Evoked-response tone-on-tone masking in the chinchilla: effect of masker frequency

Tone-on-tone masking patterns were measured at 0.5, 1, and 4 kHz using the auditory-evoked response from the inferior colliculus of the chinchilla. Masking profiles obtained with a masking level of 30 dB SPL were relatively symmetrical; however, as masker level increased, masking spread toward the high frequencies, particularly with the 0.5-kHz masker. For masker frequencies of 1 and 4 kHz, a low-threshold notch was observed in the masking profile 2/3 of an octave above the frequency of the masker. The low-threshold notch may represent a response to the distortion tone 2F1-F2. The notch was absent in the 0.5-kHz masking profile. The masking profiles obtained with the evoked response are somewhat wider, but otherwise qualitatively similar to those measured psychophysically in humans. Thus, the evoked-response procedure may provide a convenient way of evaluating the spread of masking and the presence of distortion tones in difficult-to-test subjects.