Dr. Jennifer Groh on Huberman Lab: How Gaze Reshapes Hearing

Dr. Jennifer Groh 0:00 What goes on in our brains when we think might be that we're running simulations related to the thought using that sensory, sensory motor infrastructure of the brain.

Andrew Huberman 0:11 Could you elaborate?

Dr. Jennifer Groh 0:12 So the theory is that, like, maybe when you think about a cat, for example, or you think the concept of a cat, that the mental instantiation of that, or the, the brain mechanism instantiation of having that thought is to run a little simulation in visual cortex that kind of includes what a cat looks like. A simulation in auditory cortex that, what does a cat sound like? And as I'm telling you this I'm, you know, I've used the word cat, um, what color cat are you thinking?

Andrew Huberman 0:41 I'm thinking of a, a gray cat, but I keep smelling kitty litter.

Dr. Jennifer Groh 0:45 Okay.

Andrew Huberman 0:45 'Cause my sister had cats and it drove me, the smell of kitty litter is just so aversive to me.

Dr. Jennifer Groh 0:49 Right. And s- (laughs) so you had no hesitation in telling me the color and adding an additional sensory quality. It provides an explanation for why you might, you know, be driving on the freeway and having to merge into difficult traffic and telling your, your passenger, "Okay, be quiet. I've got to, I've got to pay attention now." Like-

Andrew Huberman 1:11 Hmm. Mm-hmm. Mm-hmm.

Dr. Jennifer Groh 1:11 ... why would speech impair you from visual motor-

Andrew Huberman 1:16 Mm-hmm.

Dr. Jennifer Groh 1:16 ... if it wasn't all part of a kind of cognitive system that's, that's in operation, and maybe you need to shift some resources away from processing-

Andrew Huberman 1:25 Mm-hmm.

Dr. Jennifer Groh 1:25 ... the conversation and towards some, you know, actually dealing with the here and now sensory motor task?

Andrew Huberman 1:32 Welcome to the Huberman Lab Podcast, where we discuss science and science-based tools for everyday life. (instrumental music plays) I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. My guest today is Dr. Jennifer Groh. Dr. Jennifer Groh is a professor of psychology and neuroscience at Duke University. Her laboratory studies how our brain represents the world around us, in particular how our different senses are merged in the brain so that we can focus and learn more effectively, including how our eye movements fundamentally shape not just what we pay attention to, but how they dynamically control what our brain is capable of. What she shares is fundamental to understanding how your brain works, and also how best to focus on and learn different types of information, not just information that you might read on a page, although including that, but also what you hear, what you remember, and the very thoughts you have about your life experiences. We also discuss thinking itself. In fact, we discuss what thoughts really are, and there Dr. Groh shares with us what is perhaps the clearest and most useful definition of what thoughts are and how you can control them. As someone who has been in the field of neuroscience for nearly three decades, I must say that her explanation of what thinking is, at the neural level, at the psychological level, and at the experiential level, is the most compelling and useful one I've ever come across. Today, Dr. Groh explains how to use your experiences, the information you encounter, and knowledge of how thoughts are built up in the brain to become a better thinker, and indeed smarter. I'm certain that the information you'll learn from Dr. Groh today is not like any other discussion you've heard about the brain or psychology. I'm also certain that it will be extremely useful for anyone wishing to better understand how the brain works, how their thoughts and emotions arise, and anyone who wants to get better at learning, thinking more deeply, or simply experiencing life with more richness. Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is, however, part of my desire and effort to bring zero cost to consumer information about science and science-related tools to the general public. In keeping with that theme, today's episode does include sponsors. And now for my discussion with Dr. Jennifer Groh.

Andrew Huberman 3:41 Dr. Jennifer Groh, welcome.

Dr. Jennifer Groh 3:43 Thank you. It's great to be here.

Andrew Huberman 3:45 We've never had a proper conversation on this podcast about sensory integration. We've talked about vision, talked a little bit about hearing, little bit about touch, smell, taste, but we've never talked about how the senses come together, and that's critical to everyday life. Critical to perception.

Dr. Jennifer Groh 4:03 Absolutely.

Andrew Huberman 4:04 I know you focused perhaps mainly on the auditory system, but you really are a auditory-visual integration person. I know this because I've followed your work for a number of years.

Dr. Jennifer Groh 4:16 (laughs)

Andrew Huberman 4:16 So where in the brain do our eyes and our, our ears first come together to impact our perception of life? Like, we ... You know, the tea kettle is whistling or, you know, we hear a knock on the door, we know where the door is, we know where the tea kettle ought to be, but where do these things first collide?

Dr. Jennifer Groh 4:35 The story that is triggered by that question is a, a little bit long, so, uh, maybe I can start at the beginning of when I first got interested in this question.

Andrew Huberman 4:45 Mm-hmm.

Dr. Jennifer Groh 4:45 And so I was a college student. I was interested in neuroscience, but we didn't have a neuroscience, um, um, major, so, um, a couple of us talked, uh, a professor into offering a, a seminar in, in neuroethology and, and kind of like what he thought were sort of the coolest findings in neuroscience. Uh, and in that class, I learned about a, uh, study showing that, and I'm gonna, I'm gonna begin with the neuroscience nerdy lingo and then we'll unpack it.

Andrew Huberman 5:16 Mm-hmm.

Dr. Jennifer Groh 5:16 Um, that, uh, there's a brain structure called the superior colliculus, um, that's responsive to both visual and auditory stimuli, and that the responses to auditory stimuli depended on where the eyes were looking. Um, if you moved the eyes, the neurons' receptive field, the region in space where they were responsive to would shift, um, as the eyes moved. And that blew my mind. I could not get that out of my head, um, and it kind of set me on the track that, that I've been on ever since then.

Andrew Huberman 5:51 Mm-hmm.

Dr. Jennifer Groh 5:51 One of the things that was really interesting to me about it is that figuring out where a sound is with respect to where the eyes are looking is something that would be easy for us to do with a pencil and paper. You know, it's very simple math. If you know that, um, the sound is located, say.... uh, you know, 10 degrees to the right and your eyes are looking 10 degrees to the left, and that tells you that the sound is 20 degrees to the right of where your eyes are. Really not that hard to do. But from what I knew at that point, um, about how the brain represents this kind of spatial information, it seemed a big puzzle for how the brain might actually create these kinda moving representations of where the sound is located.

Andrew Huberman 6:36 Yeah, 'cause what you're talking about are dynamic maps.

Dr. Jennifer Groh 6:39 Yeah.

Andrew Huberman 6:39 Like, we have a... I think most people probably appreciate that we have a, a map of our body's surface.

Dr. Jennifer Groh 6:44 Right.

Andrew Huberman 6:44 A so-called homunculus.

Dr. Jennifer Groh 6:46 Yep.

Andrew Huberman 6:46 And so if w- one were to stimulate in a given region of the brain, you'd, uh, have the illusion of, uh, being touched at that location on the body. People perhaps have seen that, um, the more sensitive an area of the body, like the fingertips or lips or face, uh, or feet, the larger the representation in the brain. But what you're talking about is, is shifting maps depending on where the eyes move, and the eyes move quite a lot.

Dr. Jennifer Groh 7:12 They move quite a lot, exactly. And, and, uh, mostly we're not aware of this.

Andrew Huberman 7:17 Mm-hmm.

Dr. Jennifer Groh 7:17 Right? But if you think about it, every time your eyes move, the visual scene is shifting massively on the retina.

Andrew Huberman 7:24 Mm-hmm.

Dr. Jennifer Groh 7:25 But we don't even notice this.

Andrew Huberman 7:27 Mm-hmm.

Dr. Jennifer Groh 7:27 Um, and this is an indication that the brain is doing a ton of computation under the hood to give us that perceptual experience.

Andrew Huberman 7:34 Mm-hmm.

Dr. Jennifer Groh 7:34 Because if we were just representing reality, the reality would be these massively shifting, smeared visual scenes.

Andrew Huberman 7:43 One thing that's so intriguing to me about the auditory system is, and the visual system, is the extent to which they can contract and dilate so fast.

Dr. Jennifer Groh 7:51 Mm-hmm.

Andrew Huberman 7:52 So for instance, if I'm, uh, like w- walking to get on public transportation of some sort, like a light rail or a subway, um, I'm walki-... I, you know, there's sound going by me, may or may not be relevant, but at some point, I sit down. Chances are, I open up a book or a computer, or these days people go into their phone. And we say, "Into the phone," because there's a lot of sensory information there, but th- our visual world and our auditory world just goes shoop-

Dr. Jennifer Groh 8:20 Right.

Andrew Huberman 8:20 ... into, you know, uh, a small box, and we expect whatever we're looking at to relate to the sounds that we're hearing in that small box.

Dr. Jennifer Groh 8:32 Right.

Andrew Huberman 8:32 But if somebody says, "Excuse me, do you have a ticket?" You, you know to look up.

Dr. Jennifer Groh 8:37 Right.

Andrew Huberman 8:38 We take this for granted.

Dr. Jennifer Groh 8:39 Mm-hmm.

Andrew Huberman 8:39 Like, most people might think of course you look up. Like, the sound is coming from over there, it's now a person. But we-

Dr. Jennifer Groh 8:44 Mm-hmm.

Andrew Huberman 8:44 ... all of a sudden, shoop, we can remap our visual auditory world and all the context-

Dr. Jennifer Groh 8:50 Yeah.

Andrew Huberman 8:50 ... in, like, milliseconds.

Dr. Jennifer Groh 8:51 Right.

Andrew Huberman 8:52 So is that all happening? Um, uh, we've been talking about superior colliculus at the, in the structure, the superior colliculus, uh, below our neocortex, meaning is it below our kind of conscious awareness?

Dr. Jennifer Groh 9:05 Uh, you know, gosh, I wish we knew where conscious awareness was.

Andrew Huberman 9:08 Mm-hmm.

Dr. Jennifer Groh 9:08 I think that's an open question.

Andrew Huberman 9:10 Mm-hmm.

Dr. Jennifer Groh 9:11 Um, and it... you know, the superior colliculus is important in this story because that's where the research began. It's not that that's where the binding of visual and auditory space, you know, is necessarily fully contained there and only there.

Andrew Huberman 9:26 Mm-hmm.

Dr. Jennifer Groh 9:27 I think it's a much bigger problem, and I think what you're describing is kind of, um, you know, a-another version of this kind of, um, capturing of, um, or integrating or connecting the information from one sensory system to another, that kind of shifting your resources around is something that happens in, in a few different contexts-

Andrew Huberman 9:53 Mm-hmm.

Dr. Jennifer Groh 9:53 ... like what you're describing. And I think one of the things that's really interesting about the phone or really any screen where you're watching a video is that the sound was never coming directly from the screen where you're looking at the visual image.

Andrew Huberman 10:05 Mm-hmm.

Dr. Jennifer Groh 10:06 You know, it's coming from somewhere else. Maybe you've got earbuds in, and it's coming from the earbuds. Maybe the earbud signal is simulating what the location should be, um, if it was really coming from the screen, but it's a simulation, it's not, not actually-

Andrew Huberman 10:21 Oh, yeah, that's-

Dr. Jennifer Groh 10:22 ... reality.

Andrew Huberman 10:22 ... that's so interesting. So yeah, let's unpack this a bit. So we merge what we see with what we hear-

Dr. Jennifer Groh 10:30 Yep.

Andrew Huberman 10:30 ... if it makes sense to merge them. Like lips are moving.

Dr. Jennifer Groh 10:33 Lips are moving.

Andrew Huberman 10:34 And that's in our hand about a foot in front of us.

Dr. Jennifer Groh 10:37 Mm-hmm.

Andrew Huberman 10:37 But the sounds are coming in elsewhere.

Dr. Jennifer Groh 10:40 Right.

Andrew Huberman 10:40 This is very different, um, than, say, like, if somebody's mouth were moving and the sounds coming out of it were offset by even the tiniest bit of time, it looks weird.

Dr. Jennifer Groh 10:54 It looks totally weird.

Andrew Huberman 10:54 It looks totally weird, like-

Dr. Jennifer Groh 10:55 Yeah.

Andrew Huberman 10:56 ... like it r- like this video-

Dr. Jennifer Groh 10:56 It's uncomfortable.

Andrew Huberman 10:57 Yeah, somebody gr- uh, somebody grabbed this, uh, like th- like, ripped this video from the internet, and there's-

Dr. Jennifer Groh 11:02 Right.

Andrew Huberman 11:02 ... a time delay.

Dr. Jennifer Groh 11:03 Right.

Andrew Huberman 11:03 But we easily-

Dr. Jennifer Groh 11:05 Yeah.

Andrew Huberman 11:05 ... merge what we see with sounds.

Dr. Jennifer Groh 11:07 That's right.

Andrew Huberman 11:08 And maybe talk about this, because I, I, now I'm realizing, like, if I sit and watch a movie-

Dr. Jennifer Groh 11:12 Yeah.

Andrew Huberman 11:13 ... or at a movie theater or-

Dr. Jennifer Groh 11:14 Yeah.

