Phase synchronization
Phase synchronization is the process by which two cyclic signals converge to not only a single common frequency, but also tend to oscillate with a common phase angle.
One example of phase synchronization can be seen in the behavior of Southeast Asian fireflies. At dusk, the flies begin to flash periodically with random phases and a gaussian distribution of native frequencies. As night falls, the flies, sensitive to one another's behavior, begin to synchronize their flashing. After some time all the fireflies within a given tree (or even larger area) will begin to flash simultaneously in a burst.
Thinking of the fireflies as biological oscillators, we can define the phase to be 0° during the flash and 180° exactly halfway until the next flash. Thus, when they begin to flash in unison, they synchronize in phase.
See Also:
- Sync by S. H. Strogatz (2002).