Abstract
Classic research tells us there are two distinct systems that allow us to count the number of items in a visual display. When the number of items is large, counting is slow, effortful, and prone to error. But when the number of items is small (usually less than 5), a supposedly preattentive process called subitizing appears to operate, quickly and accurately apprehending the number of items present. Recently, however, the preattentive nature of subitizing has come into question. Here, we used a dual-task version of the classic subitizing task in order determine if subitizing is a resource-limited process. Participants were asked to accurately count the number of items in two arrays presented in quick succession. We hypothesized that if counting small numbers of items relies on preattentive or parallel processes, then the number of items in the first array should have no effect on counting performance in the second array, as long as either or both arrays were in the traditionally-defined subitizing range. Instead, we observed a continuous linear decline in accuracy for counting in the second array as a function of number of items in the first array, even when the number of items in the first array was small. Furthermore, the effect of the first array was clearly present even when the analysis was restricted to small set sizes in the second array. Interestingly, a follow-up experiment demonstrated that when subjects were not required to count the number of items in the first array, the first array had no effect on accuracy for the second array, ruling out perceptual factors and suggesting that the resource that limits subitizing performance may indeed be attention. Our results demonstrate that subitizing both affects and is affected by the amount of cognitive resources available to the viewer and may not be preattentive.
Meeting abstract presented at VSS 2012