The cerebral balance of power: confrontation or cooperation?

Two visual search experiments were carried out using as stimuli large letters made of small identical letters presented in right, or left, or central visual fields. Considering the spatial frequency contents of the stimuli as the critical variable, Experiment 1 showed that a left-field superiority could be obtained whenever a decision had to be made on a large (low frequency) letter alone, and a right-field advantage emerged when a small (high frequency) letter had to be processed. Experiment 2 showed that the two levels of structure of the stimulus were not encoded at the same rate and that at very brief exposure, only the large letter could be accurately identified. This was accompanied by a left-field superiority, whether or not the stimulus contained the target. These results are interpreted as revealing a differential sensitivity of the hemispheres to the spatial frequency contents of a visual image, the right hemisphere being more adept at processing early-available low frequencies and the left hemisphere operating more efficiently on later-available low frequencies. From these and other experiments reviewed, it is suggested that (a) cerebral lateralization of cognitive functions results from differences in sensorimotor resolution capacities of the hemispheres; (b) both hemispheres can process verbal and visuospatial information, analytically and holistically; (c) respective hemispheric competence is a function of the level of sensorimotor resolution required for processing the information available.