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Florian Van Halewyck, Ann Lavrysen, Oron Levin, Digby Elliott and Werner F. Helsen

Older adults traditionally adapt their discrete aiming movements, thereby traveling a larger proportion of the movement under closed-loop control. As the beneficial impact of a physically active lifestyle in older age has been described for several aspects of motor control, we compared the aiming performance of young controls to active and sedentary older adults. To additionally determine the contribution of visual feedback, aiming movements were executed with and without saccades. Results showed only sedentary older adults adopted the typical movement changes, highlighting the impact of a physically active lifestyle on manual aiming in older age. In an attempt to reveal the mechanism underlying the movement changes, evidence for an age-related decline in force control was found, which in turn resulted in an adapted aiming strategy. Finally, prohibiting saccades did not affect older adults’ performance to a greater extent, suggesting they do not rely more on visual feedback than young controls.

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Luc Tremblay, Timothy N. Welsh and Digby Elliott

Although proponents of the motor schema theory hold that a decrease in the reliance on afferent information will occur with practice in consort with the development of motor programs, supporters of the specificity of practice hypothesis suggest that a performer's reliance on the available sources of afferent information during acquisition increases with the amount of practice. To reconcile these competing positions, four groups of 9 participants aimed to targets under either a constant or a variable practice schedule, with or without vision of the effector. After modest (15 trials) and moderate (150 trials) practice, participants were tested in both their own and in the alternate vision condition. Results indicate mat the utilization of online kinesthetic information was enhanced through practice regardless of the availability of vision during acquisition. This was especially true for the groups practicing under a variable practice schedule.

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Pamela J. Hoyes Beehler

Hand laterality research efforts have shown a performance advantage in terms of pointing accuracy and limb speed (movement time—MVT) for the preferred hand (right-hand), and a slight reaction time (RT) performance advantage for the non-preferred hand (left-hand) for rapid manual aiming movements (Flowers, 1975; Roy, 1983; Roy & Elliott, 1986). These performance advantages for the right and left-hands, respectively, are considered an enigma in the motor behavior literature (Magill, 1993) and were investigated. The purpose of this study was to determine the effects of skill level, hand laterality, and movement direction during visuomotor processing of female athletes performing manual aiming tasks. Results showed that skill level and hand laterality did not influence the initiation of manual aiming movements; but, left direction movements were initiated faster than right direction movements. Right-hand MVT was faster than left-hand MVT; but, main effects skill level and movement direction were not significant for MVT. Skill level did interact with hand laterality and movement direction for MVT. Also, right-hand right direction movements were the easiest manual aiming tasks to complete while left-hand right direction movements were the most difficult manual aiming tasks to complete. Differences in hemispheric visuomotor processing when performing manual aiming movements based on skill level and hand laterality were discussed. Training implications for manual aiming movements were also discussed.

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James Lyons, Digby Elliott, Laurie R. Swanson and Romeo Chua

This study was designed to examine the influence of age and the availability of vision on the performance and kinematic characteristics of discrete aiming movements. Twelve young adults (19–25 years old) and 12 healthy older adults (62–82 years old) performed 130-mm aiming movements to targets with diameters of 5, 10, and 20 mm. On half the trial blocks, visual feedback about the aiming movement was eliminated upon movement initiation. Surprisingly, older adults were both as fast and as accurate as young adults regardless of the vision or target condition. While the velocity profiles of young and older adults were also similar, older adults exhibited a greater number of deviations in acceleration in both the vision and no-vision situations. Since these deviations are thought to reflect adjustments to the movement trajectory, older adults may rely more on visual and kinesthetic feedback for the control of goal-directed movement.

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Cheryl M. Glazebrook, Digby Elliott and James Lyons

We examined the planning and control of goal-directed aiming movements in young adults with autism. Participants performed rapid manual aiming movements to one of two targets. We manipulated the difficulty of the planning and control process by varying both target size and amplitude of the movements. Consistent with previous research, participants with autism took longer to prepare and execute movements, particularly when the index of difficulty was high. Although there were no group differences for accuracy, participants with autism exhibited more temporal and spatial variability over the initial phase of the movement even though mean peak accelerations and velocities were lower than for control participants. Our results suggest that although persons with autism have difficulty specifying muscular force, they compensate for this initial variability during limb deceleration. Perhaps persons with autism have learned to keep initial impulses low to minimize the spatial variability that needs to be corrected for during the online control phase of the movement.

