Psychophysical and physiological forward masking studies: probe duration and rise-time effects.

To determine if the amount of forward masking observed in single auditory-nerve fibers of the chinchilla was sufficient to account for the amount of masking observed behaviorally in humans, thresholds for the detection of several types of probe signals following a forward masker were measured in both behavioral and physiological experiments. It is necessary to use the same probe stimulus characteristics in both behavioral and physiological experiments to make valid comparisons between the two measures of forward masking. Experiment 1 was behavioral and used human listeners. Two types of probe signals were used, differing in overall duration and rise/fall times. The two probes yielded different growth of masking functions. These results further demonstrate that forward masking characteristics in behavioral experiments are critically dependent upon the parameters of the probe signal used. Experiment 2 was physiological and used chinchillas. The amount of masking for high-level maskers using the same two probe types in a physiological "forced-choice" experiment are presented. In contrast with the behavioral results, there was little or no difference in the amounts of masking observed for the two probes. In addition, the amounts of masking observed in some auditory-nerve fibers were considerably smaller than those observed behaviorally. These experiments further demonstrate that the amount of forward masking observed in single auditory-nerve fibers is inconsistent with that observed behaviorally.