Effects of high‐pass masking on the scalp‐recorded FFR in humans and cats

Abstract

Low frequency tone burst stimuli were used to elicit the scalp‐recorded frequency following response (FFR) in the presence of high‐pass maskers (with variable low frequency cutoffs) from normal hearing human subjects and anesthetized cats. Threshold shift and binaural loudness balance procedures, conducted with similar masking stimuli, were administered to compare psychophysically derived masking curves with the FFR curves. Among the results were the following: (1) At moderate to high probe‐tone levels, the amplitude of the FFR masked with a 2‐kHz cutoff ranged from a mean value of 75% for humans to a value of 55%–75% for cats. (2) At probe‐tone stimulus levels near FFR threshold, the amplitude of the FFR masked with cutoffs of 1.5, 1.8, and 2.0 kHz was equivalent to the amplitude of the unmasked FFR. (3) The FFR masking curves did not correspond with the psychophysically derived curves except at low probe‐tone stimulus levels. Although the area of stimulation (along the basilar membrane) for the FRR is broad, the most powerful input arises from the apical aspect of the cochlea (below 2 kHz). Except for lower stimulus levels, the responding area was apparently wider than the critical band around a low frequency signal. [Research supported by the Coleman fund and Hearing Research, Inc. San Francisco, CA.]