1 00:00:04,519 --> 00:00:07,680 Speaker 1: Why do you still feel the waves after you get 2 00:00:07,680 --> 00:00:10,080 Speaker 1: off a boat and when you get off the treadmill 3 00:00:10,119 --> 00:00:12,520 Speaker 1: at the gym. Why does everything seem to be flowing 4 00:00:12,640 --> 00:00:17,280 Speaker 1: past you faster? What does heartbreak have in common with 5 00:00:17,360 --> 00:00:21,520 Speaker 1: drug withdrawal? And why after you stare at a waterfall 6 00:00:21,600 --> 00:00:24,400 Speaker 1: for a while, do the rocks on the side seem 7 00:00:24,440 --> 00:00:27,760 Speaker 1: to be crawling upward? Why did people in the nineteen 8 00:00:27,840 --> 00:00:32,320 Speaker 1: eighties think their book pages had some color red in them, 9 00:00:32,400 --> 00:00:35,519 Speaker 1: but no one thought that before or after the eighties? 10 00:00:35,800 --> 00:00:37,640 Speaker 1: And what does any of this have to do with 11 00:00:37,840 --> 00:00:42,160 Speaker 1: the great philosopher Aristotle watching a horse stuck in the river? 12 00:00:46,120 --> 00:00:49,240 Speaker 1: Welcome to Inner Cosmos with me David Eagleman. I'm a 13 00:00:49,280 --> 00:00:53,080 Speaker 1: neuroscientist and author at Stanford and in these episodes we 14 00:00:53,159 --> 00:00:57,560 Speaker 1: sail deeply into our three pound universe to understand why 15 00:00:57,600 --> 00:01:09,679 Speaker 1: and how our lives look the way they do. Today's 16 00:01:09,720 --> 00:01:14,560 Speaker 1: episode is about the way the brain readjusts its circuitry 17 00:01:14,640 --> 00:01:19,760 Speaker 1: on really fast timescales, and why your brain is constantly 18 00:01:19,840 --> 00:01:23,800 Speaker 1: doing this. In the nineteen eighties, tens of thousands of 19 00:01:23,800 --> 00:01:27,839 Speaker 1: people began to notice something really weird when they looked 20 00:01:27,920 --> 00:01:31,520 Speaker 1: at a floppy disk envelope with the black and white 21 00:01:31,560 --> 00:01:35,440 Speaker 1: IBM logo on the front, the letters IBM seemed to 22 00:01:35,440 --> 00:01:38,760 Speaker 1: have a red tint, And the same thing happened when 23 00:01:38,840 --> 00:01:43,560 Speaker 1: people looked at pages in a book, the text seemed 24 00:01:43,600 --> 00:01:47,640 Speaker 1: like it was shaded red. Now, if that's not weird enough, 25 00:01:47,720 --> 00:01:50,320 Speaker 1: check this out. This only happened in the nineteen eighties. 26 00:01:50,440 --> 00:01:54,440 Speaker 1: People didn't perceive a red tint before or after this decade. 27 00:01:54,800 --> 00:01:59,800 Speaker 1: So what was changing about brains during that window. I'll 28 00:01:59,800 --> 00:02:03,720 Speaker 1: tell you the answer. But to understand this, we're first 29 00:02:03,800 --> 00:02:07,360 Speaker 1: going to step back even further in history, twenty four 30 00:02:07,520 --> 00:02:12,920 Speaker 1: hundred years further to Aristotle. Now, Aristotle, as you know, 31 00:02:13,120 --> 00:02:18,160 Speaker 1: is a philosopher and a polymath whose intellectual interests were boundless. 32 00:02:18,160 --> 00:02:21,400 Speaker 1: He wrote about essentially every subject you could imagine. But 33 00:02:21,480 --> 00:02:24,120 Speaker 1: we're coming to Aristotle not because of something he wrote, 34 00:02:24,160 --> 00:02:28,280 Speaker 1: but instead because he was insightful enough to pause and 35 00:02:28,520 --> 00:02:32,919 Speaker 1: notice when something didn't make sense. What happened is that 36 00:02:33,240 --> 00:02:37,400 Speaker 1: someone was trying to cross a fast flowing river on 37 00:02:37,480 --> 00:02:40,680 Speaker 1: his horse, and the horse got stuck halfway in the river. 