Abstract
In visual crowding, nearby objects (flankers) impair target perception. Focused spatial attention to the target location has been shown to reduce crowding. However, how attentional allocation within a group of close-by objects modulates crowding is largely unknown. Here, with probability as attentional cue, we varied the target location within a group of objects to investigate how object-based attention affected crowding. Observers reported either the inward, central, or outward letter of a letter trigram, as indicated by a pre-cue (Experiment 1) or a post-cue (Experiment 2). Probabilities of which letter position to report were 100, 80, 50, and 33 percent, with an equal number of trials for the remaining letter positions. Trigrams were briefly presented at varying eccentricities (centered at 8.6°, 10°, or 11.4°), while keeping the target location fixed throughout (at 10°). In both experiments, performance for the central letter was inferior compared to both flanking letters, and, consistent with the inward-outward anisotropy of crowding, worse for the inward compared to the outward letter. Probability affected none of the letter positions when pre-cued, but all letter positions improved with higher probabilities when post-cued. The post-cue results revealed that, despite all target letters being presented at the same spatial location, crowded letter recognition benefitted from increased attention towards a given letter position within the trigram. Hence, performance was strongly dependent on an object-based frame of reference when all letter positions within the trigram were task-relevant. We suggest that the allocation of attention within groups of task-relevant objects strongly affects the recognition of crowded items.