1 00:00:04,600 --> 00:00:07,520 Speaker 1: Why do they use a gun at the Olympics to 2 00:00:07,640 --> 00:00:11,360 Speaker 1: start sprinters? Why not use a flash of light? And 3 00:00:11,400 --> 00:00:14,160 Speaker 1: by the way, how can a sprinter come off the 4 00:00:14,240 --> 00:00:18,759 Speaker 1: blocks after the starting gun but still get disqualified for 5 00:00:18,880 --> 00:00:22,760 Speaker 1: jumping the gun? Or here's another question. If you watch 6 00:00:22,800 --> 00:00:26,200 Speaker 1: someone dribbling a basketball, it looks like when the ball 7 00:00:26,320 --> 00:00:29,880 Speaker 1: hits the ground, the sight and the sound are synchronized, 8 00:00:30,240 --> 00:00:33,040 Speaker 1: and if you back up a ways, it still looks synchronized. 9 00:00:33,560 --> 00:00:36,519 Speaker 1: But when you get to a very particular distance one 10 00:00:36,600 --> 00:00:39,560 Speaker 1: hundred and ten feet, it suddenly goes out of sync. 11 00:00:40,120 --> 00:00:42,839 Speaker 1: Why and what does any of this have to do 12 00:00:42,960 --> 00:00:48,280 Speaker 1: with Robert Oppenheimer, or television broadcasting, or the Emperor Kubla 13 00:00:48,360 --> 00:00:56,960 Speaker 1: Khan or schizophrenia. Welcome to Inner Cosmos with me David Eagleman. 14 00:00:57,080 --> 00:01:00,320 Speaker 1: I'm a neuroscientist and an author at Stanford and in 15 00:01:00,360 --> 00:01:04,400 Speaker 1: these episodes we sail deeply into our three pound universe 16 00:01:04,760 --> 00:01:08,200 Speaker 1: to understand why and how our lives look the way 17 00:01:08,240 --> 00:01:17,880 Speaker 1: they do. Today's episode is about time perception, which is 18 00:01:17,920 --> 00:01:20,200 Speaker 1: an area that I've studied in my lab for years. 19 00:01:20,560 --> 00:01:24,000 Speaker 1: For example, my first episode was on what happens when 20 00:01:24,040 --> 00:01:26,880 Speaker 1: an event seems to go into slow motion? When you're 21 00:01:26,920 --> 00:01:29,720 Speaker 1: in fear for your life. But today we're going to 22 00:01:29,760 --> 00:01:34,240 Speaker 1: talk about a different aspect of time. And specifically, what 23 00:01:34,319 --> 00:01:36,240 Speaker 1: we're going to talk about is that you have a 24 00:01:36,440 --> 00:01:39,920 Speaker 1: three pound mission control center that sits in darkness and 25 00:01:40,000 --> 00:01:43,759 Speaker 1: silence and has to figure out the timing of events 26 00:01:43,800 --> 00:01:47,680 Speaker 1: in the outside world. But this is a massive challenge 27 00:01:48,120 --> 00:01:53,600 Speaker 1: because signals stream in through different senses at different rates, 28 00:01:54,200 --> 00:01:57,280 Speaker 1: and we'll see how and why your brain works so 29 00:01:57,520 --> 00:02:01,840 Speaker 1: hard to pull off editing trail to get the timing right. 30 00:02:03,040 --> 00:02:05,760 Speaker 1: I recently saw the movie Oppenheimer, and if you haven't 31 00:02:05,760 --> 00:02:08,519 Speaker 1: seen it yet, you should. It's terrific. It's about J. 32 00:02:08,800 --> 00:02:12,880 Speaker 1: Robert Oppenheimer, who led the Manhattan Project to build the 33 00:02:12,919 --> 00:02:16,280 Speaker 1: first nuclear bomb. As you may know, the first test 34 00:02:16,400 --> 00:02:18,320 Speaker 1: of the nuclear bomb was in the middle of New 35 00:02:18,360 --> 00:02:21,040 Speaker 1: Mexico in a place called White Sands, which is a 36 00:02:21,040 --> 00:02:25,639 Speaker 1: big empty area. They weren't sure if the nuclear bomb 37 00:02:25,720 --> 00:02:30,440 Speaker 1: was going to work, because, as Oppenheimer often said, theory 38 00:02:30,600 --> 00:02:34,760 Speaker 1: takes you only so far. So after four years of 39 00:02:34,800 --> 00:02:37,920 Speaker 1: work and two billion dollars and hundreds of people on 40 00:02:37,919 --> 00:02:41,320 Speaker 1: this project, they were finally going to get a chance 41 00:02:41,440 --> 00:02:45,000 Speaker 1: to test the first ever nuclear bomb, to see if 42 00:02:45,000 --> 00:02:49,000 Speaker 1: this idea was going to work as the equations predicted. 43 00:02:49,600 --> 00:02:51,920 Speaker 1: So they set up the spot where the bomb would 44 00:02:51,919 --> 00:02:54,680 Speaker 1: be set off, and then they set up a few 45 00:02:54,840 --> 00:02:59,080 Speaker 1: observation sites, with the closest one being ten miles away 46 00:02:59,080 --> 00:03:03,320 Speaker 1: from the explosion. So in the movie we witness a 47 00:03:03,480 --> 00:03:07,960 Speaker 1: reconstruction of this scene, and it's tense because this is 48 00:03:08,000 --> 00:03:11,080 Speaker 1: the culmination of years of work, and this is the 49 00:03:11,400 --> 00:03:14,520 Speaker 1: project that might turn the tide of a world war, 50 00:03:14,880 --> 00:03:16,480 Speaker 1: and this is gonna be the first time to get 51 00:03:16,520 --> 00:03:20,800 Speaker 1: to see if it works. So the countdown clock begins, 52 00:03:21,360 --> 00:03:24,080 Speaker 1: and Oppenheimer and the rest of the scientists put on 53 00:03:24,120 --> 00:03:28,639 Speaker 1: their goggles, and finally the clock hits zero and the 54 00:03:28,680 --> 00:03:33,760 Speaker 1: detonation button is pressed and they watch this giant, white 55 00:03:33,800 --> 00:03:37,840 Speaker 1: and red pillar of fire reach up into the heavens. 56 00:03:38,760 --> 00:03:42,400 Speaker 1: And in the movie it's silent. You just hear their 57 00:03:42,800 --> 00:03:47,760 Speaker 1: heavy breathing as they watch this massive mushrooming cloud of 58 00:03:48,160 --> 00:03:54,720 Speaker 1: incendiary flames, just silence. We see the explosion, but we 59 00:03:54,800 --> 00:03:59,880 Speaker 1: hear nothing, and after about fifty seconds of this, suddenly 60 00:04:00,240 --> 00:04:05,280 Speaker 1: we the audience hear a massive shaking boom. So after 61 00:04:05,320 --> 00:04:07,760 Speaker 1: the movie, I was talking with a friend and he 62 00:04:07,960 --> 00:04:12,600 Speaker 1: hypothesized that the director had done this for cinematic effect. 63 00:04:13,040 --> 00:04:16,360 Speaker 1: The long drawn out silence was done so we could 64 00:04:16,400 --> 00:04:20,359 Speaker 1: appreciate the terrifying success of the race to build a 65 00:04:20,440 --> 00:04:24,560 Speaker 1: nuclear bomb. But I pointed out this was not a 66 00:04:24,600 --> 00:04:27,960 Speaker 1: cinematic effect. This is how it really was and how 67 00:04:28,000 --> 00:04:33,719 Speaker 1: it had to be because light travels ten miles very fast. 68 00:04:33,800 --> 00:04:38,240 Speaker 1: It only takes about point one seconds for the light 69 00:04:38,320 --> 00:04:41,560 Speaker 1: to travel from the bomb to the observation station ten 70 00:04:41,640 --> 00:04:47,000 Speaker 1: miles away. But in contrast, sound travels about a million 71 00:04:47,279 --> 00:04:51,320 Speaker 1: times more slowly. Because remember sound is just traveling by 72 00:04:51,600 --> 00:04:54,800 Speaker 1: pushing around the molecules in the air, compressing them together 73 00:04:54,880 --> 00:04:57,719 Speaker 1: and pulling them apart. And so how long does it 74 00:04:57,760 --> 00:05:04,080 Speaker 1: take sound to travel one mile About five seconds. So 75 00:05:04,200 --> 00:05:07,360 Speaker 1: for the folks at the observation station ten miles away, 76 00:05:07,720 --> 00:05:14,279 Speaker 1: the nuclear explosion was silent for fifty seconds, fifty seconds 77 00:05:14,320 --> 00:05:18,919 Speaker 1: of watching the most terrifying destructive force humans had ever 78 00:05:19,040 --> 00:05:23,840 Speaker 1: made in total silence. And this is also what it 79 00:05:23,880 --> 00:05:27,960 Speaker 1: was like for victims on the ground in Hiroshima and Nagasaki. 