137: Are Trees Real? (with Yngwie Nielsen and Morten Christiansen)

0:00Daniel, I have to ask you this. It looks like you're, I've noticed in these, it looks like you're outside, but you're not. I take it because it's dark. It should be dark where you are now. It is dark where I'm at. So here's what it really looks like. It looks like a pantry. Check it out. This is where the magic happens.

0:30Hello and welcome to Because Language, a show about linguistics, the science of language. I'm Daniel Midgley, and I'm here with Hedvig Kiergaard. Hi, Hedvig. Hi. This is going to be one of our shorter standalone episodes. We like to do these when we have a topic that we really like to dig into, and sometimes it's because it's a topic that's more current and breaking. Sometimes it's because it's more theoretically challenging, and I feel like this one is both. We found some research that we think is really exciting because of its implications for how we study language

1:01and how language works, but we needed some help. And so we have contacted the authors of this work. We'd like to welcome Yngwie Nielsen of Aarhus University. Hey, Yngwie. Hello. And Dr. Morten Kristiansen of Cornell University. Hi, Morten. Hi. I should mention I'm also at Aarhus University, by the way, part-time. I read the affiliations on your paper, and both of you are in three different places. How does that work? Do you have, like, a quantum state? Yeah, yeah.

1:32I do sort of switch back and forth in between. Rather, I'm there a few weeks a year, and then obviously we work remotely as well. Okay. But now you're being observed, so the waveform has collapsed, and you're both here with us. That's really cool. Okay. Morten, this is your third show with us, which means you're an honorary co-host, and you get to crash any episode you want. Do you want to tell us what kind of linguistics or what kind of language you're really into in your research or just for fun? Well, right now I'm actually working on a book

2:02on conversation, so I'm really into how language actually works in real life, in conversation, how we're actually using it in its sort of original medium, as it were, in face-to-face interaction, sort of almost like what we're doing right now. Of course, we're not actually physically face-to-face, but we're actually visually still, we can see each other and so on. So this is the kind of use of language that I'm really interested in. And it also bears on some of the things that we'll be talking about today, I think. Now, are you into this kind of thing because it gets us out of the abstraction

2:34and gets us into, like, brain stuff, like how we make decisions and how we perceive and is that what does it for you? No, not really in that direction. I'm more interested in understanding language as it originates in conversation. That is, what is it about our ability to use language in the here and now, in talking to each other like we're doing right now in real time? What does it mean for how we should think about the nature of language, the mental representation of language and the cognitive underpinnings of language?

3:04That's kind of what the book is all about. So it's kind of rethinking language from the viewpoint of conversation. That's a very usage-based perspective, a very functional perspective. So, like, what language is doing when we are using it in the... The medium that we're using it in have been using it for the longest amount of time. Text and these abstractions are relatively new things. Yeah, that is... Yeah, exactly.

3:35Okay. Yngwie, first-time guest. Welcome to the show. Tell us about your work and what's it about. Thanks. Well, that's a great question. It's something I'm currently pondering myself being in the middle of the PhD.

3:50Certainly, part of it is on the structure of language and this sort of remarkable ability that humans have to put together words in ways that are sometimes creative, sometimes new, but also oftentimes based largely on their own experience with the language.

4:09And, like, just taking a basic psychological perspective on that, it's a very remarkable ability. Of course, it's something that we get to practice a lot more than, say, riding a bike or whatever else kind of skill you have. It's something that you practice from very early on and that you get throughout your entire life. So, certainly, it's not surprising that we're able to do exciting and complex things. And, accordingly, the knowledge that you must obtain is also of a very complex and very interesting nature. And so, that's what I'm sort of trying to probe, I guess,

4:40is what is this knowledge exactly? And I think the fact that everyone uses language all the time is both a blessing and a curse when you're working on languages because it also means that various members of the general public also have a lot of opinions about how they think linguistics and languages work, whereas people don't have as many opinions about, like, how jet engines work because it's not something you do very often. At least, that's what I found. So, it's nice because you can often connect with people because you can say, oh, you know, have you thought about this?

5:11Because, basically, everyone has or uses language. But it can be a blessing and a curse. Now, this paper has been published in Nature Human Behavior. It's called Evidence for the Representation of Non-Hierarchical Structures in Language. Now, if that's going to make anybody in the audience bail, please don't because I think this is important stuff and we're going to make it easy and fun. But first, Morten and Yngwie, is it difficult for you to explain your work to a non-linguistic audience?

