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Uta Wolfe, Elizabeth Amis; Is active drawing of line configurations resistant to visual illusions?. Journal of Vision 2006;6(6):355. doi: 10.1167/6.6.355.
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We investigated whether both blind and visually guided production of line drawings is subject to the same distortion observed in the visual perception of such drawings. To this end we compared illusion extents associated with the perception, drawing and blind drawing of the inverted T configuration of the horizontal-vertical illusion.
In the perceptual task, subjects (n=4) viewed the configuration on a computer screen and using the arrow keys adjusted the length of the vertical line to look equal to that of the horizontal. In the production task, subjects were asked to draw on paper both with and without vision an inverted T figure with equally long horizontal and vertical lines.
Illusion extent (IE) was calculated as the percentage by which the vertical line was shorter than the horizontal at the PSE. Average IEs by subject ranged from 6–18% (perception), 16–27% (visually guided drawing) and 13–32% (blind drawing). IEs tended to be larger in the drawing conditions than in the perceptual condition. All four subjects had a significantly increased IE in at least one of the drawing conditions compared to the perception condition and only one instance of decreased IE for a drawing condition was observed. Two subjects showed a significantly larger IE for blind than for visually guided drawing, whereas one subject showed the opposite trend.
These results suggest that active drawing of simple line configurations whether blind or visually guided is distorted in the same direction as and to a greater degree than the visual perception of such configurations.
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