38 00:02:41,040 --> 00:02:44,920 Speaker 1: So Aristotle, along with some other people, ended up watching 39 00:02:45,000 --> 00:02:47,720 Speaker 1: this rescue operation. The way you might have a bunch 40 00:02:47,760 --> 00:02:50,880 Speaker 1: of people looking at a car crash nowadays. So you 41 00:02:50,960 --> 00:02:53,680 Speaker 1: have all these Greeks all standing there in their togas, 42 00:02:53,760 --> 00:02:56,640 Speaker 1: talking and chatting and watching the horse in the fast 43 00:02:56,680 --> 00:02:59,920 Speaker 1: flowing river. Now most of the people were presumably just 44 00:03:00,200 --> 00:03:03,720 Speaker 1: talking about stuff that made no difference to history. But 45 00:03:03,880 --> 00:03:08,000 Speaker 1: Aristotle stood at the side of the river intently watching 46 00:03:08,040 --> 00:03:12,640 Speaker 1: this horse. Now Here was the key about Aristotle, a 47 00:03:12,800 --> 00:03:16,480 Speaker 1: general characteristic that made him so famous to history. He 48 00:03:16,639 --> 00:03:22,320 Speaker 1: was a good observer. He paid attention. He noticed when 49 00:03:22,360 --> 00:03:25,680 Speaker 1: things were unusual, and when he found something, he would 50 00:03:25,760 --> 00:03:28,200 Speaker 1: sink his teeth into the problem and wouldn't let go. 51 00:03:28,760 --> 00:03:32,360 Speaker 1: And what he noticed here was something that possibly the 52 00:03:32,400 --> 00:03:34,160 Speaker 1: others did too, but they ignored it, and they didn't 53 00:03:34,200 --> 00:03:37,320 Speaker 1: think any further on it. What he noticed is that 54 00:03:37,400 --> 00:03:39,800 Speaker 1: once the horse got unstuck and the man made it 55 00:03:39,840 --> 00:03:43,840 Speaker 1: to the shore, and Aristotle looked away, he noticed that 56 00:03:43,880 --> 00:03:47,240 Speaker 1: everything on the land, the rocks, the huts, the trees, 57 00:03:47,320 --> 00:03:50,840 Speaker 1: everything seemed to be drifting, and they all seemed to 58 00:03:50,920 --> 00:03:55,839 Speaker 1: be moving in the opposite direction of the river. Now 59 00:03:55,840 --> 00:03:58,720 Speaker 1: you may have seen something like this too. The easiest 60 00:03:58,720 --> 00:04:03,360 Speaker 1: way to experience Aristotle's confusion and delight is to stare 61 00:04:03,400 --> 00:04:07,120 Speaker 1: at a waterfall and after you keep your eyes locked 62 00:04:07,160 --> 00:04:10,160 Speaker 1: on it for a while, look over to the rocks 63 00:04:10,200 --> 00:04:13,320 Speaker 1: on the side of the waterfall, and the rocks appear 64 00:04:13,440 --> 00:04:17,800 Speaker 1: to be moving upward. Now, this illusion that he first 65 00:04:17,839 --> 00:04:20,279 Speaker 1: made note of twenty four hundred years ago has come 66 00:04:20,320 --> 00:04:24,640 Speaker 1: to be known as the motion after effect. Why does 67 00:04:24,680 --> 00:04:29,960 Speaker 1: it happen. The activity of particular neurons in your visual 68 00:04:30,000 --> 00:04:35,159 Speaker 1: cortex represents downward motion, and the activity of other neurons 69 00:04:35,240 --> 00:04:39,840 Speaker 1: represents upward motion. And they're always locked in battle, and 70 00:04:39,920 --> 00:04:43,880 Speaker 1: most of the time the competition is evenly pitched, and 71 00:04:43,920 --> 00:04:47,960 Speaker 1: they evenly inhibit each other, and as a result, the 72 00:04:48,000 --> 00:04:52,520 Speaker 1: world appears to you to be moving neither up nor down. So, 73 00:04:52,640 --> 00:04:56,679 Speaker 1: given this, a popular explanation for the motion after effect 74 00:04:56,839 --> 00:05:01,520 Speaker 1: is fatigue. By staring at the downward motion of the waterfall, 75 00:05:01,880 --> 00:05:04,840 Speaker 1: you burn up a good deal of energy in your 76 00:05:05,160 --> 00:05:10,680 Speaker 1: downward coating neurons, and now their vigor is temporarily depleted. 