Functional-imaging studies of the brain have revealed another tantalizing clue: During the aura phase, a wave of electrical activity sweeps over the outer, furrowed layer of the brain known as the cortex, at a pace of 2 to 3 millimeters per minute.

WSJ: Stopping a Migraine Before It Starts

They discovered that by shifting the "phase" of light so that the peaks of one wave line up with the valleys of an adjacent one, the two cancel each other, creating "shadows" between waves that are smaller than the waves themselves(see diagram, p. 141).

FORBES: Trick Of The Light

They discovered that, by shifting the "phase" of light so that the peaks of one wave line up with the valleys of an adjacent wave, the two waves cancel each other out, creating "shadows" between waves that are smaller than the waves themselves(see chart).

FORBES: Trick of the Light