Neural correlates of age of acquisition on visual word recognition in Persian

The effect of Age of Acquisition (AoA) on visual word recognition is remarkable. However, there is debate about the loci of AoA effects. The Arbitrary Mapping hypothesis assumes AoA reflects mappings between input (e.g. orthography) and output (e.g. phonology) formed during the acquisition of literacy. An alternative view is that AoA reflects the acquisition of concepts. The AM hypothesis predicts reduced AoA effects on the recognition of written words with transparent mappings between orthography and phonological e.g. chair compared to written words with more opaque mappings between orthography and phonology e.g. choir. In the Persian language, mappings between letters and phonological output are predictable and transparent. However, in skilled reading, many written words become opaque due to the omission of vowels (diacritics) in adult text. Using event-related potential methods (ERP) we tested the prediction that AoA effects on ERP components would be reduced for words with transparent spellings compared to words with opaque spellings for skilled readers. We found an effect of AoA on visual word recognition in the window between 300 and 450 ms with higher N400 negativity for late acquired words and an interaction between transparency and AoA at an unexpected late component (450-700 ms) with significantly higher positivity for late acquired opaque words only. We conclude that AoA effects on Persian visual word recognition reflect arbitrary mappings between print and sound and offer a neurolinguistic account of AoA effects.