Background: During normal semantic processing, the left hemisphere (LH) is suggested to restrict right\r\nhemisphere (RH) performance via interhemispheric suppression. However, a lesion in the LH or the use of\r\nconcurrent tasks to overload the LH�s attentional resource balance has been reported to result in RH disinhibition\r\nwith subsequent improvements in RH performance. The current study examines variations in RH semantic\r\nprocessing in the context of unilateral LH lesions and the manipulation of the interhemispheric processing\r\nresource balance, in order to explore the relevance of RH disinhibition to hemispheric contributions to semantic\r\nprocessing following a unilateral LH lesion.\r\nMethods: RH disinhibition was examined for nine participants with a single LH lesion and 13 matched controls\r\nusing the dual task paradigm. Hemispheric performance on a divided visual field lexical decision semantic priming\r\ntask was compared over three verbal memory load conditions, of zero-, two- and six-words. Related stimuli\r\nconsisted of categorically related, associatively related, and categorically and associatively related prime-target pairs.\r\nResponse time and accuracy data were recorded and analyzed using linear mixed model analysis, and planned\r\ncontrasts were performed to compare priming effects in both visual fields, for each of the memory load conditions.\r\nResults: Control participants exhibited significant bilateral visual field priming for all related conditions (p < .05),\r\nand a LH advantage over all three memory load conditions. Participants with LH lesions exhibited an improvement\r\nin RH priming performance as memory load increased, with priming for the categorically related condition\r\noccurring only in the 2- and 6-word memory conditions. RH disinhibition was also reflected for the LH damage\r\n(LHD) group by the removal of the LH performance advantage following the introduction of the memory load\r\nconditions.\r\nConclusions: The results from the control group are consistent with suggestions of an age related hemispheric\r\nasymmetry reduction and indicate that in healthy aging compensatory bilateral activation may reduce the impact\r\nof inhibition. In comparison, the results for the LHD group indicate that following a LH lesion RH semantic\r\nprocessing can be manipulated and enhanced by the introduction of a verbal memory task designed to engage\r\nLH resources and allow disinhibition of RH processing.
Loading....