Young Children.

In the present study we wanted to determine why straight-ahead movements performed along one's midline are directionally more accurate than movements toward eccentric targets. We also wanted to determine whether the processes underlying this difference were the same in young children as in adults. Six-to-seven-year-old children and adults practiced a video-aiming task using different starting base and target combinations without vision of their ongoing movements. The results indicated that adults and children were directionally more accurate and less variable when pointing toward targets located straight ahead of the starting base rather than eccentric or concentric targets. This was true, regardless of whether the movement was performed along one's midline or not. These results suggest that angled movements are directionally less accurate than straight-ahead movements because of difficulty in defining the orientation of the appropriate movement vector in the workspace and/or in transforming it into appropriate motor commands. A kinematic analysis revealed large coefficients of direction and of extent variability early after movement initiation. However, these coefficients of variability were largely reduced by the occurrence of peak extent velocity, revealing that noise in initial movement planning was quickly reduced by on-line control processes. Finally, the results indicated largely similar planning and control processes for young children and adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

La différence de pente du temps de réaction au choix en fonction du mode de présentation des stimuli: Le r?le des effets de séquence.

Previous studies suggested that the linear relation between RT and presented information found for equally likely stimuli (ELS) did not hold for unequally likely stimuli (ULS). In fact, RT to low-information stimuli in the ULS condition was higher than RT to the same stimuli information in the ELS condition. A possible explanation of the discrepancy between the 2 functions is that sequential effects were not the same in the 2 conditions. This hypothesis was partially supported in an experiment involving 9 right-handed university students in a situation in which the possibility of a sequential effect was drastically reduced. A methodological approach permitting the reduction of sequential effects is proposed. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Biochemical regulation of sarcoplasmic reticulum Cl- channel from human atrial myocytes: involvement of phospholamban

Sarcoplasmic reticulum (SR) membrane vesicles derived from human atrium were characterized by specific ryanodine binding assay and fused into planar lipid bilayers. The tritiated form of the alkaloid bound to its receptor with a K(D) of 2.2 nM and a Bmax of 268 fmol/mg protein respectively. Special emphasis was placed on an anion-selective channel present in the SR membrane, which exhibited a mean conductance value of 67 pS when recorded in asymmetrical 50 mM trans/250 mM cis CsCl buffer system and a sensitivity to SITS (1 to 100 microM). Single and multiple channel activities displayed low voltage sensitivity and variability in its gating behavior which might result in spontaneous channel inactivation. However, the majority of the recordings (60%) resulted in a steady-state high open probability. The inactivated channel could be transiently reactivated with depolarizing voltage steps. This behavior is very similar, if not identical, to that observed for the SR Cl- channel in ventricular cells. The inactivation process is probably not directly related to a phosphorylation/dephosphorylation mechanism since PKA and PKG in presence of an adequate phosphorylation cocktail failed to reactivate the SR Cl- channel. In contrast, the use of a monoclonal anti-phospholamban antibody allowed the inhibition of the activity of the anionic channels. These results suggest that the regulation of the human atrial SR Cl- channel is dependent upon an interaction with phospholamban, which was clearly identified in our atrial preparations by Western blot analysis using monoclonal antibody.     

Pointage d'une position mémorisée et contexte visuel.

Determined whether a sensorimotor or cognitive encoding is used to encode a target position and save it into iconic memory. The methodology consisted of disrupting a manual aiming movement to a memorized visual target by displacing the visual field containing the target. The target was presented either centrally or in the right periphery. Participants moved their hand from the left to the right of fixation. The visual field was either stationary throughout the trial or was displaced to the right or left at the extinction of the target or at the start of the hand movement. Results showed three major effects: (1) Vision of the hand during the gesture improved the final accuracy; (2) visual field displacement produced an underestimation of the target distance only when the hand was not visible during the gesture and was always in the same direction displacement; and (3) the effect of the stationary structured visual field on aiming precision when the hand was not visible depended on the distance to the target. These results suggest that a stationary structured visual field is used to support the memory of the target position. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual perception modifies goal-directed movement control: supporting evidence from a visual perturbation paradigm

