Hemispheric contribution for two different mechanisms; filtering and pigeonholing in Broadbent's term, in very early stages of visual information processing was investigated. In the filtering condition, subjects selected the target word which was written i n the same orthography as the standard word from among comparison stimuli which were written in different types of orthography. In the pigeonholing condition, subjects selected the target word which belonged to the same semantic category as that of the standard word from among the comparison stimuli which were written in the same type of orthography. In the filtering condition, no significant visual field difference was found. whereas a right visual field advantage was obtained in the pigeonholing condition. Possible mechanisms of differential hemispheric function in reading Japanese orthography were discussed.