Andrew Huberman 11:14 ... on a big screen or my computer-

Dr. Jennifer Groh 11:17 Right.

Andrew Huberman 11:17 ... the sound is not coming from the screen. It's coming from a speaker, which is, like, uh, projecting vertically.

Dr. Jennifer Groh 11:21 Yes.

Andrew Huberman 11:22 How does that work?

Dr. Jennifer Groh 11:23 Well, not only that, but, like, the sound is jumping around in your perception as different people on the screen from different locations on the screen are, are speaking.

Andrew Huberman 11:33 Right, and they're both coming in through your ears or through the speak-... well, through the speaker.

Dr. Jennifer Groh 11:37 Whatever s- whatever means is, the sound is being delivered to you is not changing as the different s- people are, are speaking.

Andrew Huberman 11:43 Right, so let's say a dialogue on a screen between two characters-

Dr. Jennifer Groh 11:46 Right.

Andrew Huberman 11:46 ... and then maybe there's an explosion in the background-

Dr. Jennifer Groh 11:48 Right.

Andrew Huberman 11:48 ... or another character walks in the room, that the source of the sound for us, whether it's computer or speakers in the room or movie theater or-

Dr. Jennifer Groh 11:57 Right.

Andrew Huberman 11:57 ... or earbuds, is always constant.But we can quickly move the sound with our eyes? Or are eyes moving the sound-

Dr. Jennifer Groh 12:07 Yeah.

Andrew Huberman 12:07 ... with our ears?

Dr. Jennifer Groh 12:07 Let me, let me amend a little bit here, because, um, you know, it depends a lot on, like, how the sound is mixed. They can put in some spatial cues. But if they haven't done that, then it, then what we just said applies. And I think one of some of my favorite videos for, you know, for really appreciating this is of, are videos of actual ventriloquists working with their puppets. Because there they are, you know, the, the puppeteer is speaking and they're making it seem like the puppet is speaking, and they're making our perceptions switch back and forth from their own face to the puppet face, back and forth, depending on what, what they're actually saying.

Andrew Huberman 12:48 So, this is a ventriloquist that says, like, "Hey, Cornelius, how are you?" And then Cornelius says... But the-

Dr. Jennifer Groh 12:54 Yes.

Andrew Huberman 12:54 ... same person says, "I'm doing great." You know?

Dr. Jennifer Groh 12:56 Yeah. So, one of the things they're gonna learn here is-

Andrew Huberman 12:57 And they probably go, but they probably move their lips a little less when they do that?

Dr. Jennifer Groh 13:00 Yeah. They, they try to speak like this without moving their lips too much-

Andrew Huberman 13:04 Mm-hmm.

Dr. Jennifer Groh 13:04 ... um, and they sometimes will do a trick of, like, there are certain sounds that you just cannot make without closing your lips-

Andrew Huberman 13:11 Mm-hmm.

Dr. Jennifer Groh 13:11 ... uh, in front, and that's really hard to fool people about. So, for example, if it's a word that begins with a B or has a B in it, they might subtly just cover their mouth a little bit while they're making that B sound so that it's kind of misdirection like a magician would do to sort of keep you from attending too much to, to the ventriloquist and throw your attention over to the puppet. So, our perception can switch back and forth between where, um, our brains are telling us, "This is the most likely candidate for the source of this sound, so I'm gonna override what my ears are telling me to perceive the sound as coming from here versus here."

Andrew Huberman 13:52 Is this something we learn during development?

Dr. Jennifer Groh 13:55 Partly, yes. Absolutely.

Andrew Huberman 13:55 Like, do kids come into the world understanding how to merge sight and sound, or, um, or is that a learned phenomenon?

Dr. Jennifer Groh 14:00 It has to be learned and it has to be continuously updated during the course of development until you reach your adult body size. So, let me back up a little bit and talk about, how do we localize sound? Especially when we're not talking about, you know, screens and video and movies and whatno- whatnot, but just, like, out there in the, in the real world. The way we tell where a sound is coming from is by the physics of the world causing differential delays for the sound to arrive at one ear versus the other. So, sound takes a certain amount of time. You know, a sound coming from over here will get to this ear before it gets to this ear. And it'll be slightly louder in this ear than in this one.

Andrew Huberman 14:41 Because it's just closer to that ear.

Dr. Jennifer Groh 14:43 It's closer, but also there's a, a kind of acoustic shadow cast by the head.

Andrew Huberman 14:48 Mm-hmm.

Dr. Jennifer Groh 14:48 So, the sound wave has to kind of come and then go around, and there's a little, you know, there's a little sort of dip in the sound intensity cast by the shadow of the head. I like to think about the timing cues because they're really easy to calculate. So, if you know how far apart your ears are and you know what the speed of sound is, then you can figure out, what's the delay for the sound, for sound to get-

Andrew Huberman 15:12 Mm-hmm.

Dr. Jennifer Groh 15:12 ... um, to reach this ear after this ear? I often take off my glasses to measure the distance between my two ears that way.

Andrew Huberman 15:19 Mm-hmm. Mm-hmm.

Dr. Jennifer Groh 15:20 And it's something like about a half a millisecond is the largest delay you can experience.

Andrew Huberman 15:25 Half a millisecond.

Dr. Jennifer Groh 15:26 Half a millisecond. So, this is tiny, and that is for the difference between a sound here versus a sound here.

Andrew Huberman 15:35 So, something from your right versus from your left.

Dr. Jennifer Groh 15:37 Exactly.

Andrew Huberman 15:38 Yeah.

Dr. Jennifer Groh 15:38 We can obviously detect much smaller sound separations than just l- totally left versus totally right.

Andrew Huberman 15:45 Mm-hmm.

Dr. Jennifer Groh 15:45 So, there's, you know, it's an incredible feat of computational power by the brain. I think maybe we should tell the audience, um, why, you know, your brow is f- uh, is furrowed and I'm excited about this.

Andrew Huberman 15:59 Mm-hmm.

Dr. Jennifer Groh 15:59 Because half a millisecond is less than the duration of a single action potential.

Andrew Huberman 16:05 Right, and we should just remind people, action potentials are the electrical signals that neurons use to communicate with one another. These are the, the, uh, the fundamental, um, way in which our brain works.

Dr. Jennifer Groh 16:17 Right.

Andrew Huberman 16:17 Without these, we're dead.

Dr. Jennifer Groh 16:19 It's the fundamental medium of communication, um, i- in the nervous system, as you say. So, it would seem totally weird for us to be able to pro- process sensory information that is faster than the duration of that minimum increment of, of firing. You know, there's some research about how exactly this can be done, and it involves things like lots of neurons firing together and really precise, uh, synapses that, um, cause minimal delay and very high temporal precision as the signals are going from one neuron to the next.

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Andrew Huberman 19:50 So, you know, if my finger snaps, uh, with my right hand, which is what I just did, you know, uh, intuitively I know that the... it's my right hand 'cause I did it, but-

Dr. Jennifer Groh 20:00 Yeah.

Andrew Huberman 20:01 ... my brain expects that sound to arrive more quickly to my right ear than my left ear.

Dr. Jennifer Groh 20:05 Right.

Andrew Huberman 20:06 And yet, for things directly in front of me, right at my nose, (fingers snap) the idea that it's right in front of me, it, it, let's say with my eyes closed, (fingers snap) I, I know to look in front of me. I know to expect it in front of me once I open my eyes.

Dr. Jennifer Groh 20:21 Right. Right.

Andrew Huberman 20:21 Are there conditions where we think we hear something from one location, but it's actually arising from another location that's outside an experimental context?

Dr. Jennifer Groh 20:29 Absolutely. So if you have hearing loss in one ear-

Andrew Huberman 20:32 Mm-hmm.

Dr. Jennifer Groh 20:32 ... uh, and one ear only, then, um, it, it's very difficult to localize sound.

Andrew Huberman 20:37 Hmm.

Dr. Jennifer Groh 20:37 It's not completely impossible. You would imagine that it would be completely impossible if the hearing loss was complete and if this timing difference and level difference were the only cues that we use.

Andrew Huberman 20:49 Mm-hmm.

Dr. Jennifer Groh 20:50 But actually, the ear has these little folds in them, and the folds filter the sound as it comes in, uh, and in particular, it alters the frequency content of the sound.

Andrew Huberman 21:02 Really? So these little dimples inside my ears-

Dr. Jennifer Groh 21:04 Yeah.

Andrew Huberman 21:04 ... are, are useful for something?

Dr. Jennifer Groh 21:05 They're useful, and your ears are different than my ears.

Andrew Huberman 21:08 Mm-hmm.

Dr. Jennifer Groh 21:08 Um, and so you are gonna be expecting a slightly different kind of fingerprint-

Andrew Huberman 21:13 Mm-hmm.

Dr. Jennifer Groh 21:13 ... of what the sound sounds like-

Andrew Huberman 21:15 Mm-hmm.

Dr. Jennifer Groh 21:15 ... as a function of location than I would be.

Andrew Huberman 21:18 Do people with damage to their ears have issues-

Dr. Jennifer Groh 21:22 Have issues with that?

Andrew Huberman 21:23 ... hearing? I mean, it sounds like, uh, sort of a, they must, um, but like the people I know that roll jujitsu-

Dr. Jennifer Groh 21:30 Yeah.

Andrew Huberman 21:31 ... like the wrestlers, their ears-

Dr. Jennifer Groh 21:32 Oh-

Andrew Huberman 21:32 ... are always beat up.

Dr. Jennifer Groh 21:32 ... they're mashed? Okay.

Andrew Huberman 21:33 They basically don't have these folds. It's just kind of-

Dr. Jennifer Groh 21:36 Flattened?

Andrew Huberman 21:36 ... feel... Uh, yeah.

Dr. Jennifer Groh 21:37 Interesting.

Andrew Huberman 21:38 Yeah.

Dr. Jennifer Groh 21:38 Um, I don't know of any studies, but I think we can predict from first principles that they would have an initial deficit-

Andrew Huberman 21:45 Mm-hmm.

Dr. Jennifer Groh 21:45 ... uh, and that very likely, they would learn to adapt, um, and they would kinda learn their new, new set of ears and what particular frequency pattern-

Andrew Huberman 21:54 Mm-hmm.

Dr. Jennifer Groh 21:54 ... to expect from that.

Andrew Huberman 21:56 If, if the auditory system is so sensitive, why is it that I don't really hear my own voice-

Dr. Jennifer Groh 22:03 Mm-hmm.

Andrew Huberman 22:03 ... um, or if I talk out one side of my mouth, like, I sort of know-

Dr. Jennifer Groh 22:06 Okay.

Andrew Huberman 22:06 ... what I'm doing, but it doesn't, doesn't throw me off.

Dr. Jennifer Groh 22:07 Doesn't sound quite right? Yeah, yeah.

Andrew Huberman 22:08 Doesn't throw me off.

Dr. Jennifer Groh 22:09 Yeah.

Andrew Huberman 22:09 And yet, most people have the experience of watching themselves or hearing themselves speak and it feels awkward.

Dr. Jennifer Groh 22:17 Yeah.

Andrew Huberman 22:18 We don't really like to-

Dr. Jennifer Groh 22:19 Yeah.

Andrew Huberman 22:20 I, I suppose there are some people on the planet that like to hear themselves speak, but most people don't.

Dr. Jennifer Groh 22:23 Yeah.

Andrew Huberman 22:23 Most people are not-

Dr. Jennifer Groh 22:24 Right.

Andrew Huberman 22:24 It, it sound... It's like we cancel ourselves-

Dr. Jennifer Groh 22:27 Yeah.

Andrew Huberman 22:27 ... out while we speak.

Dr. Jennifer Groh 22:28 Yeah.

Andrew Huberman 22:29 But then when it's coming at us from the front, it's like, it's o-

Dr. Jennifer Groh 22:32 It's weird.

Andrew Huberman 22:33 It's odd.

Dr. Jennifer Groh 22:33 Do you like listening to this podcast, or do you kind of like-

Andrew Huberman 22:35 Well, I listen to all the podcasts to see ways that I can improve.

Dr. Jennifer Groh 22:39 Yeah.

Andrew Huberman 22:39 Um, and I like the content that, that my-

Dr. Jennifer Groh 22:42 Yeah.

Andrew Huberman 22:42 ... guests bring on, and I like-

Dr. Jennifer Groh 22:43 Yeah.

Andrew Huberman 22:43 ... the, the topics.

Dr. Jennifer Groh 22:44 But it's an awkward feeling, isn't it? To listen-

Andrew Huberman 22:46 Oh, it's always awkward.

Dr. Jennifer Groh 22:46 ... to yourself is very awkward, you're-

Andrew Huberman 22:47 Yeah, it's un-

Dr. Jennifer Groh 22:48 It's uncomfortable.

Andrew Huberman 22:49 It's uncomfortable.

Dr. Jennifer Groh 22:49 Yeah, yeah.

Andrew Huberman 22:49 It's uncomfortable.

Dr. Jennifer Groh 22:50 Before I answer that question, which is a really interesting question, I wanna loop back to the, uh, do we have to learn this? The, the other thing, um, to say about learning, uh, learning how to interpret these... the timing difference cues and the level difference cues is that a baby's head is about half the width of an adult's head.

