Cortical activation patterns during subitizing and counting

The exact amount of small number of items (1–4) can be detected fast and accurately (subitizing) while the enumeration of large number of items (over 4) is slower and error-prone (counting). Several counting-related cortical areas have been identified mainly in frontal and parietal regions, but cortical events associated with subitizing have remained unclear. Similarly, little is known about the temporal sequence of cortical activation during enumeration. In this study, we examined the temporal and spatial pattern of subitizing and counting using magnetoencephalography (MEG). During the MEG-recordings, black dots (2–8) in a visual display were shown to ten adults, who then responded with a button press as soon as they knew the number of items. The behavioural results showed a regularly reported dichotomy in enumeration of small (2–4) and large (5–8) numbers. In brain responses, pronounced activation peak during subitizing was detected around 250 ms in the bilateral posterior temporo-parietal area, which presumably reflects the function of ventral visual stream. During counting, pronounced activation was first detected in bilateral parietal areas, followed by a growing activation in the frontal cortices. The activation of frontal areas indicates the involvement of task guidance and attention, while the parietal areas activated earlier may have a key role in maintaining numerical representations and spatial attention. Brain functions during counting seem to consist of several constituent processes that reflect number processing, attention and task guidance. Our results demonstrated temporally and spatially specific brain activation for fast subitizing and effortful counting.

► Enumeration of small and large number of items is qualitatively different.
► We used magnetoencephalography to investigate the brain mechanisms of enumeration.
► Temporo-parietal areas were specifically activated during small number enumeration.
► Enumeration of larger arrays (counting) activated frontal and parietal regions.
► Neural correlates of small and large number enumeration seem to be different.