5:42Have you tried? And what secrets can you impart? Oh, do you want to start, Morten? Well, it is tricky. And this sort of paper, despite its importance, is a bit tricky. We did try writing a sort of a short, more accessible version of the paper that was also published as a research briefing in Nature Human Behavior. But yes, it is tricky on the one hand. So, explain why do people like trees?

6:13For example, what does it mean for what we actually do with language? And so on. But I think we can sort of unpack that, all four of us together here today, if we give it a try. Yeah, exactly. Because that's the first thing you've got to explain to a general audience is that linguists like to draw trees of words in a sentence, which doesn't come naturally to everyone. I've taught inter-to-linguistics and it takes a while for people to get the idea of hierarchical structure and then to present them

6:43with the idea that actually maybe we should critique that view. I think if you pitch it as like a lot of linguists think this and actually it could be this, that part can be intriguing in itself, I think. Okay, so we're starting to talk about trees, but before we get there, Yngwie, your insights so far into linguistics communication? Right. I think I'm also looking for the secret of how to make my work interesting to the, especially to my parents. I think a lot of people,

7:13when they hear that it's grammar adjacent, the connotations that that bears is the first challenge. And then the second challenge is that we all have so much experience with language and I think we take a lot for granted about how it's done and possibly also about like how complicated it is once you start digging into it a little bit. So I think that's, at least that's the approach that I've been trying to take is unpacking the complexity first and then moving on to why we believe

7:44the things we do. Okay. Well, the tree structure idea is certainly one of the more complex things that I've tried to get to my students. So maybe let's talk about that for a second. There are lots of different ways you can tree a sentence, but I guess one of the most common is you start with a letter S at the top and that means sentence and then it breaks down into two nodes. The first one could be an NP noun phrase and the second one could be a VP verb phrase and then you break it down

8:14and break it down and then at the end the leaves are words. But by showing that some groups of words are part of a subtree or maybe a treelit, I'll call them treelits. You can see the little treelits in the tree. I was going to say exactly that I tend to do it the opposite way. So start with the words in a sentence like this is a beautiful dog and then say, okay, are there any words in the sentence that you think are more closely related to each other than to other words

8:45in the sentence and then sort of do a grouping and then say, ah, this grouping is, you can understand it as hierarchical and then we can draw a tree so that brown is closer to dog than it is to this. That's usually the way I go about it. Most linguistics 101 classes introduces you to the basic ideas of trees and then linguists diversify into like lots of different ways of drawing those trees and movement in those trees and abstract theories. I want to ask why we like trees

9:15so much. Why do we love them? I love them. We use them a lot. I mean, who doesn't like trees, right? I mean, we are depending on trees for part of our oxygen, right? So along with other organisms. But I think one of the things that's interesting is that the focus on trees that there is in contemporary linguistics, it's actually a relatively new one. So the first person as far as I can work out to talk about trees that have like sentence notes,

9:46you start with that, you describe a sentence as a tree-like structure to sort of kind of characterize the hierarchical structure of it. That started with Wilhelm Wundz. He put that forward at the beginning of the 20th century as a kind of way of describing the mental structure of language. Now, that was picked up by the structuralist, of course, and then subsequently fell a bit out of favor with behaviorism, but then it came back very strongly

10:16with Chomsky and other afterwards. But prior to that, people didn't really think of sentences or language in terms of these hierarchical structures. There were some earlier sort of very sort of proto-hierarchal structures in the sort of the Middle Ages and the Renaissance, perhaps. But in general, it's actually a relatively new thing. And so I think that's important to keep in mind. And of course, there's other areas where we think of trees too. So for example, oftentimes we think of, say, evolution in terms

10:47of trees. You have these evolutionary trees. But it turns out we know now that maybe that's not actually the best sort of way of thinking about it. And then actually sort of as a little side note, one of the things that's really interesting is that Darwin kind of borrowed the notion of descent from linguistics from August Schleisler. So Schleisler in 1853 was the first person to indicate sort of relationship between languages. So this is not within a language, but between languages

11:17or how some languages are more closely related to others using a tree. And Darwin actually sort of was aware of that going on in linguistics and even referred to that in his notes and in some of his writings. So when he, three years later in 1859 in Origin of Species, he presented the notion of a tree as a way of indicating how species might be related to one another evolutionarily speaking. He was borrowing from linguistics at that time.