Andrew Huberman 23:08 Mm-hmm.

Dr. Jennifer Groh 23:08 So that means that that, you know, half millisecond for me is, you know, a quarter of a millisecond for, for a baby, and it's gonna change as they grow.

Andrew Huberman 23:17 Mm-hmm.

Dr. Jennifer Groh 23:17 So that's why you have to do all this learning. With respect to the question you just asked about like why our voices sound weird, I can say more about why they sound weird and less about why we experience it as kind of unpleasant. Maybe that-

Andrew Huberman 23:32 Mm-hmm.

Dr. Jennifer Groh 23:32 ... the weird and unpleasant connection is because, um, we're just so used to the way it actually... the way it's... the way we experience it that to hear it recorded is gonna be unfamiliar and strange. I think there's gonna be three things. Number one, the recording is not gonna capture the full spectrum of frequency content of your voice.

Andrew Huberman 23:54 Mm-hmm.

Dr. Jennifer Groh 23:55 Number two, your brain has an active mechanism for manipulating the transduction of sound in your ears. That is to say, the conversion of sound into a neuro- neural signal that's gonna go into the brain. So your brain actually controls that process.

Andrew Huberman 24:12 Mm-hmm.

Dr. Jennifer Groh 24:13 Um, and there's some thinking that it's...... you know, turning down the volume just before you speak so that you don't get blasted by the sound of your own voice.

Andrew Huberman 24:23 Hmm.

Dr. Jennifer Groh 24:23 If you think about it, like if I were speaking at this volume with my mouth this far away from my ear, like if I was speaking at this volume from here-

Andrew Huberman 24:31 Yeah.

Dr. Jennifer Groh 24:31 ... or somebody else was speaking at this volume from here-

Andrew Huberman 24:34 Right. So that the-

Dr. Jennifer Groh 24:34 ... it'd be too loud.

Andrew Huberman 24:35 Got it. So for those just listening, so, uh, Jenny's, uh, referring to ... So the distance between your mouth and your ear is a very short one, and if someone were to speak into your ear at that distance, I suppose unless they were telling you something you really wanted to hear-

Dr. Jennifer Groh 24:53 (laughs)

Andrew Huberman 24:53 ... you'd probably feel like, "Hey, get out of my personal space."

Dr. Jennifer Groh 24:57 You want somebody to, to speak a little more softly.

Andrew Huberman 24:59 Yeah. And yet we're doing it all the time.

Dr. Jennifer Groh 25:01 All the time. So-

Andrew Huberman 25:02 It's just that we're projecting it outward.

Dr. Jennifer Groh 25:04 Well, we're projecting it outward, and our brain is turning down the volume-

Andrew Huberman 25:08 Mm-hmm.

Dr. Jennifer Groh 25:08 ... um, in anticipation of what we're s- what we're saying.

Andrew Huberman 25:11 Got it.

Dr. Jennifer Groh 25:11 So it's a very, you know ... Potentially, it could be a very precisely timed volume knob that is going-

Andrew Huberman 25:18 Mm-hmm.

Dr. Jennifer Groh 25:18 ... with each little word that I say.

Andrew Huberman 25:21 So when the psychologists say that we can't speak and hear at the-

Dr. Jennifer Groh 25:24 Yeah.

Andrew Huberman 25:24 ... same time, they're 100% accurate.

Dr. Jennifer Groh 25:27 Probably.

Andrew Huberman 25:28 (laughs) That we can't speak and hear correctly.

Dr. Jennifer Groh 25:29 We cannot. And then the third thing is that, this maybe goes back to the first point about the recording doesn't capture all of it, is that some of what, um, we are picking up is actually through bone conduction. You may have bone conduction, uh, headphones. I certainly do. These are headphones that, um, they're, they don't go over the ears. They don't go in the ears. They're usually positioned right in front of the ears, delivering the vibration signals to the bone right in front of your ear. And that can get transmitted into your ears as well.

Andrew Huberman 26:01 You have these headphones?

Dr. Jennifer Groh 26:02 I have these, I have these, um-

Andrew Huberman 26:04 Why do you use these instead of in-ear earbu-

Dr. Jennifer Groh 26:06 In-ear?

Andrew Huberman 26:07 Yeah.

Dr. Jennifer Groh 26:07 'Cause it leaves my ears open so I can hear something else, so that it's safer if you're out exercising somewhere where there might be traffic-

Andrew Huberman 26:13 Mm-hmm.

Dr. Jennifer Groh 26:13 ... or something like that.

Andrew Huberman 26:15 I get

Andrew Huberman 26:16 a lot of questions about headphones and safety, and, uh, one thing that, uh, we resolved recently on the podcast, we had a guest on who's, uh, our chair of otolaryngology at Stanford, and she said that if your headphones are loud enough that somebody besides you can hear that there is a sound, not even the-

Dr. Jennifer Groh 26:37 Yeah.

Andrew Huberman 26:37 ... specific sounds-

Dr. Jennifer Groh 26:38 Yeah.

Andrew Huberman 26:39 ... uh, you are inflicting hearing damage.

Dr. Jennifer Groh 26:41 Right.

Andrew Huberman 26:42 Probably permanent hearing loss at some level. That, that-

Dr. Jennifer Groh 26:44 Yeah.

Andrew Huberman 26:45 She sets a pretty low threshold for, um, kind of like, "Be careful," but it seems important given that we now know hearing loss is correlated with dementia.

Dr. Jennifer Groh 26:55 Right.

Andrew Huberman 26:55 It makes sense. Less sensory information comes in, the brain probably says, "Oh, well, there's less stuff coming in," and starts-

Dr. Jennifer Groh 27:01 Right.

Andrew Huberman 27:01 ... turning off circuits. And then memory goes and attention goes, and there are other things obviously that can impact dementia, but, um ... So it's interesting. Um, the other question I get a lot, um, is, uh, about the Bluetooth-

Dr. Jennifer Groh 27:16 Mm-hmm.

Andrew Huberman 27:16 ... earphones. People want to know, are they safe? Is it safe to have this, like, Bluetooth arc o- you know-

Dr. Jennifer Groh 27:21 Oh, in-

Andrew Huberman 27:22 ... i- in your ears.

Dr. Jennifer Groh 27:23 In your ear?

Andrew Huberman 27:23 And, uh, we had a guest on here, uh, Matt MacDougall, who's the, uh, neurosurgeon at Neuralink-

Dr. Jennifer Groh 27:29 Mm-hmm.

Andrew Huberman 27:29 ... they're big on Bluetooth-

Dr. Jennifer Groh 27:30 Mm-hmm.

Andrew Huberman 27:30 ... there at Neuralink, but he said that the amount of, uh, radiation coming from those Bluetooth headphones-

Dr. Jennifer Groh 27:35 Mm.

Andrew Huberman 27:36 ... is considerably lower than the sort of radiation that you're exposed to all day, every day, so he wasn't concerned. Are you aware of any impact of heat? I'm not look- looking to go after EMF here if-

Dr. Jennifer Groh 27:49 Yeah.

Andrew Huberman 27:49 ... if there isn't anything there, but-

Dr. Jennifer Groh 27:50 Yeah.

Andrew Huberman 27:50 ... but of heat or of just having, um, EMF around-

Dr. Jennifer Groh 27:55 Around your ears?

Andrew Huberman 27:56 ... your ears, given the sensitivity of the bone. I mean, I'm just amazed-

Dr. Jennifer Groh 27:59 Yeah.

Andrew Huberman 27:59 ... that you can pick up sound from the bone vibrations. I mean, this is a very sensitive neural-

Dr. Jennifer Groh 28:04 Yeah.

Andrew Huberman 28:04 ... uh, sensory space is what I'm realizing.

Dr. Jennifer Groh 28:06 Right. I do think that there's, um, concerns about just how much sound exposure people are accumulating.

Andrew Huberman 28:15 Mm-hmm.

Dr. Jennifer Groh 28:15 If we live long enough, 80% of us will get hearing loss at some point in our lives.

Andrew Huberman 28:20 Bummer.

Dr. Jennifer Groh 28:21 So it's a big problem.

Andrew Huberman 28:24 Mm-hmm.

Dr. Jennifer Groh 28:24 There's certainly concerns that young people are farther along on that trajectory to hearing loss than people from older generations were at a comparable age.

Andrew Huberman 28:36 Mm-hmm.

Dr. Jennifer Groh 28:37 Um, just because there's, you know ... The earbuds are in from morning to night and volume turned up loud enough to block out surrounding sounds, you know, if you're in a-

Andrew Huberman 28:48 Mm-hmm.

Dr. Jennifer Groh 28:49 ... a loud environment. I would encourage people to give some consideration to noise-canceling headphones and to not having the volume be turned up too loud.

Andrew Huberman 28:56 Mm-hmm.

Andrew Huberman 28:57 Like to talk about the experience of listening to something, music let's say-

Dr. Jennifer Groh 29:02 Mm-hmm.

Andrew Huberman 29:02 ... through headphones versus in the room.

Dr. Jennifer Groh 29:04 Mm-hmm.

Andrew Huberman 29:06 We don't think about it too often, but it's a totally different experience. In one case, you're hearing the sound in your head.

Dr. Jennifer Groh 29:11 Yeah. Right.

Andrew Huberman 29:12 Or even listen- You know, like your phone on speaker versus wearing ear- earphones.

Dr. Jennifer Groh 29:18 Right.

Andrew Huberman 29:19 The person's voice or the music is in, in your head-

Dr. Jennifer Groh 29:22 Right.

Andrew Huberman 29:22 ... as opposed to in the room.

Dr. Jennifer Groh 29:24 Right.

Andrew Huberman 29:24 And once you think about this difference, I, I simply can't go back.

Dr. Jennifer Groh 29:28 Uh-huh.

Andrew Huberman 29:28 It's like a-

Dr. Jennifer Groh 29:29 You like the full actual speakers, or do you-

Andrew Huberman 29:32 N- Well, now I-

Dr. Jennifer Groh 29:32 ... Do you like it in your head?

Andrew Huberman 29:33 ... try to listen to music in the room.

Dr. Jennifer Groh 29:35 Yeah.

Andrew Huberman 29:35 I find that to be a-

Dr. Jennifer Groh 29:37 Yep.

Andrew Huberman 29:37 ... better experience for me. But when I hear things with headphones, I now feel like, oh, like, the sound is coming from inside my head, and it, it's a little weird.

Dr. Jennifer Groh 29:48 Yeah. Yeah.

Andrew Huberman 29:48 I don't like it so much.

Dr. Jennifer Groh 29:49 Yeah. Right. It is possible to make sound that is coming from headphones f- sound like it is coming from outside, but to do that, you have to use all three of these sound localization cues. Um, things have to be, you know, to have a, a, an appropriate timing difference, an appropriate level difference across the two ears, uh, and to use the, the frequency filtering properties of, of the ear. And since everybody's ears are a little bit different, that last step is really hard.

Andrew Huberman 30:18 But there is 3D sound, right?

Dr. Jennifer Groh 30:20 Yeah.

Andrew Huberman 30:21 Like, we think about, like, three-dimensional vision is-

Dr. Jennifer Groh 30:23 Mm-hmm.

Andrew Huberman 30:23 ... simple for people to think about.

Dr. Jennifer Groh 30:25 Mm-hmm.

Andrew Huberman 30:25 As long as they're sighted, you understand that, you know, you expect things that are closer to you to be larger.

Dr. Jennifer Groh 30:31 Mm-hmm.

Andrew Huberman 30:31 ... than if they were far away. That, we kind of, we, we learned this without thinking about-

Dr. Jennifer Groh 30:35 You've got so many wonderful cues to distance in vision, right?

Andrew Huberman 30:38 Yeah. Yeah, things in the distance are harder to resolve-

Dr. Jennifer Groh 30:40 Right.

Andrew Huberman 30:40 ... as opposed to things up close, which you can see all the detail.

Dr. Jennifer Groh 30:42 Right.

Andrew Huberman 30:42 And there are all these cues, right?

Dr. Jennifer Groh 30:45 Right.

Andrew Huberman 30:45 Uh, that we could talk about. But since we're talking about hearing-

Dr. Jennifer Groh 30:47 Mm-hmm.

Andrew Huberman 30:48 ... the sounds that we hear at a given level, we know are close, are coming from objects that are actually close or far away-

Dr. Jennifer Groh 30:58 Mm-hmm.

Andrew Huberman 30:58 ... usually based on what we see.

Dr. Jennifer Groh 30:59 Mm-hmm, yeah.

Andrew Huberman 31:00 Right? So, what is 3D sound?

Dr. Jennifer Groh 31:02 Yeah.

Andrew Huberman 31:02 How, how do I know the difference between a sound that's right in front of my face with-

Dr. Jennifer Groh 31:06 Yeah.

Andrew Huberman 31:06 ... versus far away-

Dr. Jennifer Groh 31:07 Right.

Andrew Huberman 31:07 ... with my eyes closed?

