Number Processing in Arabic and Hebrew Bilinguals: Evidence Supporting the Compatibility Effect

In the current study, a direct assessment of the effect of presentation language and format on the compatibility effect of two-digit numbers was made by contrasting performance of Arabic/Hebrew bilinguals in a digital (Hindi digits/Arabic digits) and verbal numerical comparison task (Arabic an inverted language: units-decades and Hebrew a non-inverted language: decades-units). Our data revealed in digital presentation format a regular compatibility effect in Hindi digits and Arabic digits characterized by lower reaction-time (RT) means for compatible number pairs than incompatible ones with no difference in the RT means of participants in the two languages, Arabic language–Hindi digits as a mother tongue and Hebrew language–Arabic digits as a second language. However, in verbal presentation format, different patterns of compatibility effect were found in Arabic and Hebrew verbal numbers. In Arabic number words, a regular compatibility effect was found, while in Hebrew number words, no compatibility effect was found. This reflects the influence and modulation of the lexical-syntactic structure of the language in two-digit numbers comparison. Evidently, these differences in the compatibility effect advocate and strengthen the claim that two-digit numbers comparison is influenced by the numbers presentation format. Different modes of presentation of two-digit numbers (digital vs. verbal) can lead to different number comparison styles. The parallel model accounts for the numerical comparison in digital presentation, while for the verbal numbers presentation, a revised sequential-syntactic model is preferable.