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Hugo Bruggeman, William Warren; Optic flow recalibrates the direction of walking but not throwing. Journal of Vision 2008;8(6):833. doi: 10.1167/8.6.833.
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Understanding the visuo-motor calibration of spatially-oriented movements is central to an understanding of perception and action. We investigate whether adaptation of the mapping between visual target direction and walking direction transfers to the direction of underhand throws. In an adaptation phase, participants repeatedly walked to a target in a virtual environment while the heading direction specified by optic flow was displaced 10 deg to the right of the actual walking direction (Bruggeman, Zosh, & Warren, Current Biology, 2007). Within in a few trails, they adapted and walked straight toward the target. Rushton (2004) and others have argued that the exposure to displaced flow leads to adaptation of the visual straight ahead. In contrast, we hypothesized that optic flow acts to recalibrate the visuo-motor mappings from perceived target direction to initial and ongoing walking direction. On the former hypothesis, adaptation of the straight ahead should affect any spatial-oriented movement, including throwing to the target. On the latter hypothesis, adaptation should affect only walking whereas throwing should remain unchanged. We tested these hypotheses by evaluating walking and throwing direction before and after adaptation. Participants first threw a ball to a visually specified target (they could not see the ball's trajectory and landing position) and then walked with their eyes closed to the target, as if to retrieve the ball. Prior to adaptation participants throw and walk in the same direction. However, after adaptation they walked approximately 5 deg to the left of the target, missing it by about .8 m. But their throws remained on target. Surprisingly, participants were not able to retrieve their own throws! Thus, optic flow recalibrates the visual-locomotor mapping, not the direction of visual straight ahead.
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