Abstract
Number sense is a capacity of cognition that apprehends the number of objects in a collection without invoking the requirement to refer to verbal symbols: We can ‘see’ how many objects presented, in a set, usually visually of up to about four (referred as subitizing) and can make an estimate of more than about four (Kaufman & Lord, 1949). Here, we showed that the perception of number is greatly determined by the perception of objects, where the ‘notion’ of an object [the holistic identity in the perspective of perceptual organization] could be precisely characterized as topological attributes (including connectivity and inside/outside relation). When some of the items were connected by a line or enclosed in a hollow figure, the total number of the items was underestimated directly proportional to the number of items connected or enclosed. Such a global topological effect in numerical perception is seen to be held independent of local features such as connecting form and item shape, and in a range of large and small numbers. Besides, topological effect decreased with the duration of stimulus presentation, revealing a possible early occurrence of topological perception in visual processing. Further functional Magnetic Resonance Imaging (fMRI) experiment revealed a similar pattern of neural activation for numerical distance effect and connectivity effect in human's intraparietal sulcus (IPS). The current series of studies suggests that numerical operation such as discrimination, estimation and enumeration may be based on knowledge of the perceptual objects themselves, defined by global topological attributes.