Abstract
Background. Crowding refers to the failure to identify a peripheral item when it is presented along with nearby flankers. A hallmark property of crowding is the inner-outer asymmetry; the outer flanker (eccentric) produces stronger interference than the inner one. Here we investigated the asymmetry effect using an estimation report in order to test the predictions of competing crowding models: pooling vs. substitution. Pooling models suggest that the outer flanker is more integrated with the target, which predicts either averaging errors with the outer flanker or mis-reports of the inner flanker (the less integrated flanker). Substitution models, on the other hand, suggest confusion between the target and the outer flanker, which predicts mis-reports of the outer flanker.
Method. Observers (n=22) estimated the orientation of a Gabor using a continuous report. The target was presented at 7° eccentricity. In the crowding conditions, two distractors flanked the target, one on each side, along the horizontal meridian. We characterized crowding errors with respect to each distractor separately, by fitting probabilistic models to the error distributions.
Results. Under crowding conditions, instead of the target, observers mistakenly reported (misreport errors) the outer flanker (eccentric), but not the inner flanker (closer to the fovea). This finding is in accordance with the prediction of the substitution models.
Conclusions. Our results reveal a counterintuitive finding: perception is dominated by the peripheral item rather than the one closer to the center of the visual field. Importantly, our findings support the substitution account. Namely, increased location uncertainty in the periphery, due to larger receptive fields, leads to confusion between the target and the outer flanker.