It is well known that dynamic visual information influences movement control, whereas the role played by background visual information is still largely unknown. Evidence coming mainly from eye movement and manual tracking studies indicates that background visual information modifies motion perception and might influence movement control. The goal of the present study was to test this hypothesis. Subjects had to apply pressure on a strain gauge to displace in a single action a cursor shown on a video display and to immobilize it on a target shown on the same display. In some instances, the visual background against which the cursor moved was unexpectedly perturbed in a direction opposite to (Experiment 1), or in the same direction as (Experiment 2) the cursor controlled by the subject. The results of both experiments indicated that the introduction of a visual perturbation significantly affected aiming accuracy. These results suggest that background visual information is used to evaluate the velocity of the aiming cursor, and that this perceived velocity is fed back to the control system, which uses it for on-line corrections.     

Effects of amino acids on Thiobacillus acidophilus. II. Threonine deaminase

Biosynthetic L-threonine deaminase was partially purified 73-fold with a 60% recovery from Thiobacillus acidophilus by ammonium sulfate fractionation and by Sepharose 6B-C1 chromatography. The optimal pH for enzyme activity was between 9.0 and 10.0 and no optimal pH shift was observed in the presence of L-isoleucine, an inhibitor. The enzyme was effectively inhibited by L-isoleucine and showed homotropic interaction only in the presence of L-isoleucine. Kinetic studies indicate that there are at least two threonine binding sites and at least two isoleucine binding sites. The Km for threonine is 2.5 x 10(-3) M. The inhibition due to isoleucine is reversed by low concentrations of L-valine. L-Valine at high concentration acts as a substrate analogue and competitively inhibits L-threonine binding at the active site; the K1 is 1.6 x 10(-2) M.     

Specificity of practice in a ball interception task.

Learning of an aiming task has been shown to be specific to the sources of afferent information available during practice. However, this has not been the case when a one-hand ball-catching task has been used. The goal of the present study was to determine the cause of these conflicting results. 16 undergraduates practiced an interception task in either a normal vision condition or a ball-only condition. They were all then transferred to the ball-only condition, using either the same ball trajectories as in acquisition or different ones. Being transferred from a normal vision condition to a ball-only condition resulted in a significant increase in spatial interception errors, thus supporting the specificity of practice hypothesis. Using new ball trajectories in transfer caused a significant increase in error for all participants. The pattern of errors observed when new ball trajectories were used suggests that participants had difficulty correlating information about the location of their arm via proprioception and a combination of retinal and extra-retinal information about the ball trajectory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

La différence de temps de réaction au choix observée pour chaque paire stimulus-réponse dans une tache à huit événements équiprobables.

Studied reaction time (RT) in an 8-alternative choice task. The 8 stimuli were linked either to individual response keys activated by the 8 fingers of the Ss' hands (manual condition) or to 8 different verbal responses (verbal conditions). The choice RT varied systematically as a function of the stimulus in the manual condition with the responses by the index and 4th fingers of both hands being faster than those by the 2nd and 3rd fingers. In the verbal condition with the same stimuli, but with spoken response, there was no significant variation of RT across stimuli. The results in the manual condition replicated those reported by A. T. Welford (1976, 1980) for this task. RT differences were attributed to the order of stimulus inspection that was under the Ss' control. However, the absence of interstimulus differences in the verbal condition argues against this explanation. The RT effect in the manual condition appears to be due to finger-specific differences in the speed of selecting and executing the response and not to stimulus inspection order. (English abstract) (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sensory integration in the learning of an aiming task.

Examined the role of dynamic (DVI) and static visual information (SVI) about the moving limb in motor control in an aiming task. 42 undergraduates practiced an oscilloscope aiming task. In a transfer test, the DVI regarding the displacement of the to-be-moved object could be withdrawn without altering the SVI that had been available during the learning of the task. After 200 trials of practice, withdrawing DVI produced a deterioration in the accuracy of Ss' responses. This indicates that the role played by the DVI for aiming control does not diminish with practice. The SVI cues available during movement execution did not appear to play an important role in the movement representation thought to develop through practice. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)