80 00:05:28,200 --> 00:05:31,800 Speaker 1: People who were one mile away from ground zero saw 81 00:05:31,800 --> 00:05:36,719 Speaker 1: the mushroom cloud but experienced silence for five seconds, or 82 00:05:36,760 --> 00:05:40,279 Speaker 1: if you were across town twelve miles away. You'd have 83 00:05:40,400 --> 00:05:43,839 Speaker 1: a full minute of watching what must have looked like 84 00:05:44,240 --> 00:05:49,200 Speaker 1: a colossal monstrosity that reached the sky, but it must 85 00:05:49,200 --> 00:05:52,000 Speaker 1: have felt the way it does to watch a television 86 00:05:52,000 --> 00:05:55,839 Speaker 1: with the sound off for a full minute. And of 87 00:05:55,880 --> 00:05:58,760 Speaker 1: course you know about this delay between light and sound 88 00:05:59,200 --> 00:06:03,200 Speaker 1: because of watching lightning, which is followed only later by 89 00:06:03,240 --> 00:06:06,120 Speaker 1: the thunder So it takes five seconds for sound to 90 00:06:06,200 --> 00:06:09,400 Speaker 1: travel a mile, So if you count ten seconds after 91 00:06:09,440 --> 00:06:14,000 Speaker 1: the lightning, that means it's two miles away. Okay, so 92 00:06:14,080 --> 00:06:16,560 Speaker 1: there's this difference between the speed of light and the 93 00:06:16,600 --> 00:06:20,760 Speaker 1: speed of sound. But we're about to see something very weird, 94 00:06:20,960 --> 00:06:24,000 Speaker 1: which is that, unless we're watching something like a bomb 95 00:06:24,080 --> 00:06:28,480 Speaker 1: or a thunderbolt, we don't perceive those time differences. Why 96 00:06:28,520 --> 00:06:32,040 Speaker 1: don't we perceive these normally? Since sound is a million 97 00:06:32,080 --> 00:06:35,719 Speaker 1: times slower, why doesn't someone talking to you from across 98 00:06:35,760 --> 00:06:39,640 Speaker 1: the room look like a badly dubbed film. After all, 99 00:06:39,680 --> 00:06:41,720 Speaker 1: the sight of their mouth and the sound of their 100 00:06:41,800 --> 00:06:45,040 Speaker 1: voice arrives at different times, just like the bomb or 101 00:06:45,040 --> 00:06:49,480 Speaker 1: the thunderbolt. And we're generally very sensitive to small differences 102 00:06:49,520 --> 00:06:53,440 Speaker 1: in timing. So why can't we pick this up? So 103 00:06:53,680 --> 00:06:57,080 Speaker 1: to reach our arms down into this problem. I'll give 104 00:06:57,080 --> 00:07:00,159 Speaker 1: you a do it yourself demonstration that will unmask for 105 00:07:00,200 --> 00:07:04,120 Speaker 1: you the deep weirdness of how much your brain constructs 106 00:07:04,200 --> 00:07:08,960 Speaker 1: your reality. So watch some kid dribbling in basketball. It 107 00:07:09,040 --> 00:07:12,200 Speaker 1: will seem like as the basketball is hitting the ground, 108 00:07:12,280 --> 00:07:15,760 Speaker 1: the sight and the sound of that are synchronized. Now 109 00:07:15,760 --> 00:07:17,640 Speaker 1: what you do is you start backing up. So you 110 00:07:17,760 --> 00:07:20,760 Speaker 1: back up, you back up. They're dribbling, You're watching them, 111 00:07:21,040 --> 00:07:23,960 Speaker 1: and it seems synchronized. The more and more you back up, 112 00:07:24,040 --> 00:07:28,640 Speaker 1: it still seems synchronized until you hit one hundred and 113 00:07:28,720 --> 00:07:32,800 Speaker 1: ten feet and then it doesn't seem synchronized anymore. Then 114 00:07:32,920 --> 00:07:38,040 Speaker 1: suddenly the sight and sound seem off. The basketball visually 115 00:07:38,120 --> 00:07:42,360 Speaker 1: hits the ground and then you hear the thump. It's asynchronous, 116 00:07:42,440 --> 00:07:46,080 Speaker 1: like the badly dubbed movie. So what is going on here? 117 00:07:47,000 --> 00:07:49,560 Speaker 1: Strap in, because we're about to see some things that 118 00:07:49,640 --> 00:07:53,880 Speaker 1: will blow our minds, specifically, how much editing work your 119 00:07:53,920 --> 00:07:57,800 Speaker 1: brain does behind the scenes to try to fix timing 120 00:07:57,840 --> 00:08:01,040 Speaker 1: across the senses until the difference is simply too great 121 00:08:01,040 --> 00:08:04,119 Speaker 1: and it says, okay, forget about it. So let's zoom 122 00:08:04,160 --> 00:08:06,640 Speaker 1: out for a minute and consider the big picture. Of 123 00:08:06,680 --> 00:08:11,920 Speaker 1: what your brain has to do. Your conscious perception requires 124 00:08:11,960 --> 00:08:15,920 Speaker 1: the brain to compare different streams of sensory data against 125 00:08:16,000 --> 00:08:19,920 Speaker 1: one another. You've got these different channels of information coming in. 126 00:08:20,000 --> 00:08:23,720 Speaker 1: You've got vision, hearing, touch, and so on, and your 127 00:08:23,720 --> 00:08:25,880 Speaker 1: brain has to put these together to make a big 128 00:08:25,960 --> 00:08:29,640 Speaker 1: picture of what's happening. But there's something which makes this 129 00:08:29,720 --> 00:08:33,880 Speaker 1: a really big challenge, and that is the issue of timing. 130 00:08:34,360 --> 00:08:37,600 Speaker 1: All of these streams of sensory data are processed by 131 00:08:37,600 --> 00:08:42,320 Speaker 1: the brain at different speeds. So think about sprinters at 132 00:08:42,360 --> 00:08:45,680 Speaker 1: a racetrack. It appears that they get off the blocks 133 00:08:45,800 --> 00:08:50,640 Speaker 1: the instant the gunfires, but it's not actually instantaneous. If 134 00:08:50,679 --> 00:08:54,239 Speaker 1: you watch them in slow motion, you'll see this sizeable 135 00:08:54,480 --> 00:08:58,079 Speaker 1: gap between the bang and the start of their movement. 136 00:08:58,080 --> 00:09:01,720 Speaker 1: It's about one hundred and sixty millisecond because it takes 137 00:09:01,800 --> 00:09:05,880 Speaker 1: time for signals to move through the brain, for the 138 00:09:05,920 --> 00:09:08,120 Speaker 1: bang of the gun to work its way through their 139 00:09:08,200 --> 00:09:11,360 Speaker 1: auditory system and over to their motor system and then 140 00:09:11,440 --> 00:09:14,640 Speaker 1: down the spinal cord into the leg muscles and launched 141 00:09:14,679 --> 00:09:18,640 Speaker 1: them off the blocks. In fact, if they move off 142 00:09:18,640 --> 00:09:23,760 Speaker 1: the blocks before that duration, they're disqualified because they've jumped 143 00:09:23,840 --> 00:09:28,679 Speaker 1: the gun. Because racing commissions know that this signal transmission 144 00:09:28,720 --> 00:09:31,760 Speaker 1: takes time, so the rule is that if you move 145 00:09:31,880 --> 00:09:37,000 Speaker 1: within one hundred milliseconds after the gun, you are disqualified. 146 00:09:37,720 --> 00:09:39,839 Speaker 1: This came up in July of twenty twenty two when 147 00:09:39,880 --> 00:09:43,720 Speaker 1: a hurdler named Devin Allen got off the starting blocks 148 00:09:43,760 --> 00:09:46,800 Speaker 1: too early. He didn't go before the gun went off, 149 00:09:46,800 --> 00:09:50,280 Speaker 1: he went after the gun went off. But he launched 150 00:09:50,360 --> 00:09:54,400 Speaker 1: at ninety nine milliseconds after the gun, and even for 151 00:09:54,440 --> 00:09:58,160 Speaker 1: a great athlete like him, this is below the possible 152 00:09:58,320 --> 00:10:01,240 Speaker 1: reaction time, and there was a storm of activity on 153 00:10:01,280 --> 00:10:04,640 Speaker 1: social media. But the fact is that one's reaction time 154 00:10:05,040 --> 00:10:08,920 Speaker 1: can't be that rapid. Athletes trained to make their gap 155 00:10:08,960 --> 00:10:13,880 Speaker 1: as small as possible, but their biology imposes fundamental limits. 