Auditory-nerve fiber responses to tones in a noise masker

The phase-locked responses of single auditory-nerve fibers were measured for a continuous tonal stimulus presented in a noise background. The response amplitude, the primary Fourier component of the period histogram, was found to be dependent on the relative levels of the noise and tone. Different noise-to-tone level ration resulted in quite different response amplitude; changing overall level keeping noise-to-tone constant (constant dB difference) provided little change in response. With transient stimuli, phase-locked response to the tone at noise onset was consistently greater than to a tone presented during the steady-state noise exposure. When responses were normalized to the average rate, the difference between onset and steady-state responses were not clearcut.