Does tonal information affect the early stages of visual-word processing in Thai?

Thai offers a unique opportunity to investigate the role of lexical tone processing during visual-word recognition, as tone is explicitly expressed in its script. In order to investigate the contribution of tone at the orthographic/phonological level during the early stages of word processing in Thai, we conducted a masked priming experiment—using both lexical decision and word naming tasks. For a given target word (e.g., ห้อง/hᴐ:ŋ2/, room), five priming conditions were created: (a) identity (e.g., ห้อง/hᴐ:ŋ2/), (b) same initial consonant, but with a different tone marker (e.g., ห่อง/hᴐ:ŋ1/), (c) different initial consonant, but with the same tone marker (e.g., ศ้อง/sᴐ:ŋ2/), (d) orthographic control (different initial consonant, different tone marker; e.g., ศ่อง/sᴐ:ŋ1/), and (e) same tone homophony, but with a different initial consonant and different tone marker (e.g., ธ่อง/t^hᴐ:ŋ2/). Results of the critical comparisons revealed that segmental information (i.e., consonantal information) appears to be more important than tone information (i.e., tone marker) in the early stages of visual-word processing in alphabetic, tonal languages like Thai. Thus, these findings may help constrain models of visual-word recognition and reading in tonal languages.