Comparison of hemispheric asymmetry in global and local information processing and interference in divided and...

To elucidate hemispheric asymmetry in the neurophysiologic mechanisms of global and local information processing, we investigate high-density event-related potentials (ERPs) during divided and selective attention tasks based on detection of hierarchical letters whose spatial frequency is controlled. Twelve healthy male subjects performed divided and selective attention tasks based on the detection of hierarchical letters. Spatial frequencies of hierarchical letters were controlled by high- and low-pass spatial filters. ERP modulations corresponding to the target level (global versus local) effect and the interference effect caused by similarity (similar versus dissimilar letters) were explored. In both tasks, the global and local target effects were associated with late negative modulation (300 ms) over the right and left hemispheres, respectively. The interference effect was associated with negative modulation over the contralateral hemisphere. The latency of the interference effect was greater than that of the target level effect. Early modulations (150 ms) of the target level effect showed hemispheric asymmetry during selective but not divided attention tasks. Global and local information is processed within different hemispheres while interference between global and local information arises in the contralateral hemisphere asymmetrically.