This study examined the effects of information modalities of cognitive tasks on the EEG laterality. The EEGs were recorded from six scalp areas (P3, P4, W1, W2, O1 and O2) and analyzed the power spectra and intra-hemispheric coherence (P-W, P-O, W-O) for the alpha band. The subjects were 12 male students, and all of them were entirly right-handed. Tasks were two types of the verbal tasks, which were (1) memorizing a set of 9 Chinese words and (2) squaring a double figures, and two types of the spatial tasks, which were (1) imaging and memorizing an unfamiliar picture and (2) imaging a famous picture. The instructions and task stimulus were presented by two types of information modalities. One was visualy displayed on the TV monitor without audio-channel, and the other was presented by the audio monitor without display.
Task-related EEG asymmetries were observed in each task and in each modality condition. There were, however, regional differences in the EEG asymmetry among the scalp areas. When the information modality was the audio, the parietal-, Wernicke's area- and even occipital EEG power showed the significant task-related asymmetries. However, when the modality was the video, the significant asymmetry was observed only in the occipital area. These results suggest that the audio-information were processed on more wider hemispheric area than the video-information. Therefore, the audio-tasks may demand more cognitive striving than the visual tasks.
There was no effect of cognitive task and information modality on the alpha band coherence. From the analysis of the individual differences, however, it is plausible to think that there is the preference of information modality for the cognitive processing.