Dr. Jennifer Groh 31:08 Right.

Andrew Huberman 31:08 How do I know?

Dr. Jennifer Groh 31:09 This is a computational process in the brain that we don't fully understand, and it's worth thinking about, what are, what are the available pieces of information that you could use? Sound is much more bendy than light is.

Andrew Huberman 31:21 Bendy?

Dr. Jennifer Groh 31:22 Bendy, like it bends, right? It go-

Andrew Huberman 31:24 Goes around things.

Dr. Jennifer Groh 31:25 It goes around things, whereas light is just kind of like a straight, straight shot, you know. You don't have the opportunity to use the same kind of information for sound depth that you do for vision.

Andrew Huberman 31:34 Mm-hmm.

Dr. Jennifer Groh 31:35 Um, even though you have two ears, you can't form an image and check to see whether or not the images line up-

Andrew Huberman 31:41 Mm-hmm.

Dr. Jennifer Groh 31:41 ... which is what stereo vision is.

Andrew Huberman 31:43 Mm-hmm.

Dr. Jennifer Groh 31:43 You don't have occlusion cues, that is to say, one thing being in front of the other blocks your, your ability to see the thing that's behind.

Andrew Huberman 31:51 Mm-hmm.

Dr. Jennifer Groh 31:52 So, you know, the sound can go around objects. So, there's a few different cues that we can use. Uh, one is simply, how loud is the sound?

Andrew Huberman 32:01 Mm-hmm.

Dr. Jennifer Groh 32:02 Um, things that are farther away are gonna sound quieter, but you have to know what the sound volume was out there in the world in order to interpret whether or not that is quiet or loud.

Andrew Huberman 32:16 Let's use thunder as an example because-

Dr. Jennifer Groh 32:18 Yeah.

Andrew Huberman 32:18 ... thunder sounding very loud predicts lightning that might hit you.

Dr. Jennifer Groh 32:22 Right.

Andrew Huberman 32:22 Thunder that sounds way off in the distance-

Dr. Jennifer Groh 32:24 Right.

Andrew Huberman 32:24 ... if you have an understanding of thunder and lightning, predicts a lower probability-

Dr. Jennifer Groh 32:30 Right.

Andrew Huberman 32:30 ... of you getting hit by lightning.

Dr. Jennifer Groh 32:31 Right.

Andrew Huberman 32:31 I had this experience recently. I got caught in a sudden, uh, lightning storm, thunder lightning storm in Austin, Texas, and it was coming down in sheets. And then, you know, and the thunder gets louder and louder, and you're like, "Wow." And, and then the lightning-

Dr. Jennifer Groh 32:45 And then-

Andrew Huberman 32:45 ... gets brighter and brighter, and you think, "I could get electrocuted." And, uh, it seems like a low probability event.

Dr. Jennifer Groh 32:52 Right. Depending on where you grew up, um, you might have learned as a child, like, some basics of how to tell, like when it's a good idea to, you know, get to shelter.

Andrew Huberman 33:02 Mm-hmm.

Dr. Jennifer Groh 33:02 Um, so, you know, for example, I was taught growing up, you know, you count one-one thousand, two-one thousand, whatever. As long as you can count to, like, five seconds, you're probably okay, but once you're getting to that level, you should, you know, maybe go inside. (laughs)

Andrew Huberman 33:16 There, let, take that-

Dr. Jennifer Groh 33:17 Yeah.

Andrew Huberman 33:18 ... take that one in, folks, from somebody who grew up with them.

Dr. Jennifer Groh 33:20 (laughs)

Andrew Huberman 33:20 You see the flash of lightning, you-

Dr. Jennifer Groh 33:22 One-one thousand, two-one thousand, three-one thousand, four-one thousand, five-one thousand. And if it takes longer than that before you hear the thunder, you're okay, but at that point, I would go inside.

Andrew Huberman 33:33 You may have saved some lives.

Dr. Jennifer Groh 33:34 (laughs)

Andrew Huberman 33:34 Yeah. Growing up in California, we didn't learn anything about it.

Dr. Jennifer Groh 33:38 You didn't, you didn't get that, and people who grew up in cities wouldn't have gotten this.

Andrew Huberman 33:41 Mm-hmm.

Dr. Jennifer Groh 33:41 I think in cities, it's actually very hard to see the connection between the light, lightning and the thunder.

Andrew Huberman 33:46 Mm-hmm.

Dr. Jennifer Groh 33:47 Um, but I grew up in rural Vermont, and it was, like, very obvious.

Andrew Huberman 33:51 Mm-hmm.

Dr. Jennifer Groh 33:52 Yeah.

Andrew Huberman 33:52 I grew up in the San Francisco Bay area, and I've been through so many earthquakes. And one of the things that, uh, people don't realize if they've never been in a major earthquake is that it's extremely loud. It starts with sound, not shaking.

Dr. Jennifer Groh 34:07 Yeah.

Andrew Huberman 34:07 You don't, you don't-

Dr. Jennifer Groh 34:08 Sure.

Andrew Huberman 34:08 So, th- this is, people are always saying, "California earthquakes." And, you know, and, with the A9 quake, and the Embarcadero-

Dr. Jennifer Groh 34:13 Yeah.

Andrew Huberman 34:14 ... Freeway pancaked, and the Bay Bridge, actually, a segment fell out.

Dr. Jennifer Groh 34:17 Yeah, yeah.

Andrew Huberman 34:17 People forget this. During the World Series. If that happened now, there would be so many casualties, but it was a lot less busy in the Bay area back then.

Dr. Jennifer Groh 34:24 Yeah.

Andrew Huberman 34:25 The first thing that happens in an earthquake is it sounds like a train is about to come through the room.

Dr. Jennifer Groh 34:31 Yeah, sure.

Andrew Huberman 34:31 It goes (imitates sound) . And, and then the shaking starts shortly thereafter.

Dr. Jennifer Groh 34:35 Uh-huh.

Andrew Huberman 34:36 But the sound always comes first.

Dr. Jennifer Groh 34:38 Huh.

Andrew Huberman 34:39 I always tell people this when they're afraid of earthquakes.

Dr. Jennifer Groh 34:41 Yeah.

Andrew Huberman 34:41 Like, you'll hear it before you'll feel it.

Dr. Jennifer Groh 34:42 Before you see it, feel it, yeah.

Andrew Huberman 34:43 So, if it sounds like a train is c- gonna come-

Dr. Jennifer Groh 34:45 Yeah.

Andrew Huberman 34:45 ... through the, the room, you're probably about to have an earthquake.

Dr. Jennifer Groh 34:50 Right. I think elephants use, um, sound to communicate over long distances. I, so-

Andrew Huberman 34:57 That's cool. They stomp?

Dr. Jennifer Groh 34:59 Yeah. I think so, or they can hear... yeah, they can hear things. And I think they have sensors in their feet that can pick up these vibrations that we might call sound.

Andrew Huberman 35:07 Oh, that's cool.

Dr. Jennifer Groh 35:08 Yeah.

Andrew Huberman 35:09 That's like that scene in Stand By Me-

Dr. Jennifer Groh 35:11 Yeah.

Andrew Huberman 35:11 ... where they're crossing the train tracks on a bridge.

Dr. Jennifer Groh 35:14 Yeah.

Andrew Huberman 35:14 And all the kids are just kind of moving along, and then-

Dr. Jennifer Groh 35:17 Yeah.

Andrew Huberman 35:18 ... uh, Gordie, who's the-

Dr. Jennifer Groh 35:19 Yeah.

Andrew Huberman 35:19 ... arguably one of the smarter in the bunch-

Dr. Jennifer Groh 35:21 Yeah.

Andrew Huberman 35:21 He, he's like, he's reaching down and holding the tracks-

Dr. Jennifer Groh 35:25 He's feeling the-

Andrew Huberman 35:25 ... and he feels the track shakes-

Dr. Jennifer Groh 35:27 He feels it.

Andrew Huberman 35:27 ... before he hears the, the-

Dr. Jennifer Groh 35:29 Hears it, yeah.

Andrew Huberman 35:29 ... the, um-

Dr. Jennifer Groh 35:30 Yeah.

Andrew Huberman 35:30 ... the horn, and then, of course, the smoke rounds the corner, train rounds the corner and-

Dr. Jennifer Groh 35:34 Interesting, interesting.

Andrew Huberman 35:35 Yeah, yeah.

Dr. Jennifer Groh 35:36 And with the elephants, I'm not sure. I think maybe it's not sensors in the feet, but bone conduction from the feet to the ear.

Andrew Huberman 35:42 Hmm.

Dr. Jennifer Groh 35:43 Um, and that's where it's, where it's being picked up. So, okay-

Andrew Huberman 35:47 Interesting.

Dr. Jennifer Groh 35:47 ... so your question was, if I can go back to your question.

Andrew Huberman 35:49 Mm-hmm, mm-hmm.

Dr. Jennifer Groh 35:49 It was about distance, and how do we know how far away a sound is coming from?

Andrew Huberman 35:53 Mm-hmm.

Dr. Jennifer Groh 35:53 So, the, the loudness cue requires you to know something about how loud the original stimulus at the source is. And so thunder's a wonderful example of this, because we do have quite a bit of experience with thunder, so we can kinda use how loud it is as a good cue. And it also works great because we're talking about really long distances, right? There's another pretty cool cue that you and I are probably using right now, and that is that the sound in this room is bouncing off of all the different surfaces. So, the shortest path copy of the sound is coming straight from your mouth to my ears.But in addition, there's a copy that's bouncing off of the table that's between us. That will have a s- has a longer path length, so it'll be slightly delayed. There'll be another copy that's, you know, hitting the ceiling and, and coming down to my ears.

Andrew Huberman 36:45 Oh, this is weird.

Dr. Jennifer Groh 36:46 And that is gonna have a even s- longer delay. I'm completely unaware of this, but my brain is probably using the slight differences and the kind of pattern of slight differences to figure out, you know, that you're about seven feet away from me. If we were closer to, uh, to each other, the difference between that straight path copy and the copy bouncing off of the table would be greater than it is right now, 'cause at, at this angle, with this, you know, geometry, there's really not that much difference, so the bounced off copy-

Andrew Huberman 37:20 Hm.

Dr. Jennifer Groh 37:20 ... and the straight path copy are, are pretty similar.

Andrew Huberman 37:23 I never thought

Andrew Huberman 37:24 about this.

Dr. Jennifer Groh 37:25 It's incredible, right?

Andrew Huberman 37:26 This is a way that vision is so different.

Dr. Jennifer Groh 37:28 Yeah.

Andrew Huberman 37:29 I came up through vision science-

Dr. Jennifer Groh 37:30 Yeah.

Andrew Huberman 37:30 ... mostly. Um-

Dr. Jennifer Groh 37:31 Yeah, so did I.

Andrew Huberman 37:32 And ... right, I mean, there are certain wavelengths of light that can pass through our body, like-

Dr. Jennifer Groh 37:36 Yeah.

Andrew Huberman 37:37 ... long wavelength light. That's-

Dr. Jennifer Groh 37:38 Mm-hmm.

Andrew Huberman 37:38 ... relatively new findings. I think it's really interesting and it's very healthy for us, it turns out.

Dr. Jennifer Groh 37:41 Yeah.

Andrew Huberman 37:42 You know, mitochondrial health, et cetera. But light, in general, we're not used to thinking about light and wavelengths of light going through things, unless they're translucent or transparent, like a window. Sound is constantly bouncing off everything.

Dr. Jennifer Groh 37:57 We're in a hall of mirrors for sound all the time.

Andrew Huberman 38:00 But you experience me and I experience you during this conversation as one coherent sound. Even though we are ... biologically poised to detect half a millisecond differences in the a- arrival time of the two ears, there are much greater differences in the arrival time of my voice bouncing off the table versus the walls versus the ceiling versus direct path, but you integrate them.

Dr. Jennifer Groh 38:24 And I don't hear you as saying the same thing, you know, five different times, right?

Andrew Huberman 38:28 Right.

Dr. Jennifer Groh 38:28 You know, it's one integrated whole.

Andrew Huberman 38:30 And closing one's eyes doesn't change that. If I close my eyes and you speak-

Dr. Jennifer Groh 38:34 Right.

Andrew Huberman 38:35 ... I can register to the direct path. I infer that you're right in front of me. Of course I know that, 'cause my eyes were open a second ago. But all the versions of your voice arriving, bouncing off the different surfaces or arriving at my ears, and I don't ... it doesn't, it's not confusing and it's not jarring.

Dr. Jennifer Groh 38:51 Right.

Andrew Huberman 38:51 Like if somebody came over and touched my arm, and I felt it on my arm but also a little bit on the back of my neck and a little bit on my knee, that would be weird. That w- that would be odd. You know, and we can get these sensations. There are certain places on the back, for instance, that you can feel a subtle kind of phantom touch in your foot because of the way the neural circuits are organized. And with pain, we talk about this as, like, referenced pain. You know, for internal organs, there's, they're branches of, they're, uh, of nerves, such that, you know, uh, and this shows up in, you know, Eastern medicine but also Western medicine, like someone with a, with, like, liver pain-

Dr. Jennifer Groh 39:25 Mm-hmm.