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Heather F. Neyedli and Timothy N. Welsh

Previous research has shown in a motor decision task involving a target (yielding a reward) and overlapping penalty area (yielding a loss), people initially aim closer to the penalty area than optimal. This risky strategy may be adopted to increase target hits, thereby increasing net worth. The purpose of the current study was to determine whether the starting net worth level (either 5,000 or 0 points) affected the influence of task experience on endpoint selection. It was hypothesized the 5,000-point group should adopt a less risky strategy and aim further from the penalty area than those with 0 points. Net worth affected participants’ initial endpoint where the 5,000-point group aimed further from the penalty circle, and closer to the optimal endpoint, than the 0-point group. The 0-point group adapted their endpoint over the course session to aim closer to the optimal endpoint whereas no such change was seen in the 5,000-point group. The results show that changing the participants’ reference point through initial net worth can affect the optimality of participants’ endpoint and how endpoints change with experience.

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Timothy N. Welsh and Michele Zbinden

The “proximity-to-hand” effect refers to the finding that distractors between the home position and the target cause more interference in a selective reaching movement than distractors farther from the home position. Based largely on the proximity-to-hand effect, Tipper, Lortie, and Baylis (1992) proposed that attention is distributed in an action-centered framework such that the interference caused by a specific stimulus depends on the action. The current experiments sought to determine if there is an attentional preference for stimuli closer to home or for stimuli that activate more efficiently executed actions regardless of the location. Results supported the latter hypothesis in that the greatest interference was observed when the distractor activated an action with a lower index of difficulty than the target, even though that distractor was farther from home than the target. These findings indicate that the action context mediates the influence that nontarget stimuli have on the processing of target responses.

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Darian T. Cheng, Gerome A. Manson, Andrew Kennedy and Luc Tremblay

Cheng et al. (2008) showed that when goal-directed reaching movements are performed with a 2.5 s inter-trial interval (ITI) under a randomized visual feedback schedule, individuals use online visual information on trial n to perform efficient online corrections on trial n + 1 (i.e., “reminiscence” effect). These results persisted even when participants were given knowledge of the up-coming vision condition. In this study, the ITI was extended to 5 s in an attempt to negate any effects of the preceding trial. Results from this study revealed that trials with vision were always more accurate than trials performed without vision, suggesting that individuals relied significantly on online information. Furthermore, aiming precision improved when participants knew the vision condition before each trial. It is thus suggested that the reminiscence effects are not longer evident with a 5 s ITI, which in turn allows prior knowledge of visual feedback to influence the use of online vision.

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Ann Lavrysen, Werner F. Helsen, Digby Elliott and Jos J. Adam

The one-target advantage refers to a shorter movement time for one-target aiming movements, in comparison to aiming attempts followed by a second movement. Theoretical explanations of the one-target advantage vary in the extent to which they attribute this phenomenon to prior planning or to online control mechanisms. In this research, we attempted to gain insight into the control of sequential aiming movements by manipulating the availability of online feedback during this first or second movement component. When the participants' vision was occluded during the first movement (Experiment 1) or during the second movement (Experiment 2), their performance was affected, showing that vision was important for online control of the movement sequence. A one-target advantage was found when the second movement was in the same direction as me first, but not when it was reversed with respect to the home button. Both prior planning and online control processes contribute to the one-target advantage. The degree to which these processes are important for limb control depends on the specific task demands.

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David A. Le Clair and Digby Elliott

This study examined the extent to which individuals with Down syndrome benefit from visual and verbal advance information about a manual aiming movement. Adults with Down syndrome as well as control subjects with and without mental handicaps performed 10.5-cm manual aiming movements with their preferred hand. On each trial subjects were cued about the specific movement either visually or verbally. On different trial blocks, the cue provided either 50% or 80% certainty. Nonhandicapped control subjects initiated and completed their manual aiming movements more quickly than subjects with mental handicaps. As well, individuals with Down syndrome were found to be slower and more variable in reaction time than participants in the other mentally handicapped group when valid information was provided verbally but not when the cue was provided visually. These results are consistent with the proposal that atypical hemispheric lateralization for speech perception associated with Down syndrome disrupts communication between functional systems responsible for processing of verbal language and organizing movement (Elliott & Weeks, 1993b).