Attention! Attention! Attention!
I have been reading an amazing book that reviews, summarizes, and evaluates the science of brain lateralization: The Master and His Emissary, by Iain McGilchrist. Briefly, this book demonstrates how the left and right hemispheres of the brain actually cooperate to present us the experience of embodied consciousness. The old idea that the hemispheres perform different functions has not survived the test of experiment. The hemispheres both participate in every function, but they do so in different ways. The right brain sees wholes, the left sees parts; the right tolerates ambiguity, the left does not.
Since reading the first half of this book, I have been seeing these principles at work everywhere. Looking into the refrigerator one night when I was tired, I saw that my visual field did not contain a carton of milk, pitcher of water, containers of (suspicious) leftovers, etc., but a unified field of colors without any borders. As soon as the identity of the desired snack became known, I saw every item in the refrigerator separate from the background, signalling a takeover by the left hemisphere, which specializes in identifying and manipulating objects.
So, the right hemisphere's mode of attention is generalized vigilance with a very relaxed grip on boundaries, whereas the left focuses on particulars. Both kinds of attention are needed. We get into difficulties when one kind (usually the left) is overemphasized, and reduces the scope of the other.
By the way, this does not mean I have suddenly bought into materialism; I think this division reflects something very fundamental in the nature of reality, of the Cosmos, and thus of Consciousness, which is still not local to, or generated by, the brain. Call it positive--negative, male--female, yang--yin, it's an archetypal principle more fundamental than the brain.
I had a particular epiphany recently when I applied this distinction to meditation. I trained in Zen for a number of years. You could say that Zen training, in the beginning at least, aims at getting past the conditioned reliance on the left-hemisphere mode of thought. As the student becomes more comfortable with a basic "distraction" practice like counting the breath, they may eventually graduate to shikantaza, which is usually explained as "just sitting." However, the word has an interesting etymology: it comes from the Chinese words that translate the Sanskrit terms "vipassana" and "shamatha." The former means, approximately, mindfulness and the latter tranquility. Shikantaza practice is ultimately the Middle Way between focus and relaxation, gaining the benefits of each without falling into the relentless noise of the monkey mind or the stupidity of sleep.
In practice, this feels a lot like resting in the vigilance of the right hemisphere, which is better than the left at promoting calm throughout one's consciousness. The only way we get to that point is by repeated practice.