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Nobuyuki Hirose, Naoyuki Osaka; Asymmetry in object substitution masking occurs relative to the direction of spatial attention shift. Journal of Vision 2008;8(6):771. doi: https://doi.org/10.1167/8.6.771.
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A lateral mask persisting beyond the duration of a target can reduce its visibility (object substitution masking: OSM). Y. Jiang and M. M. Chun (2001) reported that a mask on the peripheral side of the target caused stronger OSM than on the central side. Assuming that spatial attention was focused on the target, the peripheral and the central masks were always located in the same and the opposite direction of an attentional path with reference to the target in their study. We hypothesized that the asymmetry of OSM relies on the asymmetry of mask configuration relative to the attentional shift. To test this, we conducted four experiments among which the presence or absence of the relative center-periphery relationship and the presence or absence of the asymmetric mask configuration were manipulated independently and orthogonally. In Experiment 1, we successfully replicated the asymmetric OSM discovered by Jiang and Chun. In Experiment 2, we compared two mask positions symmetrically placed with respect to the line connecting the fixation and the target but found no asymmetry. In the next two experiments, to manipulate the attentional trajectory to the target, we introduced a new paradigm in which participants were asked to identify two letters, the decoy and the target, sequentially presented in different positions. In Experiment 3, asymmetric OSM was not observed even in the presence of the center-peripheral relation if the mask arrangement was symmetric with respect to the attentional path. In Experiment 4, however, the asymmetric OSM was evident even without the center-periphery relationship if the mask configuration was asymmetric relative to the attentional shift. Taken together, all of these results suggest that the asymmetric OSM occurs relative to the direction of attention shift. We propose that this kind of asymmetry might be explained by attentional momentum associated with orienting toward the target.
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