Ecological Perspectives on Hearing

What is the relationship between the auditory systems of humans and animals and the natural sounds of the real-world environment? In this episode, we speak to three of the editors of the Special Issue on Ecological Perspectives on Hearing,  Laurie M. Heller (Carnegie Mellon University), Christian Lorenzi (Ecole Normale Supérieure and Université Paris Sciences et Lettres), and Frédéric Theunissen (University of California, Berkeley), about the diverse research related to the auditory monitoring and comprehension of natural sounds and scenes.

Read all the articles from the special issue here!

Read more from The Journal of the Acoustical Society of America (JASA).
Learn more about Acoustical Society of America Publications.

Music Credit: Min 2019 by minwbu from Pixabay. 

Transcript

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Kat Setzer (00:25)

We have another special issue to discuss today, the Special Issue on Ecological Perspectives on Hearing. With me are Laurie Heller, Christian Lorenzi, and Frederick Theunissen. One other editor, Camille Desjonqueres, couldn't make it today, but we wanted to also highlight her role in the special issue. Thank you for taking the time to speak with me today. How are you?

Laurie Heller (00:55)

Great.

Christian Lorenzi (00:54)

Fine, thank you.

Frederic Theunissen (00:55)

Doing well, very thank you.

Kat Setzer (00:57)

So first tell us all about your research backgrounds.

Laurie Heller (00:59)

I'm Laurie Heller from CMU, and my research examines the human ability to use sound to understand events happening in the environment. So, in my background, I first started studying the spatial perception of sounds, and I was initially using very short bursts of noise that I could describe and make with equations and signal processing. And over the years, my research has expanded to include more and more real-world and naturalistic sounds. And so my perceptual experiments discover acoustic cues that reveal attributes of sounds and how our knowledge of that influences our recognition and perception of the sounds, and this makes it psychoacoustics. So I examine how this knowledge that we have influences which brain regions are recruited during the perception of sound events and how we combine hearing and vision, as well as asking whether sound affects the gestures that we make. And my research on sound localization included teaching naive listeners to learn to extract information from echoes about the surrounding environment. And ongoing work involves the perception of sound categories, the effects of unwanted sounds, and how to generate novel sounds and to test sound recognition in hearing-impaired listeners and improve the performance of a machine learning system for sound event classification. So applications of this research have the potential to enhance auditory displays, hearing aids, and navigations for the visually impaired.

Kat Setzer (02:25)

Very cool, very useful.

Frederic Theunissen (02:27)

So I'm Frederick Theunissen. So I'm an neuroscientist, an auditory neuroscientist at UC Berkeley. And I guess to kind of simplify things a little bit, I would say the first kind of big decade of my research has been to use natural sounds to probe the auditory system.

And I think it's been very revealing because if as you go higher into higher levels of the auditory system, using pure synthetic sounds like you know, pure tones or white noise, are not, it's not very efficient, in the sense that you don't get very very good responses, whereas using natural sounds kind of reveal kind of the complexity of of processing that happens at higher levels in auditory areas. So as I said kind of the first ten years that I was a a professor at Brooklyn I I focused on the use of natural sounds and slowly shifted to from natural sounds to kind of natural behavior ,where natural behavior is communication, and been studying animal communication and kind of what's specialized in terms of auditory processing for processing within songbirds, their whole repertoire as well as in humans speech processing.

Christian Lorenzi (03:30)

I'm Christian. I have been trained as an experimental psychologist and auditory psychophysicist and I'm now working at Ecole Normale Supérieure in Paris in France. My early work focused mostly on the role of temporal modulations in human hearing. That is these amplitude and frequency modulations conveyed by sounds and scenes, such as speech sounds and cocktail party situations as found in domestic and urban situations. It's only over the last years that my research has strongly shifted towards the study of auditory perception of natural scenes and soundscapes, such as those associated with pristine environments such as a forest, a grassland, a park or nature reserve.

Kat Setzer (04:13)

Very interesting. Okay, and that actually probably segues nicely into our next question. What are ecological approaches to hearing and why is it important to study hearing from this perspective?

Christian Lorenzi (04:22)

Well as you know, hearing research has historically mostly focused on characterizing and explaining how we humans perceive speech in various situations, including cocktail party ones, and to a lower extent music. It's only very recently that researchers like Brian Gygi and Valeriy Schafiro pioneered the study of auditory perception of everyday sounds, also called environmental sounds and Laurie Heller, who is with us, also contributed to that field. Valeriy Shafiro and his group contributed to this very special issue in JASA. 

