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The heuristic importance of dual-task paradigms is easily demonstrated in the field of hemispheric asymmetries. Dual-task paradigms have contributed to the evolution of static and dynamic models, particularly by taking into account contextual aspects as potential determinants of lateral effects. In this research area, the concept of priming refers to the processes by which an hemisphere is activated prior to the carrying out of a task. This priming effect can be forced by the execution of a secondary lateralized task. We developed a situation in which the main task was a divided-visual-field tachistoscopic matching test. According to a random-controlled situation, subjects were instructed to say whether the two stimuli were « the same » or « different » before, concurrently or after (with an inter-task interval of 1,5, 2,5 or 4 seconds) an activating task. For this latter task, the subjects were asked to beat a complex rhythm by hitting in a loop on a sensitive board. As expected, the results showed a significant increase in the number of correct responses in the activated hemisphere. Moreover, an optimum was found when the task was performed concurrently or with an interval of 1,5 second after the end of the priming task. The priming process seems to be a temporal function characterized by an immediate increase and by a later and progressive decrease in the resources of the hemisphere involved. These hemisphere- specific activation paradigms are mainly used to produce an inter-hemispheric imbalance in normal or pathological subjects. Through an inter-hemispheric imbalance it is possible to access details of hemispheric co-operation for information processing or to induce new cognitive capacities in a non-damaged hemisphere. Our results suggest the importance of optimizing these paradigms by taking into account the temporal evolution of the brain activation.
