ABR measurements in a forward‐masking paradigm

Abstract

Growth of masking and tuning curves were measured in the cat, using a forward‐masking paradigm in conjunction with farfield recording techniques. Probe tones of 3‐ms duration (20 dB above ABR threshold) were presented subsequent to 99‐ms duration maskers. Masker frequency and level were varied parametrically. Masker and probe were separated by 10 ms and were repeated every 400 ms until 500 responses to the probe had been averaged. The amplitude of the largest component of the ABR (presumably wave V) was measured for each masking condition and then was normalized to the probe response amplitude in quiet. Previous AP data indicated that plots of the decrement in probe response as a function of masker level are similar to single‐unit rate‐level functions [Abbas and Gorga, J. Acoust. Soc. Am. 69, 492–499 (1981)]. The present ABR decrement functions were steepest for frequencies below probe frequency. This effect is similar to the frequency dependence observed for AP masking data. ABR tuning curves (threshold = 50% decrement) were similar in shape to AP tuning curves although they tended to be less sharply tuned. Still, these data indicate that farfield techniques can be used to estimate response growth and frequency resolution. [Supported by NIH Grants NS14880 and NS07147.]