Using auditory reaction time to measure loudness growth in rats.

Previous studies have demonstrated that auditory reaction time (RT) is a reliable surrogate of loudness perception in humans. Reaction time-intensity (RT-I) functions faithfully recapitulate equal loudness contours in humans while being easier to obtain than equal loudness judgments, especially in animals. In humans, loudness estimation not only depends on sound intensity, but on a variety of other acoustic factors. Stimulus duration and bandwidth are known to impact loudness perception. In addition, the presence of background noise mimics loudness recruitment; loudness growth is rapid near threshold, but growth becomes normal at suprathreshold levels. Therefore, to evaluate whether RT-I functions are a reliable measure of loudness growth in rats, we obtained auditory RTs across a range of stimulus intensities, durations, and bandwidths, in both quiet and in the presence of background/masking noise. We found that reaction time patterns across stimulus parameters were repeatable over several months in rats and generally consistent with human loudness perceptual data. Our results provide important building blocks for future animal model studies of loudness perception and loudness perceptual disorders.