Physiological “release from masking”

Psychophysical “release from masking” [S. Buus, J. Acoust. Soc. Am. 78, 1958–1965 (1985)] is observed when the masking exerted by stimuli with equal power but different envelopes is compared. Depending on the masker-to-probe frequency ratio, thresholds for flat-envelope maskers are higher than those for corresponding fluctuating-envelope maskers. A similar phenomenon was previously reported for masked thresholds based on rate responses of chinchilla auditory-nerve fibers [J. B. Mott et al., Absts. A.R.O. 12 (1989)]. Those results were interpreted as suggesting that neural activity during periods of low masker energy was important for detection. The present study examined whether synchronized responses of auditory-nerve fibers also contribute to “release from masking.” Synchronized rates were measured in short-time windows, centered on periods of high and low energy in the maskers' envelopes. Synchronized rate at the probe frequency grew more rapidly as a function of level during low-energy windows than high-energy windows. Statistical thresholds based on synchronized behavior will also be reported. [Work supported by NINCDS NS23242.]