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Miranda Scolari, Andrew Kohnen, Brian Barton, Edward Awh; Attention does not influence critical spacing. Journal of Vision 2007;7(9):444. doi: 10.1167/7.9.444.
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© ARVO (1962-2015); The Authors (2016-present)
Crowding refers to the phenomenon in which nearby distractors impede target discrimination, possibly because of the excessive integration of target and distractor representations. Crowding is reduced as target-distractor distance increases, and is eliminated entirely at a distance that is labeled the critical spacing point. To determine which factors influence critical spacing, we examined three factors that are known to facilitate target identification in crowded displays: spatial attention, distractor preview, and target popout.
Previous evidence suggests that spatial attention can facilitate target processing by biasing the competitive interactions between targets and distractors in favor of the relevant stimuli (e.g., Desimone & Duncan, 1995). If this is the case, then critical spacing might also be reduced because of reductions in the strength of distractor representations. We manipulated attention by presenting peripheral cues that elicited stimulus-driven shifts of attention either towards or away from the target location. As demonstrated in previous studies, spatial cueing led to robust improvements on target discrimination. Despite these benefits, however, attention did not reduce critical spacing.
Distractor preview was examined by manipulating whether the crowding distractors were presented prior to or simultaneous with the target. Popout was examined by manipulating whether there was a salient color difference between the target and distractors. Again we found robust benefits of preview and popout in crowded displays. Furthermore, both preview and popout caused large reductions in critical spacing, perhaps by reducing the integration of target and distractor representations via Gestalt grouping cues. This hypothesis may also explain why spatial attention did not influence critical spacing, given that the bottom-up grouping cues between targets and distractors remained constant across the valid and invalid spatial cues. In this case, stimulus-driven shifts of attention may have enhanced target processing without directly influencing the tendency to group targets and distractors.
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