156 00:10:14,440 --> 00:10:17,280 Speaker 1: The brain has to register the sound and then send 157 00:10:17,280 --> 00:10:19,840 Speaker 1: the signals to the motor cortex and down the spinal 158 00:10:19,880 --> 00:10:22,920 Speaker 1: cord to the muscles of the body. Now, in a 159 00:10:23,080 --> 00:10:26,360 Speaker 1: sport where thousandths of a second can be the difference 160 00:10:26,400 --> 00:10:32,720 Speaker 1: between winning and losing, that response seems surprisingly slow. So 161 00:10:32,920 --> 00:10:36,240 Speaker 1: could the delay be shortened if we used, say, a 162 00:10:36,480 --> 00:10:40,160 Speaker 1: flash instead of a pistol to start the racers. After all, 163 00:10:40,679 --> 00:10:43,720 Speaker 1: light travels faster than sounds, so wouldn't that allow them 164 00:10:43,760 --> 00:10:47,680 Speaker 1: to get off the blocks faster? For my television show 165 00:10:47,760 --> 00:10:50,559 Speaker 1: The Brain, I went to the track and I invited 166 00:10:50,600 --> 00:10:53,160 Speaker 1: some fellow sprinters so we could all put this to 167 00:10:53,200 --> 00:10:57,560 Speaker 1: the test. So, in one condition, our sprint was triggered 168 00:10:57,720 --> 00:11:01,800 Speaker 1: by the gun. In a second condition, we were triggered 169 00:11:02,000 --> 00:11:05,280 Speaker 1: by a flash of light. And we filmed this in 170 00:11:05,400 --> 00:11:09,040 Speaker 1: super slow motion so we could compare what happened in 171 00:11:09,080 --> 00:11:12,640 Speaker 1: the two conditions. When we were triggered by the bang 172 00:11:12,679 --> 00:11:14,760 Speaker 1: of a gun, we got off the blocks at about 173 00:11:14,760 --> 00:11:18,400 Speaker 1: one hundred and sixty milliseconds, but when we were triggered 174 00:11:18,400 --> 00:11:22,479 Speaker 1: by the light, we got off the blocks more slowly, 175 00:11:22,679 --> 00:11:25,840 Speaker 1: with a longer delay, about one hundred and ninety milliseconds. 176 00:11:26,240 --> 00:11:28,880 Speaker 1: Now that seems to make no sense given what we 177 00:11:29,040 --> 00:11:32,120 Speaker 1: just talked about, with light moving a million times faster 178 00:11:32,200 --> 00:11:37,160 Speaker 1: than sound. So what gives here To understand what's happening? 179 00:11:37,200 --> 00:11:40,600 Speaker 1: We need to look at the speed of information processing 180 00:11:40,920 --> 00:11:46,400 Speaker 1: on the inside. Visual data goes through more complex processing 181 00:11:46,840 --> 00:11:51,480 Speaker 1: than auditory data, so it takes longer for signals carrying 182 00:11:51,520 --> 00:11:55,040 Speaker 1: the flash to wind their way through the visual system 183 00:11:55,440 --> 00:11:58,480 Speaker 1: then for bang signals to snake their way through the 184 00:11:58,480 --> 00:12:04,880 Speaker 1: auditory system, so light takes longer to trigger a motor response, 185 00:12:04,960 --> 00:12:26,520 Speaker 1: and that's why a pistol is used to start sprinters. Now, 186 00:12:26,600 --> 00:12:30,480 Speaker 1: scientists can prove this by putting electrodes in the auditory cortex, 187 00:12:30,480 --> 00:12:33,600 Speaker 1: which responds to the bang, or the visual cortex, which 188 00:12:33,640 --> 00:12:36,840 Speaker 1: responds to the flash, and you can see that the 189 00:12:36,960 --> 00:12:40,880 Speaker 1: speed of the brain response is faster for the bang. 190 00:12:41,880 --> 00:12:45,880 Speaker 1: But here comes the big mystery. Clap your hands in 191 00:12:45,920 --> 00:12:50,560 Speaker 1: front of you. It looks synchronized. Well, that makes no 192 00:12:50,679 --> 00:12:54,080 Speaker 1: sense because we just saw with the sprinters that your 193 00:12:54,240 --> 00:13:00,880 Speaker 1: auditory system processes information more quickly than your visuals. So 194 00:13:00,920 --> 00:13:04,760 Speaker 1: why aren't you seeing the sound and the sight out 195 00:13:04,800 --> 00:13:08,360 Speaker 1: of sync. The answer, as we'll see in a moment, 196 00:13:08,520 --> 00:13:10,920 Speaker 1: is that even though part of your brain gets the 197 00:13:10,920 --> 00:13:16,160 Speaker 1: information before another part, your consciousness goes through a lot 198 00:13:16,200 --> 00:13:20,560 Speaker 1: of trouble to sync things up. Your perception of the 199 00:13:20,600 --> 00:13:25,040 Speaker 1: outside world is the end result of fancy editing tricks. 200 00:13:25,400 --> 00:13:29,320 Speaker 1: The brain hides the difference in arrival times, and I'll 201 00:13:29,360 --> 00:13:31,440 Speaker 1: explain to you how it does this, but first I'll 202 00:13:31,440 --> 00:13:35,040 Speaker 1: give you a couple more examples. So let's step back 203 00:13:35,120 --> 00:13:40,000 Speaker 1: seventy years to the early days of television broadcasting. The 204 00:13:40,040 --> 00:13:43,960 Speaker 1: engineers realized they could be a stream of sound information 205 00:13:44,320 --> 00:13:47,280 Speaker 1: and they could be a stream of visual information. But 206 00:13:47,320 --> 00:13:50,360 Speaker 1: they were worried about how they could broadcast both the 207 00:13:50,440 --> 00:13:54,160 Speaker 1: sound and the visuals and keep them synchronized with one another. 208 00:13:54,679 --> 00:13:58,280 Speaker 1: And what they realized, quite accidentally, was that they don't 209 00:13:58,400 --> 00:14:02,200 Speaker 1: actually need to keep them perfectly synchronized. As long as 210 00:14:02,240 --> 00:14:06,360 Speaker 1: the sound and the visuals arrive to the viewer within 211 00:14:06,400 --> 00:14:09,520 Speaker 1: about eighty milliseconds of each other. That's about a tenth 212 00:14:09,559 --> 00:14:12,679 Speaker 1: of a second. Your brain does all the work of 213 00:14:12,720 --> 00:14:15,959 Speaker 1: synking these up. And if you've ever seen a movie 214 00:14:16,000 --> 00:14:18,800 Speaker 1: that seems out of sync, it means that the audio 215 00:14:18,880 --> 00:14:22,680 Speaker 1: and the video were more than eighty milliseconds away from 216 00:14:22,720 --> 00:14:26,440 Speaker 1: each other, because your brain can't tell the difference. As 217 00:14:26,480 --> 00:14:29,320 Speaker 1: long as they're within eighty milliseconds of one another, it 218 00:14:29,360 --> 00:14:34,040 Speaker 1: seems perfectly synchronized to you. And this allows us to 219 00:14:34,160 --> 00:14:38,200 Speaker 1: understand what's happening. When you're watching the kid dribbling the basketball. 220 00:14:38,640 --> 00:14:41,160 Speaker 1: It seems that as the ball is hitting the ground, 221 00:14:41,200 --> 00:14:44,200 Speaker 1: everything is synced all the way until you back up 222 00:14:44,240 --> 00:14:46,480 Speaker 1: to one hundred and ten feet and then it's not 223 00:14:46,520 --> 00:14:50,800 Speaker 1: synchronized anymore. Why well, one hundred and ten feet is 224 00:14:50,840 --> 00:14:53,680 Speaker 1: where the speed of light and the speed of sound 225 00:14:53,880 --> 00:14:58,160 Speaker 1: are reaching you at over eighty milliseconds apart. So when 226 00:14:58,200 --> 00:15:01,840 Speaker 1: they reach you at that timing apart from one another, 227 00:15:01,920 --> 00:15:05,200 Speaker 1: your brain can't sync it up anymore. But as long 228 00:15:05,240 --> 00:15:09,560 Speaker 1: as they're within that window, your brain has no problem saying, oh, okay, 229 00:15:09,600 --> 00:15:13,400 Speaker 1: those belong together, I'm gonna synchronize that. So this is 230 00:15:13,440 --> 00:15:15,800 Speaker 1: the question I turned to some years ago. If the 231 00:15:15,920 --> 00:15:19,360 Speaker 1: brain is getting all this information at different speeds, how 232 00:15:19,400 --> 00:15:23,320 Speaker 1: does it know how to synchronize things in consciousness? And 233 00:15:23,360 --> 00:15:26,280 Speaker 1: I just want to make clear how challenging this is 234 00:15:26,360 --> 00:15:29,720 Speaker 1: if you're living in the dark inside the skull, because 235 00:15:29,760 --> 00:15:33,320 Speaker 1: these timing difficulties aren't even restricted to hearing and seeing. 