  The perceived pitch of a complex harmonic sound changes if the partials of
the sound are frequency-shifted by a fixed amount. Simple mathematical rules
that the perceived pitch could be expected to follow ('first pitch-shift') are
violated in psychoacoustic experiments ('second pitchshift'). For this,
commonly cognitive cortical processes were held responsible. Here, we show that
human pitch perception can be reproduced from a minimal, purely biophysical,
model of the cochlea, by fully recovering the psychoacoustical pitch-shift data
of G.F. Smoorenburg (1970) and related physiological measurements from the cat
cochlear nucleus. For this to happen, the cochlear fluid plays a distinguished
role.