Natural sounds and scenes fall within this broad category. They correspond to animal vocalizations like bird songs or insect regulations, and geophysical sounds such as wind, rain, thunder, or stream sounds. This new field in hearing sciences that we are talking about challenges our current understanding of sound recognition and auditory scene analysis and knowledge gained primarily primarily from speech and music, as well as artificial stimuli. And this raises entirely, I think, fresh questions, such as to which extent and how can we perceive ecologically relevant information in natural scenes or soundscapes—a forest, a nature reserve, for instance—are we able to, and if we do so how that is, thanks to which mechanism do we perceive global scene features such as the time of the day, the season, the habitat type? Can we perceive the changes in bird biodiversity in the closed environments or the presence of a nearby stream, its morphology, its flow rate? Why do these natural sounds trigger strong positive or negative emotions in us? And how are these capacities altered by cochlear hearing loss and hearing aids or cochlear implants? Finally, how do modern algorithms such as those based on deep learning techniques, how these modern algorithm should tackle these issues, knowing that wind, rain, stream sounds should not be considered as masking noise and the that should be suppressed from complex scenes. So these are I think entirely novel questions.

Kat Setzer (06:34)

So what are some of the broad themes that showed up in this special issue?

Frederic Theunissen (07:37)

So I I think I found kind of five broad themes. And I think one of them, which is also very important, but is s a little bit at the margin. I think the first one is what are the defining cyclical structures of the sounds that are found in nature? And I think Christian mentioned this. You know, in this is the the way that this field is novel, is that it kind of combines biophony with geophony. So, you know, there's the sounds that are produced, and people have been you know interested in natural sounds for a long time, but really I think if you think about

 bioacoustics, they've been focusing on the sounds that are produced by animals, you know, the songbirds. Can we assess kind of biodiversity based on you know the number of species that you can detect automatically and so forth? And the geophony, which are you know the kind of the sounds that are produced by physical structure, you know, water flowing, the wind, the sound of fire, etc., which actually gives you also a lot of information, has been kind of taken more as a, you know ,background kind of signal to noise things you want to kind of detect you know the the animal vocalizations. And I think that what's interesting about this field is like both of these have a central central part, and so when you think about okay how are we going to assess kind of the structure, I think it's it's the the part that I found it kind of interesting in the special issue is that you know the kind of measures that you do to kind of characterize kind of biophany might not be the same ones that you might use to characterize a geophony. So I think that's something that is in the paper. There was a lot of use of modulation power spectrum kind of characterize sounds, which I think is actually kind of very powerful and very useful. It's a measure that allows you to take averages over long periods of time. So not to say, this particular sound has a particular pitch, but kind of if you if you take a longer average of the sound, what are the average kind of structures ,in terms of the spectral-temporal structure. And this is something that was used quite a bit, I think, in multiple articles in this special issue. There was also an article from Thoret. The title is “Rethinking Acoustic Indices to Advanced Understanding of the Relationship Between Soundscapes and the Environment,” that kind of criticizes kind of the more traditional use of the features that we use to describe sound and kind of you know pushes us to think about what would be kind of you know other indices that we might be used to kind of characterize the the sounds. The other thing that I want to mention in in this topic is, and this Christian has been part of this, is the you know the generation of databases. So the here Biodiv database that kind of you know it's a great resource to kind of do these these types of analysis and you know maybe Christian can can pitch in and say a little bit more about that and and kind of advertise that because I think it's a very valuable resource for the community as well. I don't know Christian do you want to say something in at this point before I go on to number two?

Christian Lorenzi (09:33)

Yes, building up the here Biodiv Database was a great experience because it was made possible thanks to a consortium of scientists around the world and and especially ecoacousticians or soundscape ecologists were recorded in boreal forests, tropical forests, subtropical forests, savannas ,and deserts all over the world, allowing us to extract or to to retrieve acoustic samples at different moments of the day, different seasons in these very different pristine habitats. And yes we we started I analyzing this this data and extracted this spectral-temporal modulation features that actually seem to characterize each habitat in a quite accurate way.

But there's much more we could do with this database of course. And it can be accessed upon request. There is in the paper a link to to this database, an email address you can use if you want to to have access to.