236 00:15:33,640 --> 00:15:37,160 Speaker 1: Every type of sensory information takes a different amount of 237 00:15:37,160 --> 00:15:41,400 Speaker 1: time to process and to complicate things even more, even 238 00:15:41,440 --> 00:15:44,920 Speaker 1: within a sense, there are time differences. For example, a 239 00:15:45,080 --> 00:15:48,640 Speaker 1: bright flash moves through your retina and gets to your 240 00:15:48,640 --> 00:15:53,240 Speaker 1: brain a full eighty milliseconds before a dim flash, or 241 00:15:53,240 --> 00:15:56,920 Speaker 1: as another example, it takes longer for signals to reach 242 00:15:56,960 --> 00:15:59,840 Speaker 1: your brain from your big toe than it does from 243 00:15:59,840 --> 00:16:03,800 Speaker 1: your knows So how does your brain solve all of 244 00:16:03,840 --> 00:16:09,440 Speaker 1: this temporal smearing of information. The only possible answer is 245 00:16:09,520 --> 00:16:14,160 Speaker 1: wacky and somewhat mind blowing. Your brain has to collect 246 00:16:14,320 --> 00:16:18,200 Speaker 1: up all the information from all the senses before it 247 00:16:18,320 --> 00:16:23,440 Speaker 1: decides on a story of what happened. And that means 248 00:16:23,480 --> 00:16:29,040 Speaker 1: your conscious perception is actually a delayed version of what's 249 00:16:29,080 --> 00:16:32,400 Speaker 1: happening in the world. So when you clap your hands, 250 00:16:33,120 --> 00:16:36,560 Speaker 1: your brain gathers the auditory information and the visual information 251 00:16:36,680 --> 00:16:39,680 Speaker 1: and the sensory information of your hands touching, and all 252 00:16:39,760 --> 00:16:43,480 Speaker 1: these stream in at different times, and then it puts 253 00:16:43,520 --> 00:16:47,240 Speaker 1: together its story of what just happened, and it puts 254 00:16:47,280 --> 00:16:50,720 Speaker 1: together what should go with what. And I'll explain in 255 00:16:50,720 --> 00:16:53,160 Speaker 1: a second how it does this. But the key thing 256 00:16:53,200 --> 00:16:55,840 Speaker 1: I want to make clear right now is that in 257 00:16:56,000 --> 00:17:00,480 Speaker 1: order to synchronize everything, you have to wait for all 258 00:17:00,640 --> 00:17:05,639 Speaker 1: of the information to arrive. And the strange consequence of 259 00:17:05,680 --> 00:17:10,080 Speaker 1: all this is that you live in the past. By 260 00:17:10,119 --> 00:17:14,040 Speaker 1: the time you think the moment occurs, it's already long gone. 261 00:17:14,119 --> 00:17:18,760 Speaker 1: When you perceive the clap, it's already over. Your perceptual 262 00:17:18,800 --> 00:17:24,199 Speaker 1: world always lags behind the real world. So think of 263 00:17:24,200 --> 00:17:27,480 Speaker 1: it this way. Your perception of the world is like 264 00:17:27,600 --> 00:17:31,520 Speaker 1: a live television show. Think of something like Saturday Night Live, 265 00:17:32,040 --> 00:17:36,000 Speaker 1: which is not actually live. Instead, those shows are aired 266 00:17:36,080 --> 00:17:39,560 Speaker 1: with a delay of a few seconds in case someone 267 00:17:40,119 --> 00:17:44,000 Speaker 1: cusses or falls down or has a clothing mishap. And 268 00:17:44,080 --> 00:17:47,600 Speaker 1: so it goes with your conscious life. It collects a 269 00:17:47,600 --> 00:17:52,000 Speaker 1: lot of information before it goes live, so there's an 270 00:17:52,119 --> 00:17:56,000 Speaker 1: unbridgable gap between an event occurring in the world and 271 00:17:56,040 --> 00:17:59,680 Speaker 1: your conscious experience of it. So that's why your brain 272 00:17:59,720 --> 00:18:03,200 Speaker 1: can sync the television audio at the video or the 273 00:18:03,520 --> 00:18:06,320 Speaker 1: basketball thump with the visual of it hitting the ground 274 00:18:06,359 --> 00:18:09,359 Speaker 1: or whatever. I need to emphasize that what we're talking 275 00:18:09,400 --> 00:18:13,760 Speaker 1: about here is conscious awareness. You can see from pre 276 00:18:13,880 --> 00:18:17,440 Speaker 1: conscious reactions that your motor system doesn't have to wait 277 00:18:17,520 --> 00:18:21,000 Speaker 1: before its decisions. For example, you can duck out of 278 00:18:21,040 --> 00:18:23,960 Speaker 1: the way of a swinging tree branch before you become 279 00:18:24,040 --> 00:18:27,399 Speaker 1: consciously aware of it, or you can start jumping when 280 00:18:27,440 --> 00:18:31,400 Speaker 1: there's a loud sound before you're consciously aware that there 281 00:18:31,480 --> 00:18:34,320 Speaker 1: was a sound. Your body always tries to act as 282 00:18:34,400 --> 00:18:39,000 Speaker 1: quickly as possible, even before the participation of awareness, but 283 00:18:39,080 --> 00:18:45,040 Speaker 1: your conscious perception takes its time. Now that raises a question, 284 00:18:45,119 --> 00:18:48,640 Speaker 1: what is the use of perception, especially since it lags 285 00:18:48,680 --> 00:18:55,639 Speaker 1: behind reality and it's retrospectively attributed, and it's generally outstripped 286 00:18:55,680 --> 00:18:59,960 Speaker 1: by these automatic, unconscious systems. The most likely answer is 287 00:19:00,080 --> 00:19:04,640 Speaker 1: that your perceptions are like objects that your cognitive systems 288 00:19:04,680 --> 00:19:07,760 Speaker 1: can work with later. So it's important for the brain 289 00:19:08,040 --> 00:19:12,120 Speaker 1: to take sufficient time to settle on its best interpretation 290 00:19:12,240 --> 00:19:15,960 Speaker 1: of what just happened, rather than stick with its initial 291 00:19:16,040 --> 00:19:21,400 Speaker 1: rapid interpretation. Its carefully refined picture of what just happened 292 00:19:21,800 --> 00:19:24,160 Speaker 1: is all that it's going to have to work with later, 293 00:19:24,560 --> 00:19:30,320 Speaker 1: so it invests the time. So this brief waiting period 294 00:19:30,400 --> 00:19:34,199 Speaker 1: before consciousness, this is what allows your sensory systems to 295 00:19:34,880 --> 00:19:39,960 Speaker 1: discount the various delays imposed, But it has the disadvantage 296 00:19:40,000 --> 00:19:43,639 Speaker 1: of pushing your perception into the past. Now, there's a 297 00:19:43,680 --> 00:19:47,080 Speaker 1: distinct survival advantage to operating as close to the present 298 00:19:47,119 --> 00:19:49,840 Speaker 1: as possible. An animal doesn't want to live too far 299 00:19:49,880 --> 00:19:52,800 Speaker 1: in the past. Therefore, it may be that a tenth 300 00:19:52,800 --> 00:19:56,560 Speaker 1: of a second window is the smallest delay that allows 301 00:19:57,040 --> 00:19:59,680 Speaker 1: higher areas of the brain to account for the delays 302 00:19:59,760 --> 00:20:02,840 Speaker 1: create in the first stage of the system while still 303 00:20:02,920 --> 00:20:06,879 Speaker 1: operating near the border of the present. Among other things, 304 00:20:06,920 --> 00:20:10,520 Speaker 1: this strategy of waiting for the slowest information to arrive 305 00:20:11,320 --> 00:20:16,280 Speaker 1: has the advantage of allowing object recognition to be independent 306 00:20:16,400 --> 00:20:19,360 Speaker 1: of lighting conditions. So I mentioned a minute ago about 307 00:20:19,640 --> 00:20:23,320 Speaker 1: bright and dim flashes moving through the system at different speeds. 308 00:20:23,880 --> 00:20:28,560 Speaker 1: So imagine a striped tiger coming toward you under the 309 00:20:28,600 --> 00:20:33,119 Speaker 1: forest canopy, and he's passing through successive patches of sunlight. 310 00:20:33,640 --> 00:20:37,840 Speaker 1: Imagine how difficult recognition would be if the bright and 311 00:20:37,880 --> 00:20:41,600 Speaker 1: the dim parts of the tiger caused incoming signals to 312 00:20:41,640 --> 00:20:45,359 Speaker 1: be perceived at different times. You'd perceive the tiger breaking 313 00:20:45,359 --> 00:20:49,359 Speaker 1: into different space time fragments just before you became the 314 00:20:49,400 --> 00:20:54,960 Speaker 1: tiger's lunch. Somehow, the visual system has evolved to reconcile 315 00:20:55,320 --> 00:20:59,320 Speaker 1: these different speeds of incoming information. After all, it is 316 00:20:59,440 --> 00:21:06,280 Speaker 1: advantageous to recognize tigers regardless of the lighting conditions. Now, 317 00:21:06,320 --> 00:21:10,240 Speaker 1: this hypothesis that the system waits to collect information over 318 00:21:10,280 --> 00:21:13,119 Speaker 1: the window of time that it's all streaming in this 319 00:21:13,160 --> 00:21:15,960 Speaker 1: supplies not only to vision, but more generally, to all 320 00:21:16,040 --> 00:21:20,119 Speaker 1: the senses. So, for example, my lab measured that in 321 00:21:20,240 --> 00:21:22,679 Speaker 1: vision you wait at least a tenth of a second, 322 00:21:23,080 --> 00:21:25,879 Speaker 1: But the size of this window might be different for 323 00:21:26,080 --> 00:21:29,440 Speaker 1: hearing or