Distinct Mechanism For The Numerical Comparison And Priming Distance Effect

In the field of numerical cognition, numerous investigations have conducted to reveal how numbers are represented in the human brain and disclosed two ubiquitous numerical effects:numerical comparison distance effect and numerical priming distance effect. The comparison distance effect (CDF) is the finding that the comparison of two numbers is more difficult when they are close to each other in their magnitude than when they are far apart. The priming distance effect (PDF) is the finding that when a target number is preceded by a prime number, participants respond more quickly when the prime-target numerical distance is smaller. And more notably, a decrease in the size of the CDE with increasing age and numerically representational precision has been shown. However, an opposite tendency for the PDE has been discovered. The representational overlay hypothesis thought that it is more representational overlap between neighboring numbers that make it more difficult to discriminate between them than faraway numbers in numerical comparison tasks, which results in the comparison distance effect. However, more representational overlap between nearby numbers, which may be used to as prime numbers and target numbers, do decrease response lateness to targets numbers in the numerical priming task. Although accepting that the existence of a PDE clearly favors the representational overlap hypothesis, nevertheless, the monotonic connection view has stressed the role of response-related-processes for the CDE.Given the conflicting hypotheses as reviewed above, this study aimed to explore whether there was dissociation between the CDE and PDE in the human brain. To our best knowledge, this is the first imaging study to explicitly and simultaneously focusing on the CDE and PDE. In order to shed further light on the relationship between them, we used two independent but matched tasks to probe the CDE and PDE simultaneously. Moreover, we evaluated the precision of numerical representation of individual participant by virtue of number line estimation task to test which CDE or PDE was more commensurate with the representational overlap view.Based on extant studies which shown that human brain parietal lobe is the crucial locus of core numerical processing, the present study first test whether or not parietal regions of interests (ROIs) defined by the result of ALE (activation likeness estimation) meta-analysis of numerical processing were sensitive to CDE and PDE both. The results showed robust CDE and PDE at the both behavioral and neural level. The significant CDE were observed in right parietal lobe, however, the significant PDE in left parietal lobe. Moreover, the significant CDE appeared ahead of PDE.The second study differentiated the representational overlap view between the monotonic connection view by virtue of number line estimation task. The results found that the significant correlation was only observed between the precision of numerical representation and the size of CDE.To sum up the results, the present study suggested that distinct neural mechanism for the numerical comparison and priming distance effect. CDE stemmed from the numerical representational overlap. All these results proved the representational overlap view and monotonic connection view in part. Future research should focus on the essence of PDE.