Poster C57, Sunday, March 26, 5:00 – 7:00 pm, Pacific Concourse
EARLY FEEDBACK FROM FRONTAL TO OCCIPITO-TEMPORAL CORTEX DURING VISUAL WORD RECOGNITION
Yu Li1, Sachiko Kinoshita1, Paul Sowman1, Anne Castles1; 1Macquarie University
Previous studies have shown that skilled readers can rapidly differentiate visual words from symbol strings by about 200 ms after stimulus onset. A recent MEG study further found that during the very early stages of visual word processing, activity in the left inferior frontal gyrus (left IFG) exerts a stronger top-down influence on the left ventral occipito-temporal cortex (left vOT) for real words than for meaningless symbols (Woodhead et al., 2014). However, questions remain about the nature of this top-down influence, specifically whether it reflects lexical-semantic or phonological effects. The aim of the current study was to shed light on this question using dynamic causal modelling (DCM). Fifteen adults participated in a MEG experiment in which they viewed four types of visual stimulus: real words (RW), pseudowords (PW), consonant strings (CS) and false fonts (FF). Six reading-related nodes were chosen in the DCM analysis. Through the specific contrasts of RW vs PW (lexical-semantic effect), PW vs CS (phonology effect) and CS vs FF (low-level letter effect), we were able to examine the nature of the early top-down influences. The results showed that within 200 ms after stimulus onset, the connection from left IFG to left vOT was stronger for PW than for CS and for RW than for PW, indicating that both lexical-semantic and phonological information are implicated in the top-down influence from the left IFG to left vOT. These results add to our understanding of the nature of high-level feedback effects during the early stages of visual word recognition.
Topic Area: LANGUAGE: Lexicon