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Susan M. Menees, Jessica Lowenfeld, Lothar Spillmann; Dark phantom motion. Journal of Vision 2004;4(8):860. doi: 10.1167/4.8.860.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We investigated factors related to the perception of a moving dark phantom bar to test the spatial limits of illusory perception. The phantom bar was defined as a region darker than the background and moving like a solid bar from left to right. Method: Four observers with normal or corrected-to-normal vision participated. The dark phantom was produced by switching on and off, sequentially from left to right, vertical rows of lights in an array of lights on a monitor. The vertical spread of the lights (0.74 to 3,67 degrees of visual angle) and the vertical height of a dark occluding region (1.47 to 13 degrees of visual angle) were varied. The rate at which the rows were turned on and off was held constant. Observers rated the strength of “connectedness” of the phantom bar across the occluder and “blackness” of the phantom compared to the background. Results: The perception of a phantom bar declined significantly with increasing occluder height. Connectedness ratings, however, followed an inverted U pattern with vertical spread: dots separated by 0.74, 2.94, and 3.67 degrees of visual angle had lower connectedness ratings than the 1.47 and 2.21 degrees of visual angle conditions. This pattern was more pronounced for larger occluder heights. Blackness ratings varied with occluder height and vertical spread in the same manner as the connectedness ratings. They also correlated positively with connectedness ratings. Conclusion: Occluder height and vertical spread of the lights affected the strength of perception of a moving dark phantom bar. Perception of the phantom bar is diminished over greater spatial extents of the occluder. Phantom perception was poorest, however, for the widest and narrowest vertical spread conditions. In this case, the varying vertical spread of the light array may affect phantom perception by varying figure-ground perception (Brown & Weisstein, 1988) or by producing changes in luminance of the occluder(Sakurai & Gyoba, 1985).
DAAD grant to 1st author; DFG SP 67/8-1
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