Spatio-temporal boundary formation: the role of local motion signals in boundary perception.

Spatio-temporal boundary formation (SBF) refers to a perceptual process responsible for perception of moving, bounded surfaces from sequential changes in spatially separated local elements. Previous research has indicated that this process produces perception of global form, continuous boundaries and global motion from spatially and temporally sparse element changes. In the present paper, we sought to distinguish between two classes of models for SBF: form-precedes-motion and motion-precedes-form models. Experiment 1 tested the effects of the addition of spurious motion signals, a manipulation that should affect a motion-precedes-form computation but not a form-precedes-motion computation. Shape identification in a 10-alternative forced-choice procedure was disrupted by this manipulation, supporting the former class of models. A particular computational scheme, edge orientation from motion (EOFM) instantiating a motion-precedes-form model is described and tested in Experiment 2. The EOFM model should be disrupted when initiating element changes occur in a certain type of sequential order, relative to randomly arranged changes. Sequential changes markedly disrupted performance, supporting this EOFM approach. The results favor motion-precedes-form models of SBF and are consistent with the particular computational scheme proposed.