We have shown previously that crowded words, despite being unidentifiable and unclassifiable, still generated robust semantic priming in a subsequent lexical decision task (Yeh, He, & Cavanagh, in press, Psychological Science). Here we further explore the brain mechanisms for such semantic activation from crowded words using event-related fMRI. Participants conducted a lexical decision task for a Chinese single-character word or non-word that was presented in isolation or with four non-word flankers surrounding it. Following a 500 ms fixation display, a target for the lexical decision task was presented at a 5-degree eccentric location on top of the fixation sign for 500 ms. Eye positions were monitored to ensure the retinal position of the isolated and crowded target. The BOLD activation was collected on a Bruker 3T magnet. In the contrast of words versus non-words, we found that the crowded and isolated conditions activated the same brain regions for processing visual words. These include the left Fusiform Gyrus (FG) for orthographic processing, the left Middle Temporal Gyrus (MTG) for semantic representation, and the left Inferior Frontal Gyrus (IFG) for controlled retrieval and selection of semantic knowledge. For crowded words, the time course analysis revealed a more short-lived activation of the two sematic processing areas, MTG and IFG, compared to the activation pattern of isolated words. These results provide neural correlates for the observed behavioral semantic priming effect from crowded words with the same set of word/non-word stimuli. We conclude that semantic processing indeed occurs for severely crowded words, which activate a similar semantic network as do isolated words in the brain.
Meeting abstract presented at VSS 2012