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John Philbeck, Adam J. Woods; Does perceived effort influence verbal reports of shape?. Journal of Vision 2007;7(9):422. doi: 10.1167/7.9.422.
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Witt et al. (2004) reported that perceived effort (manipulated by throwing a heavy vs. light ball) influences perceived egocentric distance. If distance perception errors result in a perceptually-slanted ground plane, changes in perceived distance should alter the perceptual slant of the ground surface, but not the perceived aspect ratio of shapes lying on the ground. However, if ball-throwing changes perceived distance only for the immediate location of the throwing target, one might expect effort-related changes in aspect ratio judgments.
Two groups of participants threw to a target (4, 6, or 8m distant) using a heavy ball (0.91kg, n=23) or a light ball (0.32kg, n=22). After the third throw, participants viewed an L-shape lying flat on the ground at the same distance as the target and gave a verbal estimate of its depth-to-width aspect ratio. Physical aspect ratios ranged from 0.75 to 2.25. The size of the frontal leg of the L-shape was 0.6m. In a separate study (n=24), we closely replicated Witt et al.'s methodology to confirm the effect of ball throwing on verbal reports of distance.
Aspect ratios were systematically underestimated, but the ball-condition comparison did not reach significance (F=2.5, p=0.11). Women gave smaller ratios than men (F=4.7, p=.03), perhaps due to sex-related eye-height differences. Importantly, there was no effect of ball throwing on verbal reports of egocentric distance (F=3.1, p=0.082), although there was a trend for the heavy-ball group to give somewhat SMALLER distance estimates.
Despite following their methodology closely, we could not replicate Witt et al.'s effect of ball throwing on verbal distance estimates. The robustness of this effect may rely crucially on methodological features that remain unknown. This leaves the possible effect of effort on perceived shape unclear, but emphasizes the need to more fully characterize the relation between effort and perceived egocentric distance.
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