How dynamic is interhemispheric interaction? Effects of task switching on the across-hemisphere advantage.

Interaction between the cerebral hemispheres may allow both hemispheres to contribute their processing resources in order to cope efficiently with complex tasks [Banich, M. (1998). The missing link: the role of interhemispheric interaction in attentional processing. Brain and Cognition, 36, 128-157]. The current study investigated whether the benefits of interhemispheric interaction arise because of top-down knowledge about the task built up over the course of a block of trials or because of the processing demands present in a single trial. Participants performed a less computationally complex physical identity task and a more complex adding task on within-visual field and across-visual field trials. Task differences in interhemispheric interaction were compared between the blocked and mixed conditions to investigate whether frequent task switches altered the pattern of interhemispheric resource recruitment. A similar interaction between task difficulty and trial type (across- or within-visual field presentation) was obtained for both the blocked and mixed conditions. The degree of task-dependency of interhemispheric interaction was not altered in the mixed condition. This finding supports the view that interhemispheric interaction becomes beneficial in response to the processing demands of an individual trial rather than as a result of top-down task knowledge

Individual differences in white matter anatomy predict dissociable components of reading skill in adults.

We used diffusion tensor imaging (DTI) to investigate relationships between white matter anatomy and different reading subskills in typical-reading adults. A series of analytic approaches revealed that phonological decoding ability is associated with anatomical markers that do not relate to other reading-related cognitive abilities. Thus, individual differences in phonological decoding might relate to connectivity between a network of cortical regions, while skills like sight word reading might rely less strongly on integration across regions. Specifically, manually-drawn ROIs and probabilistic tractography revealed an association between the volume and integrity of white matter underlying primary auditory cortex and nonword reading ability. In a related finding, more extensive cross-hemispheric connections through the isthmus of the corpus callosum predicted better phonological decoding. Atlas-based white matter ROIs demonstrated that relationships with nonword reading were strongest in the inferior fronto-occipital fasciculus and uncinate fasciculus that connect occipital and anterior temporal cortex with inferior frontal cortex. In contrast, tract volume underlying the left angular gyrus was related to nonverbal IQ. Finally, connectivity underlying functional ROIs that are differentially active during phonological and semantic processing predicted nonword reading and reading comprehension, respectively. Together, these results provide important insights into how white matter anatomy may relate to both typical reading subskills, and perhaps a roadmap for understanding neural connectivity in individuals with reading impairments

Individual Differences in the Effect of Orthographic/Phonological Conflict on Rhyme and Spelling Decisions

<div><p>In typical readers, orthographic knowledge has been shown to influence phonological decisions. In the present study, we used visual rhyme and spelling tasks to investigate the interaction of orthographic and phonological information in adults with varying reading skill. Word pairs that shared both orthography and phonology (e.g., <i>throat/boat</i>), differed in both orthography and phonology (e.g., <i>snow/arm</i>), shared only orthography (e.g., <i>farm/warm</i>), and shared only phonology (e.g., <i>vote/boat</i>) were visually presented to university students who varied in reading ability. For rhyme judgment, participants were slower and less accurate to accept rhyming pairs when words were spelled differently and to reject non-rhyming pairs when words were spelled similarly. Similarly, for spelling judgments, participants were slower and less accurate when indicating that word endings were spelled differently when words rhymed, and slower and less accurate when indicating that words were spelled similarly when words did not rhyme. Crucially, while these effects were clear at the group level, there were large individual differences in the extent to which participants were impacted by conflict. In two separate samples, reading skill was associated with the extent to which orthographic conflict impacted rhyme decisions such that individuals with better nonword reading performance were less impacted by orthographic conflict. Thus, university students with poorer reading skills may differ from their peers either in the reading strategies they use or in the degree to which they automatically access word form information. Understanding these relationships is important for understanding the roles that reading processes play in readers of different skill.</p></div