77 00:05:10,760 --> 00:05:15,280 Speaker 1: So the battle tips in favor of the upward encoding neurons, 78 00:05:15,640 --> 00:05:19,440 Speaker 1: and as a result of this unbalanced activity, you perceive 79 00:05:19,800 --> 00:05:22,839 Speaker 1: that the rocks are climbing upward. You have this net 80 00:05:22,920 --> 00:05:28,000 Speaker 1: movement upward. Now, this fatigue hypothesis is very appealing in 81 00:05:28,040 --> 00:05:33,120 Speaker 1: its simplicity, but it's wrong. Why because it can't explain 82 00:05:33,240 --> 00:05:37,240 Speaker 1: some critical facts about the illusion. So imagine you watch 83 00:05:37,680 --> 00:05:40,960 Speaker 1: the downward waterfall for a while and then you close 84 00:05:41,000 --> 00:05:44,320 Speaker 1: your eyes tightly, say, for three hours you close your eyes. 85 00:05:44,680 --> 00:05:49,159 Speaker 1: When you reopen your eyes, you'll see the rocks crawling upward. 86 00:05:49,600 --> 00:05:52,400 Speaker 1: And what that tells us is it's not about a 87 00:05:52,440 --> 00:05:57,599 Speaker 1: temporary energy depletion in neurons. There's something deeper going on here. 88 00:05:58,560 --> 00:06:01,440 Speaker 1: And here's what that deeper thing is is the illusion 89 00:06:01,520 --> 00:06:06,120 Speaker 1: comes about not because of passive fatigue, but instead because 90 00:06:06,160 --> 00:06:10,880 Speaker 1: of an active recalibration in your brain. Your visual system 91 00:06:10,920 --> 00:06:16,000 Speaker 1: is exposed to continuous downward motion, and after a while 92 00:06:16,160 --> 00:06:21,000 Speaker 1: it comes to assume this is the new normal. At first, 93 00:06:21,400 --> 00:06:25,240 Speaker 1: downward motion is dramatic information to your brain, but after 94 00:06:25,320 --> 00:06:29,360 Speaker 1: a while of staring, you receive no new information from 95 00:06:29,480 --> 00:06:32,960 Speaker 1: downwardness here. So, as far as your brain is concerned, 96 00:06:33,560 --> 00:06:37,040 Speaker 1: this is the new reality, a world that flows more 97 00:06:37,160 --> 00:06:42,720 Speaker 1: down than up. So your visual system carefully rebalances its 98 00:06:42,839 --> 00:06:47,720 Speaker 1: expectations to mirror the world to expect more downward than 99 00:06:47,839 --> 00:06:51,560 Speaker 1: upward activity. Now, when you look away from the waterfall 100 00:06:51,600 --> 00:06:56,160 Speaker 1: and toward the cliff side. This recalibrated set point becomes 101 00:06:56,279 --> 00:07:00,400 Speaker 1: obvious because now rocks and trees are flowing upward toward 102 00:07:00,440 --> 00:07:04,839 Speaker 1: the sky. Your set point has shifted. In other words, 103 00:07:04,839 --> 00:07:10,520 Speaker 1: what counts as standing still has shifted. Why well, your 104 00:07:10,560 --> 00:07:14,200 Speaker 1: brain always wants to set up a ground truth so 105 00:07:14,240 --> 00:07:18,080 Speaker 1: that it can be better at detecting change. In this case, 106 00:07:18,120 --> 00:07:21,120 Speaker 1: when your visual field is filled with the site of 107 00:07:21,160 --> 00:07:26,280 Speaker 1: the waterfall, your brain is working to subtract off all 108 00:07:26,320 --> 00:07:30,239 Speaker 1: that downward motion. All that downward motion is no longer 109 00:07:30,640 --> 00:07:32,920 Speaker 1: informative in the way that it