11:47Of course, now we know that actually that way of thinking about trees and evolution is actually not completely the right way because there's a lot of what's called horizontal gene transmission going on. So between species that are not related. So of course that happens a lot in bacteria, but it happens even in our ancestry as well. That's why, given that we are all of Northern European descent, we also, all of us have a certain amount of Neanderthal genes in our genome. And that's actually come from crossbreeding

12:19across species, which according to these strict trees shouldn't happen. So really what you get instead is these reticulated trees. And it turns out that I think also when it comes to actual language and the sentence, we might be thinking about the representation as a network rather than as these beautiful trees. So I think the reason why we like trees is it can actually be quite useful in terms of describing the structure and getting people to understand that yes, there are words that go together in certain ways in the way that Hedwig was talking about earlier,

12:50that they can be quite useful at a descriptive level. But it's a completely different matter to say that this is actually what's going on in the head as such. So I think we shouldn't throw the trees away. It's not, no, we're not suggesting that. And they could be quite useful in getting people to understand there are some interesting relationships between words and sentences and so on. But I think it's important that we might want to rethink whether tree-like structures is also what's in the head when we're using language like what we're doing right now.

13:20Yeah, I think that's really important to know why you're applying a technique. I have met people who like to draw trees or sentences who say, oh, like, I think this is an efficient computational way of explaining the structure I'm after. But when asked, oh, do you think humans do this in their heads, say, oh, I have no idea. I make no claims on that. And for me, as a more like functional user space person, I'm kind of like, well, in that case, I don't know if I care that much. Like, in that case, we're just like solving puzzles and maybe teaching computers how to

13:51emulate us or something like that. But we're not really explaining what humans are actually doing. As a small side note, at the Institute I work at, Max Planckens for Ocean Anthropology, there's a lot of research on Neanderthals. And I recently was sampled for my DNA and I'm going to find out how much Neanderthal I am. I'm very excited. Oh, we'll look forward to that. Yeah, I'll tell you my testersel. So if we're not looking at trees, if we're moving away from trees or treelets, I've always thought that, you know, we represent sentences

14:22as trees, but we hear the words sequentially, almost like they're beads on a string. They seem to come in chunks. So one thing I've gotten from the paper is we're kind of contrasting trees in which the words are constituents versus chunks, like pieces of text that are just simply next to each other without any claims on that hierarchical structure, like beads on a string. Am I getting that right from the paper? Well, it's a good question. So it's hard to get out of the tree

14:53like thinking, right? You need some kind of other frame of mind. And indeed, chunks is possibly one way, right? It's another way of saying linear or sequential structure, right? or serial structure. So yes, things that are next to each other. Though, I think by just saying next to each other, we might also be capturing some language phenomena that might not be in the head, right? So it's a little difficult to say exactly where we put this chunk term. Certainly, if you look through a corpus

15:23and you look through a text, you can find lots of things that are next to each other that are perhaps not necessarily part of the knowledge we have of a language, though certainly many of them are. Okay. So just to make this super clear, oh, go ahead, Heather. No, I was going to ask if we can maybe take an example sentence. I have a sample. So, for example, here is the red book that my father bought. So that's a sentence and we could, we hear the words one by one, but we could represent it by a tree. But your paper mentions constituents.

15:54Like, for example, in the sentence, here is the red book that my father bought, the red book would be a constituent because that would fit as a tree lit and there's no bits of that three-word phrase that go outside of a tree lit as far as I would draw it. Or my father bought. I think that would be a tree lit as well. I think that would be a constituent because it's a tree lit depending on how you draw the tree. But book that my,

16:25those are three words that I think would cut across different tree lits. So they're not a constituent. They're just three words. So in the experiment, as I understand it, you might want to give people these three words to see if their brains go, I have no idea about the internals of this. Or, yep, I can totally see those three words as a unit even though they're not a tree lit. Am I kind of getting there? Yeah, so that's certainly half,

16:55that's part of it is you can see that people do treat these chunks like units at least to the same level of evidence that we think people treat words like units, which is again an assumption, right? So for instance, if you look at how frequent the phrases, well, that predicts how good you are at processing the phrase over and above how frequent the component words and component phrases are. Moreover, how meaningful it is. Now, it might sound a little strange to talk about how meaningful things

17:26that book that my is, but there is indeed a little variation if you ask people in how meaningful they are. And that too matters in terms of how people process them. So there does seem to be a sense by which, yes, they are treated as units, at least to the same extent that we can claim that words are treated as units. Can I do a test on the sentence? I want to dance. So a lot of tree structure that people would propose would put to dance as one unit and want to dance

