Object-centered attentional biases and object recognition contributions to scene segmentation in left- and right-hemisphere-damaged patients

Participants viewed elongated rectangular displays in which two regions shared a central contour. In experimental stimuli, the central contour portrayed a known object on one, high-denotative, side. In control stimuli, no known objects were portrayed on either side of the central contour, but one side of each control stimulus was a scrambled version of one of the high- denotative regions, matching it on all factors known to influence scene segmentation other than object recognition. For each display, participants decided whether the left or the right region was more likely to be an object. Paradoxically, both right-hemisphere- (RH) and left-hemisphere- (LH) damaged individuals were more likely to see objects lying on the contralesional rather than the ipsilesional side of the central contour. This tendency is attributed to an object-centered attentional bias toward the central contour when objects lie on its contralesional side and away from the central contour when objects lie on its ipsilesional side. Object-centered attentional biases were stronger following RH than LH damage. Elderly control participants showed a slight bias in the same direction as RH-damaged individuals. More high-denotative regions than scrambled regions were seen as objects, even when object-centered attention was biased away from the central contour carrying the object recognition information. The latter result suggests that the object recognition processes contributing to scene segmentation are preattentive.