this paper, we propose the short-cut rule, which states that, other things being equal, human vision prefers to use the shortest possible cuts to parse silhouettes. We motivate this rule, and the well-known Petters rule for modal completion, by the principle of transversality. We present five psychophysical experiments that test the short-cut rule, show that it successfully predicts part cuts which connect boundary points given by the minima rule, and show that it can also create new boundary points

this article we argue that "unit formation" and the localization of units in depth cannot be separated as these authors have suggested and that the identity hypothesis is therefore incorrect. In order to assess this claim, we must consider the possible meanings of the terms "units" and "unit FIG. 1. Two displays illustrating the difference between modal and amodal completion. Panel a is typically perceived as a continuous white square lying on top of four black disks against a white background. Because the square is the same color as the background surrounding the disks, there are locations where the square does not contribute any contrast to the image. The visual system interpolates the representation of the near surface across these gaps in the image data. This phenomenal continuation of the overlying layer is known as "modal completion." Panel b is typically perceived as a continuous black shape which is partly obscured by a gray ring. The sense of continuity of a more distant layer hidden behind a near, opaque surface is called "amodal completion." formation" that were offered by these authors, which we consider in detail below. Because Kellman and colleagues have claimed that "The identity hypothesis applies to the perceptual process of contour and surface interpolation " (Kellman, 2001, p. 94), we focus attention on the identity hypothesis as it applies to these properties (i.e., surfaces and contours). In what follows, we also argue that there is no psychologically meaningful concept of "unit" or "unit formation" for which Kellman and Shipley's claim is, or even could be, true. In support of this assertion, we present phenomenological demonstrations, psychophysical data, and theoretical principles that demonstrate that modal and amodal completion exhibit differe...

this paper, we address the question of what, in general, is the precise relationship between these two proposals

ns and the direction of motion of a partially occluded figure regulate the perceived shape and ap- et al., 1984) all contribute to the clarity of illusory contours in static images. These results have inspired neural parent movement of illusory contours formed from moving image sequences. These results demonstrate models which invoke contour completion mechanisms that generate contours parallel to their orientation, and/ the existence of neural mechanisms that reconstruct occlusion relationships from both real and inferred or mechanisms that generate contours approximately orthogonal to the inducing contour's orientation. Here, image velocities, in contrast to the static geometric mechanisms that have been the focus of studies to we report a class of illusory contours elicited by moving patterns which suggest that a distinct class of mecha- date. nisms are involved in synthesizing illusory contours from moving im

It is an exciting time to study visual object perception. Although object perception research has a long tradition, lately its visibility in cognitive science and neuroscience has greatly increased. One reason for heightened interest is that diverse areas of research now suggest a central role for objects in many aspects of human cognition, including the

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