Frederic Theunissen (10:29)

Okay, so moving on. So the kind of the second broad theme is how humans perceive the sounds and what information they can inquire about the environment. And I think Christian touched on this too. This is also novel in this thing. And as I was saying, you know, perception is about extracting meaning from sounds. And we've done this obviously a lot with speech. It's so natural for us, but we've also done it with music, and we've also done it with you know animal vocalizations. But here I think what's novel here is to do it with soundscapes, and what kind of information can you get about soundscapes. And I mentioned this before you know this is like, you know, what season it is what time of day it is ,what is the quality of the environment, and this is something that I think there's really multiple papers that that have touched on this and in this issue. 

The third topic is the human emotional response to natural sounds, and I again I think  this is going to be interesting. There's such a large body of literature on emotional responses, little bit to speech, but a lot to music, and much less in terms of emotional responses to natural sounds. And it’s going to be some interesting work there. It's been touched in multiple papers in this, including in papers that also look at hearing deficits and the appreciation of natural sounds. So it another theme the special issue.

The number four is one that is a little bit thin. It's how the human ,or I would say animal auditory system, can process these sounds. There's really only one article and it's a modeling article from Shihab Shama that that touches on this. I say it's a little thin. I mean this is actually my area, and I'm sorry I didn't contribute, but I actually don't have much to say yet in this in this area. So it's I think it's something that is too bad that we didn't have more papers in it. But I think it's just the state the state of the field is that there's actually not that much research in this area. But my guess is that this is something that will grow quite a bit in the near future. 

And then the fifth topic is how humans with listening deficits perceive these sounds. So I think there's four papers overall that are looking at, you know, mechanisms that link hearing deficits to kind of impair ecological and emotional listening of natural sounds. 

And then the last topic/broad theme ,and this is the one that I think is a little bit, I mean I'm glad to hear what Christian and Laurie have to say about this, but slightly a little bit on the margin, but it's a huge part of bioacoustics, which is computational acoustics. And so you know there's obviously kind of machine learning techniques and computational methods to kind of automatically record from natural sounds and kind of assess this, and these have been used to kind of assess kind of biodiversity. And you know, these have been touched in a special issue. I mean, I think there's multiple papers that that kind of mention these approaches. How this is going to be kind of you know merged, I think, with the goal of kind of this human, you know, auditory ecology, I think remains to be remains to be seen. But obviously, I mean we're in the age of AI, so this is going to be a big part of it as well.

So I think those are at least my take of the five kind of core broad themes and then this kind of computational approaches.

Kat Setzer (13:46)

It certainly sounds like the special issue covers quite a bit of ground. So what sort of listeners and sounds were studied in this issue?

Laurie Heller (13:54)

So there's actually a wide range of listeners. We have human listeners and also machine listeners in this issue. And the human listeners, there are normal-hearing listeners, there are also those with hearing impairment. And there are also a culturally distinct group of herders from Senegal, that are compared to some French control groups in terms of how they listen to natural sounds in their environment. And some studies also included some animal listeners.

Kat Setzer (14:27)

Very cool. So you mentioned that many of the articles pertain to the auditory monitoring of natural sounds and scenes, either by assessing auditory behavior or by characterizing the acoustic information available in natural scenes. Can you tell us about some of the notable research that was published?

Christian Lorenzi (14:44)

Well I was especially excited by two complementary studies actually conducted by Marine Taffou and Haiping Huang that revealed that spectral temporal modulation cues such as those conveyed by conveyed by animal vocalizations trigger emotional responses in humans and probably modulate their perceptual salience.

More precisely, Marine Taffou shows that negative emotions, that is negative valence, felt in response to mammal, insect ,and bird sounds, are associated with high perceived roughness, which in turn is derived from the higher irregularity and width of the spectral temporal modulations, which makes roughness actually an ecologically meaningful auditory code that drives emotional reactions to animal sounds in humans and their salience within the soundscape. And with a different sound database, Huang, Picou, and Martens showed that emotional valence ratings were systematically associated with modulation depth at low and high audio frequencies. And this relationship was weaker in listeners with hearing loss, consistent with a compressed range of emotional responses to these sounds found in hearing-impaired people.

