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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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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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Seung-oh Choi, Harry J. Meeuwsen, Ron French, and Jill Stenwall

Behavioral, response outcome, and response kinematic measures were analyzed for 6 adults (5 males and 1 female) with profound mental retardation (PMR). Participants performed 30 error-free simple linear aiming movements on a digitizing tablet during 7 acquisition, 3 retention, and 4 transfer days. A one-way ANOVA on the number of trials to reach 30 error-free responses revealed that adults with PMR improved, learned the skill, and transferred it to a new situation. The 2 × 3 × 3 (Phase × Day × Block) repeated measures ANOVAs for response outcome and kinematic measures indicated that participants were able to initiate movement faster with practice. However, practice did not result in changes in kinematic response measures.

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Wan-Xiang Yao and Mark G. Fischman

This study investigated, in aiming movements, the conditions needed to produce a single movement and those needed to produce secondary submovements. Using a 2 × 2 (Temporal Constraint × Spatial Constraint) factorial design with repeated measures on both factors, subjects moved a stylus from a starting position to a target position 12 cm away. They participated in two testing sessions on consecutive days. The first session involved two nonrestrictive target (a set of crosshairs) conditions, moving to the target either within a goal of 400 ms (temporal-accuracy procedure) or within a minimum time (time-minimization procedure). In the second session the subjects performed two strict-target (circle) conditions, moving to the target either within a goal of 400 ms or within a minimum time. The results showed that the two strict-target conditions had a greater percentage of trials containing multiple-submovements than the two nonrestrictive target conditions, regardless of temporal requirements. Therefore, whether an aiming movement contains a single movement or multiple submovements may be a function of spatial constraints regardless of temporal constraints. It appears that with respect to the nature of the speed-accuracy tradeoff, spatial constraints are an important factor.

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Esa M. Rantanen and David A. Rosenbaum

There is anecdotal evidence of drift in various reciprocal motor tasks, but as far as is known, no investigations into this phenomenon have been reported. Yet, systematic drift can potentially explain a significant proportion of the total variability in motor output. Three experiments were conducted to ascertain the nature of drift in reciprocal aiming tasks and to develop methods and measures to isolate and quantify drift for analyses. We also evaluated a computational posture-based model of reaching movements with respect to the findings of the experiments. Drift was observed in all three experiments, generally toward the middle of the joint motility range. Simulations based on the model produced drift to the middle of the task movement range rather than middle of the joint movement range. Adding noise to the model could increase its power for simulating the underlying principles of movement control as reflected in performance features such as drift.

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Robert R.A. van Doorn

The execution of a fast aimed movement takes less time when it is performed in isolation than when it is followed by a movement to a second target. The most recent explanation of this so-called one-target advantage (OTA) is the movement integration hypothesis. The first movement is slowed down to enable a neuromuscular integration of the first and second movements so that a presumably smooth transition between the two movements can take place. The present study shows that the time increase underlying the OTA does not happen just before the transition takes place, but is located in the initial part of the first movement element of the two-tap sequence. It is discussed how such a temporal occurrence relates to the transition of the first movement to the second.

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Robert R.A. van Doorn and Pieter J.A. Unema

A display gain setting defines the mapping of a movement to the real-time visual display. In two experiments we investigated how the acquired adaptation to low and high display gain affected motor control of single aimed stylus movements. Experiments differed with respect to how gain was varied. In Experiment 1, gain was realized by manipulating the surface displacements with a constant display. The results show an expected linear decrease of movement time and spatial accuracy, which is in sharp contrast with the often-reported U-shaped relation. Experiment 2 was run to study the influence of visual feedback in low- and high-gain conditions. The manipulation of gain was realized by display variation with unaltered surface displacements. The linear increase of movement time and feedback processing with gain and the unaltered spatial accuracy across conditions, suggested that participants actively adapted to the displayed visual information in altered gain conditions.

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Robert R.A. van Doorn and Pieter J.A. Unema

The present study showed that movement execution depends on the direct visual environment. We replicated findings of an earlier study that showed a difference between real time information via a trace of the unfolding trajectory, and cursor feedback constituting real time information about the changing movement location. Detailed analyses involving subdividing a movement into four successive sections revealed that movements governed by trace feedback were typically slower and required more feedback guidance near the occurrence of peak velocity. The present study further showed that movement behavior under the two visual modes diverged even more due to the presence of a static object positioned within the action area of the movement. Movements in the trace feedback condition were affected by the presence of an object in the second half of the movement trajectory when the movement reached peak deceleration. Discussion focuses on the differences between the two modes of online visual information.

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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.

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Yeou-Teh Liu, Tsung-Yu Hsieh, and Karl M. Newell

Recent studies have shown more than one time scale of change in the movement dynamics of practice. Here, we decompose the drift and diffusion dynamics in adaptation to performing discrete aiming movements with different space-time constraints. Participants performed aiming movements on a graphics drawing board to a point target at 5 different space-time weightings on the task outcome. The drift was stronger the shorter the time constraint whereas noise was U-shaped across the space-time conditions. The drift and diffusion of adaptation in discrete aiming movements varied as a function of the space-time constraints on performance outcome and the spatial, temporal, or space-time measure of performance outcome. The findings support the postulation that the time scale of movement adaptation is task dependent.