Abstract:

Auditory-nerve fibers synchronize to the envelope of SAM stimuli over a wide range of modulation parameters. Synchronization is found at all characteristic frequencies and shows moderate gain differences between fibers of different spontaneous rate. Modulation transfer functions are uniformly low pass, with an upper frequency limit that systematically increases with characteristic frequency. As expected, envelope phase locking in bushy cells of the anteroventral cochlear nucleus is nervelike, but marked transformations occur in other cell classes. Phase-locking gain is very high in onset cells in posteroventral cochlear nucleus. High gains are also seen in the dorsal cochlear nucleus; however, small changes in stimulus parameters often result in large changes in gain and phase. In general, it is unclear whether high gains are functionally significant, or rather a mere reflection of the transient response properties of cells. There is evidence for the latter in one class of high-gain cell. Effects of modulation on average rate are small in the auditory nerve, but can be large in cochlear nucleus and, with binaural stimulation, in the olivary complex. The lateral superior olive and its bushy cell afferents provide an example of a circuit in which temporal envelope information is converted into average rate changes. [Work supported by NIDCD.]