This Fish Is The Master Of The Poignant Pause

IRA FLATOW: This is Science Friday. I’m Ira Flatow. A bit later in the hour, we’ll talk about what happens when the quest for knowledge takes scientists a bit too far, from ancient Egypt to Thomas Edison. But first, when you’re listening to a well practiced speaker, maybe during a lecture or a political event, or even your favorite public radio show, you might notice that they’ll take advantage of pauses in a sentence.

This type of nuance in communication may seem distinctly human, but it turns out we’re not the only species that takes advantage of pauses in communication to make a point. Joining me now to tell us a little more about this is sci-fi producer Kathleen Davis. Hi Kathleen.

KATHLEEN DAVIS: Well, hello there.

IRA FLATOW: Oh, good pause in there. Tell me a little bit more about this story you’ve brought us.

KATHLEEN DAVIS: So we know that lots of different types of creatures communicate with each other in different ways, but electric fish do something a little bit different. Are you familiar with electric fish?

IRA FLATOW: Just a little bit. Are we talking here about electric eels?

KATHLEEN DAVIS: So we’re talking specifically about electric fish, so more of your traditional fish. But these fish discharge electric pulses pretty much constantly. And so these pulses tell other fish basic identifying information. And the thing is, when they want to alert other fish to something of high importance, they pause.

IRA FLATOW: They pause, huh.

KATHLEEN DAVIS: Yeah. So this study really piqued my interest, as you can tell. So I decided to go to the expert. Dr. Bruce Carlson is a professor of biology at Washington University in St. Louis, and he has been studying electric fish for decades.

DR. BRUCE CARLSON: Yeah, Yeah. I’ve been studying these fish for over 20 years now. And what has originally captivated me and what still really intrigues me about this fish is the fact that they possess this entire sensory system. This entire world of communication that is totally foreign to us, that we have no direct access to ourselves. We cannot directly perceive electricity in the way these fish can. And it’s fascinating to me to think that there is a sensory system out there and a mode of communication that we just can’t access.

KATHLEEN DAVIS: Now the electric fish that you studied most recently is known as the “baby black whale,” is that right?

DR. BRUCE CARLSON: Yeah that’s it’s common name.

KATHLEEN DAVIS: OK great. And listeners can go on our website to see photos of this fish at sicencefriday.com/electricfish. But give us your best physical description of this fish for people who are just listening.

DR. BRUCE CARLSON: Well I think it’s common name is a pretty good descriptor, the baby black whale. It has the basic body shape of what you would expect from a whale, kind of like a sperm whale I would say, but it’s much, much smaller. And it varies from individual to individual but they tend to vary from a coppery color to a dark chocolate color.

KATHLEEN DAVIS: And you said that they’re much smaller than whales. How small are we talking about?

DR. BRUCE CARLSON: We’re talking in the range of a few inches to maybe 10 inches or so.

KATHLEEN DAVIS: So this is a fish that uses electrical pulses. So at a baseline level, how often do they discharge these pulses.

DR. BRUCE CARLSON: For the most part they’re doing it constantly.

KATHLEEN DAVIS: Wow.

DR. BRUCE CARLSON: If you go to one of these bodies of fresh water in Africa where these fish are found and you drop an electrode in the water, and then you monitor the voltage on a computer or oscilloscope or you listen to it on an audio amplifier, you will hear clicks and pops all over the place. These fish are just constantly ticking along.

KATHLEEN DAVIS: And we actually have a clip of one of these instances of you dropping an electrode in some water. Let’s listen to that.

[ELECTRIC POPPING]

KATHLEEN DAVIS: Tell me what is going on in that audio clip.

DR. BRUCE CARLSON: So what you’re hearing there is multiple fish in the vicinity of the electrode that are all discharging their electric organ. So if you were just to listen to one isolated fish in an aquarium, you would hear something like pop pop pop, pop pop pop pop pop pop pop pop pop.

Now you can imagine, you take five of those fish and put them into that same aquarium, it’s suddenly going to get much more hectic. All their pops are going to be going at the same time and it’s going to be a din of electricity. Well you can imagine if you go into the wild in a spot where these fish are found in abundance, it’s going to sound like a frying pan.

KATHLEEN DAVIS: OK interesting. So if you’re looking at the baseline pulses for two fish, are those baseline pulses going to be the same or are they going to be unique depending on the fish?

DR. BRUCE CARLSON: So the actual pulses themselves are unique for each fish.

KATHLEEN DAVIS: OK.

DR. BRUCE CARLSON: So if you look at the electrical waveform of these pulses of electricity, which is it’s like if you were to look at an EKG trace of your heartbeat. That’s a plot of voltage over time. And every time that your heart beats, there’s a characteristic waveform and it looks exactly the same from heartbeat the heartbeat of a heartbeat. Well it’s like that for each fish.

Every time a given fish discharges its electric organ, that electrical waveform looks the same from pulse to pulse to pulse. But it’s slightly different in other fish. And it’s even more different between different sexes of the same species of fish, and it’s even more different between different species of these fish. So that pulse, the electrical waveform of that pulse, it carries identifying information about species, sex, reproductive status, dominance status, and possibly even individual identity.

