Response modulation of auditory-nerve fibers by AM stimuli: effects of average intensity

Auditory-nerve responses were obtained for characteristic frequency tones which were amplitude modulated by sinusoids. Response modulation (RM) was determined from folded histograms which were synchronized to the modulating wave form. As the average intensity increased from threshold, RM increased to a maximum and then decreased, and the shape of the RM function resembled that described previously for incremental responses. However, unlike the latter, the RM function could not be predicted directly from the steady-state rate-intensity function. In general, the maximum RM occurred at a higher intensity than predicted, and RM occurred over a wider range of average intensities than predicted. The results are interpreted as reflecting a dynamic response characteristic with an operating range that exceeds that determined from the steady-state rate-intensity function.