  Time-reversal symmetry breaking is a key feature of nearly all natural
sounds, caused by the physics of sound production. While attention has been
paid to the response of the auditory system to "natural stimuli," very few
psychophysical tests have been performed. We conduct psychophysical
measurements of time-frequency acuity for both "natural" notes (sharp attack,
long decay) and time-reversed ones. Our results demonstrate significantly
greater precision, arising from enhanced temporal acuity, for such "natural"
sounds over both their time-reversed versions and theoretically optimal
gaussian pulses, without a corresponding decrease in frequency acuity. These
data rule out models of auditory processing that obey a modified "uncertainty
principle" between temporal and frequency acuity and suggest the existence of
statistical priors for naturalistic stimuli, in the form of sharp-attack,
long-decay notes. We are additionally able to calculate a minimal theoretical
bound on the order of the nonlinearity present in auditory processing. We find
that only matching pursuit, spectral derivatives, and reassigned spectrograms
are able to satisfy this criterion.
