The role of transient attention in crowding and feature binding

Crowding refers to the failure to identify a peripheral object due to nearby objects (flankers). A hallmark of crowding is the inner-outer asymmetry, i.e., the outer flanker (more peripheral) produces stronger interference than the inner one. Here, by manipulating attention, we tested the predictions of two competing accounts: the attentional account, which predicts a positive attentional effect on the asymmetry (i.e., attention to the outer flanker will increase the asymmetry), and the receptive field size account, which predicts a negative attentional effect. In Experiment 1, observers estimated a Gabor target orientation. A peripheral pre-cue draws attention to one of three locations: target, inner or outer flanker. Probabilistic mixture modeling demonstrated the asymmetry by showing that observers often misreported the outer flanker orientation as the target. Interestingly, the outer cue led to a higher misreport rate of the outer flanker, and the inner cue led to a lower misreport rate of the outer flanker. Experiment 2 tested the effect of asymmetry and attention on binding errors (e.g., reporting the tilt of one presented item with the color of another item). Observers reported both the tilt and color of the target. Attention increased target reports in both dimensions and led to a decrease in target binding. However, attention did not lead to a decrease in flanker biding errors. The results are consistent with the attentional account of crowding and suggest that the locus of spatial attention plays an essential role in crowding and the inner-outer asymmetry.