High-capacity preconscious processing in concurrent groupings of colored dots

Significance A critical visual process is segmenting a scene into objects to be processed (foreground) and the remainder (background). Humans are extraordinarily good at segmentation, but how they accomplish this still is not well understood. An important component process in segmentation is grouping by similarity, for example, by color, shape, size, etc., thereby organizing visual information into coherent chunks for subsequent stages in object recognition. That our subjects can also group dissimilar items shows that the grouping process itself is much more complex than previously believed. Furthermore, we present a fully quantitative account of the inclusiveness/exclusiveness of the grouping process and of its extraordinary perceptual capacity. The amount of information preconsciously utilized to form a group is many times greater than is consciously available. Grouping is a perceptual process in which a subset of stimulus components (a group) is selected for a subsequent—typically implicit—perceptual computation. Grouping is a critical precursor to segmenting objects from the background and ultimately to object recognition. Here, we study grouping by color. We present subjects with 300-ms exposures of 12 dots colored with the same but unknown identical color interspersed among 14 dots of seven different colors. To indicate grouping, subjects point-click the remembered centroid (“center of gravity”) of the set of homogeneous dots, of heterogeneous dots, or of all dots. Subjects accurately judge all of these centroids. Furthermore, after a single stimulus exposure, subjects can judge both the heterogeneous and homogeneous centroids, that is, subjects simultaneously group by similarity and by dissimilarity. The centroid paradigm reveals the relative weight of each dot among targets and distractors to the underlying grouping process, offering a more detailed, quantitative description of grouping than was previously possible. A change detection experiment reveals that conscious memory contains less than two dots and their locations, whereas an ideal detector would have to perfectly process at least 15 of 26 dots to match the subjects’ centroid judgments—indicating an extraordinary capacity for preconscious grouping. A different color set yielded identical results. Grouping theories that rely on predefined feature maps would fail to explain these results. Rather, the results indicate that preconscious grouping is automatic, flexible, and rapid, and a far more complex process than previously believed.