Noise masking of tone responses and critical ratios in single units of the mouse cochlear nerve and cochlear nucleus.

Responses of single units in the cochlear nerve and cochlear nucleus to tone bursts in a background of continuous white broadband noise were recorded. Tone and noise intensities ranged from threshold to saturation levels. Masking of the tone response by the noise was demonstrated by comparing peristimulus-time histograms and spike rates recorded during the tone and between tone presentations. The response of a unit to masking was found to be predictable based upon the difference in its rate of response to the tone and to the noise when the tone was masked. Several nonlinearities of the masking process are described. The most prominent one is an increase in the difference between tone and noise levels at the threshold of masking with increasing tone levels, i.e. neural critical ratios increase with increasing tone level. On the average, the frequency dependence of single unit effective bandwidths and of critical ratio bandwidths is similar to that of mean behavioral critical ratio bands.