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Joo-Hyun Song, Ken Nakayama; Automatic adjustment of visuo-motor readiness. Journal of Vision 2006;6(6):398. doi: 10.1167/6.6.398.
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Subjects more rapidly initiated reaching to a single lone target than to an odd-colored target among distractors, reflecting differentiated states of sensori-motor readiness for easy vs. hard tasks. This occurred only when trials were presented in separate blocks. The pattern was eliminated when the two trial types were randomly mixed, showing homogenization; increased latencies for single trials, and decreased latencies for odd-colored trials. The faster movement initiation in the odd-colored target task was accompanied by curved trajectories, directed initially toward a distractor but corrected in mid-flight. Two possible hypotheses could account for this differentiated adjustment in visuo-motor readiness when the different trials are presented in separate blocks: (1) explicit knowledge of upcoming trial types (2) history of the very recent past, i.e. repetition of same type of trials. To distinguish between these two accounts, we included a third condition where the trial types were predictably alternated. Contrary to the explicit knowledge hypothesis, this also led to homogenization of initiation latencies and curved trajectories. From this and additional experiments manipulating the length of same type repetitions, we conclude that explicit knowledge of upcoming trials plays no observable role in determining visuo-motor readiness. This is determined only by the very recent history of trial repetitions.
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