Asymmetrical Coupling of Neural Activities for Speech Codes and Meaning in Visual Word Perception

Abstract:
Behavioral studies have shown that speech codes (i.e., phonology) and word meaning are activated automatically during visual word perception. However, the extent to which word reading automatically engages phonological recoding remains a crucial question in understanding visual word perception. This study used functional magnetic resonance imaging (fMRI) techniques to reveal an asymmetrical reduction of neural activities associated with the processing of word meaning and phonology. When subjects' attention was directed to the meaning of a visually-presented word in a semantic-judgment task, brain regions previously linked to phonological and meaning processes were both activated. However, when subjects' attention was directed to the speech codes of a word in a rhyming-judgment task, little activation was observed in the semantic regions (i.e., the temporal and the left anterior-inferior prefrontal regions). Identical stimuli and response characteristics were employed for both experimental tasks. These results support behavioral studies that suggest that in normal word reading, the perception of word meaning necessarily couples with the activation of speech codes. These results also raise questions about the degree to which the perception of word meaning may bypass phonology.