  Two trains of light pulses at periods that are equally shifted from the
harmonics of a missing fundamental, are combined in a nonlinear crystal. As a
result of a noncollinear phase matched second order nonlinear generation, a new
train of pulses is obtained. When the temporal width of the input pulses is
large, the frequency of the resulting pulse train follows the observations from
classical experiments on the perception of virtual pitch by the brain. On the
other hand, when the width of the input pulses is small, the generated pulse
train exhibits much lower frequencies, analogous to those observed in the motor
neural system. Our experimental set up allows us to explore, systematically and
continuously, the transition between these two regimes, while at the same time
demonstrate that coincidence detection in quadratic nonlinear systems has
functionalities similar to those observed in the nervous system.