Andrew Huberman 39:26 ... will register that in their shoulder, you know, and it, or-

Dr. Jennifer Groh 39:28 Yeah.

Andrew Huberman 39:28 ... and we think, "Oh, this is crazy." No, it's not crazy. The- there's actually branches that, that support that referenced pain. But we don't do this with hearing.

Dr. Jennifer Groh 39:37 Yeah.

Andrew Huberman 39:38 We shut it all down and we just collect the, the ... we, we make, we draw a conclusion.

Dr. Jennifer Groh 39:43 Right.

Andrew Huberman 39:46 Wild.

Dr. Jennifer Groh 39:46 It's wild, isn't it?

Andrew Huberman 39:47 It's totally wild. Uh, are you about to tell me that our voices are also causing vibrations in the objects around us and that we just can't detect them? Why are we not like the elephants? How come we-

Dr. Jennifer Groh 39:57 Uh, maybe we are like the elephants. I don't know.

Andrew Huberman 40:00 Is it the case that low frequency sounds can travel further with respect to our ability to detect them?

Dr. Jennifer Groh 40:09 Mm-hmm.

Andrew Huberman 40:09 So I, you know, I don't wanna get into a conversation about frequency of sound and-

Dr. Jennifer Groh 40:13 Yeah.

Andrew Huberman 40:13 ... and intensity and vers- high versus low frequency, 'cause that's, that's really about the physics of sound.

Dr. Jennifer Groh 40:19 Right, right.

Andrew Huberman 40:20 But ultimately, we filter the physics of sound through our nervous system. So ... if I want to signal to somebody far away, I would probably want, like, a big bass drum or a gong. I would not try to whistle to them far away. Or if I could pick a horn that was a, a deep, like (imitates deep horn)

Dr. Jennifer Groh 40:43 Mm-hmm.

Andrew Huberman 40:43 ... versus like (imitates high-pitched horn)

Dr. Jennifer Groh 40:45 (laughs)

Andrew Huberman 40:46 I'd want bass.

Dr. Jennifer Groh 40:48 So there's a few things wrapped up here. One is that the lower frequencies bend more, bend more easily, so they, they can go around these objects better.

Andrew Huberman 40:57 Mm-hmm.

Dr. Jennifer Groh 40:58 So if you're talking really la- long distances, you know, the odds that there's something in the path that you wanna-

Andrew Huberman 41:03 Mm-hmm.

Dr. Jennifer Groh 41:04 ... the sound to go around are, are, are ... go up. Uh, another thing that's wrapped up here is that we tend to lose high frequency hearing before we lose low frequency hearing.

Andrew Huberman 41:16 Mm-hmm.

Dr. Jennifer Groh 41:17 And so, the lower frequencies are audible to more people, and, and are louder to people than the higher frequencies.

Andrew Huberman 41:25 So you're saying it's because they can bend around objects.

Dr. Jennifer Groh 41:28 Well, I don't really know what the choices that are being made are-

Andrew Huberman 41:32 Mm-hmm.

Dr. Jennifer Groh 41:32 ... by the people whose job it is to figure these kinds of things out. But I'm sure that there's some thought being given to the receiver, you know, the, the people, and what they can, what they can perceive. So, let's take a couple other examples of warning systems that-

Andrew Huberman 41:48 Mm-hmm.

Dr. Jennifer Groh 41:48 ... that humans use. The gas in a gas stove doesn't have an intrinsic odor to it.

Andrew Huberman 41:54 Hm.

Dr. Jennifer Groh 41:55 There's an odorant that's been added. Um-

Andrew Huberman 41:57 That rotten egg, sulfur smell.

Dr. Jennifer Groh 41:59 That rotten egg n- uh, yeah, exactly. And so, you know, that was chosen a long time ago to be added, and, you know, turns out to be a good thing, because it doesn't, doesn't really smell like anything else. It's not pleasant, but everybody can detect it. I don't-

Andrew Huberman 42:13 Mm-hmm.

Dr. Jennifer Groh 42:13 ... know of any cases of people that can't smell that unless they have a generalized, uh, anosmia where they can't smell anything.

Andrew Huberman 42:21 Mm-hmm.

Dr. Jennifer Groh 42:21 Traffic lights are maybe a little bit of a less of a win, because you've got red versus green. And 6% of the population is red/green colorblind-... which operationally means not that you can't see a red stimulus or a green stimulus, but that you can't tell the difference, um, you know, whether or not something is red or green.

Andrew Huberman 42:42 Yeah, I should just say that, um, that most red-green color-blind people tend to be males-

Dr. Jennifer Groh 42:48 Yes.

Andrew Huberman 42:48 ... just because of where the, the gene mutation is in the, in the genome. And they don't see r- ... People always want to know, like, what, what does red look like to them.

Dr. Jennifer Groh 42:57 Yeah.

Andrew Huberman 42:58 Uh, r- red and green look kind of more orange-ish, burnt brown-orange color, and dogs see the world that way all the time.

Dr. Jennifer Groh 43:06 Right. So if you do a color-matching experiment, I ... my understanding is something along the lines of people with red-green color blindness will map both red and green onto yellow-

Andrew Huberman 43:16 Mm-hmm.

Dr. Jennifer Groh 43:16 ... and not-

Andrew Huberman 43:17 Yeah, that's right.

Dr. Jennifer Groh 43:17 ... and not be able to tell the difference. It's not the k- kind of, uh, cartoon view of, like, it looks black and white.

Andrew Huberman 43:23 There are people who are completely monochromatic, but it's very rare.

Dr. Jennifer Groh 43:27 Very rare.

Andrew Huberman 43:27 Very, very rare.

Dr. Jennifer Groh 43:28 Yeah.

Andrew Huberman 43:28 And there are other forms of color blindness that are more subtle, and color blindness ... People should ... We'll put a link to this. Uh, Jay and Maureen Neitz up at the University of Washington have a terrific, um ... They run a color vision lab.

Dr. Jennifer Groh 43:39 Mm-hmm.

Andrew Huberman 43:39 She's a molecular biologist. He's more of a psychophysicist. And they have some really great color vision tests there that people can take, and many people find that they have subtle color vision deficits.

Dr. Jennifer Groh 43:49 Yeah, yeah.

Andrew Huberman 43:50 Uh, w-

Dr. Jennifer Groh 43:50 Exactly.

Andrew Huberman 43:51 But, but they don't consider themselves fully color blind, but every once in a while, uh, uh, monochromats usually know-

Dr. Jennifer Groh 43:57 Yeah, monochromats.

Andrew Huberman 43:57 ... that they're seeing the world in black and white.

Dr. Jennifer Groh 43:59 Right. And a lot of what, you know, is under this heading is, is really more an anomaly than a complete absence of an ability to distinguish red from green. But back to our traffic lights. So, you got your red versus green signaling something very different, and most places have those lights oriented vertically, which gives you a second cue to what's, what needs to be conveyed here. So-

Andrew Huberman 44:23 Not the same light switching.

Dr. Jennifer Groh 44:24 Right. It's not the same light switching-

Andrew Huberman 44:26 Mm-mm.

Dr. Jennifer Groh 44:26 Um, and one is on top, and the other's on the bottom.

Andrew Huberman 44:29 Mm-hmm.

Dr. Jennifer Groh 44:29 It's more of a problem when, uh, in some intersections, the, the, the set of three lights is oriented horizontally.

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Andrew Huberman 47:39 So really, what we're talking about i- that I'd like to drill into even deeper across senses, but primarily with sound, is, you know, how space, uh, how the physical environment shapes our p- our perception of things.

Dr. Jennifer Groh 47:53 Yeah, yeah.

Andrew Huberman 47:54 Um, and I'm also very interested in the vi- the relationship between vibration and sound, given that our ears contain the apparatus to detect sound frequency but also, uh, have to do with, you know, balance and, and vibration.

Dr. Jennifer Groh 48:10 Mm-hmm.

Andrew Huberman 48:11 Most of us have had the experience of someone pulling up next to us in a car, blasting bass really loud-

Dr. Jennifer Groh 48:16 Oh, yeah.

Andrew Huberman 48:16 ... and our windows start shaking, and their windows-

Dr. Jennifer Groh 48:18 Right.

Andrew Huberman 48:18 ... start shaking.

Dr. Jennifer Groh 48:19 Right.

Andrew Huberman 48:19 Can we talk just about how objects have a, a, a resonant frequency?

Dr. Jennifer Groh 48:23 Right.

Andrew Huberman 48:24 I think this is pretty interesting-

Dr. Jennifer Groh 48:25 Right.

Andrew Huberman 48:25 ... and then people will inevitably want to know about how humans have a resonant frequency-

Dr. Jennifer Groh 48:29 Mm-hmm.

Andrew Huberman 48:29 ... and we do. I believe that certain frequencies of sound can shape our emotional state.

Dr. Jennifer Groh 48:33 Oh, sure. I mean, that's music, right?

Andrew Huberman 48:37 ... for example, right?

Dr. Jennifer Groh 48:37 For example.

Andrew Huberman 48:38 It just, for some reason, when we break it down to one frequency and it's not-

Dr. Jennifer Groh 48:42 Mm-hmm.

Andrew Huberman 48:42 ... um, packaged in music, people somehow think it's, like, woo or mysticism and it's-

Dr. Jennifer Groh 48:48 Mm-hmm.

Andrew Huberman 48:48 ... it's not.

Dr. Jennifer Groh 48:49 Mm-hmm.

Andrew Huberman 48:49 I mean, the, I'm fascinated by this, like, the gong, like, gongs as an ancient tool for j- well, trying to orient people's emotional state or signal.

Dr. Jennifer Groh 48:58 Mm-hmm.

Andrew Huberman 48:58 Like, if we hear (imitates gong) going, it sounds ominous, right? If we hear chirping of birds-

Dr. Jennifer Groh 49:06 Yeah.

Andrew Huberman 49:06 ... we know they're birds. But if we hear light, um, you know, in the Disney movies that, you know-

Dr. Jennifer Groh 49:10 Yeah.

Andrew Huberman 49:10 ... it's been a long time since I've seen a Disney movie, but the, the kind of the, the, the, the stuff of fluttering is high frequency. High frequency movement tends to be high frequency sound. So w- m- how do you think about the relationship between frequency and emotion and resonant frequency? I mean, it's a vast landscape.

Dr. Jennifer Groh 49:29 Yeah.

Andrew Huberman 49:29 But I'd love your thoughts on this.

Dr. Jennifer Groh 49:31 Yeah. So can we, can we go into the music realm to talk about this?

Andrew Huberman 49:35 Please, I think that's intuitive for many people.

Dr. Jennifer Groh 49:37 Okay. Okay, good.

Andrew Huberman 49:38 Yeah.

Dr. Jennifer Groh 49:38 So one of the things that I think is fascinating about music is that it's universal and nobody really knows what it's for. Like, it's pretty clear that language is useful to us, right?

Andrew Huberman 49:53 Mm-hmm.

Dr. Jennifer Groh 49:53 It, you know, helps us exchange information.

Andrew Huberman 49:56 Mm-hmm.

Dr. Jennifer Groh 49:56 So pretty obvious that language is, is a benefit, a survival benefit for individuals and for the species as a whole.

Andrew Huberman 50:04 Mm-hmm.

Dr. Jennifer Groh 50:05 We don't really have as clear a view of why music, you know, what role did music play in our, um, success, uh, in evolution, natural selection. You know, music is, it really is universal, um, every human culture has it. Um, there is some variation as to whether or not, um, a culture embraces melody, embraces harmony, but every culture has rhythm. You can't have melody or harmony without rhythm. It doesn't make any sense, right? Like, imagine, imagine a familiar tune like Happy Birthday, but the duration of the notes was completely arbitrary, you know?

Andrew Huberman 50:49 Yeah, it would sound crazy.

Dr. Jennifer Groh 50:50 It would sound crazy. It's, it would not be recognizable to us as Happy Birthday. But you can, um, you can play it fast, you can play it slow, you can play it, you know, pitch shift it up or pitch shift it down, musical terms, in a different key, and we would recognize that as, like, a particular, you know, song. Um, so that's what I mean about rhythm being, uh, really critical. Um, and the criticality of rhythm offers up the following kinda wild, uh, theory. This is not my theory, um, I wish I could quote whosever theory it is, but it is that perhaps what rhythm, what music and rhythm is for, is to help us act in concert with one another and be louder than any of us could be by ourselves.

Andrew Huberman 51:40 Mm.

Dr. Jennifer Groh 51:41 Um, and to scare off predators and competitors. So, for example, imagine a pack of hyenas are surrounding a kill from, you know, a, a lion, the lion is long since sated and got, has gone away, but now a bunch of scrawny humans wanna scare off, uh, the hyenas. If they go after the hyenas all stomping their feet together and shouting together, it's gonna be a lot louder than any one person could do by themselves.

Andrew Huberman 52:14 Oh, I like this theory.

Dr. Jennifer Groh 52:15 It's kinda nice, right?

