PHYSIOLOGICAL OBSERVATIONS OF AUDITORY MASKING: II. EFFECT OF MASKING INTENSITY

Abstract

Click action potentials were recorded from round window and auditory nerve of cats. Action potential depression produced by pure tone masking and recovery from this depression were studied. It was found that: 1) Increasing masking intensity depresses masked A. P. [action potential] amplitude but has little effect on recovery rate. 2) With increasing masking intensity, the depressing effect of masking duration increases. 3) Plots of "amount" of masking duration effect versus masking intensity bear a striking resemblance to the cochlear microphonic input-output curve. The depressing effect of masking duration may, therefore, be related to microphonic generating end organ activity. 4) As masking intensity is increased through 50-60 db, there is a sharp increase in post-masking depression and in "amount" of masking duration effect. Also, per- stimulatory A. P. amplitude reaches a minimum at this intensity level. The intensity area around 50-60 db may, therefore, represent a "transition zone" produced either by two different masking mechanisms or by a single mechanism which becomes non-linear. Possible correlations between these observations and psycho-physical observations were discussed.