Neural Volleying: Upper Frequency Limits detectable in the Auditory System

THE discovery that nerve fibres exhibit a refractory period which limits the number of impulses produced in a given time dealt a death blow to early ‘telephone’ theories, which postulated that information concerning the frequency of a tone (or a Fourier component of a complex sound) was faithfully reproduced by the rate of discharge of an individual fibre. Simple ‘telephone’ theories of neural encoding of pitch were replaced by ‘volley’ theories 1 in which stimulus frequency was encoded in the auditory nerve as a whole. According to ‘volley’ theory, different fibres firing at sub-multiples of the stimulating frequency produce a composite discharge that faithfully reproduces the frequency of the stimulating wave-form.