Ultrasonic Hearing in Cats

Did you know your cat is eavesdropping? Not on you (boring human), but on the ultrasonic sounds of its tiny prey! In this episode, we speak to Charlotte Kruger, the lead author of “Ultrasonic Hearing in Cats and Other Terrestrial Mammals,” about how our feline friends' ears allow them to hear things humans cannot.

Read the associated article: M. Charlotte Kruger, Carina J. Sabourin, Alexandra T. Levine, and Stephen G. Lomber. (2021) “Ultrasonic Hearing in Cats and Other Terrestrial Mammals.” Acoustics Today 17(1). https://doi.org/10.1121/AT.2021.17.1.18.

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Transcript

Kat Setzer (KS)

00:06

Welcome to Across Acoustics, the official podcast of the Acoustical Society of America’s Publications office. On this podcast, we will highlight research from our four publications, The Journal of the Acoustical Society of America, also known as JASA, JASA Express Letters, Proceedings of Meetings on Acoustics, also known as POMA, and Acoustics Today. I'm your host, Kat Setzer, Editorial Associate for the ASA.

Joining me today is Charlotte Kruger of McGill University. We will be discussing her article, “Ultrasonic Hearing in Cats and Other Terrestrial Mammals,” which appeared in the spring 2021 issue of Acoustics Today. Thanks for taking the time to speak with us today, Charlotte, how are you?

Charlotte Kruger (CK)

00:53

I'm doing well. Yes, thank you for having me on your podcast.

KS

00:56

First, tell us a bit about your research background. How'd you get into studying cat hearing?

CK

01:02

So I did my undergraduate degree in biology with a focus on animal physiology, because I've always really liked animals, and I find it interesting to learn about the abilities that animals have that will help them thrive in different environments, or to learn about how animals use specialized physiological features that sometimes do unique to them as a species to survive. And during my time as an undergrad student, I had the opportunity to work in Dr. Stephen Lomber’s lab, where we use cats as a model for studying the auditory system and to study how the brain changes following acoustic experiences. This was a good fit for my interests, and I really enjoyed the type of questions that the lab’s research was addressing when it came to auditory physiology. And I then joined Dr. Lomber’s group as a graduate student, which is what I'm working on now, and I'm doing a project that's focusing on investigating the cat's ability to hear ultrasonic signals.

KS

02:02

That is so cool. So to give our listeners a bit of a background for today's discussion, what is ultrasound and how is it used by animals in general?

CK

02:10

So 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 kilohertz, and any sounds with frequencies above 20 kilohertz are considered ultrasonic. And this is the definition that we all agree on, but this distinction is subjectively based on the range that we as humans can hear. And it doesn't really have a biological basis. And, actually, long before humans started using ultrasonic frequencies, animals have been using ultrasound for various beneficial reasons. And some of these uses include detecting prey or finding mates, and just for communicating with other animals as well. So the ability to produce and to hear these ultrasonic sounds can therefore kind of create somewhat of a private communication channel.

KS

03:04

That makes sense. So how does cat's ultrasonic hearing compare to that of other animals? What do they actually do with these extended hearing ranges?

CK

03:15

Yeah, they have a very wide hearing range compared to other mammals. And even though the literature agrees that cats can hear ultrasonic frequencies, the full extent of their perception still remains unclear. And we also know that rodents, such as mice and rats, they are typical prey of cats, and rodents also emit ultrasonic vocalizations. And rodents use these ultrasonic sounds to communicate with other rodents for mainly social communicative interactions. For example, they have ultrasonic calls for finding and attracting mates, for displaying aggression and territoriality, and for alarm calls just to name a few. So we believe that cats use their ultrasonic hearing abilities to eavesdrop, if you will, and thereby localize their rodent prey. And then to take a page out of Dr. Lomber’s book when he gives talks or presentations, I'll say this is the part where we would now like to apologize to any audience members that might work with rodent models. So we are sorry that our model system preys on your model system.

KS

04:23

That's really funny. So how do you measure ultrasonic hearing in cats? What kind of experiments have you done?

