a period of 10 ms. The corresponding train of impulses would contain gaps of 10 ms, 20 ms, 30 ms, 40 ms, etc. Such a group of gaps can only be generated by a 100 Hz tone. The set of gaps for a sound above the maximum neural firing rate would be similar except it would be missing some of the initial gaps, however it would still uniquely correspond to the frequency. The pitch of a pure tone could then be seen as corresponding to the difference between adjacent gaps. Another solution Modern research suggests that the perception of pitch depends on both the places and patterns of neuron firings. Place theory may be dominant for higher frequencies. However, it is also suggested that place theory may be dominant for low, resolved frequency harmonics, and that temporal theory may be dominant for high, unresolved frequency harmonics. Experiments to distinguish rate and place effects on pitch perception Experiments to distinguish between place theory and rate theory using subjects with normal hearing are difficult to devise, because of the strong correlation between rate and place: large vibrations at a low rate are produced at the apical end of the basilar membrane while large vibrations at a high rate are produced at the basal end. The two stimulus parameters can, however, be controlled independently using cochlear implants: pulses with a range of rates can be applied via different pairs of electrodes distributed along the membrane and subjects can be asked to rate a stimulus on a pitch scale. Experiments using implant recipients (who had previously had normal hearing) showed that, at stimulation rates below about 500 Hz, ratings on a pitch scale were proportional to the log of stimulation rate, but also decreased with distance from the round window. At higher rates, the effect of rate became weaker, but the effect of place was still strong. References Psychoacoustics Theories