Crowding is modulated by global stimulus configuration

In crowding, neighbouring elements impair the perception of a target. Crowding is often considered a consequence of spatial pooling of visual information. We investigated the role of configural effects in crowding by manipulating the global stimulus configuration while keeping constant the orientation, spatial frequency, and spatial phase of the elements making up the stimuli. We measured contrast and orientation discrimination thresholds for a peripheral Gabor target that was flanked on both sides by seven Gabor patches. When the target and the flanking Gabors were of equal length, discrimination performance was strongly impaired. However, when changing the stimulus configuration by (i) making the flanks either shorter or longer than the target or (ii) constructing each flank from two or three small Gabors, the impairment was largely reduced, even abolished. These results challenge simple pooling accounts of crowding. We suggest crowding is weak or absent whenever the target and flanks do not form a coherent texture, even when their 'low-level' properties are matched. A target that stands out avoids crowding.