So altogether I think these results, and that's the reason why it's exciting me, extend our knowledge on the role of modulation information in hearing. An ambitious research program that, as you know, was initiated long time ago in the seventies and that focused at that time especially on speech intelligibility in domestic and urban situations. And that was renewed actually in the early two thousands by Nandini Singh and Frederick Theunissen, thanks to their canonical study on the modulation power spectrum analysis applied to natural sounds. So I think that all these papers in these special issues, including that from Nicole Miller-Viacava, points to the fact that the spectral sample modulation cues do not necessarily only assist us in communication, as in the case of speech perception, but also in monitoring sounds from the environment and triggering the appropriate actions.

Kat Setzer (16:56)

Interesting.

Laurie Heller (16:58)

What Christian just said about the salience of spectro-temporal modulations has also been studied a paper by Liu and Elilali in this special issue where salience is very scientifically studied so that we know how important sounds are in a complex, longer-term scene with a lot of different kinds of sounds in it. People would not only rate how salient a sound seemed, but also, you know, how important it was. And they studied things like the recognition and the acoustics, and they teased those apart and found this role of perceptual salience that is not just about how recognizable sounds are or specific acoustic properties, but really more related to what the sounds are and what they mean for us, which makes a lot of sense, and it suggests this important role in the monitoring, auditory monitoring of our environment to know what's happening around us, that that certain properties that suggest certain kinds of sound sources that may be more important to us—in this paper they found alarms getting the most attention—also get the most physiological response. So there's sort of a loop there where you can see that more important things then get heightened physiologically as well. So that was a physiological connection. 

And another one is a paper by Shihab Shamma on modeling the ways in which our auditory system responds to sound, looking at examples of how the cochlea processes sound initially, but also computationally modeling higher-level processing as well that pulls out spectral and temporal modulations and looks at them for natural sounds--water flowing and rates of water flowing in the stream—or

different times of day in a Kenyan savannah, things like that. There's actually a lot more in the supplementary methods, aside from the paper that you might see right when you first look in the JASA paper, of all different kinds of environments And you can see how there might be certain kinds of cues that are perceptually processed to sort of help us understand how humans and other organisms might be processing these important things about our environment that haven't been as well studied yet.

Frederic Theunissen (19:12)

So yeah, I also chose two papers to highlight and the first one is “Auditory discrimination and identification of the time of day of natural soundscapes,” from Apoux et al. And Christian is one of the authors of that one. And the second one is Perceiving temporal rhythms in the Sahelian soundscape of Senegal: A pilot interdisciplinary study bridging psychoacoustics, ecology, and anthropology” from Thoret et al. And I chose these two papers for a couple of reasons. I think the first one is that they're the, you know, I think probably the best examples in the special issue of the extraction of meaning from soundscapes. And I think I mentioned this already a couple of times, is that you know, soundscapes are where thought, I think, a lot in terms of auditory scene analysis. And when other people think about auditory scene analysis, it’s like foreground, background, extracting signal from background noise ,or separating sound sources. And and these are a little bit different, it’s like, no, we're actually going to extract the meaning from the soundscape, right? We're going to see what information there is in these background sounds. And the other part that is kind of novel, I think, in this and kind of pioneering is that a lot of the kind of knowledge that we had about how humans perceive their natural environments are from ethnographic kind of studies that report, you know, this kind of deep knowledge of you know, native people, for you know the birds based on their sounds and you know the recognition of the quality of the environment and so forth. And maybe you know Christian can correct me, but I believe that these are like you know the first or some of the first studies that actually taking this in a controlled environment in the laboratory and ask these questions directly.

Christian Lorenzi (20:58)

Yes, I believe so.

Frederic Theunissen (21:00)

And that and that's you know ,quite it's kind of what we need to do as scientists and at the same time I think it raises some questions.  So what are the results? So the results I think are pretty clear is that you know there is definitely information about time of day. This information changes as a function of the latitude. So some environments have yeah, give you more information about time of day than other environments. And then the second one is that there's information about seasons. What's interesting and challenging is that I think as humans, you know, we're able to detect these differences, and at least in the lab and out of context, it's a lot harder to actually identify, to actually put a label onto, you know ,what season it is or what time of day, even though you can actually detect the difference. And in the Thoret paper, it was you know again one of these great papers because he kind of compared naive French listeners to actually herders who live in that environment and are outside and you know are, you know,  experts in kind of processing this environment and found no differences between the two. And you know, I mean they're very candid about the fact that this is a pilot study, but interesting that when you put the things out of context, maybe the information is a lot harder to, you know, in this kind of unimodal way to kind of process and extract this. And so this is something that, you know, is… I think raises, you know, raises questions about how to do this research correctly, whether we would need to go to multimodal kind of approaches to really be able to kind of capture, you know, how information is processed, and increase the sample size, of course, and then explore more environments, and so forth. So this is just the beginning. I know that Christian also enjoyed this paper, so maybe you want to add something, Christian about this approach. I know and you're one of the pioneers too, so you know