was, and so the 110 00:07:32,960 --> 00:07:36,920 Speaker 1: circuitry it adjusts itself so that it can be maximumly 111 00:07:36,960 --> 00:07:41,160 Speaker 1: sensitive to new information. Now, if you watch for it 112 00:07:41,200 --> 00:07:44,080 Speaker 1: the way Aristotle would, you'll see that this kind of 113 00:07:44,120 --> 00:07:48,040 Speaker 1: recalibration happens to you all the time. Think about when 114 00:07:48,040 --> 00:07:51,200 Speaker 1: you're on a small boat on the ocean. You are 115 00:07:51,360 --> 00:07:53,960 Speaker 1: rocking with the waves for a while, and then when 116 00:07:54,000 --> 00:07:56,680 Speaker 1: you get off the boat, the land seems to be 117 00:07:56,800 --> 00:07:59,040 Speaker 1: rocking for a while. It feels as though you're still 118 00:07:59,120 --> 00:08:01,720 Speaker 1: on the water. Now you may have thought about it 119 00:08:01,760 --> 00:08:04,080 Speaker 1: this way, Hey, my body thinks it's still on the water. 120 00:08:04,400 --> 00:08:08,240 Speaker 1: What you're actually feeling is a negative image of the 121 00:08:08,280 --> 00:08:11,560 Speaker 1: water's motion. And you may have noticed this sort of 122 00:08:11,600 --> 00:08:15,560 Speaker 1: illusion if you're a runner. So here's what normally happens. 123 00:08:15,600 --> 00:08:19,560 Speaker 1: Your body sends motor commands to the legs. It says, okay, 124 00:08:19,560 --> 00:08:23,840 Speaker 1: move fast, and correlated with your running is a visual 125 00:08:23,880 --> 00:08:27,560 Speaker 1: sensation where the visual world is flowing by your eyes 126 00:08:27,680 --> 00:08:31,960 Speaker 1: as a result. But when you run on a treadmill 127 00:08:32,040 --> 00:08:35,520 Speaker 1: at the gym, your brain is sending the same signals 128 00:08:35,520 --> 00:08:38,959 Speaker 1: to your legs. Run fast, but now your visual system 129 00:08:39,360 --> 00:08:43,400 Speaker 1: doesn't get the world flowing past. Instead, you're looking at 130 00:08:43,440 --> 00:08:45,920 Speaker 1: the gym wall in front of you the whole time. 131 00:08:46,600 --> 00:08:51,720 Speaker 1: So now when you step off, you experience the treadmill illusion. 132 00:08:52,360 --> 00:08:55,000 Speaker 1: With each step you take toward the locker room, the 133 00:08:55,040 --> 00:08:58,880 Speaker 1: world seems to stream by at a faster pace. It 134 00:08:58,920 --> 00:09:02,080 Speaker 1: looks as though you're moving forward more quickly than you 135 00:09:02,120 --> 00:09:06,199 Speaker 1: really are. Why does it happen Because your brain has 136 00:09:06,240 --> 00:09:10,000 Speaker 1: an expectation about how the act of moving your legs 137 00:09:10,440 --> 00:09:13,920 Speaker 1: should translate to the flow of the visual scene past 138 00:09:14,000 --> 00:09:17,560 Speaker 1: your eyes, and now after the treadmill, it's had to 139 00:09:17,960 --> 00:09:22,640 Speaker 1: adjust that relationship. So now there's an after effect. This 140 00:09:22,720 --> 00:09:26,760 Speaker 1: is just like with Aristotle's horse or the waterfall or 141 00:09:26,800 --> 00:09:29,240 Speaker 1: the feeling that you're still rocking after you get off 142 00:09:29,280 --> 00:09:34,320 Speaker 1: the boat. Your brain is readjusting its expectations about the world. 