Hemispheric asymmetry in stimulus size evaluation.

In the present study a possible hemispheric asymmetry in size evaluation was tested. Subjects were presented with geometrical Vanderplas type figures of various sizes and shapes. The stimuli were exposed in pairs, for 100 ms, one after another. The subject's task was to decide (by pressing one of three buttons) whether the second stimulus was the same as, smaller or bigger than the first one. The first stimulus in each pair was exposed unilaterally (randomly in the left or right visual field), and the second one in the centre of the screen. Three different interstimulus intervals (ISI) were used: 50 ms, 500 ms, and 2,000 ms. The results showed shorter reaction times for left visual field presentation than for right visual field presentation at the 50 ms and 500 ms interstimulus interval. No laterality effect occurred at the 2,000 ms ISI. The results indicate a right hemisphere predominance in stimulus size evaluation. Moreover, they suggest that hemispheric asymmetry is not a stable feature of the brain but is a dynamic process that may change in the course of information processing.