Digit Repetition Effect in Two-Digit Number Comparison

Previous data from two-digit number naming show that when target and prime numbers share one digit at different positions (e.g., target 28 and prime 86 or 72) an inhibition effect may be observed (Ratinckx, Brysbaert, & Fias, 2005). Such an effect has been ascribed to the mechanism of morpho-phonological transcoding from Arabic to verbal format. We evaluate the alternative hypothesis of an inhibition effect arising during the Arabic form processing when two different syntactic values have to be assigned to the same single digit. In Experiments 1 and 3, a digit repetition effect was observed in number comparison tasks, even when phonological transcoding is blocked by an articulatory suppression task. Conversely, Experiment 2 showed that no digit repetition effect can be found with number comparison of verbal written numbers. Results are compatible with an Arabic-syntactic processing stage, where units and decades are decomposed and where each single digit is activated and recognized.