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FEATURED ARTICLE
Human Hearing in the Underwater Environment
Brandon M. Casper and Matthew A. Babina
Hearing is a key sense that informs us about our environ- ment. The cues we obtain from sounds grab our attention, allow us to communicate, and warn us of danger. Human hearing has evolved to detect sounds in air. As a result, anyone who has tried snorkeling or Scuba diving or have put their head underwater in a bathtub has noticed that the world sounds very different. With ears underwater, sounds seem quieter, as though the listener has cotton stuffed in their ears. Moreover, in air, when one hears a sound, one can usually tell if it is coming from the left or right and, to a lesser degree, if it is from the front or back. Underwater, although a diver can hear a boat’s engine, identifying where the sound is coming from is challeng- ing. This is because early terrestrial vertebrates evolved to hear well in air, and these adaptations are not the same as those needed for the underwater hearing abilities pos- sessed by aquatic ancestors.
It makes evolutionary sense that human in-air hearing is better than their underwater hearing. Nevertheless, human underwater hearing may not be quite as bad as you think. The goal of this article is to introduce the field of human underwater hearing and to touch on several aspects of the topic that investigators have explored over the last century. It includes discussions of the mechanism of hearing underwater, underwater hearing thresholds, sound localization, and concerns about noise exposure and potential hearing damage. This article presents a broad overview of peer-reviewed literature and govern- ment technical reports.
Of Minnows and Men
Stetter (1929), a well-known German investigator of fish hearing, published a famous image of a research sub- ject submerged in a clear-sided tank (Figure 1). Stetter’s experiment compared the underwater hearing ability of humans with that of the common minnow (Phoxi- nus laevis L.) to a 662-Hz tone produced by a whistle.
To adjust the level of the signal, another experimenter walked up and down a hall outside of the room blow- ing the whistle. The subject would move their finger if they could hear the sound. Details on the minnow testing were not as clear in the paper, but the conclusion reached by the investigators was that the minnow’s hearing was much more sensitive than the human’s. This is possibly the first article on human underwater hearing.
How Do We Hear Underwater?
From this early study, it was established that minnows and many other fishes have more sensitive underwa- ter hearing than humans. Why is this? Keep in mind that vertebrate hearing evolved in the earliest fishes to function in water (Fay and Popper, 2000). Once early vertebrates came onto land, they could not hear unless
https://doi.org/10.1121/AT.2022.18.1.23
Volume 18, issue 1 | Spring 2022 • Acoustics Today 23
Figure 1. Classic image depicting possibly the first experiment in human underwater hearing. While Stetter is keeping the subject submerged (right), another scientist in a different room is blowing a whistle while moving closer and further from the subject. Karl Von Frisch (left), later winning the Nobel Prize, is observing the subject’s responses. From Stetter (1929), used with permission.