Abstract
This study examined the effects of target contrast and transient attention - the stimulus-driven component of spatial attention- on crowding at various eccentricities. Previous studies have found that precueing attention can improve identification accuracy and reduce the elevation of contrast and orientation threshold in crowding, but were inconclusive regarding the ability of attention to reduce the spatial extent of crowding (i.e., the critical distance). Reducing target-flankers similarity has also been shown to improve performance and reduce the extent of flankers' interference, but target contrast behaves differently -only when the target has a higher contrast than the flankers crowding is reduced.
To test how accuracy and the critical distance are affected by precueing, manipulation of contrast, and manipulation of eccentricity we performed 4 experiments in which the observers had to indicate the orientation of a target presented with 2 flankers. In two experiments we tested the effects of precueing transient attention. On the cued trials, a small dot appeared adjacent to the target location prior to its onset, and on the neutral trials a small circle appeared in the center. In the other two experiments we examined the effects of target contrast. We employed three contrast conditions: a) both target and flankers had high contrast; b) both target and flankers had low contrast; and c) the target had a higher contrast than the flankers. Additionally, in all four experiments we systematically manipulated target eccentricity and target-flankers distance.
The results show that both precueing target location and increasing target contrast improved accuracy and reduced the critical distance. Interestingly, when both the target and flankers had high contrast, accuracy was higher than when both had low contrast, though, the critical distance was not affected. Similar effects were found at all eccentricities. These findings are discussed with regard to the current views on crowding.