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Digby Elliott, Kathryn L. Ricker, and James Lyons

Fifteen participants practiced a two-target sequential aiming movement with either full vision of the movement environment, vision during flight, or vision while in contact with the first target. After 100 acquisition trials, participants performed a retention test in their own condition and then were transferred to each of the other two vision conditions. Both performance and kinematic data indicated that rather than becoming less dependent on visual information with practice, subjects learned to adjust their movement trajectories to use the visual information available in their particular vision condition. Although transfer to a degraded vision condition disrupted performance, when vision was augmented participants quickly adjusted their aiming trajectories to use the added information. The findings suggest that at least part of learning involves the development of rapid and efficient procedures for processing afferent information, including visual response-produced feedback.

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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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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 Glazebrook, Digby Elliott, James Lyons, and Luc Tremblay

This study investigated inhibition of return in persons with and without Down syndrome (DS) when visual or verbal cues were used to specify a target in a crossmodal paradigm. Individuals with DS and without DS performed manual aiming movements to a target located in right or left hemispace. The target was specified by an endogenous visual or verbal stimulus. Both groups were significantly slower when responding to the same target as the previous trial when the target was cued in a different modality. Although participants with DS initiated and executed their movements more slowly, they demonstrated a similar pattern of inhibition as people without DS, suggesting that inhibitory processes are functioning normally in persons with DS.

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Steve Hansen, James L. Lyons, and Katherine M. Keetch

This study examined the performance of the upper limbs during responses to previously cued and un-cued locations. Participants made unimanual and bimanual responses under homologous and non-homologous muscular control, within a cuetarget (Experiment 1; n = 10), and a target-target (Experiment 2; n = 10) aiming protocol. The inhibition of return (IOR) to a target location was expected to increase with (a) an increase in the organization of the movement response required, and (b) the decrease in the muscular coupling under which the bimanual movement was performed. IOR was observed in both experiments when participants completed their movements in either the unimanual or homologous conditions, but not in the non-homologous condition. In addition, reaction times were significantly shorter when a movement preceded the response than when no manual response was made to the initial visual cue. The results indicate that common processing delays in response to exogenously cued targets are dependent on the muscular control of those responses. Thus, this study provides evidence that IOR is moderated by the muscular control under which the bimanual movement was performed indicating an influential involvement of the motor system in both the movement planning and movement response to multiple target stimuli.

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James W. Roberts, James Lyons, Daniel B. L. Garcia, Raquel Burgess, and Digby Elliott

The multiple process model contends that there are two forms of online control for manual aiming: impulse regulation and limb-target control. This study examined the impact of visual information processing for limb-target control. We amalgamated the Gunslinger protocol (i.e., faster movements following a reaction to an external trigger compared with the spontaneous initiation of movement) and Müller-Lyer target configurations into the same aiming protocol. The results showed the Gunslinger effect was isolated at the early portions of the movement (peak acceleration and peak velocity). Reacted aims reached a longer displacement at peak deceleration, but no differences for movement termination. The target configurations manifested terminal biases consistent with the illusion. We suggest the visual information processing demands imposed by reacted aims can be adapted by integrating early feedforward information for limb-target control.

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Steve Hansen, Bridget Sheahan, Melinda Wu, James Lyons, Timothy N. Welsh, and Digby Elliott

Adults with Down syndrome (DS), an undifferentiated developmental delay (UnD) and no developmental delay practiced a manual target aiming task either with or without on-line visual feedback. Following acquisition, participants performed a retention test involving the same sensory condition available during practice, followed by a transfer test under the other sensory condition. Although the participants with UnD were highly dependent on visual feedback for movement accuracy, participants with DS relied more on either kinesthetic feedback or feedforward control for spatial precision. Participants in all three groups improved their movement times with practice. This improvement was associated both with an increase in peak velocity and a reduction in the time required to decelerate their aiming movements. Contrary to our expectations, improvements in performance were not specific to the sensory conditions available during practice.

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Nicola J. Hodges, Sheri J. Cunningham, James Lyons, Tracey L. Kerr, and Digby Elliott

Frith and Frith (1974) suggested that adults with Down syndrome have difficulty planning goal-directed movements and therefore are more reliant on feedback than other mentally disabled people. The purpose of the study was to examine this hypothesis directly through the manipulation of visual feedback. Twelve adults with Down syndrome, 12 mentally disabled adults without Down syndrome, and 12 nondisabled adults performed simple aiming movements to targets of three different diameters. While the target was always visible, on half the trial blocks vision of the movement was occluded upon response initiation. Subjects with Down syndrome exhibited longer movement times than other subjects, regardless of vision condition. In terms of target-aiming consistency, subjects with Down syndrome were actually less affected by the elimination of visual feedback than subjects in the other mentally disabled group. While adults with mental disabilities appear to be more reliant on visual feedback for the control of goal-directed movement, this dependence is not a specific characteristic of Down syndrome.

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Digby Elliott, Timothy N. Welsh, James Lyons, Steve Hansen, and Melinda Wu

Williams syndrome (WS) is a genetic disorder that causes general cognitive and developmental delays. Compared to persons with Down syndrome (DS) at the same developmental level, individuals with WS generally exhibit superior expressive language abilities, but have difficultly with tasks that require the visual control of movement. Recently it has been suggested that this latter problem reflects a deficit in dorsal stream function. In the present study, this hypothesis was investigated by examining the kinematics of rapid aiming movements. The performance of the participants with WS (n = 4) was compared to the performance of participants with DS (n = 8), with undifferentiated developmental delays (n = 8), and from the general population (n = 8). In partial support of the dorsal deficit hypothesis, the results suggest that, compared to people from the other groups, the participants with WS had difficulty in preparing their movements on the basis of the visual and other information available to them. This was particularly evident in their inability to properly scale movement velocities to the amplitude of the movements and in the number of discrete corrections made during movement execution.