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 Ultrasonic Hearing in Cats and Other Terrestrial Mammals
M. Charlotte Kruger, Carina J. Sabourin, Alexandra T. Levine, and Stephen G. Lomber
   What is the first thought that comes to your mind when you read the word “ultrasound”? Most readers of Acous- tics Today might associate ultrasound with pregnancy or perhaps specialized detection technology on ships and airplanes. Some might also think about echolocat- ing animals. But what about terrestrial mammals? The ones that walk the earth among us? Although the use of ultrasound in echolocating mammals (e.g., bats, dol- phins, and whales) is well-known, our understanding of ultrasonic perception in nonflying terrestrial mammals is limited. Here we discuss the frequencies perceived and the biological importance of ultrasound for four land-dwelling mammals as well as what is currently known about the various areas in the brain that allow these animals to process ultrasound.
What We Know About Ultrasound
Ultrasonic sounds differ from “regular” sounds because their frequencies are too high for humans to detect. The upper hearing limit for humans is considered to be 20 kHz, and sounds with a frequency above 20 kHz are con- sidered ultrasonic. This is the agreed on definition, yet this distinction is subjectively based on the range that we, as humans, can hear and has no biological basis per se.
Despite not being able to hear ultrasound, humans often capitalize on its presence. The most familiar use would be clinical applications of ultrasound (e.g., Ketterling and Sil- verman, 2017). These include pregnancy scans, observation of pathology progression, and treatments such as the elimi- nation of kidney stones (Simon et al., 2017). In industrial environments, ultrasound is used as a nondestructive test to measure the thickness and quality of objects. Even though ultrasound can be useful for humans in a variety of settings, public exposure to airborne ultrasound is suggested to also cause adverse effects, such as nausea, dizziness, and failure to concentrate (Leighton et al., 2020). However, this is not the case for many animals. Long before humans started utilizing ultrasonic frequencies, animals have been using ultrasound for various beneficial reasons.
Signals containing ultrasound play a pivotal role in the lives of many species. Well-known uses include prey detection, finding mates, and communicating with con- specifics. High frequencies have very short wavelengths and therefore attenuate more rapidly when traveling through air compared with lower frequencies. Therefore, ultrasonic production and hearing create a private com- munication channel that subverts detection by prey as
  18 Acoustics Today • Spring 2021 | Volume 17, issue 1
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Figure 1. Frequencies for the hearing abilities of mice and rats (Mus musculus and Sigmodon hispidu, respectively; Masterson and Heffner, 1980), elephants (Elephas maximus; Heffner and Heffner, 1982), domestic cats (Felis catus; Heffner and Heffner, 1985), domestic dogs (Canis lupus familiaris; Heffner, 1983), and short-tailed fruit bats (Carollia perspicillata; Koay et al., 2003) at 60 dB sound pressure level (SPL) as well as familiar human applications of ultrasound (Jensen, 2007; Carovac et al., 2011; Harvey et al., 2014).

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