Christian Lorenzi (22:55)

Pioneers, I don't know. But what these studies showed, and that may not be a surprise, but it had to be studied with psychoacoustical tools, is that in pristine environments such as the forest, soundsapes change smoothly across the day, from dawn to midday to dusk and night. And the fact that these changes are smooth actually allows us humans to build up relatively stable representations of the closed acoustic world, allowing us and I will quote William Fay, allowing us to build a sense of place and time, and thus also allowing us to detect unlikely and potentially dangerous events. So in line with the so called prediction predictive coding theory. So for that reason I think that studying perception of time of day may eventually feed this new line of research along the predictive coding.

Kat Setzer (23:49)

Right, right. So there also seem to be a few different disciplines that showed up in the special issue human auditory perception, ecoacoustics and bioacoustics, and computational acoustics. How do each of these areas of research expand our understanding of the auditory system and the natural sounds of real-world environments?

Frederic Theunissen (24:08)

Yeah, okay, so I thought a lot about this question, and I found it kind of difficult, difficult to answer, but I'll do my best. And I think it's difficult because it's kind of projecting towards the future more than actually talking about, I think, the topics that were covered in this, particularly in terms of understanding the auditory system, because there was very few papers that actually kind of did, like, neurophysiology or, you know, any kind of measures in terms of auditory responses. 

But let me let me tell you kind of what I think. So one topic that I think is very interesting, at least for me, kind of you know made me think about auditory processing, is again this idea of the structure in auditory scenes that you find in nature, versus, you know, the structure of speech or the structure of animal vocalizations, all these sounds that are more transient, highly informative, that have been really kind of studied extensively in terms of processing in auditory areas. And I think that you know that this is something too that, you know, we should investigate is that we are clearly, you know, as humans, we know more and more about, for example, speech processing and how specific areas of cortical auditory system are specialized for speech, both at the level of like you know, gross anatomy and circuits, and we know almost nothing about whether there is also specialization for the processing of, you know, the textures that you find in natural sounds, kind of what Laurie mentioned, things that are kind of have longer time scales. It seems like, you know, those qualities are different, and that we might actually be processing these maybe in parallel channels, and this is something I think that would be interesting to study.

The second one I think is the emotional responses. And again, I think in addition, this has been studied a lot with music, very little with auditory scenes and environmental sounds. And if you introspect a little bit about this, I think the emotional content is different. I think it'd be simplistic to think that maybe environmental sounds have a little bit more of a flattened response in terms of emotional responses. But it is like, you know, calming sounds, and you know, you kind of you know get re-centered, and I mean it has this kind of whereas in music you could get you know excited. But I think there's something interesting about how emotion and memory, you know, are going to affect our perception and our responses to natural sounds. That is probably similar in some ways to the way that, you know, let's say music elicits those, but also but also different. And definitely the emotional component has been touched in this issue but I think it's there's definitely a lot of room for exploration in that area.

Yeah, and then the last one is I mentioned computational acoustics. I think it's you know the machine learning for monitoring ecosystems has really focused a lot on biodiversity and less so in, you know, like the effect of the drought or, you know, the you know, kind of climate change and things like this, and so I think this is another area where we might actually be able to do a lot if we can characterize, you know, with the work that kind of, you know, for example Christian is doing in different latitudes, how you can measure different aspects of the environment and in terms of how much water there is and so forth. And so I think this is another area that that is very fascinating and that has a lot of I think potential for kind of future monitoring.

Kat Setzer (27:46)

So one of the goals of the special issue was to help explain why the human auditory system is the way it is. The issue actually ended up including a perspective article that discussed evolutionary pressures on listening. What sort of adaptations seem to have evolved in the human hearing system and how do these adaptations perform in modern soundscapes?