touch. If I touch your toe and your 324 00:21:29,520 --> 00:21:32,520 Speaker 1: nose at the same time, you will feel those touches 325 00:21:32,520 --> 00:21:36,520 Speaker 1: as simultaneous. And that's really surprising, because the signal from 326 00:21:36,520 --> 00:21:39,920 Speaker 1: your nose reaches your brain well before the signal from 327 00:21:39,960 --> 00:21:43,080 Speaker 1: your toe. Why didn't you feel the nose touch when 328 00:21:43,080 --> 00:21:46,320 Speaker 1: it first arrived. Did your brain wait to see what 329 00:21:46,440 --> 00:21:48,880 Speaker 1: else might be coming up the pipeline of the spinal 330 00:21:48,920 --> 00:21:51,720 Speaker 1: cord until it was sure that it had waited long 331 00:21:51,840 --> 00:21:55,320 Speaker 1: enough for the slower signals from the toe. Strange as 332 00:21:55,320 --> 00:21:57,760 Speaker 1: that sounds, that might be correct, and it may be 333 00:21:57,760 --> 00:22:02,560 Speaker 1: that for a unified sensory perception of the world, you 334 00:22:02,680 --> 00:22:07,000 Speaker 1: have to wait for the slowest overall information to get there, 335 00:22:07,600 --> 00:22:11,800 Speaker 1: and given conduction times along whims, this leads to my 336 00:22:12,160 --> 00:22:16,480 Speaker 1: strange but testable hypothesis that I mentioned in episode thirteen, 337 00:22:16,880 --> 00:22:21,040 Speaker 1: which is that tall people may live further in the 338 00:22:21,080 --> 00:22:24,560 Speaker 1: past than short people because they have to wait for 339 00:22:24,680 --> 00:22:27,480 Speaker 1: the signals all the way from their toes before they 340 00:22:27,520 --> 00:22:33,360 Speaker 1: put together their unified perception. Okay, but how does your 341 00:22:33,359 --> 00:22:37,919 Speaker 1: brain know how to put all these signals together? So 342 00:22:38,000 --> 00:22:42,320 Speaker 1: to think about this, let's turn to the Mongol emperor 343 00:22:42,480 --> 00:22:46,440 Speaker 1: Kublai Khan, who ranged from twelve sixty to twelve ninety four, 344 00:22:46,640 --> 00:22:51,000 Speaker 1: and founded the Yuan dynasty. Now he had conquered the 345 00:22:51,240 --> 00:22:54,679 Speaker 1: largest kingdom the world had ever known. His kingdom reached 346 00:22:54,720 --> 00:22:58,800 Speaker 1: from the Pacific to the Black Sea, and from Siberia 347 00:22:58,840 --> 00:23:03,959 Speaker 1: to modern day Afghanis. His territory covered a fifth of 348 00:23:04,000 --> 00:23:08,679 Speaker 1: the world's inhabited areas, so it was absolutely enormous. He 349 00:23:08,800 --> 00:23:12,639 Speaker 1: situated himself in what is modern day Beijing. And the 350 00:23:12,720 --> 00:23:14,879 Speaker 1: thing to note is that this was back in the 351 00:23:14,960 --> 00:23:18,879 Speaker 1: day before iPhones and telegraphs and trains or email or 352 00:23:18,920 --> 00:23:22,119 Speaker 1: anything like that. And so the question is, how in 353 00:23:22,160 --> 00:23:27,800 Speaker 1: the world could Kubla Khan know his own empire. There's 354 00:23:27,800 --> 00:23:30,760 Speaker 1: no way he could travel even a tiny fraction of 355 00:23:30,800 --> 00:23:35,320 Speaker 1: a territory that large in his entire lifetime. So how 356 00:23:35,359 --> 00:23:39,840 Speaker 1: could the Great Khan know what his empire contained? The 357 00:23:39,960 --> 00:23:45,280 Speaker 1: answer is he hired emissaries like the Venetian traveler Marco Polo, 358 00:23:45,680 --> 00:23:48,760 Speaker 1: and these people would travel out to the distant reaches 359 00:23:48,760 --> 00:23:51,679 Speaker 1: of his empire and they would convey news back to 360 00:23:51,760 --> 00:23:54,719 Speaker 1: him about what was going on in the empire. And 361 00:23:54,800 --> 00:23:57,240 Speaker 1: he hired many emissaries that would go out in different 362 00:23:57,240 --> 00:24:00,840 Speaker 1: directions and bring news back to him about what was 363 00:24:00,880 --> 00:24:04,760 Speaker 1: going on. Now, I've never heard a historian talk about this. 364 00:24:04,880 --> 00:24:08,840 Speaker 1: But I imagine the Great Con must have faced a 365 00:24:08,960 --> 00:24:15,040 Speaker 1: tough problem what events in his empire occurred in which order. 366 00:24:15,840 --> 00:24:18,720 Speaker 1: Because of wars and weather and other issues, people might 367 00:24:18,880 --> 00:24:23,040 Speaker 1: travel at different paces, so the different emissaries would come 368 00:24:23,040 --> 00:24:26,200 Speaker 1: back to him at different times. One emissary comes back 369 00:24:26,240 --> 00:24:29,440 Speaker 1: and reports that a war has just ended, and another 370 00:24:29,480 --> 00:24:33,080 Speaker 1: emissary comes back and reports that a war has just begun, 371 00:24:33,160 --> 00:24:35,760 Speaker 1: and they're talking about the same war. But they got 372 00:24:35,800 --> 00:24:39,520 Speaker 1: back to the capitol at different times. And so the 373 00:24:39,600 --> 00:24:44,080 Speaker 1: question is how did the Great con synchronize all these signals. 374 00:24:44,760 --> 00:24:46,600 Speaker 1: The thing I want to make clear is that the 375 00:24:46,640 --> 00:24:50,800 Speaker 1: timing problem Kubla Khan had is the same problem the 376 00:24:50,920 --> 00:24:54,240 Speaker 1: brain has, which is to say, it's getting all these 377 00:24:54,240 --> 00:24:58,080 Speaker 1: different streams of information that come in at different paces. 378 00:24:58,960 --> 00:25:01,400 Speaker 1: And because your brain is locked up in the dark 379 00:25:01,520 --> 00:25:05,120 Speaker 1: tower of the skull, its only contact with the outside 380 00:25:05,119 --> 00:25:09,119 Speaker 1: world is via the electrical signals exiting and entering along 381 00:25:09,160 --> 00:25:13,360 Speaker 1: the highways of nerve bundles. So you've got touch information 382 00:25:13,480 --> 00:25:16,080 Speaker 1: streaming up the body, You've got auditory coming in, you've 383 00:25:16,119 --> 00:25:19,480 Speaker 1: got visual information coming into the brain. But the issue 384 00:25:19,640 --> 00:25:21,960 Speaker 1: is that all of these things get processed by the 385 00:25:22,000 --> 00:25:25,000 Speaker 1: brain at different speeds and at different places in the brain. 386 00:25:25,440 --> 00:25:29,439 Speaker 1: So your brain faces this enormous challenge how to stitch 387 00:25:29,560 --> 00:25:33,359 Speaker 1: together the incoming signals in the best way to make 388 00:25:33,400 --> 00:25:36,680 Speaker 1: a story about what just happened in the outside world. 389 00:25:37,480 --> 00:25:39,720 Speaker 1: For example, as we just saw, when I clap my hands, 390 00:25:39,720 --> 00:25:43,320 Speaker 1: the auditory signals get processed first, then the visual signals, 391 00:25:43,400 --> 00:25:46,920 Speaker 1: and yet they seem synced up. What this tells us 392 00:25:47,520 --> 00:25:51,080 Speaker 1: is that the brain is somehow pulling off major video 393 00:25:51,200 --> 00:25:54,320 Speaker 1: editing tricks, and we're going to find out how. Now, 394 00:25:54,320 --> 00:25:56,560 Speaker 1: my lab has studied this for years, and the first 395 00:25:56,600 --> 00:25:59,320 Speaker 1: thing to appreciate is that your brain doesn't figure this 396 00:25:59,400 --> 00:26:04,800 Speaker 1: out pass. It does this by involving your own actions. 