Estimating loudness in animals

Abstract

Although auditory acuity experiments in animals are valuable, this is not how animals typically encounter real world sounds. It is also important to know how animals respond to stimuli at more ‘‘realistic’’ intensities. The perception of above-threshold level sounds has been well documented in humans, but is much less studied in animals, where acoustic communication is important for survival. In humans, equal loudness contours are used to show that loudness does not increase with intensity equally at all frequencies. Loudness is a subjective experience, however, and much harder to measure in animals. Reaction time is one untrained response that can be used to gauge how different or similar two stimuli are: high intensities yield short and low intensities yield long reaction times. Comparing reaction times across frequencies (equal latency contours) in birds and mammals show results that are similar to equal loudness contours obtained in humans. At low SPLs equal-latency contours closely parallel threshold curves, while at high SPLs the contours flatten and all frequencies are perceived as being about the same loudness. These results in animals should be considered when thinking about aspects of acoustic communication such as sound transmission, vocal signals designs, and sound-attenuating properties of the environment.