Normally, people are able to switch flexibly between the two hemispheric modes of cognition. The composer can use precise musical notation to plot out the separate instrumental lines of an orchestral score, then sit back and listen to how the whole thing sounds. (Miller, Lawrence, PhD. Inner Natures. Brain, Self & Personality. p 79-80. NY: Ballantine Books, 1990.)
The hemispheres alternate cycles of efficiency every 90-100 minutes (from high spatial-low verbal, to high verbal-low spatial). Learners switch from right- to left-brain dominant sixteen times throughout the day. Students need 5-10 minute breaks every 90 minutes. (Jensen, Eric. Brain-Based Learning (Revised). p 42-44. CA: The Brain Store, 2005.