Andrew Huberman 52:17 I'll tell you why in a moment, but please continue.

Dr. Jennifer Groh 52:19 And then that kind of concerted working together as a group, and you could sort of see that, like, once you had the, the basics of like... And here I'm talking, when I say once you have, I'm really imagining on an evolutionary scale that any, for anything to come about and endure requires that it increase our fitness at every stage of the way.

Andrew Huberman 52:43 Mm-hmm.

Dr. Jennifer Groh 52:44 So initially, you might get that rhythm thing going on, um, but then that would be satisfying to people, like, if you had a mutation that made acting together feel good for some reason, and then it would come along with this benefit of, of competing with the hyenas for the lion kill, and then would kind of potentially feed on itself of, like, well, even more cooperative action, feeling good together allows us to then do other things together that we can't do individually.

Andrew Huberman 53:22 Have you ever seen the, uh, it's a, a song and a, um, I don't exactly know what to call it, uh, the chanting and the song of, of Maori in New Zealand?

Dr. Jennifer Groh 53:35 Mm-hmm. Yeah.

Andrew Huberman 53:35 They'll do this before rugby games.

Dr. Jennifer Groh 53:37 Oh, right, the-

Andrew Huberman 53:38 Because the All Blacks are-

Dr. Jennifer Groh 53:39 Yeah.

Andrew Huberman 53:39 ... are one of the best rugby teams in the world. There's an incredible video-

Dr. Jennifer Groh 53:43 Uh-huh.

Andrew Huberman 53:43 ... um, that a friend of mine, she always sends this to me when, um, uh, when I'll say something like, "Oh, you know, what do you think of something that was on the news?" Or something. And she'll, and she'll send, there's, uh, an incredible case of in the government in New Zealand, I think it's a, I don't know if they use parliament or what-

Dr. Jennifer Groh 54:00 Mm-hmm.

Andrew Huberman 54:00 ... or what, there's an example of, um... Some (laughs) okay, I'll just say it how it is. They're-

Dr. Jennifer Groh 54:04 Yeah.

Andrew Huberman 54:05 Some white politician reads out some, you know, proclamation maybe like, uh, that's up for a vote, and then all of a sudden, it will-

Dr. Jennifer Groh 54:11 Yeah.

Andrew Huberman 54:11 ... start in one corner of this, uh, very majestic, like-

Dr. Jennifer Groh 54:16 Yes.

Andrew Huberman 54:16 ... government building, um, looks sort of like our Congress-

Dr. Jennifer Groh 54:20 Right.

Andrew Huberman 54:20 ... but it's, it's different, uh, and she'll start chanting, and then-

Dr. Jennifer Groh 54:23 Mm-hmm.

Andrew Huberman 54:23 ... and it's like wide eyes, there's no blinking.

Dr. Jennifer Groh 54:25 Mm-hmm.

Andrew Huberman 54:25 It's very interesting, and they're stomping and there's clapping, and then all of a sudden-

Dr. Jennifer Groh 54:28 Mm-hmm.

Andrew Huberman 54:28 ... it starts, other people start joining in with her.

Dr. Jennifer Groh 54:31 Right.

Andrew Huberman 54:32 And you're-

Dr. Jennifer Groh 54:32 And it gets really loud-

Andrew Huberman 54:33 And you're, and you're like, they're-

Dr. Jennifer Groh 54:33 ... when they're together.

Andrew Huberman 54:35 A, you know, you know a number of things immediately. A, they're pissed.... two, they're not gonna stand for this, three, there are a lot of them, and four, like, they're not to be messed with.

Dr. Jennifer Groh 54:45 They're united.

Andrew Huberman 54:46 They're united.

Dr. Jennifer Groh 54:47 Yeah.

Andrew Huberman 54:47 A- admittedly, I had to have someone look this up, it's called haka. Uh, and it's incredible because you immediately f- understand how these people feel. And it's a, "No, we're not gonna take that-"

Dr. Jennifer Groh 54:59 Right.

Andrew Huberman 54:59 ... kind of stance. At least in the context of this government example.

Dr. Jennifer Groh 55:02 Right.

Andrew Huberman 55:03 In terms of pre-rugby match, it's really a display of vigor, uh, and we are primates after all.

Dr. Jennifer Groh 55:13 Right, right.

Andrew Huberman 55:13 All, all, we are old world primates.

Dr. Jennifer Groh 55:15 Yep.

Andrew Huberman 55:16 Um, and vigor displays-

Dr. Jennifer Groh 55:18 Mm-hmm.

Andrew Huberman 55:18 ... uh, run through all the old world primate species-

Dr. Jennifer Groh 55:21 Yeah.

Andrew Huberman 55:21 ... including us.

Dr. Jennifer Groh 55:22 Yeah.

Andrew Huberman 55:22 Um, and we-

Dr. Jennifer Groh 55:23 I think it's definitely a vigor display.

Andrew Huberman 55:25 Like stomping, making one's body big.

Dr. Jennifer Groh 55:26 Right.

Andrew Huberman 55:27 And the lack of blinking is something that, you know, as a vision scientist, I caught onto early.

Dr. Jennifer Groh 55:31 Yeah.

Andrew Huberman 55:31 Like, no one's doing this and, and blinking a lot. They're, they're showing that they will not break their attention until this is complete. And somebody not blinking while staring directly at you-

Dr. Jennifer Groh 55:43 Mm-hmm.

Andrew Huberman 55:43 ... is a command for your att- attention as well.

Dr. Jennifer Groh 55:46 And it's even in our language, isn't it? "So-and-so didn't blink."

Andrew Huberman 55:49 That's right. They don't blink, they're not afraid, they're-

Dr. Jennifer Groh 55:52 Right.

Andrew Huberman 55:53 ... uh, you know, these days because of the craziness of the political socio landscape-

Dr. Jennifer Groh 55:59 Mm-hmm.

Andrew Huberman 55:59 ... with assassinations and very strong personalities-

Dr. Jennifer Groh 56:02 Mm-hmm.

Andrew Huberman 56:03 ... and government and online, and because, I mean, you know, how media now, to at least some extent-

Dr. Jennifer Groh 56:08 Mm-hmm.

Andrew Huberman 56:08 ... different form of media, not politics, but, you know, I'm so, um, intrigued by the idea that some people are capturing people's attention and loyalty not just by virtue of what they say, but the certainty with which they say it. Now, that's not a new theme, but also the timbre of their voice-

Dr. Jennifer Groh 56:28 Yeah.

Andrew Huberman 56:28 ... the refusal-

Dr. Jennifer Groh 56:29 Mm-hmm.

Andrew Huberman 56:30 ... to entertain dissenting voices, but also how a lot of voices are just not the right timbre and frequency-

Dr. Jennifer Groh 56:39 Mm-hmm.

Andrew Huberman 56:39 ... and delivered in the way that these people have obviously mastered-

Dr. Jennifer Groh 56:43 Mm-hmm.

Andrew Huberman 56:43 ... their ability to command other people's attention-

Dr. Jennifer Groh 56:45 Mm-hmm.

Andrew Huberman 56:45 Like, it's a, it's a, uh, because this stuff hits at a primitive level, right? People aren't necessarily just voting on issues.

Dr. Jennifer Groh 56:52 Yeah. Yeah.

Andrew Huberman 56:52 They're voting on feeling. We've known this.

Dr. Jennifer Groh 56:54 Right.

Andrew Huberman 56:55 So, in any case, the, the haka is a, is a beautiful example of what you're describing.

Dr. Jennifer Groh 56:59 Right. Well,

Dr. Jennifer Groh 57:00 and the other thing is that music plays a role in, um, in say the military and in war. I read somewhere that the military is the largest employer of musicians in this country.

Andrew Huberman 57:12 Interesting.

Dr. Jennifer Groh 57:13 Yeah.

Andrew Huberman 57:14 Makes sense.

Dr. Jennifer Groh 57:15 Well, you know, I thought, it was a surprise to me when I first-

Andrew Huberman 57:18 Yeah.

Dr. Jennifer Groh 57:18 ... first heard it.

Andrew Huberman 57:19 Yeah, surprising to me, but it, it makes-

Dr. Jennifer Groh 57:20 Yeah.

Andrew Huberman 57:20 I mean, somebody's gotta play Taps, usually that's one-

Dr. Jennifer Groh 57:22 (laughs)

Andrew Huberman 57:23 ... that's one horn though.

Dr. Jennifer Groh 57:24 Right, you get one-

Andrew Huberman 57:24 Right?

Dr. Jennifer Groh 57:24 Right. So, and I think the other, you know, possible angle for all of this is, you know, there are things in many species that are not o- obviously beneficial. Take the peacock for example, that, the, that enormous investment in plumage, in very colorful tail feathers is not something that is directly adding to the survival skills of the male peacock, but rather it's something the female peacocks like. Um, and so that tends to feed on itself too. So, that's another way that music could get into our, you know, panoply of human characteristics without necessarily directly leading to something like being able to get more food. Like, the rhythm thing gives us more food.

Andrew Huberman 58:09 Mm-hmm.

Dr. Jennifer Groh 58:09 People who are good at music might end up, um, with more offspring than people who, um, weren't good at music. That would be, that would be the sort of, uh, general idea behind that, that part of the theory.

Andrew Huberman 58:22 In many now older movies, um, typically it was a man singing to a woman.

Dr. Jennifer Groh 58:29 Mm-hmm.

Andrew Huberman 58:30 Or in the movie Say Anything, John Cusack-

Dr. Jennifer Groh 58:33 Yeah, with the stick.

Andrew Huberman 58:33 ... simply used a boo- a boombox, right?

Dr. Jennifer Groh 58:35 Yep. Yeah, right.

Andrew Huberman 58:36 Um, uh, or, um, poetry-

Dr. Jennifer Groh 58:39 Mm-hmm.

Andrew Huberman 58:39 ... creative works, but expressed out loud were the way that, um, courtship took place. Um, Erich Jarvis was on this podcast.

Dr. Jennifer Groh 58:51 Okay.

Andrew Huberman 58:51 I don't know if you know Eric-

Dr. Jennifer Groh 58:52 Yeah.

Andrew Huberman 58:52 ... at the Rockefeller.

Dr. Jennifer Groh 58:53 Mm-hmm.

Andrew Huberman 58:54 And, and he's a very, um, accomplished dancer. I don't know if you know this-

Dr. Jennifer Groh 58:58 Yeah.

Andrew Huberman 58:58 ... but he was supposed to be in the Alvin Ailey Dance Company-

Dr. Jennifer Groh 59:00 Mm-hmm.

Andrew Huberman 59:00 ... he decided to become a neuroscientist instead.

Dr. Jennifer Groh 59:01 Mm-hmm.

Andrew Huberman 59:02 But as I understand, he's still a good dancer.

Dr. Jennifer Groh 59:04 Yeah.

Andrew Huberman 59:04 Um, and he was saying that he thought that perhaps primitive vocalizations evolved first.

Dr. Jennifer Groh 59:09 Mm-hmm.

Andrew Huberman 59:10 So, vocalizations of disgust or pleasure-

Dr. Jennifer Groh 59:13 Mm-hmm.

Andrew Huberman 59:13 ... or fear or excitement. Then he thought perhaps came song and dance.

Dr. Jennifer Groh 59:18 Mm-hmm.

Andrew Huberman 59:19 So, song and body movement-

Dr. Jennifer Groh 59:20 Mm-hmm.

Andrew Huberman 59:21 ... to signal what one was feeling-

Dr. Jennifer Groh 59:23 Mm-hmm.

Andrew Huberman 59:23 ... or what their intention was. And then perhaps spoken language came after that. Makes sense, I just think we don't know.

Dr. Jennifer Groh 59:32 Yeah, we don't know, and I think it's kinda interesting. There's, there are maybe sort of two, um... Like, I think with the songbird, they are signaling things like vigor and fitness and territoriality, um, and things like that. They're not conveying something symbolic. Whereas the, you know, vocalizations in the primate tend to mean something specific.

Andrew Huberman 59:56 Mm.

Dr. Jennifer Groh 59:57 You know, sometimes I wish I, you know, could have a time machine and I could go back and, you know, look at what happened-

Andrew Huberman 1:00:04 Mm-hmm.

Dr. Jennifer Groh 1:00:05 ... in earlier stages of e- of evolution and just kinda see, well, what is the lineage that... What is the sequence of events that led us to, to have language, that led us to have music? Did it come from the same process as birds, you know, songbirds, or did it come from a completely parallel process? I mean, I think we do see that evolution can ar- arrive at similar characteristics through different means, in different places, in different times. So, you know, could be par- you know, kind of convergent parallel process-

Andrew Huberman 1:00:39 Mm-hmm.

Dr. Jennifer Groh 1:00:39 ... or it could be something different.

Andrew Huberman 1:00:41 I feel like music, um, conveys intention.... music can tell a story, and music, because of the way that it organizes language, provided there's lyrics-

Dr. Jennifer Groh 1:00:54 Mm-hmm.

Andrew Huberman 1:00:54 ... um, into like riffs and motifs and melodies-

Dr. Jennifer Groh 1:00:59 Mm-hmm.

