How element visibility affects visual enumeration

The task of detection requires that at least one target component (i.e. “feature”) be detected, while the task of identification requires the detection and integration of multiple features into a recognizable object. Enumeration seems to involve aspects of both feature detection and object identification. As in identification, it requires the detection of multiple features, but as in detection, it does not require the explicit encoding of a global form. Enumeration of briefly presented objects is accurate up to the “subitizing capacity” of 3–5 items. We discuss the relation of enumeration to visual detection and identification by considering the effect of target visibility on subitizing capacity. We found that while the distribution of enumeration responses changes with contrast, subitizing capacity is generally invariant with contrast until it nears detection threshold. These results suggest that component detection (associated with number estimation) and component integration (associated with subitizing) behaved differentially as contrast was manipulated. We speculate that subitizing capacity is linked to the approximate number of detected features adequate for recognizing shapes.