  We describe a geometric method to quantify wave patterns observed in the
nervous system, which are non-stationary and with a mixture of spiral, target,
plane and irregular waves. The method analyzes fluctuations of the energy
angular distribution in two-dimensional Fourier spectrum of wave patterns,
which reflects changes of the orientation distribution of wavefronts. We show
that the number of the genuine peaks in generalized phase spectrum is close to
the number of the coherent space-time clusters arising in wave patterns, and
propose to use the number as a complexity measure.