Andrew Huberman 1:00:59 ... and choruses that-

Dr. Jennifer Groh 1:01:00 Mm-hmm.

Andrew Huberman 1:01:01 ... it makes it very easy to remember things. I'd like to talk a little bit about the possible neural underpinnings of this.

Dr. Jennifer Groh 1:01:07 Hmm.

Andrew Huberman 1:01:07 Uh, two things come to mind. First of all, you mentioned, uh, the ABCs.

Dr. Jennifer Groh 1:01:10 Mm-hmm.

Andrew Huberman 1:01:11 You know, A, B, C, D, E, F, G... Almost everybody knows that, um, that melody. And it's probably easier to remember all those letters in that form as opposed to A, B, C, D, E, F, G, H, I-

Dr. Jennifer Groh 1:01:27 Oh, sure.

Andrew Huberman 1:01:27 ... you know, uh, because you break it up.

Dr. Jennifer Groh 1:01:29 Right.

Andrew Huberman 1:01:29 And, and, and I, I'm almost certain this is true because I have a good friend, and he's a very accomplished musician, and he's an incredible songwriter and lyricist. He's written lyrics for a number of other artists, not just himself, and h- he has like several bands. He writes a song a day.

Dr. Jennifer Groh 1:01:43 Uh-huh.

Andrew Huberman 1:01:43 It's crazy, he writes a s-

Dr. Jennifer Groh 1:01:44 Whoa.

Andrew Huberman 1:01:44 He released a song a day during the pandemic.

Dr. Jennifer Groh 1:01:46 Whoa.

Andrew Huberman 1:01:47 Great songs. And occasionally, because I'm such a fan of his music, I'll say, "There's that one song, like what's that-

Dr. Jennifer Groh 1:01:53 Uh-huh.

Andrew Huberman 1:01:53 ... the, what's the lyric?" You know, and then, and, and he'll say, "Oh yeah, no, I, I don't... I don't remember." He'd go, and then he'll start and then he'll remember it. And I mean, he's got thousands of songs in his-

Dr. Jennifer Groh 1:02:05 Uh-huh.

Andrew Huberman 1:02:06 ... in his, uh, library of songs he's written and sings. And I said, "So when you're on stage, how does it work?" He said, "As long as I can remember the first two words or three words-

Dr. Jennifer Groh 1:02:13 Yeah.

Andrew Huberman 1:02:14 ... uh, of a verse, the rest just kind of spills out of me."

Dr. Jennifer Groh 1:02:16 Yes.

Andrew Huberman 1:02:17 I think that's how song organizes language, uh, because it's very hard to memorize like a, a speech, but you can memorize a song, no problem.

Dr. Jennifer Groh 1:02:28 Yeah, and it, that's my experience too, that if I know the first couple of words of a verse, I've got the rest of the verse.

Andrew Huberman 1:02:35 Mm-hmm. Yeah.

Andrew Huberman 1:02:37 It, it's so interesting. I, so in the brain, uh, we haven't talked too much about brain structures yet, but maybe we can do that.

Dr. Jennifer Groh 1:02:44 Yeah, right. Yeah.

Andrew Huberman 1:02:44 Um, and not to fill people's minds with names of things, 'cause I always say like, it doesn't matter if it's called the superior colliculus or the superior schmaliculus. It doesn't matter unless-

Dr. Jennifer Groh 1:02:53 It doesn't matter.

Andrew Huberman 1:02:54 ... it, what, but what's interesting are the properties of these different brain structures.

Dr. Jennifer Groh 1:02:58 Right, right.

Andrew Huberman 1:02:58 So, um, I think about the ears as, you know, separating different frequencies of sound, and then there's a bunch of other important stuff. No disrespect to the auditory neuroscientists, but-

Dr. Jennifer Groh 1:03:06 Mm-hmm.

Andrew Huberman 1:03:07 ... but the, as you said, the, in the superior colliculus is where hearing and vision and the other senses come together. They're mapped onto one another.

Dr. Jennifer Groh 1:03:15 It turns out that the story is more complicated and more interesting than that. I got hooked on that particular study that I mentioned at the beginning. So this was auditory signals in the superior colliculus being affected by the position of the eyes at the time the sound was presented. And now our audience knows about how sound is localized. We haven't talked that much about how visual information is localized. I think 'cause mostly that's fairly obvious, that your, your eye is kind of a little camera and light hits a particular s- uh, location on the retina, and that retinal location tells us what the location of the visual stimulus is.

Andrew Huberman 1:03:54 Mm-hmm.

Dr. Jennifer Groh 1:03:55 But it tells us the location of the visual stimulus with respect to the direction the eyes are pointing. But our sound localization cues are with respect to, um, where's the sound with respect to the head. So this finding that neurons were responsive to sound but cared very much about the position of the eyes was really, you know, a startling finding when it first came about. When I set up my own lab, I basically set out to find out, well, where's, where does this computation happen? Where is the brain, um, incorporating information about eye movements into the processing of, of sound? You know, we, we knew from the literature was, okay, the superior colliculus is one of the places, but you know, does it, does it happen in the superior colliculus or does it happen in a different brain area? And so we kind of marched along the auditory pathway in brain areas that, I call them part of the auditory pathway because they're much more closely connected to the ear than to anything else, um, and because at the time nobody thought there were visual signals in these areas. We thought it was just auditory. That too turned out not to be true, but they're definitely much more auditory than visual. And what we found was that in each of these areas, eye movements affect the auditory signals there too, even though they weren't in this convergent structure of the superior colliculus. So we, we decided that it would take a long time to march through every brain area, and that it might be worth sort of jumping over a few brain areas and looking in the ear itself. So I need to give the audience a little bit more information about what, you know, what is possible in the ear and why that seemed like a reasonable thing to do. It has some little muscles in it. There are two muscles that control the bones of the middle ear, uh, and then inside the cochlea, there are, uh, cells called outer hair cells that can actually expand and contract, just the way a little muscle could.

Andrew Huberman 1:05:58 We should explain, the cochlear is this snail-shaped structure that has the, essentially the, we call them neurons, but these sensory cells that-

Dr. Jennifer Groh 1:06:05 Yes.

Andrew Huberman 1:06:06 ... that vibrate according to the frequency of the sound, and this is critical for our perception of sound.

Dr. Jennifer Groh 1:06:11 Exactly.

Andrew Huberman 1:06:12 And you have one on each side.

Dr. Jennifer Groh 1:06:13 You have one on each side. It's snail-shaped and it's connected. Uh, the vestibular, um, your balance structures are also connected to this as well. And to just describe the flow of information, you have, you've your, got your outer ear, you've got your ear canal, you have your eardrum, you've got these little bones that connect the eardrum to the cochlea, and so there's muscles that, um, that affect the motion of those little bones, and then there's cells inside the cochlea that can also act like muscles. These structures, um, get input from the brain. So we thought, well, if they're getting top-down input from the brain, are they getting a top-down input from the brain that carries information about, about the position of the eyes? You know, that it seemed like...... it seemed kind of like a wild possibility, but not completely out of left field. Like, there was a, a possible mechanism here that we could imagine. And the neat thing about this is that, um, we didn't have to do something like stick an electrode into these muscles because they're attached to the bones and attached to the eardrum. And so, if they were being manipulated by a top-down signal from the brain, they would tug these bones and then that would tug the eardrum, and when the eardrum moves, normally it moves in response to sound, but if it moves in the absence of sound, it's gonna make a sound.

Andrew Huberman 1:07:40 Mm-hmm.

Dr. Jennifer Groh 1:07:41 So, you could put a microphone in the ear canal to see whether or not anything was happening in connection with eye movements. And this too wasn't out in left field to do this, because, um, there's already kind of known signals generated by these kinds of structures that are measured by clinicians, by audiologists and, and otolaryngologists. Um, you can put a microphone in the ear and you can measure things called otoacoustic emissions. The-

Andrew Huberman 1:08:08 They basically ... your ears are making sounds, folks.

Dr. Jennifer Groh 1:08:10 Your ears are making sounds, folks.

Andrew Huberman 1:08:12 I know, I know, it's weird to-

Dr. Jennifer Groh 1:08:12 It's kinda wild.

Andrew Huberman 1:08:13 Some people make more of them than others.

Dr. Jennifer Groh 1:08:15 Some people make more of them than others.

Andrew Huberman 1:08:16 Yeah.

Dr. Jennifer Groh 1:08:16 Exactly. So, we wanted to know if any of these little sounds were being generated with eye movements, and I wouldn't be here telling you this story if it didn't turn out that yes, they do. So, we were able to measure that the eardrum is, is basically moving in connection with, with every eye movement, every saccadic eye movement. These are the fast, jerky eye movements. There's other kinds of eye movements and we haven't yet tested them. The signal is very precisely time-locked to the onset of the eye movement, and the effect, um, is different in the two ears so that if your eyes are moving to the left, the eardrum on the right is gonna kinda, uh, bulge inward then outward then inward. I might have this backwards, um, but whatever the right ear is doing, the left ear is doing the opposite, so that the eardrums are gonna be moving in the same direction. One is gonna be inward when the other is going outward.

Andrew Huberman 1:09:12 Like a wave.

Dr. Jennifer Groh 1:09:13 Like a wave, exactly. Like a wave, not like a, a, not like-

Andrew Huberman 1:09:17 Not like flapping.

Dr. Jennifer Groh 1:09:17 Not like flapping.

Andrew Huberman 1:09:19 (laughs)

Dr. Jennifer Groh 1:09:19 Exactly. You know, we're still actually at pretty early days in understanding this process, and, and, um, what it's for, but it's a very precise signal. Turns out to carry information, uh, about how far the eyes are moving to the left or to the right, as well as a, uh, a bit less, but some information about vertical movements as well.

Andrew Huberman 1:09:38 Mm-hmm.

Dr. Jennifer Groh 1:09:39 And we think that this may be kind of the first step in that integration of visual and auditory information.

Andrew Huberman 1:09:48 Which would be the critical first step if the major goal of this integration of visual and auditory is for localization of sounds.

Dr. Jennifer Groh 1:09:56 Right.

Andrew Huberman 1:09:56 Because the, uh, you know, in, um ... As, uh, a neuroscientist, you know, like, there's so many different areas of neuroscience.

Dr. Jennifer Groh 1:10:05 Mm-hmm.

Andrew Huberman 1:10:05 Like, I used to marvel at, you know, you go to a meeting, you got people saying "consciousness" and working on consciousness.

Dr. Jennifer Groh 1:10:10 Mm-hmm.

Andrew Huberman 1:10:10 You have people trying to figure out how-

Dr. Jennifer Groh 1:10:12 Mm-hmm.

Andrew Huberman 1:10:12 ... a single photoreceptor works, or a single hair cell works.

Dr. Jennifer Groh 1:10:15 Yeah.

Andrew Huberman 1:10:15 And so, when I think about a sensory system-

Dr. Jennifer Groh 1:10:17 Mm-hmm.

Andrew Huberman 1:10:17 ... I think about layers of sophistication-

Dr. Jennifer Groh 1:10:19 Mm-hmm.

Andrew Huberman 1:10:20 ... and how they likely evolved. Like, very briefly, I mean, the visual system first evolved to detect light and dark on the order of 24 hours, so you know the difference between nighttime and daytime, which means even with the total inability to see objects, you are safer if you know when to stay in and when to go out. And then at some point, we evolved the ability to, um ... Probably motion detection came f- before the ability to send, to see detail-

Dr. Jennifer Groh 1:10:52 Yeah.

Andrew Huberman 1:10:52 ... 'cause it's way more important to know if something's-

Dr. Jennifer Groh 1:10:54 Yeah. Yeah.

Andrew Huberman 1:10:54 ... big and coming at you-

Dr. Jennifer Groh 1:10:56 Right.

Andrew Huberman 1:10:56 ... big and moving away-

Dr. Jennifer Groh 1:10:57 Right.

Andrew Huberman 1:10:57 ... or s-

Dr. Jennifer Groh 1:10:57 Or help you stay oriented, like, with respect to, like, knowing what's up and what's down-

Andrew Huberman 1:11:03 Right.

Dr. Jennifer Groh 1:11:03 ... and staying upright.

Andrew Huberman 1:11:04 That's right.

Dr. Jennifer Groh 1:11:04 Yeah.

Andrew Huberman 1:11:04 And just like, uh, the falling, uh, reflex is probably the most important reflex in the vestibular system-

Dr. Jennifer Groh 1:11:09 Mm-hmm.

Andrew Huberman 1:11:10 ... to brace yourself so you don't-

Dr. Jennifer Groh 1:11:11 Mm-hmm.

Andrew Huberman 1:11:11 ... you have a l- lesser chance of dying if you fall. (laughs)

Dr. Jennifer Groh 1:11:14 Yeah. (laughs)

Andrew Huberman 1:11:14 Right? Everyone, you know-

Dr. Jennifer Groh 1:11:15 Yep.

Andrew Huberman 1:11:16 Uh, if the visual world suddenly goes up very quick-

Dr. Jennifer Groh 1:11:18 Right. Right.

