  In the theory of resonant mode coupling, the parent and child modes are
directly related in frequency and phase. The oscillations present in the fast
rotating Delta Scuti star KIC 8054146 allow us to test the most general and
generic aspects of such a theory. The only direct way to separate the parent
and coupled (child) modes is to examine the correlations in amplitude
variability between the different frequencies. For the dominant family of
related frequencies, only a single mode and a triplet are the origins of nine
dominant frequency peaks ranging from 2.93 to 66.30 cycles per day (as well as
dozens of small-amplitude combination modes and a predicted and detected third
high-frequency triplet). The mode-coupling model correctly predicts the large
amplitude variations of the coupled modes as a product of the amplitudes of the
parent modes, while the phase changes are also correctly modeled. This differs
from the behavior of 'normal' combination frequencies in that the amplitudes
are three orders of magnitude larger and may exceed even the amplitudes of the
parent modes. We show that two dominant low frequencies at 5.86 and 2.93 cycles
per day in the gravity-mode region are not harmonics of each other, and their
properties follow those of the almost equidistant high-frequency triplet. We
note that the previously puzzling situation of finding two strong peaks in the
low-frequency region related by nearly a factor of two in frequency has been
seen in other Delta Scuti stars as well.