143 00:09:34,960 --> 00:09:37,680 Speaker 1: In the case of the treadmill, it's how the active 144 00:09:37,760 --> 00:09:41,000 Speaker 1: moving your legs should translate to the flow of the 145 00:09:41,080 --> 00:09:43,679 Speaker 1: visual scene past your eyes, and when you go back 146 00:09:43,720 --> 00:09:48,480 Speaker 1: to the normal world, there's an after effect. As another example, 147 00:09:48,520 --> 00:09:52,240 Speaker 1: you've surely noticed color after effects. If you stare at 148 00:09:52,280 --> 00:09:54,440 Speaker 1: a red dot for a little while and then you 149 00:09:54,480 --> 00:09:57,040 Speaker 1: look somewhere else and blink, you'll see the dot, but 150 00:09:57,160 --> 00:09:59,720 Speaker 1: now it looks green. Or if you stare at something 151 00:09:59,760 --> 00:10:01,920 Speaker 1: bright yellow for a little while and then you look away, 152 00:10:02,240 --> 00:10:05,720 Speaker 1: you'll see the opposite color blue. And these types of 153 00:10:05,840 --> 00:10:11,560 Speaker 1: color after effects can be surprisingly sophisticated. So consider something 154 00:10:11,640 --> 00:10:16,720 Speaker 1: called the McCullough after effect, named after the researcher Celeste McCulloch, 155 00:10:16,760 --> 00:10:19,920 Speaker 1: who discovered this in the nineteen sixties. So really get this. 156 00:10:20,000 --> 00:10:22,160 Speaker 1: I want you to imagine a bunch of black and 157 00:10:22,160 --> 00:10:24,839 Speaker 1: white lines like black white, black white, black white. Now 158 00:10:24,880 --> 00:10:27,720 Speaker 1: imagine a group of these that are horizontal and a 159 00:10:27,720 --> 00:10:31,480 Speaker 1: separate group of these that are vertical. Now, this can't 160 00:10:31,520 --> 00:10:33,760 Speaker 1: just be imagined as an illusion, but has to be 161 00:10:33,800 --> 00:10:36,200 Speaker 1: looked at to work. So please find a picture of 162 00:10:36,240 --> 00:10:39,400 Speaker 1: these lines on eagleman dot com Slash podcast to go 163 00:10:39,480 --> 00:10:42,200 Speaker 1: over there and take a look at this. Okay, So 164 00:10:42,240 --> 00:10:45,559 Speaker 1: look farther down the page and you'll see lines that 165 00:10:45,600 --> 00:10:47,880 Speaker 1: look the same as these black and white lines, but 166 00:10:47,960 --> 00:10:51,720 Speaker 1: now they're colored. The horizontal lines are green and the 167 00:10:51,800 --> 00:10:54,400 Speaker 1: vertical lines are red. And what I want you to 168 00:10:54,400 --> 00:10:57,319 Speaker 1: do is stare at these colored lines for a bit, 169 00:10:57,440 --> 00:11:00,920 Speaker 1: like a few minutes. The green lines go side side, 170 00:11:00,960 --> 00:11:04,200 Speaker 1: the red lines go up and down. Now go back 171 00:11:04,240 --> 00:11:07,240 Speaker 1: to the original black and white lines and you'll see 172 00:11:07,240 --> 00:11:11,840 Speaker 1: something amazing. You'll see that the spaces between the black 173 00:11:11,880 --> 00:11:16,280 Speaker 1: and white horizontal lines now look reddish, and the spaces 174 00:11:16,360 --> 00:11:20,640 Speaker 1: between the black and white vertical lines look greenish. This 175 00:11:20,679 --> 00:11:23,400 Speaker 1: is the McCullock effect. You gotta try this for yourself. 176 00:11:23,440 --> 00:11:28,000 Speaker 1: It's really worthwhile. Now why does it happen. It's because 177 00:11:28,040 --> 00:11:32,440 Speaker 1: when you stared at the colored lines, your brain said, hey, wait, 178 00:11:32,559 --> 00:11:36,520 Speaker 1: for some strange reason, everything horizontal is appearing green to 179 00:11:36,559 --> 00:11:39,560 Speaker 1: me and everything vertical is looking red to me. But 180 00:11:40,120 --> 00:11:44,360 Speaker 1: those features shouldn't really be correlated, and so it adjusts 181 00:11:44,400 --> 00:11:49,120 Speaker 1: itself to cancel out this strange relationship. Going on, and 182 00:11:49,120 --> 00:11:51,640 Speaker 1: when you look at the black and white lines