Christian Lorenzi (28:04)

Ah, well… Why is the human auditory system the way it is? That's certainly the most exciting question, and that's probably the reason why we're here, but also the most difficult to answer to. So I'm not an evolutionary biologist, but I will try and speculate. But Laurie and Frederic please join me if you would like to correct me on this. 

So as far as I understand, for most part of our species’ history, which is about, let's say, three hundred thousand years long, we humans have been mostly exposed to natural soundscapes, mostly composed of what? Animal vocalizations, such as bird songs and insect regulations on one hand, and geophysical sounds, such as wind, rain, and thunder and river sounds. These soundscapes being shaped, that's the most important thing, by ecological processes and patterns. Think about the water cycle or recurrent patterns of animal vocal activity at dawn and dusk.

So natural soundscapes actually are not noisy, they are highly structured, they are relatively simple, and as I just said before, relatively predictable, which might not be the case of urban soundscapes. So thus from an evolutionary perspective, but—careful, I’m speculating here—our auditory system has mostly assisted us humans in monitoring our close environments, orienting, estimating resources, danger, and opportunity for action. So these ideas are to some extent discussed in the by Alexander Francis and Daniel Strauss in this special issue. This means that our auditory system has been shaped, probably shaped and probably optimized, by evolutionary pressures to perform certain tasks on the basis of the statistical regularities present in the acoustic world. These tasks are the so-called monitoring ones, and the statistical regularity to which our auditory system should be tuned to are those characterizing natural scenes rather than urban or domestic soundscapes.

So Francis and Strauss posit that evolution shaped so-called deeply entrenched mechanism for monitoring the acoustic environment for threats and opportunities— alerting, orienting. So characterizing these statistical regularities using the current massive acoustic databases of natural soundscapes collected around the world by soundscape ecologists and ecoacousticians, and using these massive and ecologically valid soundscape databases to explore auditory sensitivity of human listeners in monitoring tasks constitutes the main aim of this so-called ecological approach. So in other words, we aim at asking brand new questions such as to which extent and how can we perceive this ecologically relevant information in natural scenes, as time of day, season, flow rate of a nearby stream, bird biodiversity.

Kat Setzer (31:12)

Interesting, interesting. Very cool. So what are some of the emerging disciplines that appeared in this issue?

Laurie Heller (31:18)

One of the goals of the special issue was to highlight some emerging disciplines, and the one we just spoke of, this connection between psychoacoustics and evolutionary biology, and cross-cultural analysis of how we perceive sounds in our environment, natural sounds, soundscapes, that's I would say an emerging area, right? There are a few papers on it but not a lot. And another one is explainable eco-acoustics. That is a bridge between computational acoustics in ecology, and several papers on the issue are focused on not just describing the soundscapes with objective numbers, which is, I mean that's a great start, but they're also trying to make those descriptions relevant to the listener, right, who's perceiving these soundscapes and trying to connect those things. So I would say those are the two main emerging disciplines that are sort of represented in the issue.

Kat Setzer (32:18)

So those were the ones that were represented. Were there any areas of research that didn't come up in the special issue that are important to consider when thinking about ecological perspectives on hearing?

Laurie Heller (32:27)

Yeah, certainly. There are some issues that we didn't emphasize just because they're already robustly covered in Acoustical Society publications, in other areas. So some things were maybe not emphasized, like speech or underwater bioacoustics, that really have their own technical areas. They weren't emphasized here, although they were certainly included.

But other areas were not represented just because there is not a lot of research on them, and there weren't any submitted to this special issue in particular. So that would be, for example, there's some papers showing how there might be sensitivity to different environmental properties through sound, but not so much how that might be changed by, say, changes in our environment over time, for better or for worse. So that sort of study of, you know, how we're sensitive to that, either humans or animals, and it is just sort of not very well represented in here. And another thing that's not so well represented is the development of auditory processing of natural sounds. How is that affected by exposure? You know, how much is inherited from our ancestors, how much of it is affected by exposure and is exposure at a young age important, and cultural factors as well. So those are things that are not well represented in the issue, and not as well represented in the field either. So

Kat Setzer (33:57)

But hopefully we'll see more later. 

Laurie Heller (33:58)

Hopefully, yeah.

Frederic Theunissen (33:59)

Yeah.

Kat Setzer (34:00)

So where do you see research related to ecological perspectives on hearing going in the future?