397 00:26:04,960 --> 00:26:09,080 Speaker 1: Your own actions are the secret to understanding how everything 398 00:26:09,080 --> 00:26:13,040 Speaker 1: gets synchronized. And what I've proposed is that your brain 399 00:26:13,119 --> 00:26:15,960 Speaker 1: goes through so much trouble to get all this timing 400 00:26:16,080 --> 00:26:20,919 Speaker 1: right because of one issue causality. Because one of the 401 00:26:20,920 --> 00:26:25,240 Speaker 1: most fundamental things that any animal does is figure out 402 00:26:25,520 --> 00:26:28,359 Speaker 1: whether it was the one that caused something or not. 403 00:26:29,359 --> 00:26:34,840 Speaker 1: And fundamentally judging what caused what requires looking at the 404 00:26:35,200 --> 00:26:54,880 Speaker 1: order of events. So imagine you're walking in the forest 405 00:26:55,040 --> 00:26:58,000 Speaker 1: and you make a step and you hear a twig crack, 406 00:26:58,680 --> 00:27:01,600 Speaker 1: you can assume that was me because of you. But 407 00:27:01,680 --> 00:27:05,080 Speaker 1: if you hear the twig crack just before you land 408 00:27:05,080 --> 00:27:08,400 Speaker 1: your step, then you'd better be worried about a mountain lion. 409 00:27:09,480 --> 00:27:15,560 Speaker 1: So causality requires a temporal order judgment, which is to say, 410 00:27:16,000 --> 00:27:18,160 Speaker 1: did I put out the action and then I got 411 00:27:18,160 --> 00:27:21,560 Speaker 1: sensory feedback, in which case I'm going to take credit 412 00:27:21,600 --> 00:27:25,919 Speaker 1: for having done that, Versus I got sensory feedback and 413 00:27:25,960 --> 00:27:28,280 Speaker 1: then I did some action, in which case I'm not 414 00:27:28,359 --> 00:27:30,480 Speaker 1: taking credit for that. I had nothing to do with that. 415 00:27:31,560 --> 00:27:35,480 Speaker 1: And what we're often talking about is tens of milliseconds 416 00:27:35,480 --> 00:27:37,920 Speaker 1: one way or the other as the only difference between 417 00:27:37,920 --> 00:27:42,000 Speaker 1: these scenarios. But animals are very sensitive to this, and 418 00:27:42,040 --> 00:27:45,239 Speaker 1: at bottom, this is the challenge that animals have to 419 00:27:45,280 --> 00:27:48,480 Speaker 1: figure out. And as we've seen, the reason this is 420 00:27:48,520 --> 00:27:52,240 Speaker 1: really difficult is because the speed of sensory signals differs 421 00:27:52,680 --> 00:27:56,520 Speaker 1: and also they can change. So, for example, when you 422 00:27:56,560 --> 00:28:01,360 Speaker 1: go from a bright outdoors into a dimly lit room, 423 00:28:01,720 --> 00:28:04,080 Speaker 1: the speed at which your eyes are talking to your 424 00:28:04,119 --> 00:28:07,639 Speaker 1: brain slows down by quite a bit. And what that 425 00:28:07,760 --> 00:28:10,840 Speaker 1: means is that now your vision and your motor actions 426 00:28:11,080 --> 00:28:13,679 Speaker 1: are out of sink a little bit. So if right 427 00:28:13,720 --> 00:28:15,840 Speaker 1: when you walked into the dim room, I threw you 428 00:28:15,880 --> 00:28:18,520 Speaker 1: a ball, you'd probably miss it. I don't know if 429 00:28:18,560 --> 00:28:21,880 Speaker 1: you've ever played volleyball right when the sun's going down, 430 00:28:22,200 --> 00:28:25,080 Speaker 1: but everyone's having good time, and then right as the 431 00:28:25,200 --> 00:28:27,760 Speaker 1: sun's going down, everyone starts getting hit in the face 432 00:28:27,800 --> 00:28:31,159 Speaker 1: with the ball and so on. Because what's happening is 433 00:28:31,200 --> 00:28:34,920 Speaker 1: your time is getting out of sync. Now, now that's 434 00:28:34,960 --> 00:28:37,959 Speaker 1: an example of a short term fast change, but on 435 00:28:38,000 --> 00:28:41,600 Speaker 1: a longer time scale, as you grow from a baby 436 00:28:41,640 --> 00:28:44,360 Speaker 1: to an adult, it takes a longer time to send 437 00:28:44,400 --> 00:28:48,160 Speaker 1: signals out to your hand and get signals back. And 438 00:28:48,200 --> 00:28:50,640 Speaker 1: so all of this led me to think a while ago, 439 00:28:50,880 --> 00:28:54,800 Speaker 1: somehow the brain is having to figure out what its 440 00:28:55,080 --> 00:28:59,840 Speaker 1: expectations are. It's having to modulate on the fly how 441 00:28:59,840 --> 00:29:03,160 Speaker 1: long it expects for signals to come back. And so 442 00:29:03,240 --> 00:29:06,920 Speaker 1: I hypothesize that the brain is always doing this on 443 00:29:06,960 --> 00:29:11,960 Speaker 1: the fly. It's always recalibrating, it's readjusting the expected time 444 00:29:12,000 --> 00:29:14,880 Speaker 1: that it takes for signals to come in. But how 445 00:29:14,920 --> 00:29:19,080 Speaker 1: does it do that? And the answer is by interacting 446 00:29:19,160 --> 00:29:21,880 Speaker 1: with the world. Because whenever you touch things, or you 447 00:29:22,000 --> 00:29:25,040 Speaker 1: kick things, or you do anything like that. Your brain 448 00:29:25,160 --> 00:29:29,640 Speaker 1: is saying, okay, everybody, synchronize your watches. I'm putting out 449 00:29:29,640 --> 00:29:32,440 Speaker 1: an action, and what I expect is that I'm going 450 00:29:32,520 --> 00:29:34,160 Speaker 1: to see it and hear it and feel it all 451 00:29:34,200 --> 00:29:38,360 Speaker 1: at the same time. That's the prior expectation that it 452 00:29:38,360 --> 00:29:40,680 Speaker 1: comes to the table with. And if I hit the 453 00:29:40,680 --> 00:29:45,280 Speaker 1: table and it goes hit knock like that, my brain 454 00:29:45,320 --> 00:29:49,480 Speaker 1: will adjust the timing. In other words, your brain doesn't 455 00:29:49,480 --> 00:29:52,520 Speaker 1: know in advance how long your limbs are, or what 456 00:29:52,560 --> 00:29:55,360 Speaker 1: the lighting level is, or how fast sound travels and 457 00:29:55,360 --> 00:29:58,200 Speaker 1: so on. It just figures out what it needs by 458 00:29:58,840 --> 00:30:02,560 Speaker 1: reaching out and interacting with the world. It just needs 459 00:30:02,560 --> 00:30:05,720 Speaker 1: to embed the single assumption that if it sends out 460 00:30:05,760 --> 00:30:08,800 Speaker 1: an action such as a knock on the table or 461 00:30:08,800 --> 00:30:11,360 Speaker 1: a clap of the hands, all the feedback should be 462 00:30:11,400 --> 00:30:16,240 Speaker 1: assumed to be simultaneous, and any delays between the senses 463 00:30:16,560 --> 00:30:22,200 Speaker 1: should be adjusted until simultaneity is perceived. In other words, 464 00:30:22,560 --> 00:30:26,040 Speaker 1: the best way to predict the expected timing of the 465 00:30:26,080 --> 00:30:28,800 Speaker 1: signals is to interact with the world. Is to go 466 00:30:28,800 --> 00:30:31,160 Speaker 1: out and touch and kick and push and knock on 467 00:30:31,280 --> 00:30:34,560 Speaker 1: the world, and your brain makes the assumption that all 468 00:30:34,560 --> 00:30:37,960 Speaker 1: the feedback is simultaneous. The best way to predict the 469 00:30:38,000 --> 00:30:41,760 Speaker 1: future is to create it. You cause something and all 470 00:30:41,800 --> 00:30:48,200 Speaker 1: the consequences should be synchronized. That's how you keep yourself calibrated. So, 471 00:30:48,560 --> 00:30:52,280 Speaker 1: just to be clear, what this suggests is that if 472 00:30:52,320 --> 00:30:56,600 Speaker 1: the feedback signal arrives with a delay, the brain's going 473 00:30:56,640 --> 00:30:59,640 Speaker 1: to adjust things to make it seem like it happened 474 00:30:59,680 --> 00:31:03,560 Speaker 1: close in time. So I took this hypothesis and in 475 00:31:03,600 --> 00:31:07,760 Speaker 1: my lab we created a very simple experiment. You come 476 00:31:07,760 --> 00:31:10,520 Speaker 1: into the lab and you're seated in front of a button, 477 00:31:11,080 --> 00:31:14,400 Speaker 1: and whenever you hit the button that causes a flash 478 00:31:14,400 --> 00:31:17,160 Speaker 1: of light. You press the button, the light flashes, But 479 00:31:17,280 --> 00:31:21,760 Speaker 1: then we sneakily inject a small delay in there, let's 480 00:31:21,760 --> 00:31:25,520 Speaker 1: say one hundred milliseconds. So you hit the button and 481 00:31:25,560 --> 00:31:29,400 Speaker 1: then the flash of light appears. What happens very quickly 482 00:31:29,440 --> 00:31:33,480 Speaker 1: is that your brain adjusts to the delay. Because you're 483 00:31:33,560 --> 00:31:36,600 Speaker 1: the one causing it, the button and the light are 484 00:31:36,600 --> 00:31:41,840 Speaker 1: interpreted as simultaneous, or at least close to simultaneous. So 485 00:31:42,080 --> 00:31:44,560 Speaker 1: after just a couple of hits, it doesn't feel like 486 00:31:44,720 --> 00:31:48,240 Speaker 1: one hundred millisecond delay. It feels like the button pressed 487 00:31:48,240 --> 00:31:50,560 Speaker 