Experimental Psychology, in press Position coding in two-digit Arabic numbers: Evidence from number decision and same-different tasks

Digit position coding in two-digit Arabic numbers was examined in two masked priming experiments. In Experiment 1, participants had to decide whether the presented stimulus was a two-digit Arabic number (e.g., 67) or not (e.g., G7). Target stimuli could be preceded by a prime which i) shared one digit in the initial position (e.g., 13-18), ii) shared one digit but in a different position (83-18), iii) was a transposed number (8118). Two unrelated control conditions, equalized in terms of the distance between primes and targets with the experimental conditions were also included (e.g., 79-18). Results showed a priming effect only when prime and target shared digits in the same position. Experiment 2 employed a masked priming same-different matching task –a task that has been successfully employed in the literature on letter position coding. Results showed faster response times when prime and target shared digits –including the transposed-digit condition– relative to the control conditions. Thus, the identity of each digit in the early stages of visual processing is not associated with a specific position in 2-digit Arabic numbers. We examine the implication of these findings for models of Arabic number processing.