Petter's effect in patterns formed by outlined surfaces

In patterns formed by two equally colored or by two transparent overlapping surfaces of different size that alternately appear in front of one another, the larger surface has a greater probability of appearing in front of the smaller surface. This effect is known as Petter's effect. The present study found that Petter's effect also occurred in patterns formed by colorless outlined surfaces. In these patterns Petter's effect was smaller than in chromatically homogeneous patterns. The results agree with the possibility that Petter's effect occurred in patterns formed by outlined surfaces because relative size was a cue to visually perceived distance.