Andrew Huberman 1:11:18 ... you know you're falling.

Dr. Jennifer Groh 1:11:19 Right.

Andrew Huberman 1:11:20 And then comes, you know, additional layers of sophistication like-

Dr. Jennifer Groh 1:11:23 Mm-hmm.

Andrew Huberman 1:11:23 ... like fine detail, color vision.

Dr. Jennifer Groh 1:11:25 Mm-hmm.

Andrew Huberman 1:11:25 Color vision probably evolved last.

Dr. Jennifer Groh 1:11:27 Mm-hmm.

Andrew Huberman 1:11:28 These trichromatic color vision.

Dr. Jennifer Groh 1:11:30 Mm-hmm.

Andrew Huberman 1:11:30 But a- and then so when the auditory system, I think, like the same thing. You need to be able to know probably, um, which direction a sound is coming from, is it low or high frequency, um, and then and on and on.

Dr. Jennifer Groh 1:11:44 Right.

Andrew Huberman 1:11:45 You know, and so I think about that e- e- like, in the motor system that the oldest we know the, the evolutionary history of the genes that, uh, that are expressed and, like, the motor neurons that move the trunk-

Dr. Jennifer Groh 1:11:55 Mm-hmm.

Andrew Huberman 1:11:55 ... are the same ones that undulating, uh-

Dr. Jennifer Groh 1:11:59 Fish.

Andrew Huberman 1:12:00 ... fish use.

Dr. Jennifer Groh 1:12:00 Uh-huh.

Andrew Huberman 1:12:01 And, uh, actually this will get us back to sound, I promise.

Dr. Jennifer Groh 1:12:03 Uh-huh.

Andrew Huberman 1:12:03 And then there's the, these additional layers of motor neurons that have been added through evolution, the ones that flap the fins, and then-

Dr. Jennifer Groh 1:12:09 Mm-hmm.

Andrew Huberman 1:12:09 ... the, the final addition-

Dr. Jennifer Groh 1:12:11 Mm-hmm.

Andrew Huberman 1:12:12 ... are the motor neurons that control fine movement of the fingers.

Dr. Jennifer Groh 1:12:15 Mm-hmm.

Andrew Huberman 1:12:15 So, I have this kind of obsession with this because if you look at music that's very, um, primitive, right? Like, you just look historically-

Dr. Jennifer Groh 1:12:27 Mm-hmm.

Andrew Huberman 1:12:28 ... speaking. I'm not casting judgment on music, just historically. Um, it's rich in base tones relative to high frequency tones, and dance that we assign as primitive-

Dr. Jennifer Groh 1:12:40 Mm-hmm.

Andrew Huberman 1:12:40 ... tends to involve a lot of movement of the, of the trunk. You're not, people aren't just, like flapping their fingers and toes out there, right?

Dr. Jennifer Groh 1:12:46 Yeah. Yeah, yeah.

Andrew Huberman 1:12:47 Now, so the, as you go from low to high frequency-

Dr. Jennifer Groh 1:12:50 Mm-hmm.

Andrew Huberman 1:12:50 ... there's a body map of low to high frequency.

Dr. Jennifer Groh 1:12:53 Mm-hmm.

Andrew Huberman 1:12:53 And actually, if when people are making a very detailed point-

Dr. Jennifer Groh 1:12:56 Mm-hmm.

Andrew Huberman 1:12:56 ... they'll often, like, like point with their fingers. They'll move their fingers.But when we wanna emphasize a big point-

Dr. Jennifer Groh 1:13:02 Mm-hmm.

Andrew Huberman 1:13:02 ... we use our whole body.

Dr. Jennifer Groh 1:13:04 Yeah.

Andrew Huberman 1:13:04 We put our whole body into it. So, I actually believe that all the sensory systems are mapped to one another-

Dr. Jennifer Groh 1:13:09 Uh-huh.

Andrew Huberman 1:13:09 ... in a way that goes from low frequency to high frequency.

Dr. Jennifer Groh 1:13:11 Yeah.

Andrew Huberman 1:13:12 Intensity is important.

Dr. Jennifer Groh 1:13:13 Right.

Andrew Huberman 1:13:14 And direction is important.

Dr. Jennifer Groh 1:13:15 Right.

Andrew Huberman 1:13:15 Me pointing at you, which I f- even feels funny to do-

Dr. Jennifer Groh 1:13:18 Right. Yeah.

Andrew Huberman 1:13:18 ... because we're on good terms-

Dr. Jennifer Groh 1:13:19 Yeah. (laughs)

Andrew Huberman 1:13:19 ... as far as I, I, as far as I'm concerned, I, we're on good terms.

Dr. Jennifer Groh 1:13:22 I didn't blink. (laughs)

Andrew Huberman 1:13:22 You know, um, it's very different than, than, uh, me standing back. And if I come at you with my whole body-

Dr. Jennifer Groh 1:13:28 Mm-hmm.

Andrew Huberman 1:13:28 ... it's very different-

Dr. Jennifer Groh 1:13:29 Mm-hmm.

Andrew Huberman 1:13:29 ... than if I point a finger, for instance.

Dr. Jennifer Groh 1:13:31 Mm-hmm. Mm-hmm.

Andrew Huberman 1:13:31 Right? So, I feel like-

Dr. Jennifer Groh 1:13:32 Mm-hmm.

Andrew Huberman 1:13:32 ... these things probably evolved from this, i- i- in parallel. And, and as you pointed out before, they serve an adaptive role.

Dr. Jennifer Groh 1:13:40 Right.

Andrew Huberman 1:13:41 So, the fact that position of the eyes can change the way I hear seems wild.

Dr. Jennifer Groh 1:13:46 Yeah.

Andrew Huberman 1:13:46 And that's a wild thing. Um, i- is the inverse also true? Is, is where I listen affecting, um, how my eye ... yeah, my, where I hear something typically directs my head movement and my eye movement. So this is just the same thing in reverse.

Dr. Jennifer Groh 1:14:02 It's all part of, think it's all part of an integrated system. Um, you know, we talked about the top-down control over the ear, but there's a lot of top-down control over vision too. And some of it is a little easier to understand than what I just described, because blinking is top-down control over vision. Uh, eye movements, top-down control over vision. Focusing the lens of your eye-

Andrew Huberman 1:14:25 Mm-hmm.

Dr. Jennifer Groh 1:14:25 ... right, that's also top-down control.

Andrew Huberman 1:14:28 Mm-hmm.

Dr. Jennifer Groh 1:14:28 Um, there are descending connections from the brain to the retina itself that nobody understands. A- apologies to the people working on this. I really want you to keep working (laughs) on this, but I feel like there isn't a clear theory yet about what exactly these descending connections might be doing. From what I know about it, they are, uh, you know, pretty diffuse connections, pretty broad branching of, of neurons, uh, throughout the retina. Or not throughout the whole retina, but, but probably not well-suited to manipulating fine spatial detail, but could very well be suited to incorporating some kind of circadian influence to the retina itself, or something else that, that you want the same signal to be broadly available throughout the retina.

Andrew Huberman 1:15:17 I'd like to take a quick break and acknowledge our sponsor, Helix Sleep. Helix Sleep makes mattresses and pillows that are customized to your unique sleep needs. Now, I've spoken many times before on this podcast about the fact that getting a great night's sleep is the foundation of mental health, physical health, and performance. When we aren't doing that on a consistent basis, everything suffers. And when we are sleeping well and enough, our mental health, our physical health, and our performance in all endeavors improves markedly. Now, the mattress you sleep on makes a huge difference in terms of the quality of sleep that you get each night. How soft that mattress is, how firm it is, how breathable it is, all play into how well you'll sleep, how much deep sleep you get, how much rapid eye movement sleep, and it needs to be tailored to your unique sleep needs. So if you go to the Helix website, you can take a brief two-minute quiz, and it will ask you questions such as, "Do you sleep on your back, your side, or your stomach? Do you tend to run hot or cold during the night?" Things of that sort. Maybe you know the answers to those questions, maybe you don't. Either way, Helix will match you to the ideal mattress for you. For me, that turned out to be the Dusk mattress, D-U-S-K. I started sleeping on a Dusk mattress about three and a half years ago, and it's been far and away the best sleep that I've ever had. So if you'd like to try Helix, you can go to helixsleep.com/huberman, take that two-minute sleep quiz, and Helix will match you to a mattress that is customized for your unique sleep needs. Right now, Helix is giving a special offer to Huberman Podcast listeners of up to 27% off site-wide. Again, that's helixsleep.com/huberman.

Andrew Huberman 1:16:45 I wanna talk a little bit about physical spaces.

Dr. Jennifer Groh 1:16:49 Yeah.

Andrew Huberman 1:16:50 Recently, I was in New York and someone took me to Grand Central, where there are these incredible, um, arches in one of the hallways there.

Dr. Jennifer Groh 1:17:00 Mm-hmm.

Andrew Huberman 1:17:00 Um, people should check this out. It's really, really cool.

Dr. Jennifer Groh 1:17:03 It is beautiful.

Andrew Huberman 1:17:04 It's beautiful. I mean, you have this high ceiling main, kinda, chamber-

Dr. Jennifer Groh 1:17:08 Mm-hmm.

Andrew Huberman 1:17:08 ... room of the, of Grand Central. Um, and there's also a, a hallway off to one side where you can go into a corner-

Dr. Jennifer Groh 1:17:19 Mm-hmm.

Andrew Huberman 1:17:19 Do you know about this? Um, uh, and you can face into the corner-

Dr. Jennifer Groh 1:17:24 Uh-huh.

Andrew Huberman 1:17:24 ... like you were going to, you know, like you're facing the corner in shame, but you're not. And whoever you're with can go to the opposite diagonal corner.

Dr. Jennifer Groh 1:17:33 Oh, yeah. Yeah.

Andrew Huberman 1:17:34 The ceiling is shaped like a, a, somewhat of a dome.

Dr. Jennifer Groh 1:17:37 Uh-huh.

Andrew Huberman 1:17:38 It's contoured, but it's more or less a, a small-

Dr. Jennifer Groh 1:17:40 Right.

Andrew Huberman 1:17:40 ... a small dome. But you are easily 25 feet away from this person-

Dr. Jennifer Groh 1:17:47 Yep.

Andrew Huberman 1:17:47 ... that you're there with. Again, diagonal corner. And if you speak at a very, very low volume, they can hear you on the opposite side.

Dr. Jennifer Groh 1:18:01 Yeah. Yeah.

Andrew Huberman 1:18:02 And if they speak, you can hear them. And what's wild is there's a lot of noise in the environment.

Dr. Jennifer Groh 1:18:07 Yeah.

Andrew Huberman 1:18:07 This is Grand Central Station.

Dr. Jennifer Groh 1:18:09 Yeah. Yeah.

Andrew Huberman 1:18:10 And we played with this a little bit, like if high frequency sounds do s- seem to travel a little bit, a little bit better-

Dr. Jennifer Groh 1:18:16 Okay.

Andrew Huberman 1:18:16 ... in this, uh, i- environment.

Dr. Jennifer Groh 1:18:18 In that particular setting, yeah.

Andrew Huberman 1:18:18 Because if one person laughs, you can hear it very clearly.

Dr. Jennifer Groh 1:18:20 Uh-huh.

Andrew Huberman 1:18:21 Um, but you can whisper, and they'll hear you. And they're 25 feet away-

Dr. Jennifer Groh 1:18:27 Yeah.

Andrew Huberman 1:18:27 ... in a major city with a ton of city noise.

Dr. Jennifer Groh 1:18:30 Right.

Andrew Huberman 1:18:31 And so obviously, the sound waves are traveling along the ceiling.

Dr. Jennifer Groh 1:18:33 On that parabola.

Andrew Huberman 1:18:35 Uh-

Dr. Jennifer Groh 1:18:35 Yeah.

Andrew Huberman 1:18:35 And I, it's just, it's a, it's a, you know, no pun intended, it's a mind bend-

Dr. Jennifer Groh 1:18:40 (laughs)

Andrew Huberman 1:18:40 ... to experience sound-

Dr. Jennifer Groh 1:18:42 Yeah.

Andrew Huberman 1:18:42 ... coming from some pl- from a distance far away, not through an, a device, that is clearly being spoken at a low level, like a whisper, but you can hear it. In the same way that it always weirds me out when I'm in San Diego in the winter and the days are short-... but it's, like, 80 degrees. Like, when days are short, it's supposed to be cold there.

Dr. Jennifer Groh 1:19:08 Yeah, yes.

Andrew Huberman 1:19:08 Love San Diego.

Dr. Jennifer Groh 1:19:09 Yes.

Andrew Huberman 1:19:09 Great, great tacos, great people, but, um, they're always talking about tacos down there, but, um, it's so strange to be in a short day where it's hot.

Dr. Jennifer Groh 1:19:20 Yes.

Andrew Huberman 1:19:20 Because even if I go visit my relatives in Argentina who experience Christmas in the summer, the days are long and it's hot, and it's Christmas and Santa Claus is supposed to be on a sleigh