Processing numeracy with distractor’s variation: A RT-ERP study

Nan, Y., and Luo Y.-J.
Key Laboratory of Mental Health, Institute of Psychology, Chinese Academy of Sciences, Beijing, China

The fast and accurate apprehending of small sets of 1-3 items arouses more and more interest in neuropsychological research. What is the nature of the mental process for quantifying numbers that do not exceed three? Are subitizing and counting two different types of processings with different neural substrate, or the same process but with different difficulty? The Event-Related Potentials (ERPs) were recorded while 14 normal young subjects (age range 18-23 years) were counting the number of the presented rectangles. The goal of the present research is to investigate the enumeration abilities with or without distractors, and sheds light on the relationship of subitizing and counting. We hypothesized that if subitizing and counting are processed functionally similar results should show no difference of their temporal patterns across all the levels of the experiment. The results show that the good ERP predicator of the functional difference of the two enumeration processings: the discontinuity of the effects of the variation of distractors from the subitizing range to the counting range. The electro-physiological evidences support the idea of the two processes being implemented in functional different systems. The distractor’s number variation caused different type of ERPs waveforms in two enumeration processings. For subitizing, a more pronounced negative-going effect was found than counting, mainly in parietal area. It better demonstrated the difference of the two enumeration abilities from a new perspective. It also compensated the early behavioral methods’ shortcomings of poor temporal resolution and gave us a clear understanding of the temporal patterns of the two enumeration processings, the results confirmed the argument that subitizing and counting are two functionally different processings, they can be differentiated by the different effects of the variation of distractors.