again, 183 00:11:52,280 --> 00:11:56,439 Speaker 1: you're seeing the after effect. The horizontal lines were being 184 00:11:56,640 --> 00:12:00,720 Speaker 1: internally shifted in your brain towards the opposite color red, 185 00:12:01,080 --> 00:12:05,000 Speaker 1: and the vertical lines toward green. And again, I just 186 00:12:05,040 --> 00:12:07,439 Speaker 1: want to be clear, this has nothing to do with fatigue, 187 00:12:07,760 --> 00:12:11,199 Speaker 1: because in nineteen seventy five, two researchers showed that if 188 00:12:11,240 --> 00:12:14,760 Speaker 1: you stare at these red and green lines for fifteen minutes, 189 00:12:14,800 --> 00:12:17,960 Speaker 1: the after effect can last three and a half months. 190 00:12:18,960 --> 00:12:24,320 Speaker 1: So your brain is always doing an active recalibration of 191 00:12:24,360 --> 00:12:28,240 Speaker 1: the world out there. And this active recalibration is why 192 00:12:28,360 --> 00:12:31,400 Speaker 1: in the nineteen eighties many people began to see the 193 00:12:31,440 --> 00:12:34,520 Speaker 1: text in the books appearing to have a red tint 194 00:12:34,720 --> 00:12:38,280 Speaker 1: because at that time the population had just begun to 195 00:12:38,400 --> 00:12:42,760 Speaker 1: use computer monitors to do word processing. And as some 196 00:12:42,840 --> 00:12:47,720 Speaker 1: of you remember, unlike modern monitors, these early monitors only 197 00:12:47,760 --> 00:12:51,839 Speaker 1: displayed one color green, and so you typed a bunch 198 00:12:51,880 --> 00:12:54,800 Speaker 1: of lines of text on the screen and it looked 199 00:12:54,840 --> 00:12:59,360 Speaker 1: like horizontal lines of green on a black background. So 200 00:12:59,400 --> 00:13:03,520 Speaker 1: people would say there at these horizontal green rows for 201 00:13:03,720 --> 00:13:05,840 Speaker 1: hours at a time, all day while they were doing 202 00:13:05,880 --> 00:13:09,240 Speaker 1: their computer work. And so when they picked up a book, 203 00:13:09,800 --> 00:13:13,520 Speaker 1: the horizontal lines of black and white text were shaded 204 00:13:14,000 --> 00:13:18,079 Speaker 1: with the complementary color red. It was the McCullock effect. 205 00:13:18,559 --> 00:13:24,080 Speaker 1: Their brains were adjusting to a world of horizontal green lines, 206 00:13:24,440 --> 00:13:28,680 Speaker 1: and their reality changed accordingly. Now I mentioned that the 207 00:13:28,679 --> 00:13:32,040 Speaker 1: computer users in the nineteen eighties also experienced this illusion 208 00:13:32,040 --> 00:13:36,040 Speaker 1: when they looked at the IBM logo emblazoned on the 209 00:13:36,080 --> 00:13:38,840 Speaker 1: front of the floppy disk sleeve. If any of you 210 00:13:38,960 --> 00:13:43,160 Speaker 1: remember the old IBM logo, it's the three letters spelled 211 00:13:43,160 --> 00:13:46,800 Speaker 1: out of horizontal lines, as though you're looking at IBM 212 00:13:47,320 --> 00:13:50,680 Speaker 1: put through a egg slicer, And so the logo, just 213 00:13:50,720 --> 00:13:54,680 Speaker 1: like the horizontal lines in the book, looked tinged with red, 214 00:13:55,000 --> 00:13:58,679 Speaker 1: and designers at IBM were flummixed about this because they 215 00:13:58,679 --> 00:14:01,440 Speaker 1: had definitely not printed they're black and white design with 216 00:14:01,480 --> 00:14:04,880 Speaker 1: any red in it, and yet everyone was insisting that 217 00:14:05,040 --> 00:14:09,600 Speaker 1: they had. So all these after effects teach us something wild. 218 00:14:10,200 --> 00:14:12,280 Speaker 1: Even though you just open your eyes and look around 219 00:14:12,360 --> 00:14:15,440 Speaker 1: the world and assume you're just seeing reality out there, 220 00:14:15,880 --> 00:14:20,320 Speaker 1: in fact, your brain is doing massive work behind the scenes. 