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Devin K. Brady, Jascha D. Swisher, David C. Somers; Effects of attention on the spatial extent of crowding. Journal of Vision 2006;6(6):590. doi: 10.1167/6.6.590.
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The recognition of a peripherally presented target letter is impaired by the presence of nearby flanking distractors. The spatial extent (or “critical spacing”) of this crowding effect scales with target eccentricity. The critical spacing has been suggested to reflect either the spatial resolution of attention, or alternatively low-level cortical scaling properties that are not subject to cognitive control. However, previous work on crowding and attention has yielded mixed results, with some studies showing (e.g. Van der Lubbe and Keuss 2001) and others failing to show (e.g. Nazir 1992) attentional effects, leaving this issue unresolved.
To help address this question, we have adapted a simple endogenous precueing paradigm. Briefly presented low-contrast letters flanked by higher contrast distractors are displayed parafoveally in one of two possible locations. An arrow cue indicates the position of the upcoming target with 75% validity. Using a performance measure, we find that the effects of cue validity vary both with flanker position and training: in highly trained subjects, cue validity has little effect; conversely, in relatively naive subjects we find the strongest cueing effects with closely spaced flankers. This finding reconciles several apparently conflicting prior results, and suggests a strong perceptual learning component in the identification of crowded stimuli.
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