RIGHT-HEMISPHERE SEMANTIC PERFORMANCE AND COMPETENCE IN A CASE OF PARTIAL INTERHEMISPHERIC DISCONNECTION

Various forms of right hemisphere (RH)-spontaneous or provoked-perform ance changes were observed in a partial split-brain patient. Variation s in hemispheric activation levels and their interhemispheric balance were retained as the most plausible mechanisms for accounting for thes e facts. This article presents our attempts to obtain higher RH lexica l semantic performance than that observed in a preliminary study where RH performance was at chance level: two forms of the dual-task paradi gm were used in order to improve the expression of an assumed RH poten tial for lexical semantics. Experiment 1 was aimed at activating the R H with a visuo-spatial task as a prior activity before each semantic d ecision trial. Experiment 2 was intended to overload LH processing sys tems with a concurrent verbal memory task and induce RH release from L H inhibition. As expected, better RH lexical semantic performance was obtained in these two conditions. Using pictures as stimuli, the aim o f Experiment 3 was to observe the spontaneous temporal course of RH im plementation in a semantic decision task devoid of written words. Thes e results are discussed along with the issues of performance/competenc e and the dynamics of neurocognitive function. (C) 1994 Academic Press , Inc.