Non-rigid illusory contours and global shape transformations defined by spatiotemporal boundary formation

Abstract

Spatiotemporal boundary formation (SBF) is the perception of form, global motion, and continuous boundaries from relations of discrete changes in local texture elements (Shipley and Kellman, 1994). In two experiments, small, circular elements underwent small displacements whenever an edge of an invisible (virtual) object passed over them. Unlike previous studies that examined only rigidly translating objects, we tested virtual objects whose properties changed continuously. Experiment 1 tested rigid objects that changed in orientation, scale, and velocity. Experiment 2 tested objects that transformed non-rigidly taking on a series of shapes. Robust SBF occurred for all of the rigid transformations tested, as well as for non-rigid virtual objects, producing the perception of continuously bounded, smoothly deforming shapes. These novel illusions involve perhaps the most extreme cases of visual perception of continuous boundaries and shape from minimal information. They show that SBF encompasses a wider range of illusory phenomena than previously understood, and they present substantial challenges for existing models of SBF.

From Flashes to Edges to Objects: Recovery of Local Edge Fragments Initiates Spatiotemporal Boundary Formation

“…These findings offer new insight about the perception of contours and objects from sparse texture element changes. Most previous SBF displays had exclusively used 2D virtual objects (e.g., Shipley and Kellman, 1993a , 1994 , 1997 ; Cicerone et al, 1995 ; Cunningham et al, 1998 ; Erlikhman et al, 2014 ; but see Chambeaud et al, 2014 ). The demonstration that SBF can occur for short edge fragments indicates that such fragments can be recovered without more global shape information and that such fragments are the likely basic units in SBF.…”

The neural representation of objects formed through the spatiotemporal integration of visual transients

“…As the object boundary passed the center of a Gabor element, that element changed position by moving in a random direction by 18 arc min or changed orientation to a new, random orientation. Both orientation and position changes of this magnitude have been previously shown to produce SBF (Shipley and Kellman 1993; Erlikhman, Xing, and Kellman 2014). At the beginning of a stimulus block, the virtual object was set to have a random diameter between 2° and 12° and expanded or contract at a rate of 1.5% of its size per frame up to a maximum diameter of 12° and a minimum diameter of 2°.…”

“…SBF is therefore a spatiotemporal process in that information about the object's shape arrives gradually over time and is incomplete, with many regions of the boundary missing and requiring interpolation. SBF is also a robust phenomenon – shapes can be seen even though their properties may change in between element transformations such as changes in orientation, velocity, size, and even curvature (i.e., non-rigid deformations; see Erlikhman, Xing, and Kellman 2014). An example of an SBF stimulus and the shapes used in the study can be seen in Figure 1 and Movie 1.…”