Behavioral Models Loudness, Hyperacusis, and Sound Avoidance

Loudness is the subjective perception of an acoustic stimulus that is most closely correlated with sound intensity. The dynamic range of loudness perception spans more than 120 dB, but how the auditory system is able to encode this information remains largely a mystery. Hearing loss and other medical conditions can disrupt intensity coding, often leading to loudness recruitment or in some cases hyperacusis, a sometimes debilitating condition in which moderate intensity sounds are perceived as intolerably loud, which evoke fear or instill sound avoidance. Insights into the neural mechanisms that give rise to normal or aberrant loudness perception can be aided by the development of animal models that can “tell the auditory physiologist” just how loud, annoying, or aversive a sound is. These behavioral measures of loudness can then be correlated with various electrophysiological or brain imaging metrics to the acoustic properties of the sound. In this chapter, we describe an operant behavioral technique for measuring reaction time-intensity functions that has proved to be highly effective in assessing the normal growth of loudness and two abnormal forms of loudness growth, recruitment, and hyperacusis. We also describe another behavioral technique to test for sound avoidance that takes advantage of a rodent’s innate aversion to brightly illuminated open spaces. Novel methods for inducing loudness recruitment, hyperacusis, and sound aversion are also described.