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Michael K. McBeath, Igor N. Dolgov, Thomas G. Sugar; The axis of an american football leads observers to misjudge where it is headed. Journal of Vision 2005;5(8):731. doi: 10.1167/5.8.731.
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This study examines the influence of the axis of an American football on its perceived direction of motion. Experiment 1 was of a web survey examining beliefs of the behavior of an American football in flight. The results confirm that most people believe the ball travels with its axis essentially aligned with its trajectory both horizontally and vertically. Experiment 2 used an 8-Camera motion capture laboratory to determine the actual orientation of the axis of a thrown football relative to the direction of its trajectory. The results confirm that the axis consistently tilts horizontally toward the side of the throwing arm, while vertically maintaining a more constant orientation than the trajectory. Experiment 3 compared performance for observers estimating the final destination of thrown volleyballs versus footballs when viewed from the side. Observers were significantly more accurate with volleyballs [F(1,9) = 17.82, p = 0.002], and with footballs exhibited a significant bias to indicate balls were headed more in the direction that they were tilted [r2 = 0.53, p P&P , 1999), which demonstrates a perceptual bias to perceive a symmetric shape that moves off-axis as traveling more than actual in the direction in which its axis is aligned. The current work confirms the existence of this bias in a real-world, 3-D setting. The findings support that observers maintain an expectation consistent with the regularity that symmetric objects, like life-forms, typically move along paths aligned with their axes of symmetry and elongation.
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