Proceedings of the Annual Meeting of the Cognitive Science Society

We present an experiment where subject's subitizing performance for linear dot arrays was analyzed using Differential Time Accuracy Functions. This technique uses accuracy and reaction time data to decompose overall response latency into stimulus-limited and post-stimulus processing. Our results show that subitizing is a phenomenon produced by the effects of increased numerosity on stimulus?limited processes alone. They also suggest that the familiar guessing strategy for the largest arrays in reaction time measures of subitizing results from a reduction in post?stimulus processing. Subjects appear to extract the perceptual characteristics of all arrays but presumably fail for the largest and therefore default to guessing. Existing theories of subitizing are evaluated in light of these results.