Theories of Hearing

A significant part of the history of the hearing sciences is bound up with two "theories of hearing." These two theories are mainly about how the peripheral auditory system, the inner ear, codes for the frequency of sound, and how that frequency code accounts for the perception of pitch. While sound contains more information about its source than just frequency, frequency and the resulting pitch perception are the key attributes of sound for most aspects of perception.  Discussions about how the inner ear codes for frequency stared in the mid 19th century and continues in one form or another today.

The Place Theory suggests the each auditory nerve fiber is uniquely sensitive to a particular frequency of sound stimulation. Thus, the code for frequency is provided by which nerve fiber is firing. This is a like a telephone switch board. The switch board operator (the brain) can determine what phone is ringing (the frequency of the input) by which light on the switch board that lights up (nerve fiber firing). That is, the lights on the switchboard code for which phone is actually ringing. George von Bekesy is often credited with espousing the place theory of hearing.

The other theory is the "Temporal Theory." This theory suggests that the temporal pattern of neural discharges codes for frequency. For a periodic signal the nerve discharges in synchrony with the stimulus's periodicity, and thus the reciprocal of that neural periodicity provides an estimate of frequency. Glen Wever is often associated with the temporal theories, probably because of his suggestion of the "volley principal." The volley principal suggested a way in which the nervous system could provide a temporal code for high-frequency sounds, where the refractory properties of single auditory nerve fibers prevent them for coding for the periodicities of high frequencies. The volley principal suggests that if one fiber fired to every other periodic stimulus fluctuation, and another fiber the every third fluctuation, and so on, then the sum of the activity of all of the participating fibers could capture the actual periodicity of a high-frequency sound. That is, no one nerve fiber can capture the periodicity of a high-frequency sound, but the volley of neural activity from many different nerve fibers might. 

Today most hearing scientists appreciate that both the Place and the Temporal Theories play a crucial role in coding for sound. The theories are still debated at a more detailed level, especially in regard to neural mechanisms of complex pitch perception.