  Several theories of early sensory processing suggest that it whitens sensory
stimuli. Here, we test three key predictions of the whitening theory using
recordings from 152 ganglion cells in salamander retina responding to natural
movies. We confirm the previous finding that firing rates of ganglion cells are
less correlated compared to natural scenes, although significant correlations
remain. We show that while the power spectrum of ganglion cells decays less
steeply than that of natural scenes, it is not completely flattened. Finally,
we find evidence that only the top principal components of the visual stimulus
are transmitted.
