Counting in everyday life: discrimination and enumeration.

Enumerating the number of items in a set accurately and quickly is a basic mathematical skill. This ability is especially crucial in the more real-life situations, where relevant items have to be discriminated from irrelevant distracters. Although much work has been done on the brain mechanisms and neural correlates of the enumeration and/or discrimination process, no agreement has been reached yet. We used event-related potentials (ERPs) to show the time course of brain activity elicited by a task that involved both enumeration and discrimination at the same time. We found that even though the two processes run to some extent in parallel, discrimination seems to take place mainly in an earlier time window (from 100 ms after the stimulus onset) than enumeration (beyond 200 ms after the stimulus onset). Moreover, electrophysiological evidence based on the N2 and P3 components make it reasonable to argue for the existence of a dichotomy between subitizing (for sets of less than four items) and counting (for sets of four and more items). Source estimation suggests that subitizing and counting, though being distinct brain processes, do recruit similar brain areas.