Academic journal article Research Quarterly for Exercise and Sport

Guiding Movements with Internal Representations: A Reach-and-Grasp Task

Academic journal article Research Quarterly for Exercise and Sport

Guiding Movements with Internal Representations: A Reach-and-Grasp Task

Article excerpt

We investigated participants' ability to use internal representations of the environment to guide prehensile movements, when visual feedback was not available. Reaching and grasping performed with concurrent visual feedback was compared to conditions in which participants actively formed spatial images and passively encoded images from visually presented information. Movement times, the proportion of time spent after peak velocity and peak apertures, were greater when concurrent visual feedback was unavailable. Movement times increased as a function of premovement occlusion length, with passively encoded images resulting in shorter movement durations than actively formed images. The findings indicated that participants adapted their movement trajectories to compensate for the degradation of stored spatial information, when concurrent visual feedback was not available.

Key words: grasping, memory trace, motor processes, spatial imagery

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Everyday experience demonstrates that we can interact with our immediate environment without concurrent visual feedback. For example, a person can pick up a coffee mug without looking at his or her hand or navigate a familiar room in the dark. While these movements are less precise than when performed with vision of the environment, the ability to perform them suggests that we can use an internal representation of the external environment by using visuospatial imagery (Chua & Weeks, 1994; Elliott & Maraj, 1994).

Logie (1995) made a distinction between spatial images that are developed through effortful construction of environmental information and those that are developed from information readily available from the visual array. The former case involves the active manipulation of the spatial properties of objects (e.g., mental rotation) to form an internal representation of the environment. in the latter case, spatial information is presented visually and then retained in memory for later use. Of interest in the present research was whether the active manipulation of spatial information would lead to a more stable representation of the environment compared to when spatial information was passively encoded from a visual scene. One may argue that a representation constructed from the effortful generation of spatial information would be more resistant to decay than one readily encoded from visually presented information. On the other hand, it might be that a more vivid representation could be formed when environmental i nformation was presented visually, compared to when it was constructed from the manipulation of internally represented spatial features.

In the present experiments, participants were required to reach for and grasp a wooden dowel lying at varying orientations on a table. Participants performed the movement with and without concurrent visual feedback. Wing, Turton and Fraser (1986) found that maximum grip aperture was greater and occurred earlier in the trajectory when movements were performed without visual feedback compared to when vision was available. Similarly, Marteniuk, Ivens, Brown, and Kalbfleisch (1996) showed that reaching and grasping with vision had shorter movement times than without vision and that movement times increased as a function of the no vision premovement delay. The increases in movement time were due primarily to an increase in time spent during deceleration. Therefore, it seems that when visual feedback is not available, participants compensate for the degradation of stored spatial information and the lack of precise visual monitoring during the homing-in phase by forming larger grip apertures and spending more time d uring movement deceleration.

Of particular interest here was participants' ability to use actively and passively encoded spatial information, when concurrent visual feedback was not available. Participants were required to encode spatial information actively in a condition where they viewed the dowel at a start orientation and were instructed to rotate the dowel mentally from the start orientation to a target orientation. …

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