[Effect of conflict frequency associated with presentation hemifield on global/local processing]

We used a global/local processing task with hierarchically structured visual stimuli to investigate whether each hemisphere independently modulates visual selectivity depending on conflict frequency. In both of the present experiments, a hierarchical pattern consisting of large (global) letter made up of small (local) letters was briefly presented to unilateral visual-field (LVF/RVF) and the congruency between the local and global levels was manipulated. An important manipulation was that the congruency ratio in a given block differed between the two visual-fields (80% and 20%). We required right-handed participants to identify the global (Experiment 1) and local level (Experiment 2) of the hierarchical stimulus. The results showed that when the stimuli were projected to the nondominant hemisphere for the task demand (left hemisphere in the global task and right hemisphere in the local task) the size of the interference (local interference in Experiment 1 and global interference in Experiment 2) was larger in the 80% congruent condition than in the 20% congruent condition, whereas it was invariant when the stimuli were projected to the dominant hemisphere. These results demonstrate that each hemisphere independently works cognitive control.