Independent Recognition of Numerosity Requires Attention

The overlap of numerical and non-numerical properties in concrete object arrays raises the question of how these input dimensions interact. Two studies were conducted to address this question and showed that changing the object identity (while retaining the numerosity) and changing the numerosity (while retaining the object identity) both resulted in attenuated recognition of object arrays. However, this interference differed across development. In adults interference was asymmetrical (i.e. changing the object identity has greater effect on memory for numerosity than changed numerosity had on object identity). In contrast, children showed a symmetrical pattern of interference. These results imply that for adults, processing numerosity might be an attention-demanding process compared to a spontaneous object perception. Children, however, processed neither the object identity nor numerosity independently.