Abstract
To investigate the processes for discriminating surface depth and boundary form of objects in three-dimensional space, event-related brain potentials (ERPs) were recorded from 12 students who were performing a detection task to one of orthogonal combinations of depth (crossed/uncrossed disparity) and form (vertical/horizontal square) generated by dynamic random-dot stereograms (RDSs) in random sequence. Stimuli were classified by the task relevance: relevant depth and form (D+F+, i.e., target), relevant depth (D+F−), relevant form (D−F+) and irrelevant depth and form (D-F-). Stimuli having the relevant values of depth or form elicited more negative potentials than the irrelevant stimuli, which are named selection negativities (SNs) that are associated with selection of nonspatial visual features (Harter & Aine, 1984). Depth and form SNs started at around 200 ms post-stimulus over the lateral occipital sites, and the initial phase was elicited irrespective to the relevance of the other feature, suggesting independent selection of stereoscopic depth and form. The subsequent phase increased when the other feature was relevant for stimuli with crossed disparity, in which the convex surface had the boundary in the same depth plane, but not for stimuli with uncrossed disparity, in which the surface and boundary were located in different depth planes. These findings address electrophysiological evidence on initially independent and following integrative processes of stereoscopic boundary and surface into the perception of a single object in three-dimensional visual world.