Preattentive surface and contour grouping in Kanizsa figures: evidence from parietal extinction.

Visual extinction commonly occurs after unilateral, parietal brain damage and manifests in a failure to identify contralesional stimuli when presented simultaneously with other, ipsilesional stimuli - but full awareness for single stimulus presentations. However, extinction can be substantially reduced when preattentive grouping operations link fragmentary items across hemifields into a coherent object. For instance, one study demonstrated preserved access to bilateral stimulus segments when these could be grouped to form a Kanizsa square [Mattingley, J. B., Davis, G., & Driver, J. (1997). Preattentive filling-in of visual surfaces in parietal extinction. Science, 275, 671-674]. Here, we investigated the relative contributions of distinct object attributes to the spared access in Kanizsa figure completion in extinction, by systematically varying the degree to which bilateral surface filling-in and contour interpolations group disparate items. We demonstrate that surface information can substantially reduce extinction, whereas contour completions showed comparably smaller influences. In summary, such graded influences of object attributes support recurrent models of grouping, first, linking fragmentary parts into coherent surfaces and, second, interpolating the precise boundaries.