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Craig S. Chapman, Ravi Doobay, Melvyn A. Goodale; Looking forward to a correction: Obstacle avoidance during online correction. Journal of Vision 2009;9(8):1166. doi: 10.1167/9.8.1166.
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The dorsal stream codes information crucial to the planning and online control of reaches to targets in dynamic and cluttered environments. Two specific dorsally-mediated abilities are online correction for changes in target location and the avoidance of obstacles. In online correction, abrupt changes in target location occurring during a reach result in automatic corrections toward the new target location (Pisella et al., Nature Neuroscience, 2000). In obstacle avoidance, objects that interfere with a reach are automatically avoided by maximizing the distance away from them (Schindler et al., Nature Neuroscience, 2004). The current study was designed to test whether both of these abilities can be performed concurrently. Participants made reaches to a target that, on two-thirds of the trials, remained stationary and on the other third ‘jumped’ (at movement onset) to a new location (10cm further in depth and 10cm to the left or right). When present, single objects (i.e. potential obstacles) were placed in one of four positions at a depth beyond the initial target, thus causing no initial interference. Importantly, on trials when the target jumped, the objects sometimes became obstacles that could interfere with the reach. Our results confirm previous findings; first, on the no-jump trials, obstacles positioned beyond a target have no interfering effect (Chapman & Goodale, Experimental Brain Research, 2008); second, on the no-obstacle jump trials, participants made automatic online corrections. Critically, when the target jumped in such a way that an object suddenly became an obstacle, we observed clear - and rapid - avoidance behaviour, an effect that was not present when the target jumped but the objects did not become obstacles. In other words, participants showed exquisite sensitivity to obstacles in their online corrections. These findings suggest that potential as well as current obstacles are automatically coded during movement planning, presumably by the dorsal stream.
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