Uniform degradation of auditory acuity in subjects with normal hearing leads to unequal precedence effects.

Objective: The aim of this study was to investigate whether a controlled unilateral reduction in auditory acuity at the higher audiometric frequencies would have an effect on the variability in responses obtained on a task designed to measure the precedence effect. Design: The experiment was conducted with participants located in a large sound proof, anechoic room, and psychophysical tests were conducted with long-duration noise burst stimuli. Reduction in auditory acuity was created by inserting a specially designed earplug in the ear of participants with normal hearing. The earplugs produced a highly reliable increase in the thresholds for detecting high-frequency sounds in the blocked ear with the largest effect at the highest frequencies (4 and 8 kHz). Across-participant variability in tone-detection threshold was less than ±5 dB. The measurement of lag-burst thresholds with and without the insertion of earplugs was used to characterize the precedence effect. The lag-burst threshold was defined as the shortest lag-burst delay that yielded a perception of two different noise bursts. Results: Although performance was stable across participants in the condition without the earplug, a substantial increase in variability in the lag-burst thresholds was found in the earplug condition. Conclusions: These results indicate that a uniform unilateral degradation in auditory acuity leads to increased variability in performance on tasks measuring fusion in the precedence effect. The outcome suggests that variable perception of the precedence effect by individuals with clinically diagnosed hearing loss might be due to factors other than a reduction in auditory acuity per se.