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Elric Elias, Timothy D. Sweeny; Integration and segmentation. Journal of Vision 2019;19(10):95a. doi: https://doi.org/10.1167/19.10.95a.
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Integration and segmentation are fundamental computations in vision, and they serve opposing purposes. Integration occurs, for example, in ensemble coding, whereby perceivers make fast and efficient generalizations about large amounts of information. In contrast, segmentation perceptually exaggerates visual features away from category boundaries, promoting quick-but-crude binary distinctions. Integration and segmentation must work in parallel, yet they are typically examined in isolation. Understanding of how they may conflict is thus surprisingly incomplete. We conducted three experiments examining the ensemble perception of aspect ratio, a visual feature roughly equivalent to “tallness/flatness”, to investigate this potential conflict. In the first two experiments, observers viewed a set of shapes with heterogeneous aspect ratios for 250-ms and used a cursor to adjust a test shape to match the average of the set on each trial. Observers’ distribution of errors across trials served as an index of the precision of ensemble coding. We expected conflict when observers attempted to make a summary judgement about sets of features that spanned a category boundary. Indeed, ensemble coding operated less precisely for sets that included tall and flat shapes, compared to sets that included tall or flat shapes. We suspected that this occurred because sets which spanned the category boundary were perceived as more being heterogeneous than those that did not, even though our sets were carefully matched in terms of physical variability. Replicating previous work (Suzuki & Cavanagh, 1998) we showed in a third experiment that segmentation exaggerated the appearance of individual shapes near the tall/flat category boundary. Segmentation may thus disrupt the integration required for efficient ensemble coding by exaggerating a set’s perceived heterogeneity. This work adds to the understanding of integration by demonstrating aspect ratio integration, and also by showing that integration can be constrained by another fundamental computation in the visual system, segmentation.
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