Sex difference in hemisphere specialization was examined using the Salthouse-type tasks where both verbal and spatial codes are equally involved and available. In Experiment ~ (N = 20), female and male students were given a low-demand task in which stimuli contained 3 digits in 6 vertically arranged boxes. These stimuli were presented in either the left or the right visual field tachistoscopically. Females were better in two response indices (correct identification of both numbers and their locations, and identification of numbers). Visual field difference was not shown in either group of subjects. In Experiment 2, subjects (N=20) were given a high-demand task using stimuli containing 4 digits in 16 boxes. Females were better in correct identification of both numbers and their locations, and in identification of numbers, whereas no difference was shown in the identification of locations. Males showed a tendency towards a right visual field advantage; however, females showed no visual field difference. Using 20 subjects, the findings of Experiment 2 were replicated in Experiment 3 where Kana letters were used instead of numbers. Based upon these findings, hemisphere function of sex difference and the validity of previously proposed laterality models to explain sex difference were examined.

Key words: sex difference, hemisphere specialization, cognitive competitive task,task demand