Five Red Apples are Larger than Five Green Apples: The Effect of Object Features on Numerosity Recognition

Abstract representation of number is a cornerstone of maturity, by which humans perceive numerical equivalence between various sets of objects. However, it is still unclear how humans perceive and retain the abstract nature of number from concrete numerical stimuli. Two experiments were conducted using a novel memory paradigm to clarify this issue. In Experiment 1, participants were asked to study sets of concrete objects and identify either familiar numerosity or familiar object shape, which were independently manipulated to create congruent and incongruent pairs. Results showed that the numerical cues interfered with object shape recognition and the object shape cues interfered with numerosity recognition. However, the magnitude of interference on numerosity recognition was larger than that on object recognition. These results suggest that individuals tend to integrate all of the visual properties present in the stimulus and use them to process numerical quantity even when the integrated input is not required for a given task. In Experiment 2, the instructions were the same as in Experiment 1 except that the participants were offered an attention-biased training session. The results suggest that independent processing of numerosity tends to be utilized only with cued attention later in development. Therefore, we concluded that unlike symbolic number processing, non-symbolic numbers are processed in a non-abstract manner, which may change later depending on observers’ expertise.