Unattentive speech processing is influenced by orthographic knowledge: evidence from mismatch negativity.

How far can acquired knowledge such as orthographic knowledge affect pre-existing abilities such as speech perception? This controversial issue was addressed by investigating the automaticity of the influence of orthographic knowledge on speech processing. Many studies demonstrated this influence in active, lexico-semantic speech processing tasks. However, it has never been observed when speech is unattended. Here, the Mismatch Negativity (MMN), an automatic index of experience-dependent auditory traces, was recorded in an unattended oddball paradigm manipulating the orthographic congruency between frequent and deviant spoken riming words. Both orthographically congruent and incongruent deviant words elicited a typical MMN over the fronto-central regions, with a stronger response in the incongruent condition. The finding showed that the orthographic dimension of spoken words influences a physiological marker of speech processing although participants were required not to attend to the auditory input. This provides evidence for an impact of acquiring a written code on speech processing.