1: and the flash are happening at the same time. Why 488 00:31:51,080 --> 00:31:53,800 Speaker 1: it's because your brain is the one putting out the action, 489 00:31:54,320 --> 00:31:58,640 Speaker 1: so it knows what to expect. And then we pull 490 00:31:58,720 --> 00:32:02,080 Speaker 1: the big trick on you after your brain is used 491 00:32:02,080 --> 00:32:06,280 Speaker 1: to this delay and thinks this is simultaneity. Now you 492 00:32:06,360 --> 00:32:09,800 Speaker 1: press the button, and we make the flash happen immediately, 493 00:32:09,920 --> 00:32:15,040 Speaker 1: no delay. And what is your perception? You think that 494 00:32:15,080 --> 00:32:19,120 Speaker 1: the flash happened before you hit the button, So you 495 00:32:19,200 --> 00:32:22,400 Speaker 1: hit the button, the flash occurs immediately, and you say, WHOA, 496 00:32:22,440 --> 00:32:27,080 Speaker 1: I didn't do that. It flashed just before I hit it. Now, 497 00:32:27,080 --> 00:32:30,760 Speaker 1: this is amazing to witness because this is an illusory 498 00:32:30,840 --> 00:32:35,240 Speaker 1: reversal of action and effect. You hit the button, but 499 00:32:35,400 --> 00:32:40,760 Speaker 1: you believe the consequence happened before your action. Your brain 500 00:32:40,840 --> 00:32:43,880 Speaker 1: gives you the wrong answer because it has adjusted it 501 00:32:43,920 --> 00:32:48,240 Speaker 1: expects a certain delay, and now we've tricked it. Now, 502 00:32:48,280 --> 00:32:51,160 Speaker 1: this is a very simple experiment that you can reproduce 503 00:32:51,200 --> 00:32:53,360 Speaker 1: at home with a little bit of programming, but it's 504 00:32:53,400 --> 00:32:57,280 Speaker 1: a really big deal because it demonstrates that the timing 505 00:32:57,360 --> 00:33:00,680 Speaker 1: you perceive in the world is not what it's truly 506 00:33:00,760 --> 00:33:05,400 Speaker 1: happening out there, but an easily manipulated story put together 507 00:33:05,520 --> 00:33:08,720 Speaker 1: by your brain now. I presented this research at a 508 00:33:08,800 --> 00:33:11,440 Speaker 1: university recently, and a professor there came up to me 509 00:33:11,480 --> 00:33:14,320 Speaker 1: afterwards and asked me about something. He said, they just 510 00:33:14,360 --> 00:33:18,160 Speaker 1: got a new telephone system installed and he types at 511 00:33:18,200 --> 00:33:20,880 Speaker 1: his desk all day and sometimes he turns to the 512 00:33:20,880 --> 00:33:24,240 Speaker 1: phone and dials the number, and his impression was that 513 00:33:24,320 --> 00:33:28,600 Speaker 1: the line starts ringing just before he hits the final number. Well, 514 00:33:28,640 --> 00:33:32,160 Speaker 1: I immediately understood what was happening here, although he wasn't 515 00:33:32,200 --> 00:33:36,120 Speaker 1: aware of it. His computer keyboard has a delay between 516 00:33:36,400 --> 00:33:39,320 Speaker 1: hitting the key and a letter appearing on the screen. 517 00:33:39,360 --> 00:33:42,560 Speaker 1: Typically for computers that's about one hundred milliseconds, but we 518 00:33:42,680 --> 00:33:46,800 Speaker 1: never notice it because we calibrate to the delay. Anyway, 519 00:33:47,000 --> 00:33:50,040 Speaker 1: he now turns to the phone, and this new system 520 00:33:50,120 --> 00:33:53,120 Speaker 1: has a much smaller delay. So when he hits the 521 00:33:53,160 --> 00:33:57,000 Speaker 1: final number on the phone, the ringing starts, but it 522 00:33:57,120 --> 00:34:00,280 Speaker 1: feels like it happens just before he hit the final 523 00:34:00,400 --> 00:34:06,600 Speaker 1: number key. He's experiencing this illusory reversal of action and effect, 524 00:34:06,840 --> 00:34:09,920 Speaker 1: and it's because the delay of the two machines is different. 525 00:34:10,280 --> 00:34:14,120 Speaker 1: He's calibrated to one, and suddenly the delay is different 526 00:34:14,200 --> 00:34:16,759 Speaker 1: on the other. And by the way, you can turn 527 00:34:16,800 --> 00:34:19,919 Speaker 1: this into a game of sorts. My graduate student John 528 00:34:20,000 --> 00:34:25,279 Speaker 1: Jacobson was inspired by this discovery to program an unbeatable 529 00:34:25,360 --> 00:34:28,480 Speaker 1: game of rocks, as or paper. So here's how that goes. 530 00:34:28,640 --> 00:34:31,000 Speaker 1: There's a countdown and then you hit a key to 531 00:34:31,080 --> 00:34:33,880 Speaker 1: register whether you're throwing a rock or as or a paper, 532 00:34:34,040 --> 00:34:36,680 Speaker 1: And just like in the game, the computer presents its 533 00:34:36,800 --> 00:34:39,879 Speaker 1: choice at the same time, or so you think it's 534 00:34:40,000 --> 00:34:43,560 Speaker 1: actually waiting one hundred and fifty milliseconds and seeing what 535 00:34:43,600 --> 00:34:46,600 Speaker 1: you did, But it feels simultaneous to you because your 536 00:34:46,600 --> 00:34:49,960 Speaker 1: brain adjusts to you pressing the button and you're seeing 537 00:34:49,960 --> 00:34:52,239 Speaker 1: the result on the screen. And then every once in 538 00:34:52,280 --> 00:34:54,680 Speaker 1: a while the delay gets dropped, so it feels like 539 00:34:54,719 --> 00:34:58,440 Speaker 1: the computer answered before you, even though it was again 540 00:34:58,640 --> 00:35:02,440 Speaker 1: just registering your press and reacting immediately. You have the 541 00:35:02,520 --> 00:35:06,520 Speaker 1: feeling that you reacted after it and that you answered 542 00:35:06,560 --> 00:35:09,480 Speaker 1: exactly the wrong thing. And by the way, I'll just 543 00:35:09,560 --> 00:35:11,680 Speaker 1: mention that my students and I ran a bunch of 544 00:35:11,719 --> 00:35:16,319 Speaker 1: experiments in which we showed that this temporal recalibration can 545 00:35:16,480 --> 00:35:19,880 Speaker 1: last through time, which, as you may remember from episode 546 00:35:19,920 --> 00:35:24,680 Speaker 1: twenty four, is exactly what happens with the motion after effect. 547 00:35:24,719 --> 00:35:28,640 Speaker 1: When you say, watch a downward waterfall for a while, 548 00:35:28,719 --> 00:35:31,680 Speaker 1: and then you see everything moving upward. It turns out 549 00:35:31,719 --> 00:35:34,520 Speaker 1: if you watch the waterfall and close your eyes and 550 00:35:34,560 --> 00:35:38,520 Speaker 1: then open your eyes later, the illusion still happens. And 551 00:35:38,600 --> 00:35:42,240 Speaker 1: without going into details, this indicates the mechanism by which 552 00:35:42,320 --> 00:35:47,800 Speaker 1: the active recalibration happens under the hood in the neural circuitry. Anyway, 553 00:35:48,000 --> 00:35:50,720 Speaker 1: my lab published some years ago a model in which 554 00:35:51,120 --> 00:35:56,040 Speaker 1: recalibrations of motion are exactly the same mechanism as the 555 00:35:56,080 --> 00:36:00,480 Speaker 1: recalibrations in the time domain. In other words, words, this 556 00:36:00,520 --> 00:36:04,560 Speaker 1: suggests the possibility that the brain uses exactly the same 557 00:36:04,680 --> 00:36:09,640 Speaker 1: circuitry for time and space. I'll skip the details here, 558 00:36:09,680 --> 00:36:12,399 Speaker 1: but for interested parties, I've linked to the paper at 559 00:36:12,400 --> 00:36:16,400 Speaker 1: eagleman dot com slash podcast. Okay, so we can show 560 00:36:16,760 --> 00:36:21,640 Speaker 1: that the brain constantly recalibrates its timing. But remember this 561 00:36:21,680 --> 00:36:24,880 Speaker 1: isn't just a party trick of the brain. It's critical 562 00:36:24,960 --> 00:36:28,440 Speaker 1: to solving the problem of causality. The only way this 563 00:36:28,560 --> 00:36:32,160 Speaker 1: problem can be accurately solved in a brain with lots 564 00:36:32,160 --> 00:36:35,920 Speaker 1: of senses where timing is always changing is by keeping 565 00:36:35,960 --> 00:36:39,759 Speaker 1: the expected time of signals actively calibrated so that you 566 00:36:39,800 --> 00:36:45,200 Speaker 1: can determine before and after, even with these different sensory pathways, 567 00:36:45,200 --> 00:36:48,960 Speaker 1: so your brain's always making this adjustment. But here's something 568 00:36:49,000 --> 00:36:53,319 Speaker 1: really important. Let's return to what we saw with this recalibration. 