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Cary S Feria, Myron L Braunstein, George J Andersen; Judging distance across discontinuities in the frontal plane. Journal of Vision 2003;3(9):645. doi: 10.1167/3.9.645.
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Recent research on the “discontinuity effect” has shown that perceived distance along a textured surface is reduced when the surface contains a texture discontinuity (e.g., Feria & Braunstein, VSS, 2002; Sinai, Ooi, & He, Nature, 1998). The present study examined the effects of the number and types of boundaries between textured regions and of more local factors in determining judged distance across discontinuities. The displays consisted of a frontal plane containing one or more vertical lines and three dots arranged in an inverted L. Observers judged the distance between the two vertically separated dots by adjusting the separation of the two horizontally separated dots. In Exp. 1, the line texture was continuous or divided into two, three or four regions by shifting portions of the texture horizontally. Judged distance was reduced when one discontinuity was present and was reduced further with two or three discontinuities. In Exp. 2, the vertical lines were continuous or were offset horizontally along a curved boundary. In a third condition, the line segments produced in the second condition were rearranged randomly in the horizontal dimension to eliminate the implicit boundary contour. More distance was judged in the continuous condition than in the curved boundary condition, with the random condition intermediate. In Exp. 3, either a single continuous vertical line, a discontinuous vertical line (broken into segments that were offset horizontally), or no line was presented with the three dots. More distance was judged when a single continuous line was placed next to the vertically separated dots than when the line was discontinuous or absent. These results suggest that the discontinuity effect results from both a reduction in perceived distance when the extent being judged is interrupted by implicit contours at texture boundaries and from an increase in judged distance when even a single continuous contour is located parallel to the extent being judged.
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