Metacontrast masking of target-area internal contours and target overall surface brightness: the case of mutually...

Metacontrast masking is by no means a unitary phenomenon, as is evidenced in recent studies showing differences between masking of surface- and contour properties of target stimuli (Breitmeyer et al., 2006; Ishikawa et al., 2006). Optima of masking appear earlier for contour processing and feature-specific operations compared to the variety of brightness processing that shows up in area filling-in phenomena. The present study explored whether this rule of processing - contours first and area filling-in afterwards - will be sustained if target and mask are, respectively, a central and a peripheral part of a coherent or incoherent meaningful visual object. Observers were presented with gray-level targets (images of the central part of a visual object) that were masked by a following, spatially surrounding mask, which was a complementary part of that object. Consistently with earlier findings, it appeared that salient visibility of contours which belonged to the internal spatial area of the target part of the object was established earlier and the whole-surface brightness quality (i.e. gray level) later in the course of target microgenesis. The unexpected facilitative effect of within-object coherence on target visibility which appeared at longer stimuli onset asynchrony (SOA) between target and mask parts of the object and only with large target and mask supports either some bias effects or lateral facilitatory interaction between iso-oriented parts of target-mask configuration having long time constants. The absence of the effects of coherence and inversion of target-plus-mask composite with small stimuli does not support the reentrant, top-down accounts of object processing in the context of metacontrast interactions.