Activation during Semantic and Phonological Processing: Cross-paradigm Interference in Functional Imaging

Abstract:
Abstract: Cross paradigm interference often obscures results in behavioral testing (e.g., Dagenbach et al., 1989). It may also influence the dynamics of brain activation in functional imaging. In this study, we compared patterns of brain activation during semantic and phonological processing using functional magnetic resonance imaging (fMRI) methods. Eighteen right-handed adult volunteers were randomly assigned to three experimental groups. One group performed semantic categorization, word, and pseudoword rhyming tasks in the same experimental session. The other two groups performed either the word rhyming or semantic categorization tasks. The stimuli were presented visually in a box-car design with each critical task alternating with a control task which required responses to a visual feature. Stimuli were virtually identical in all tasks except that pseudowords differed from the word stimuli by their initial consonants. Results of the study showed strong tendency of bilateral activation when semantic and word rhyming tasks were mixed in the same experimental session. Activation patterns also differ in other respects between the mixed and unmixed groups. These results suggest that multi-task functional imaging in a single session may induce neural activities nonessential to the cognitive function under investigation. Consequently, interpretations of functional anatomy based on multi-task studies must be viewed cautiously.