Sensory coding and the second spectra of natural signals

Natural auditory and visual stimuli are shown to demonstrate consistent non -Gaussian signatures: their phase-only second spectra behave approximately as the inverse square root of frequency, a property which is due to a predo minance of difference beats between Fourier components at slightly offset f requencies. These second spectra also demonstrate statistical scale invaria nce, a hypothesis which is tested explicitly by computing phase-only second spectra from bandpass-filtered data. The bandpass frequency selectivity ob served experimentally in sensory cells is shown to be qualitatively consist ent with a strategy of exploiting the non-Gaussian structure of natural sig nals.