ASA 124th Meeting New Orleans 1992 October

4pPPa19. On the nature of nonmonotonic notches in input/output functions of 2f[sub 1]--f[sub 2] acoustic distortion products.

Dept. of Otolaryngol. and Commun. Sci., Med. Univ. of South Carolina, 171 Ashley Ave., Charleston, SC 29425-2242

To better understand the nature of nonmonotonic notches in input/output (I/O) functions of 2f[sub 1]--f[sub 2] acoustic distortion products (ADP), I/O functions were examined in 10 young, normal-hearing human subjects in conjunction with measurements of the ADP fine frequency structure [Gaskill and Brown, J. Acoust. Soc. Am. 88, 821--839 (1990)]. Primary frequencies were incremented in 1/32-oct. steps, the f2/f1 ratio was 1.2, and the primary levels were equal. ADP fine structure was measured over a 1/6 to 1/3 octave surrounding either 2000 or 4000 Hz with primary levels between 45 to 65 dB SPL in 2.5-dB steps. As primary level increased, a downward frequency shift of the peaks and valleys of the ADP fine structure was observed. This shift is responsible for the nonmonotonic notch and the wide variety of shapes of the I/O functions. As a result, even small changes in the frequency or level ratio of the primaries can drastically alter the shape of the I/O function. [Work supported by NIH-NIDCD P50-DC00422.]