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Steve Hansen, Digby Elliott and Michael A. Khan

The utility of ellipsoids for quantifying central tendency and variability throughout the trajectory of goal-directed movements is described. Aiming movements were measured over 2 days of practice and under full-vision and no-vision conditions. A three-dimensional optoelectronic system measured the movements. Individual ellipsoid locations, dimensions, and volumes were derived from the average location and the spatial variability of the effector’s trajectory at proportional temporal periods throughout the movement. Changes in ellipsoid volume over time illustrate the evolution in motor control that occurred with practice and the processes associated with visual control. This technique has the potential to extend our understanding of limb control and can be applied to practical problems such as equipment design and evaluation of movement rehabilitation.

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Niamh Reilly, Gavin P. Lawrence, Thomas Mottram and Michael Khan

The perceptual-motor impairments of individuals with Down syndrome (DS) are attributed to central (e.g., neurophysiology deficits that affect the retrieval or initiation of motor programs) and peripheral (e.g., anatomical deficits relating to issues with inertia of limb mechanics and muscle organization) processes. However, recent research suggests that central deficits do not affect the integration between movements. We investigate the impact of central and peripheral DS deficits on movement integration by examining the planning and execution of multiple-target multiple-arm movements. Individuals with DS, typically developing (TD), and individuals with an undifferentiated intellectual disability (UID) completed five aiming tasks: a one target; a one-arm, two-target extension; a two-arm, two-target extension (movement one was performed with one arm and movement two performed with the other); a one-arm, two-target reversal; and a two-arm, two-target reversal. Movement times (MTs) to the first target were longer in the two-target tasks compared with the one-target task. For the one-arm, two-target reversal task, this effect emerged only in individuals with DS. These results indicate that individuals with DS use central processing for movement integration similarly to their TD and UID counterparts but cannot exploit peripheral-level integration to enhance integration in one-arm reversal tasks.

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Michael A. Khan, Trevor Hale, Michael I. Carry and Ian M. Franks

The purpose of this research was to examine the role of distance and location information in the production of rapid aiming movements. Participants performed an aiming task consisting of horizontal left-handed elbow flexion movements that translated to movements of a cursor on an oscilloscope screen. The location of the home position and the target on the oscilloscope screen were fixed but me initial angle of the elbow was varied randomly. Participants were informed mat the required distance was always constant. Initial impulse and error correction phases were analyzed to examine whether separate spatial codes for distance and position were used in the control of these two movement phases. The results indicated mat initial impulse endpoints and the final positions of the limb overshot the target from the leftmost starting positions, while they undershot me target from me rightmost starting positions. Also, varying the initial angle of the elbow had a greater influence on me final position of the limb than initial impulse endpoints.

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Gavin P. Lawrence, Michael A. Khan, Stuart Mourton and Pierre-Michel Bernier

The objective of the current study was to determine whether the reliance on visual feedback that develops with practice is to due utilizing vision to adjust trajectories during movement execution (i.e., online) and/or to enhance the programming of subsequent trials (i.e., offline). Participants performed a directional aiming task with either vision during the movement, dynamic feedback of the trajectory of the movement or the movement endpoint. The full vision condition was more accurate during practice than the other feedback conditions but suffered a greater decrement in performance when feedback was removed. In addition, the reliance on trajectory feedback was greater compared with the endpoint feedback. It appears that the reliance on visual feedback that develops with practice was due to both online and offline processing.

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Michael A. Khan, Gavin P. Lawrence, Ian M. Franks and Digby Elliott

The purpose of the present study was to establish the contribution of visual feedback in the correction of errors during movement execution (i.e., online) and the utilization of visual feedback from a completed movement in the programming of upcoming trials (i.e., offline). Participants performed 2 dimensional sweeping movements on a digitizing tablet through 1 of 3 targets, which were represented on a video monitor. The movements were performed with and without visual feedback under 4 criterion movement times (150, 250, 350, 450 msec). We analyzed the variability in directional error at 25%, 50%, 75%, and 100% of the distance between the home position and the target. There were significant differences in variability between visual conditions at each movement time. However, in the 150-msec condition, the form of the variability profiles did not differ between visual conditions, suggesting that the contribution of visual feedback was due to offline processes. In the 250-, 350-, and 450-msec conditions, there was evidence for both online and offline control, as the form of the variability profiles differed between the vision and no vision conditions.