The Role of Target Salience in Crowding

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Abstract
We studied ‘crowding’ in the parafovea using orientation identification of a Gabor target as the task, and flanking Gabors on an isoeccentric circle as distractors. Orientation-discrimination thresholds were raised by nearby flanking distractors. This crowding effect was increased by the number of distractors and decreased by the spatial separation between target and distractors. Crowding was greatest when the target was in the centre of the distractor array and smallest when the target was on the edge of the array. A cue indicating the position of the target improved performance when the position was otherwise unknown and the spatial separation between target and distractors was large, but the cue had no significant effect when separation was small. Increasing the contrast of the target relative to the distractors reduced crowding, but targets of smaller contrast than that of the distractors are even harder to identify than those of the same contrast. Putting the target and distractors in different depth planes decreased crowding for some observers, but there were qualitative individual differences. A large (say, 45°) difference in orientation between target and distractors caused the target to ‘pop out’ in a presence/absence task, despite the evidence from other studies that crowding is still found in these conditions. We conclude that salience has, at best, modest effects on crowding.
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