CK

04:32

So the hearing abilities of animals in general are determined mainly using behavioral audiometry. So what this means is that animals are trained to listen for a sound cue, and they're then trained to make an observable response to indicate that they were able to hear that cue, and this is usually in return for a food reward. And so as the experimenters, we can then vary the properties of the sound that we present to the animals during the task, for example, we can change the loudness or the frequency, and then see if the animals respond to the sounds that we played to them. So in the cats, we train them to listen to the sound cue, and to indicate whether they heard it by walking towards the target. The sounds that we present to them vary in frequency, and we use specialized speakers to include sounds that have ultrasonic frequencies, because we are interested in investigating their ultrasonic hearing abilities.

KS

05:25

Okay, that all makes sense. So what have you found about how cats’ auditory pathways process ultrasound?

CK

05:33

So sound waves in general, including those that are ultrasonic, travel through the outer and the middle ear before being transferred to the cochlea in the inner ear. So the cochlea is a spiral, almost shell-like structure that looks all rolled up. So within the cochlea, there's a structure called the basilar membrane, which will vibrate when sound is presented to the ear. So let's imagine for a moment unrolling the cochlea and the basilar membrane, so it's now one long strip instead of a spiral. On the one end, which we'll call the apical end, we have a flexible and wide basilar membrane. On the other end, which is the basal end, the membrane is more narrow and stiff. So we have this gradient of membrane stiffness as we move from the one end to the other. Now, like I just mentioned, the basilar membrane vibrates when exposed to sound. And the difference in stiffness of the different parts of the membrane results in the apical end of the membrane vibrating maximally when sounds with low frequencies are presented to the ear, whereas the base will vibrate maximally when high frequency sounds are presented to the ear. And this type of gradient arrangement is called tonotopy. 

So then, when the basilar membrane vibrates, it in turn stimulates different parts of the cochlea, based on where the vibration is taking place, and ultimately results in electrical signals being sent up the auditory pathway, passing through the brainstem, until it's eventually being relayed by the nuclei in the thalamus to the final destination in the brain, which is called the auditory cortex. So this tonotopic arrangement that we see in the cochlea, it's also maintained in the structures of the ascending auditory pathway. So the electrical signals that originate in the different parts of the cochlea, travel up the auditory pathway in an organized manner, and is represented in a tonotopic arrangement in the auditory cortex as well.

KS

07:28

Can you tell us a bit more about the auditory cortex of cats’ brains?,

CK

07:33

Yes, the cat auditory cortex is quite similar to the human auditory cortex. So in addition to this tonotopic arrangement, it's also made up of many different areas that process many types of sounds. And, for example, there are regions that process the location of sound and regions that can distinguish different voices and other regions that categorize different types of sounds like is it a dog barking? Is it a car horn? Is it an Ed Sheeran song?

KS

07:59

What kind of insights can be gained from studying cat's hearing?

CK

08:03

So studying how animals hear in general helps us to better understand how these animals interact with their environments—so how they find food to survive, how they escaped danger, and how they interact with other animals, whether it be from their own species or from different species. And studying the cat hearing also gives us insight into how their brains generally process different sensory signals, and more specifically, how the brain encodes signals that have different properties. So for example, sounds with varying frequencies. I also think that by studying these animals, it allows us to really appreciate the remarkable abilities when it comes to sensory systems.

KS

08:41

Yeah, I totally agree. So finally, if I figure out how to communicate ultrasonically, is my cat more likely to listen to me?

CK

08:51

Well, the sensory world of cats is very different from the world that we as humans perceive. But ultimately, I think if you were able to vocalize ultrasonically, your cat will still be a cat and probably not really care about what humans have to say.

KS

09:05

Oh, well. Well, thanks for taking the time to speak to us today. I'm sure all of the cat lovers listening to our show will be happy to learn more about their feline friends.

CK

09:15

It was a pleasure.

KS

09:19

Thank you for tuning into Across Acoustics. If you'd like to hear more interviews from our authors about their research, click subscribe and find us on your preferred podcast platform.