| Abstract No.: | B-G2191 |
| Country: | Canada |
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| Title: | THE EFFECT OF VISUAL FEEDBACK ON OBSTACLE AVOIDANCE DURING REACH-TO-POINT MOVEMENTS |
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| Authors/Affiliations: | 1 Craig Chapman*; 1 Melvyn Goodale;
1 University of Western Ontario, London, ON, Canada.
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| Content: | Objectives: Human reaching behaviour displays sophisticated obstacle avoidance. Previous patient work has identified dorsal stream visuomotor processing as being integral to this ability (Schindler et al., 2004, Nature Neuroscience, 7(7):779-784, Rice et al., 2006, Experimental Brain Research, 174(1):176-188). Recently, we demonstrated that the obstacle avoidance system in normal participants is sensitive to both the position and size of obstacles (Chapman & Goodale, CAN 2007). A limitation in these previous studies was that reaches were performed without visual feedback, and were made to no specific target (i.e. target was a strip instead of a point). Many studies have shown that both the introduction of visual feedback and the order in which the feedback is received significantly alter performance in simple visuomotor tasks (e.g. Jakobson & Goodale, 1991, Experimental Brain Research, 86(1):199-208). Thus, the current study sought to directly compare participant’s obstacle avoidance behaviour when vision was available (VF) during a reach movement made to a specific point, versus when no vision was available (NVF). In addition we varied the order in which VF and NVF trials were presented to examine the impact of trial history on reach movements.
Materials and Methods: 24 right-handed participants performed right-hand reaches to a target (40cm away) in the presence of one, two or no obstacles placed mid-reach (25cm). Combined with positional changes there were 8 different obstacle configurations. The experiment was divided into three visual-feedback-order conditions: blocked (all VF trials occurred together, separate from NVF trials), alternating, and random. The order participants received the blocked, alternating, or random trials was counterbalanced. Hand trajectories were recorded with an OPTOTRAK infrared camera, which tracked the position of 3 infrared markers attached to the participant’s right hand.
Results: In addition to replicating the previous work of obstacle avoidance with no visual feedback, we show that robust avoidance behaviour persists for reaches made with visual feedback and to a specific target. The order that visual feedback was received had a significant impact on avoidance behaviour. Across several kinematic measures, VF trials show significant differences compared to NVF trials but only during the blocked condition.
Conclusions: In addition to extending our knowledge of the obstacle avoidance system, these results support previous findings (Song & Nakayama, 2007, Journal of Vision, 7(5):2,1-9) that argue the motor system is automatically adjusted by recent trial history and is not affected by the explicit knowledge about the nature of an upcoming trial that is available with alternating trials.
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