[Visual field differences in a letter classification task in unilateral and bilateral presentation conditions].

Abstract

Kimura's "access model" (1966) of functional difference between the two cerebral hemispheres was examined in a letter classification task. Subjects were required to judge whether or not two Japanese Kana letters in different forms, simultaneously or successively presented, had the same phonemes. Letter stimuli were tachistoscopically projected unilaterally in either right visual field (UR) or left visual field (UL), or bilaterally one in each visual field (B). In successive condition, three interstimulus-interval (ISI) conditions were provided, and bilateral pairs were divided into BL and BR conditions according to the visual field of the first letter. RTs for UR were shorter than UL both in simultaneous and successive conditions. Bilateral pairs in simultaneous condition showed shorter RTs than UL. In successive condition, both BL and BR showed longer RTs than UR in all ISI conditions. The fact that RTs for BL did not approach to UR suggested the necessity of some additional assumptions to Kimura's access model. Reservation of the processing of first stimuli was discussed as one of the possible interpretations for the present results.