To coordinate ballistic actions with visual targets forces need to be calibrated against distances. In 2 studies adults threw a baseball with an underhand toss to land on a visible target that was 12m away. Subjects were equipped with a sound system so they could not hear where the ball landed. They wore liquid crystal goggles and were fitted with a hand-pressure switch, so the transparent goggles went opaque when the ball left the hand. There was no information about whether throws were long or short, so throw distances indicate the target-to-force calibrations brought to the task, not ones fine-tuned to ball or target. However, people could monitor differences in intended forces in the efferent copy and the feedback forces for each throw, and improve the consistency of their throw-forces from trial to trial. In Experiment 1 people tossed the ball 100 times -- everybody threw short, averaging 9.5m throws to the 12m target, with some averaging 3-4m throws! The throw distances did not change across the trials. People were unaware of their errors a?? they were shocked in follow-up interviews. Believing their throws were accurate, they worked to become more consistent, monitored their proprio-kinesthetic force feedback from trial to trial, and threw with significantly more consistency during the second block of trials compared with the first. Study 2 was similar to Study 1, except half the subjects could see where the balls landed. Anova showed both groups threw too short during the early trials; those without vision continued to throw short, but those with vision threw further and further with practice. Continuing work is focused on kinematic analysis of the release-angles and release-forces of the throws, and on vision-substitution applications to the throws of athletes who are blind.
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