Physical similarity (and not quantity representation) drives perceptual comparison of numbers: evidence from two Indian notations.

Numerical quantity seems to affect the response in any task that involves numbers, even in tasks that do not demand access to quantity (e.g., perceptual tasks). That is, readers seem to activate quantity representations upon the mere presentation of integers. One important piece of evidence in favor of this view comes from the finding of a distance effect in perceptual tasks: When one compares two numbers, response times (RTs) are a function of the numerical distance between them. However, recent studies have suggested that the physical similarity between Arabic numbers is strongly correlated with their numerical distance, and that the former could be a better predictor of RT data in perceptual tasks in which magnitude processing is not required (Cohen, 2009a). The present study explored the Persian and Arabic versions of Indian numbers (Exps. 1 and 2, respectively). Naïve participants (speakers of Spanish) and users of these notations (Pakistanis and Jordanians) participated in a physical same-different matching task. The RTs of users of the Indian notations were regressed on perceptual similarity (estimated from the Spanish participants' RTs) and numerical distance. The results showed that, regardless of the degree of correlation between the perceptual similarity function and the numerical distance function, the critical predictor for RTs was perceptual similarity. Thus, participants do not automatically activate Indian integers' quantity representations, at least not when these numbers are presented in simple perceptual tasks.