Orientation-crowding within contours

Abstract

We examined how crowding (the breakdown of object recognition in the periphery caused by interference from "clutter") depends on the global arrangement of target and distracting flanker elements. Specifically we probed orientation discrimination using a near-vertical target Gabor flanked by two vertical distractor Gabors (one above and one below the target). By applying variable (opposite-sign) horizontal offsets to the positions of the two flankers we arranged the elements so that on some trials they formed contours with the target and on others they did not. While the presence of flankers generally elevated orientation discrimination thresholds for the target we observe maximal crowding not when flanker and targets were co-aligned but when a small spatial offset was applied to flanker location, so that contours formed between flanker and targets only when the target orientation was cued. We also report that observers' orientation judgments are biased, with target orientation appearing either attracted or repulsed by the global/contour orientation. A second experiment reveals that the sign of this effect is dependent both on observer and on eccentricity. In general, the magnitude of repulsion is reduced with eccentricity but whether this becomes attraction (of element orientation to contour orientation) is dependent on observer. We note however that across observers and eccentricities, the magnitude of repulsion correlates positively with the amount of release from crowding observed with co-aligned targets and flankers, supporting the notion of fluctuating bias as the basis for elevated crowding within contours.

Detecting distortions of peripherally presented letter stimuli under crowded conditions

“…The results from our second experiment show that distorted targets do not pop out from undistorted flankers (and vice versa). This is interesting in light of the extensively documented effects of target-flanker similarity in crowding (Estes, 1982;Wilkinson et al, 1997;Kooi et al, 1994;Bernard & Chung, 2011;Chung et al, 2001;Chakravarthi & Pelli, 2011;Glen & Dakin, 2013;Livne & Sagi, 2007;2010;Herzog et al, 2015;Manassi et al, 2013;Saarela et al, 2009;Sayim & Cavanagh, 2013). If we define "similarity" at the level of "distortedness", then in Experiment 1 the distorted target becomes less similar to the undistorted flankers as distortion amplitude increases.…”

Dissociable effects of visual crowding on the perception of colour and motion

“…Given the presence of repulsion in our data (similar to the pattern of direction repulsion more broadly; 40, 78), we followed models of the tilt illusion (31,32,79,80), and the physiology of MT/V5 neurons (81), by adding inhibitory surrounds to the population response. This is also similar to weighted averaging models of crowding that simulate repulsive errors using negative weights (62).…”

“…Experiments S1-S3: Crowding for motion and colour with increased flanker numbers Experiments 1-3 reported in the main text used two flankers to induce crowding, positioned along the radial axis with respect to fixation. We selected this configuration because radial flankers have the strongest influence on crowding (61), and because the effect of radial vs. tangential flankers on target appearance can vary depending on their contour alignment with the target (62)(63)(64). It is possible however that other configurations could increase the strength of crowding, and in turn that combined effects of crowding on motion and colour judgements may become more apparent with this increased strength.…”

Chinese-character crowding—I. Effects of structural similarity

“…Contour alignment was found to modulate crowding strength (Chakravarthi & Pelli, 2011;Glen & Dakin, 2013) and might contribute to the weakened crowding in the scrambled-character crowded condition. Rotation was involved when we scrambled the characters and could have made alignment of strokes from target and from flankers less likely.…”