Suppression and the dynamic range of hearing.

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 those experiments 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 reducing the excitation 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 0.8fc and 1.2fc (where fc was the pedestal frequency), each having a level either the same as, or 10 dB below the pedestal level, and a notched noise with a spectrum level 40 dB below the level of the sinusoids. Detection thresholds were measured to ensure that the complex was effective in masking spread of excitation. Weber fractions were measured at two pedestal frequencies, 1 and 4 kHz, and at eight pedestal levels at each frequency, covering a range of 70 dB. The results indicate that, although the masking complex raised the Weber fraction by up to 10 dB in some conditions, performance was no worse at high levels than at medium or low levels. This suggests that the auditory system can maintain a large dynamic range in the absence of suppression and spread of excitation.