Laurie Heller (34:04)

You know, we were just talking about emerging issues. I do think one of the future directions is having really perceptual metrics and biologically inspired frameworks to connect to our computational models and also measurement of the environment and the sounds. So this sort of connection between computational models and human and auditory models. So I think that's a great direction for the future. And I also think just better understanding how the physical properties of the sound sources in the world are connected to acoustics and how sensitive we are or are not. Like there's some things maybe we really don't tell the difference between, ad those are also important to know about. So that's a  future direction, I think, that's going to be helped by all of the surrounding research on measurement and understanding different natural features that we are sensitive to. And then of course connecting to emotion and neuroscience in particular I think is a growing direction.

Frederic Theunissen (35:07)

Yeah, I mean I think I already mentioned some of the things and I'll just you segue with what Laurie said. I think the neuroscience part of it is really unknown. Completely, you know, we know so little about how soundscapes are processed in a way that would be distinct from, you know, just general auditory processing, right? I mean this is really I think when we when we're talking about extracting meaning from soundscapes or emotional responses, that transformation is a, you know, in terms of what where it is in your brain and what happens and how is it related to, you know, the transformations that we do in terms of processing speech and music is something that is completely unexplored and I think would be fascinating.

And then I think the I  mentioned this already, but I think the in terms of the human, you know, psychophysics, it's also something that we, that's just started in this issue, trying to really kind of quantify this and measure this and doing this across cultures, and across habitats, across ages for development, you know, with different levels of experience is something that I think would also be very fruitful.

Christian Lorenzi (36:17)

Well yes,  I also believe it's urgent to study the extent to which we humans perceive acoustic changes caused by human activity in our close environment and how this influences behavior. There clearly is and I will quote the title of the paper by Francis and Strauss, there clearly is “a mismatch between auditory priors and contemporary acoustic environments.” So are we sensitive to a drop in bird biodiversity in gardens, parks, and nature reserves? Are we sensitive to selective logging in a forest? To a chemical pollution caused by pesticides? Can we hear that? Can we hear a coming flood? It looks like some people can do this in the Mekong area. I don't know whether it's right or wrong. To take an example, Amandine Gasc, an ecoacoustician who co-authored several papers in this special issue, demonstrated several years ago that experts can detect a drop in cricket stridulations within natural soundscapes recorded in New Caledonia. And this drop resulted from the invasion of electric ants (Wasmannia auropunctata), that is that are nearly invisible to the naked eye. So the ear seems to know things about the integrity of our environment that the eyes may totally ignore.

So in this spirit, I think it's important to extend auditory research to listening capacities and behaviors of people living in rural and deep rural areas, rather than always concentrating, as we did before, on urban and domestic environments and cocktail party situations, etcetera. So many activities, such as those associated with agriculture, actually may depend strongly on auditory skills. Think about beekeepers, who in in all likelihood are listening to the to their hives to anticipate swarming. So all these reflections may pave the way of an entirely new research program in hearing sciences and create exciting interfaces with ecology, but also physical geography and earth sciences. So I really strongly hope that hearing sciences will move towards ecology and related environmental sciences, this opens so many exciting scientific opportunities and potentially I believe useful applications.

Laurie Heller (38:43)

I just realized that we as far as future directions should have mentioned clinical audiology also. But there yeah, there's you know, real world situational awareness for patients that have hearing impairment or as hearing assistive devices is really starting to be emphasized, starting to be really included into some audiological processes and devices and that should improve in the future. I do predict that that will even have greater emphasis and beneficial effects for the patients.

Kat Setzer (39:12)

Yeah, those are some really interesting areas of research that could be considered. So do you guys have any closing thoughts?

Laurie Heller (39:18)

Yeah, we may discover things about human hearing capabilities that we didn't know by asking about these really fundamental types of listening.

Kat Setzer (39:29)

Right, right. That makes a lot of sense. Yeah. Well, it is so interesting to think about how we hear in relation to the natural world and how it affects our hearing or has imp how our hearing has developed. And hopefully we do continue to see more research in this area in the future. Thank you for taking the time to talk to me again about this special issue today, and have a great day.

Frederic Theunissen (39:48)

Thank you. Have a great day, everybody.

Laurie Heller (39:49)

Thank you.

Christian Lorenzi (39:49)

Thank you, thank you, have a great day. Au revoir.