Crowding is directed to the fovea and preserves only feature contrast

The abundant literature on crowding offers fairly simple explanations for the phenomenon, such as position uncertainty or feature pooling, but convincing evidence to support these explanations is lacking. In part, this is because the stimuli used for crowding studies are usually letters or other complex shapes, which makes it hard to determine exactly what kind of information is lost. In our experiment, we asked observers to identify simultaneously the slants (left or right) of three horizontally aligned Gabor targets. The targets were presented at 6 degrees in the periphery, and their size and separation were chosen to incur strong crowding. The loss of information about the position or orientation of individual members of the Gabor triads does not explain our results. Instead, crowding appears to be a particular form of collective information loss. Firstly, the outmost target was crowded much less than the other targets, which rules out explanations based on simple pooling and shows that crowding has a pronounced foveal directionality. Secondly, the specific pattern of confusion shown by all the observers indicates that the only reliable information available to them was orientation contrast, that is, the number (and, to a lesser degree, the location) of sites where slant changed. Thus, crowding appears to spare only the most salient peripheral information, which supports the hypothesis that crowding is caused by limitations of attentional resolution.