KATHLEEN DAVIS: So if I’m a fish, an electric fish, and you are an electric fish, we would both have our baseline pulses but they would be slightly different. Is that right?

DR. BRUCE CARLSON: Exactly.

KATHLEEN DAVIS: So now let’s talk about your recent research that showed that pauses play a role in communication between these fish. Tell me what you found in this study.

DR. BRUCE CARLSON: Well what we found is that recording from sensory neurons in these fish that respond to the electric communication signals of other fish, what we found is that when you repeatedly stimulate those neurons with stimuli that mimic the communication signals of another fish, their responses get weaker and weaker over time. And what was required to reset their sensitivity back to the baseline was to insert a long pause in the stimulation.

And a pause of about one or two seconds or so was sufficient to allow these neurons to recover back to their baseline level of sensitivity. And the really interesting thing we found is that this is also reflected in the fish’s behavior. And even more interesting in this is that communicating fish, they seem to be exploiting this phenomenon in the brains of fish that are listening to them.

So when this fish are housed together and actively communicating with each other, they’re more likely to generate pauses during communication. And they’re also more likely to produce especially informative communication signals right after a pause. And so what this suggests is that when two fish are communicating with each other, when one fish wants to have an especially strong impact on the other fish, it takes a brief pause, and then it hits it with a especially important communication signal.

KATHLEEN DAVIS: OK, so while as people we may pause to make a point while we speak, it sounds like these fish are kind of doing the same thing. It’s that break in the equilibrium gets the attention of other fish, is that right?

DR. BRUCE CARLSON: Yeah, it’s very similar. So we know some of the most effective public speakers out there are well known to make effective use of pauses during their public speaking. But we also know that this is something that we do subconsciously just in our normal everyday language interaction with each other.

We tend to insert pauses into our ongoing speech, and we tend to insert them right before words that have especially high information content or that might be surprising based on the context. And it seems that these fish are doing something very similar.

And this mechanism operating in the brain of receivers, it needs this reset to recover its baseline level of sensitivity, this exact same mechanism might be operating in humans and other animals as well. And that might explain why it is that we use these pauses in our communication system to emphasize the signals that come after the pause.

KATHLEEN DAVIS: Now do you think that they are doing this consciously?

DR. BRUCE CARLSON: There’s no reason to assume that they’re doing this consciously. And we don’t need to assume this because we know we do this unconsciously. We do this automatically in our everyday conversational speech. And so there’s no reason to think that a fish isn’t doing likewise, that it’s just doing what would just comes naturally to it in communicating information.

KATHLEEN DAVIS: Now I’m going to play a clip here of electric fish pulses, and you’re going to be able to tell that there is a difference throughout in terms of the speed and in between the different pulses. So let’s listen to that.

[ELECTRIC POPPING]

KATHLEEN DAVIS: Now can you tell what is possibly being communicated by those pulses?

DR. BRUCE CARLSON: Yeah, so that was a recording of a single fish isolated in an aquarium and so you could nicely hear the distinct pops. And we don’t have a translator. We can’t translate in real time exactly what’s being said. But what we do know is through lots of behavioral studies by my lab and many other labs, we’ve been able to relate the production of certain kinds of patterns to different behavioral contexts.

And we’ve been able to playback some of these patterns to fish to see how they respond behaviorally. And in doing that we’ve been able to discover that some of these signals, they seem to communicate information such as, this is my territory, back off. Or, I’m aggressive, I’m going to attack. Or, I submit, you win. Or, I’m reproductively active and I’m looking for a mate.

KATHLEEN DAVIS: Now as somebody who has studied this type of fish for so long, I would imagine that this is a pretty exciting discovery. But what does it tell you about what we still don’t know about communication in the animal kingdom at large.

DR. BRUCE CARLSON: Well, I think what it tells us is a lot of things that we might take for granted as being uniquely human, especially when it comes to human language, which is certainly special compared to other animal communication systems, that it may not be special in any kind of binary way in which it’s a quantum leap from animal communication systems to human language. Instead, it may be an amalgamation of various features that are found in a variety of animal communication systems that are brought together in a unique way.

So this idea of pauses in communication, these have been described in many different animals, not just humans and not just our fish, but many species of animals. And I think the interesting thing that we discovered here is that that may have evolved across animal communication systems because it’s an effective way for senders to have an impact on their recipients. It’s an effective way to transmit this information. And by studying these fish we were able to discover a pretty fundamental and basic neural mechanism that might be responsible for this.

KATHLEEN DAVIS: Well this is fascinating stuff and unfortunately we are out of time. But in the style of an electric fish I would like to thank you for joining me today.

DR. BRUCE CARLSON: Well, thank you for having me.

KATHLEEN DAVIS: Dr. Bruce Carlson is a professor of biology at Washington University in St. Louis.

IRA FLATOW: And thank you producer Kathleen Davis with that pause that refreshes.

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