17:57as another unit and then I want to dance as the whole unit. I think that's how most like introductory linguistics classes would group those. Two belongs more to dance than to anything else. However, if we look historically, we have actually merged want and two, you could argue, to a wanna. And that arguably crosses between two different constituents, two different tree, did you say tree lets? I'm using the term tree lets. I hope that's okay. Yeah. So that's an example maybe of something

18:28that is not only super frequent so that people treat one, two as one unit, but they're so frequent even that they make it into a word. Is that the kind of things we're looking for? I think that's one of the effects of sort of when you have these sort of frequent occurring sort of chunks or sub-chunks that they can sort of merge together so there's a whole field of linguistics called grammaticalization that's all about how these kind of phenomena can show up. But that's probably a story for a different podcast

18:58at some point. Love grammaticalization. But part of that I mean part of the theory is that part of that comes from repeated use that it becomes compressed both in terms of the duration but also it takes on its own role so it also very interestingly you can use it in certain contexts but not other contexts so for example there's another example like going to that goes into Ghana so say I'm going to go to the store for example but what you can't say

19:30I'm going to the store so you can see I'm going to the store but you can't say I'm going to the store but they take on some new roles as well so language is wonderful in the way it changes all the time and grammaticalization is one of the ways in which you get these changes that come into play and part of that is driven by at least according to the sort of the people who do work on this is sort of on the frequency of these items as they occur and so on and they kind of get shortened and can take on

20:02different meanings as well also and Ghana is really tightly fused like when I tell my daughters to stop watching TV will you please stop watching TV they can't say I'm going they have to say I'm going to I'm going to it turns into something like going to oh that's weird I was going to so Ghana and wanna or actually want to and going to are examples of things that straddle different constituents so they're the kind of candidates that your paper

20:34is addressing can you tell us more about the experiments and how people behaved sure so what we talked about before I guess is this is it treated as a unit right is the chunk treated as a unit that's that's only half of the story because we sort of wanted to say all right we're building on work that says it's treated as a unit but are we also generalizing some sort of structural knowledge across different chunks right so that's so in that case

21:05it's not enough to say here we can see it being treated as a unit we need to show some sort of generalization if that makes sense right okay so what we want to know then is do people perceive these chunks that straddle treelets are they able to perceive them as part of a pattern exactly so so let's give them beads on a string and see if they can recognize them as valid things and if they can then there's no need for us to presume that we process

21:35language in tree like units it starts to look like beads on a string are actually real right exactly or to borrow the phrase from before as real as you can show the trees to be so we can't claim to show that there are no trees but we can claim to show that there is more than just trees and then the rest becomes how do you what do you make of that okay so we're not trying to overturn we're not trying to chop down all the trees we're trying to show that there's a

22:06little bit more well we are but we are not there yet so oh we tapped into their secret agenda Daniel but also still trees can be useful for on the descriptive level so but what we want to do is that get rid of the trees in theories of how we process and use language but but you know we're not there yet and you know it's a it's science we're trying to do science so we can only say as much as our evidence allows us to this is

22:37what Ingrid was pointing out exactly okay very humble very good well from reading through the paper these experiments revolve around a lot of priming so can I tell you what I know about priming and then you can tell me how you used this my understanding of priming is that there have been experiments where you get somebody in the lab and you say right we're going to show you three things but don't worry about the first two things only worry about the third thing we're only focusing on the third thing and when you see the third thing

23:07hit a button as soon as you can whether it's a word or not a word right word or not word that's all you got to do for the third thing just hit a button as soon as you can whether that thing is a word or a non-word and then you show them three things so you go not a word not a word word and they go oh that's a word and they hit the word button but maybe somebody else will get it like this not a word word word

23:37and they'll go the third thing was a word but they'll do it slightly faster because that second thing was a word and that sort of paved the way for them to say that third thing was a word yeah yeah so priming is a word that's used by many people in different ways but what you're pinpointing there is exactly the way we think of it you can think of it as sort of very very recent exposure or very very recent experience somehow

24:07facilitating what you are doing in the moment right if you're friends with a linguist you might have experienced that like they want to know how you say a certain word but they don't want to say the word because they don't want to prime you to pronounce it a certain way so instead you might say like oh the fruit that grows on a tree that's mostly red and you put in a pig's mouth and you want them to say apple but you want to know if they say apple or I actually