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Jeffrey Nador, Adam Reeves; Crowding beyond Bouma's bound . Journal of Vision 2016;16(12):239. doi: 10.1167/16.12.239.
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© ARVO (1962-2015); The Authors (2016-present)
Previous research has demonstrated that applying onset transients to crowded targets can improve their orientation discriminability (Greenwood, Sayim & Cavanagh, 2014), but does not influence the spatial extent of flanker interference (critical spacing). At last year's VSS, we argued that this effect depends on observers' endogenous attention to the target location. Indeed, when target-flanker spacing and eccentricity are varied randomly from trial to trial, the effect of the transient is reversed – hindering target identification only at near spacing. Method: on each trial, observers saw an RSVP stream of letters at fixation, while 2 target Gabors appeared, one left and one right of fixation, throughout each 1s long trial. Targets were flanked by similarly-oriented Gabors. They were presented at 4 or 8 deg eccentricity, with center-to-center spacings of ¼, ½, or ¾ target eccentricity, randomized trial-to-trial. Observers shifted endogenous attention and evaluated the tilt of the Left or Right target Gabor depending on whether the letter 'L' or 'R' appeared at a randomized time during the RSVP. Results: Crowding was independent of target-flanker spacing, and blinking the target at near spacings hindered performance immediately following the endogenous attentional shift. However, when the concurrent RSVP task was replaced with an arrow indicating Left or Right prior to each trial, crowding decreased at wider spacings, with critical spacing roughly equal to ½ eccentricity (Bouma's bound). These effects can be explained if (1) during an attention shift, the attended region is more than 18 deg across, and (2), once attention is focused enough to exclude the flankers, crowding is reduced. Before then, blinking the target hurts at near spacing because it improves processing of all the stimuli in the attended region - not just the target, but also the flankers.
Meeting abstract presented at VSS 2016
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