ASA 124th Meeting New Orleans 1992 October

3aPP9. Suppression and the dynamic range of hearing.

Christopher J. Plack

Neal F. Viemeister

Dept. of Psychol., Univ. of Minnesota, 75 E. River Rd., Minneapolis, MN 55455

The results from experiments that have examined intensity discrimination in the presence of notched noise indicate that spread of excitation is not necessary for the auditory system to maintain a large dynamic range. In these experiments, however, the notched noise and the pedestal were simultaneously present. It is possible, therefore, that the notched noise suppressed the pedestal, and increased the dynamic range by effectively reducing the stimulus level [A. R. Palmer and E. F. Evans, Hear. Res. 7, 305--323 (1982)]. In the experiment described here, spread of excitation was masked nonsimultaneously in order to avoid suppressive effects. The brief sinusoidal pedestal was presented in a 13-ms gap between two bursts of a masking complex. The masking complex consisted of two sinusoids at frequencies of 0.8f and 1.2f (where f was the pedestal frequency), each having a level 10 dB below the pedestal level, and a notched noise with a spectrum level 50 dB below the pedestal level. Detection thresholds were measured to ensure that the complex was effective in masking spread of excitation. Weber fractions were measured at two signal frequencies, 1 and 4 kHz, and at eight pedestal levels (40--110 dB SPL in 10-dB steps) at each frequency. The results indicate that, even at the highest pedestal level, the masking complex raised the Weber fraction only slightly. This suggests that the auditory system can maintain a large dynamic range in the absence of suppression and spread of excitation. [Work supported by NIDCD Grant No. DC00683.]