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Sukhvinder S. Obhi, Melvyn A. Goodale; Evidence for differential weighting of egocentric and allocentric cues in delayed and real-time actions. Journal of Vision 2005;5(8):128. doi: 10.1167/5.8.128.
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Converging lines of evidence suggest that the presence of non-target landmarks affects the performance of delayed target-directed movements (Diedrichsen et al., 2004; Sheth and Shimojo, 2004). In the present experiment, we examined the effects of non-target landmarks on the accuracy and precision of delayed and immediate target-directed pointing movements. In our experiment, the landmarks were present just prior to and during the presentation of the target; they were never present during the execution of the movement. Constant and variable errors were significantly lower for delayed pointing when landmarks were present during encoding as compared to when they were absent. With absolute errors, a landmark-advantage was evident even for immediate actions. The locus of this “landmarks benefit” appears to be in the target-encoding phase because we never re-presented the landmarks after target presentation. We suggest that, when available, allocentric cues are combined with egocentric information, and thus serve to improve the accuracy of the representation of target location. In addition, we suggest that the relative weighting given to egocentric and allocentric representations is a function of the time-course of the movement task, with allocentric representations becoming more useful and egocentric representations less useful as the movement is delayed.
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