Global stimulus configuration modulates crowding.

In crowding, neighboring elements impair the perception of a peripherally presented target. Crowding is often regarded to be a consequence of spatial pooling of information that leads to the perception of textural wholes. We studied the effects of stimulus configuration on crowding using Gabor stimuli. In accordance with previous studies, contrast and orientation discrimination of a Gabor target were impaired in the presence of flanking Gabors of equal length. The stimulus configuration was then changed (1) by making the flankers either shorter or longer than the target or (2) by constructing each flanker from two or three small Gabors. These simple configural changes greatly reduced or even abolished crowding, even though the orientation, spatial frequency, and phase of the stimuli were unchanged. The results challenge simple pooling explanations for crowding. We propose that crowding is weak whenever the target stands out from the stimulus array and strong when the target groups with the flanking elements to form a coherent texture.