  In the standard picture of structure formation, initially random-phase
fluctuations are amplified by non-linear gravitational instability to produce a
final distribution of mass which is highly non-Gaussian and has highly coupled
Fourier phases. Second-order statistics, such as the power spectrum, are blind
to this kind of phase association. We discuss the information contained in the
phases of cosmological density fluctuations and their possible use in
statistical analysis tools. In particular, we show how the bispectrum measures
a particular form of phase association called quadratic phase coupling, show
how to visualise phase association using colour models. These techniques offer
the prospect of more complete tests of initial non-Gaussianity than those
available at present.