569 00:36:53,840 --> 00:36:57,080 Speaker 1: A person hits the button, but if we've just removed 570 00:36:57,160 --> 00:37:00,200 Speaker 1: the delay, they say, WHOA, that wasn't me. The light 571 00:37:00,280 --> 00:37:04,399 Speaker 1: flashed before I did anything. And that got me thinking 572 00:37:04,480 --> 00:37:08,239 Speaker 1: about something because I realized I had seen that kind 573 00:37:08,280 --> 00:37:12,200 Speaker 1: of reaction before. So when I saw participants saying that 574 00:37:12,360 --> 00:37:17,239 Speaker 1: wasn't me, I thought that looks really familiar. Specifically, this 575 00:37:17,360 --> 00:37:22,000 Speaker 1: is called credit misattribution, and this is where you cause 576 00:37:22,080 --> 00:37:24,239 Speaker 1: something but you deny that you were the one who 577 00:37:24,280 --> 00:37:27,800 Speaker 1: did it. And this is one of the striking symptoms 578 00:37:27,840 --> 00:37:32,600 Speaker 1: that we see in schizophrenia. A person suffering from schizophrenia 579 00:37:32,840 --> 00:37:36,080 Speaker 1: will often do something and not take credit for it. 580 00:37:36,080 --> 00:37:38,680 Speaker 1: They believe that it was not them who caused the 581 00:37:38,760 --> 00:37:42,080 Speaker 1: thing to happen, and then it's perfectly rational for them 582 00:37:42,120 --> 00:37:44,759 Speaker 1: to cook up a different sort of explanation for it 583 00:37:45,040 --> 00:37:48,040 Speaker 1: and say someone else is doing it, or this was 584 00:37:48,160 --> 00:37:51,200 Speaker 1: caused by a signal from a radio tower or whatever, 585 00:37:51,280 --> 00:37:53,680 Speaker 1: but it's not me that did it. Whatever's going on, 586 00:37:54,600 --> 00:37:58,080 Speaker 1: And so some years ago, I started to hypothesize that 587 00:37:58,160 --> 00:38:04,600 Speaker 1: schizophrenia may actually be a problem with time recalibration. What 588 00:38:04,680 --> 00:38:08,280 Speaker 1: if you're not properly adjusting the timing of your inputs 589 00:38:08,280 --> 00:38:10,840 Speaker 1: to your outputs, you would have a very difficult time 590 00:38:11,520 --> 00:38:16,200 Speaker 1: judging causality. But that's just the beginning. I immediately started 591 00:38:16,200 --> 00:38:21,560 Speaker 1: thinking about another symptom of schizophrenia, which is auditory hallucinations. 592 00:38:22,600 --> 00:38:26,560 Speaker 1: So here's the thing. Under normal circumstances, you're always talking 593 00:38:26,560 --> 00:38:30,120 Speaker 1: to yourself. You have an internally generated voice, and you 594 00:38:30,280 --> 00:38:32,640 Speaker 1: listen to that. And by the way, if you're thinking, 595 00:38:33,000 --> 00:38:37,280 Speaker 1: what internal voice, that's the internal voice. But what happens 596 00:38:37,680 --> 00:38:41,799 Speaker 1: if you get the timing wrong, even by a few milliseconds, 597 00:38:41,840 --> 00:38:45,680 Speaker 1: such that you thought you were hearing the voice just 598 00:38:45,840 --> 00:38:49,680 Speaker 1: before feeling like you generated it, you would have to 599 00:38:49,719 --> 00:38:52,760 Speaker 1: conclude that it was somebody else's voice, not your own. 600 00:38:53,200 --> 00:38:56,880 Speaker 1: And it's all simply because the timing is off between 601 00:38:56,960 --> 00:39:00,560 Speaker 1: generating the voice and listening to it. And if thinking 602 00:39:00,640 --> 00:39:03,279 Speaker 1: led me and my students to run experiments at a 603 00:39:03,600 --> 00:39:08,120 Speaker 1: county mental health facility with people who had schizophrenia, and indeed, 604 00:39:08,160 --> 00:39:12,399 Speaker 1: we found that people with schizophrenia do not recalibrate their 605 00:39:12,480 --> 00:39:16,400 Speaker 1: timing as well as healthy controls do. So when we 606 00:39:16,480 --> 00:39:18,960 Speaker 1: give them a test like hit the button and did 607 00:39:18,960 --> 00:39:21,640 Speaker 1: the flash of light occur before or after, and we 608 00:39:21,760 --> 00:39:26,640 Speaker 1: measure their recalibration, it's much less or it's absent. Now, 609 00:39:26,680 --> 00:39:29,320 Speaker 1: like all science, this is going to require many more studies, 610 00:39:29,360 --> 00:39:32,600 Speaker 1: but if this is the right way to think about schizophrenia, 611 00:39:32,960 --> 00:39:37,279 Speaker 1: it completely changes our approach to it. It means that 612 00:39:37,360 --> 00:39:41,800 Speaker 1: instead of throwing pharmacological solutions at it, which have limited success, 613 00:39:42,680 --> 00:39:45,800 Speaker 1: just imagine if you could give somebody a video game 614 00:39:46,080 --> 00:39:48,879 Speaker 1: that they play for a few minutes and then their 615 00:39:48,920 --> 00:39:54,120 Speaker 1: auditory hallucinations go away because we've recalibrated their timing. So 616 00:39:54,239 --> 00:39:56,920 Speaker 1: this is work I'm pursuing now, and it all began 617 00:39:57,080 --> 00:40:02,399 Speaker 1: with these very simple experiments. So to wrap up today's episode, 618 00:40:02,560 --> 00:40:05,439 Speaker 1: it's an ongoing passion of mind to figure out how 619 00:40:05,480 --> 00:40:09,240 Speaker 1: the brain constructs reality. And there are very few things 620 00:40:09,280 --> 00:40:13,799 Speaker 1: weirder than time. What we saw today is that to 621 00:40:13,920 --> 00:40:19,000 Speaker 1: synchronize the incoming information from the senses, our conscious awareness 622 00:40:19,080 --> 00:40:22,319 Speaker 1: has to lag behind the physical world. But none of 623 00:40:22,320 --> 00:40:26,440 Speaker 1: that is obvious to your perception. And even weirder, the 624 00:40:26,600 --> 00:40:31,359 Speaker 1: order of sensory events in the world is dynamically recalibrated, 625 00:40:31,680 --> 00:40:34,520 Speaker 1: so you can hit a button that causes a flash, 626 00:40:34,680 --> 00:40:38,840 Speaker 1: but under different circumstances, you'll believe that happened before or after, 627 00:40:38,960 --> 00:40:42,040 Speaker 1: and we can easily change that around. And this is 628 00:40:42,080 --> 00:40:46,600 Speaker 1: because your brain can't automatically know what the timing should be, 629 00:40:47,320 --> 00:40:51,600 Speaker 1: especially as sensory timing changes all the time. So your brain, 630 00:40:52,160 --> 00:40:57,640 Speaker 1: living in darkness, constantly interacts with the world to recalibrate 631 00:40:57,760 --> 00:41:00,759 Speaker 1: its timing. It says, I'm going to knock on something now. 632 00:41:00,920 --> 00:41:05,480 Speaker 1: Everyone synchronize your watches. And this matters to the brains 633 00:41:05,680 --> 00:41:08,440 Speaker 1: so much to get all this timing right, because this 634 00:41:08,600 --> 00:41:14,160 Speaker 1: is the basis of judging causality, and when that recalibration 635 00:41:14,400 --> 00:41:17,440 Speaker 1: isn't working well, it makes it difficult to interpret the 636 00:41:17,440 --> 00:41:22,680 Speaker 1: world as we see in schizophrenia. And this episode points 637 00:41:22,719 --> 00:41:25,680 Speaker 1: us back to a fundamental lesson that we've seen a 638 00:41:25,719 --> 00:41:30,000 Speaker 1: lot in earlier episodes, with visual illusions and auditory illusions. 639 00:41:30,880 --> 00:41:35,839 Speaker 1: Reality is not passively received by our brains, but is 640 00:41:36,000 --> 00:41:45,520 Speaker 1: actively constructed. Go to Eagleman dot com slash podcast for 641 00:41:45,640 --> 00:41:49,360 Speaker 1: more information and to find further reading, and send me 642 00:41:49,400 --> 00:41:53,600 Speaker 1: an email at podcast at eagleman dot com with questions 643 00:41:53,680 --> 00:41:56,600 Speaker 1: or discussion, and I'll be making more episodes in which 644 00:41:56,640 --> 00:42:02,560 Speaker 1: I address those. Until next time, I'm David Eagleman, and 645 00:42:02,680 --> 00:42:04,480 Speaker 1: this is Inner Cosmos.