The Effect of a Below-Threshold Continuous Tone on the Threshold of Subjects with Abnormal Adaptation

Six subjects with abnormal adaptation tracked their thresholds on a Békésy audiometer for a fixed frequency interrupted pure tone stimulus presented in conjunction with a continuous tone of the same frequency at levels 20, 10 and 5 dB below that of the interrupted tone. The presence of the continuous tone below the threshold for the interrupted tone produced abnormal adaptation in four of the subjects, and narrowing of the excursion width of the tracings in three of the subjects. Effects of the below-threshold continuous tone were found in subjects with cochlear lesions, as well as in subjects with retro-cochlear lesions. It is concluded that continuous stimulation does not have to be at threshold to produce abnormal adaptation in susceptible individuals.