An Imaging Study of Working Memory: The Effects of Concurrent Articulation on Phonological Tasks and the Cerebellum's Role

Recent work has shown that cerebellar patients have difficulty with particular types of rhyme judgments (pairs with phonological and orthographic mismatch), as well as working memory tasks (Ben-Yehudah and Fiez, 2008). Both working memory and rhyme judgment tasks can be disrupted by concurrent articulation (Gathercole and Baddeley, 1994; Besner 1987), indicating a possible set of common regions in the cerebellum. In a review investigating the effects of concurrent articulation on phonological judgment tasks, Besner (1987) found differential effects for rhyme judgments compared to homophone and non-word homophone judgments. Interestingly, there may be differences even within rhyme judgments where word pairs with mixed phonological and orthographic (visual) similarity are more affected by concurrent articulation (Johnston and McDermott, 1986). We performed a behavioral experiment (Experiment 1) to replicate the effects found by both Besner and Johnston and McDermott. Our behavioral experiment found similar results. Concurrent articulation decreased the accuracy of rhyme judgments but not homophone and non-word homophone judgments; within the rhyme judgment task, word pairs with mixed phonology and orthography were the most affected. In order to elucidate the potential role of the cerebellum in these tasks, we designed a neuroimaging experiment (Experiment 2) with both a working memory component and a phonological tasks component. We identified a set of ten regions that were positively active during the working memory task and used this set of regions to explore potential regions of overlap between working memory and rhyme judgment, but not homophone and non-word homophone judgments. Of the ten regions active for the phonological tasks, only one bilateral region in the superior cerebellum showed a significant task effect. Counter to what we had hypothesized, it showed greater activation for the homophone and non-word homophone judgments than the rhyme judgments. While our results show a separation of the tasks in this bilateral region, further study is necessary to help explain why we saw lower activation for rhyming in this region and why we were unable to identify any rhyme specific areas within the cerebellum