Right hemisphere semantic performance and competence in a case of partial interhemispheric disconnection

Various forms of right hemisphere (RH)-spontaneous or provoked--performance changes were observed in a partial split-brain patient. Variations in hemispheric activation levels and their interhemispheric balance were retained as the most plausible mechanisms for accounting for these facts. This article presents our attempts to obtain higher RH lexical semantic performance than that observed in a preliminary study where RH performance was at chance level: two forms of the dual-task paradigm were used in order to improve the expression of an assumed RH potential for lexical semantics. Experiment 1 was aimed at activating the RH with a visuo-spatial task as a prior activity before each semantic decision trial. Experiment 2 was intended to overload LH processing systems with a concurrent verbal memory task and induce RH release from LH inhibition. As expected, better RH lexical semantic performance was obtained in these two conditions. Using pictures as stimuli, the aim of Experiment 3 was to observe the spontaneous temporal course of RH implementation in a semantic decision task devoid of written words. These results are discussed along with the issues of performance/competence and the dynamics of neurocognitive function.