221 00:14:20,680 --> 00:14:25,240 Speaker 1: It's always recalibrating itself on the fly to try to 222 00:14:25,360 --> 00:14:28,640 Speaker 1: improve what it's seeing, to try to get rid of 223 00:14:28,680 --> 00:14:32,400 Speaker 1: information that doesn't matter, so it can surface the information 224 00:14:32,440 --> 00:14:35,960 Speaker 1: that does matter. And this active recalibration of the world 225 00:14:36,200 --> 00:14:39,600 Speaker 1: that's happening behind the scenes. This applies to everything. How 226 00:14:39,680 --> 00:14:42,960 Speaker 1: much motion is in the world, how stable the ground is, 227 00:14:43,320 --> 00:14:46,400 Speaker 1: whether vision flows past us when we move our legs, 228 00:14:46,760 --> 00:14:50,360 Speaker 1: whether lions are infused with color. None of the stuff 229 00:14:50,400 --> 00:14:55,479 Speaker 1: is decided in our genetics. It's all calibrated by our experience. 230 00:15:12,000 --> 00:15:15,800 Speaker 1: Now I want to take this concept of adaptation one 231 00:15:15,920 --> 00:15:19,120 Speaker 1: level deeper. I want to introduce the concept that your 232 00:15:19,120 --> 00:15:24,760 Speaker 1: brain is making things invisible if they are expected. So 233 00:15:24,840 --> 00:15:27,000 Speaker 1: take this as an example. Let's say you take a 234 00:15:27,120 --> 00:15:30,040 Speaker 1: yellow ping pong ball and you cut it exactly in half, 235 00:15:30,400 --> 00:15:33,840 Speaker 1: and you lay one hemisphere over each eye, and what 236 00:15:33,880 --> 00:15:37,080 Speaker 1: you'll see is the whole world is an even blanket 237 00:15:37,080 --> 00:15:40,720 Speaker 1: of yellow color. But within a few moments you don't 238 00:15:40,720 --> 00:15:44,080 Speaker 1: see any color at all. It's as though you're blind. 239 00:15:44,240 --> 00:15:48,760 Speaker 1: Your visual system just assumes that the world has become yellower, 240 00:15:49,160 --> 00:15:51,880 Speaker 1: and so it adapts so that you'll be sensitive to 241 00:15:52,040 --> 00:15:54,800 Speaker 1: other changes. So you should try this. You can find 242 00:15:54,840 --> 00:15:59,240 Speaker 1: any sort of totally featureless scene that's entirely one color 243 00:15:59,680 --> 00:16:02,040 Speaker 1: and fill your eyes with it. Like walk up to 244 00:16:02,120 --> 00:16:05,160 Speaker 1: a wall that's entirely painted red. Walk up real close. 245 00:16:05,200 --> 00:16:07,680 Speaker 1: Your eyes are filled with red, and you'll see the 246 00:16:07,840 --> 00:16:13,560 Speaker 1: color will quickly drain away to neutral. Your brain says, hey, 247 00:16:13,560 --> 00:16:16,880 Speaker 1: there's no more information here. I expect this color, So 248 00:16:16,880 --> 00:16:21,920 Speaker 1: I'm going to adjust things so that becomes invisible and 249 00:16:21,960 --> 00:16:24,320 Speaker 1: I'll tell you something else. The scene doesn't even have 250 00:16:24,400 --> 00:16:28,880 Speaker 1: to be featureless for things to fade away. So in 251 00:16:28,920 --> 00:16:33,840 Speaker 1: eighteen oh four, a Swiss physician named Ignos Troxler noticed 252 00:16:33,880 --> 00:16:37,000 Speaker 1: something really stunning, which is, if you stare at a 253 00:16:37,200 --> 00:16:40,440 Speaker 1: central point in the middle of a bunch of blobs 254 00:16:40,480 --> 00:16:44,320 Speaker 1: of color, all the busyness in the periphery, all those 255 00:16:44,360 --> 00:16:48,880 Speaker 1: blobs will eventually disappear. I have an example of this 256 00:16:48,960 --> 00:16:51,480 Speaker 1: on eagleman dot com slash podcast. Check it out. It's 257 00:16:51,560 --> 00:16:54,880 Speaker 1: really amazing. What you do is you keep your gaze 258 00:16:54,920 --> 00:16:57,560 Speaker 1: fixed right in the middle of the picture, and you'll 259 00:16:57,560 --> 00:17:00,800 Speaker 1: see there's all these smooth blobs of color, and within 260 00:17:00,840 --> 00:17:04,240 Speaker 1: about ten seconds, if you're keeping your eyes still, all 261 00:17:04,280 --> 00:17:09,639 Speaker 1: these surrounding blobs just start to disappear into the background, 262 00:17:09,880 --> 00:17:13,080 Speaker 1: and soon you are looking at what appears to be 263 00:17:13,560 --> 00:17:17,199 Speaker 1: a blank page. Now this is wild, and if you 264 00:17:17,280 --> 00:17:19,720 Speaker 1: move your eyes around just a bit, all these blobs 265 00:17:19,760 --> 00:17:23,720 Speaker 1: come back into your consciousness. This illusion is called the 266 00:17:23,920 --> 00:17:27,400 Speaker 1: Troxlur effect, and what it demonstrates is that if there's 267 00:17:27,440 --> 00:17:29,920 Speaker 1: a blob of something in your peripheral vision that is 268 00:17:30,000 --> 00:17:35,360 Speaker 1: not changing at all, it will evaporate from your perception. Now, 269 00:17:35,359 --> 00:17:38,560 Speaker 1: what is going on here? The answer is that your 270 00:17:38,640 --> 00:17:44,120 Speaker 1: visual system is always seeking motion and change. Something that's 271 00:17:44,160 --> 00:17:47,280 Speaker 1: fixed and none changing doesn't really matter, and it quickly 272 00:17:47,320 --> 00:17:53,720 Speaker 1: becomes invisible. Good information is expected to update, and things 273 00:17:53,760 --> 00:17:58,320 Speaker 1: that don't change get ignored by the system. So what 274 00:17:58,480 --> 00:18:03,040 Speaker 1: prevents your kitchen, your workplace from becoming like a Troxler 275 00:18:03,160 --> 00:18:07,639 Speaker 1: illusion with all the motionless features disappearing. Well, First, most 276 00:18:07,640 --> 00:18:10,840 Speaker 1: of the world is made up of hard edges, not blobs, 277 00:18:10,880 --> 00:18:13,639 Speaker 1: and those are easier for your visual system to hang onto. 278 00:18:14,119 --> 00:18:18,520 Speaker 1: But there's a deeper reason, although you're not generally aware 279 00:18:18,520 --> 00:18:23,760 Speaker 1: of it. Your eyes are constantly jumping and jiggling around. 280 00:18:24,160 --> 00:18:27,880 Speaker 1: So just observe a friend's eyeballs. You'll notice that her 281 00:18:28,000 --> 00:18:32,520 Speaker 1: eyeballs are making about three rapid jumps every second of 282 00:18:32,560 --> 00:18:36,760 Speaker 1: her waking life. These are called thecods. Bang bang bang bang, bang, 283 00:18:37,080 --> 00:18:40,000 Speaker 1: And if you watch even more closely, you'll find that 284 00:18:40,040 --> 00:18:43,280 Speaker 1: in between the big jumps, her eyes are constantly performing 285 00:18:43,320 --> 00:18:50,240 Speaker 1: these little micro jitters. They're called microsucods. Bang. Now, is 286 00:18:50,280 --> 00:18:55,040 Speaker 1: something wrong with your friend's eyes? No, these rapid movements, 287 00:18:55,119 --> 00:18:57,680 Speaker 1: both the big and the small. What they're doing is 288 00:18:57,720 --> 00:19:03,040 Speaker 1: they're keeping the image on the retina fresh totally unconsciously, 289 00:19:03,119 --> 00:19:08,040 Speaker 1: her eyes are working to maintain a constantly changing image. 290 00:19:08,520 --> 00:19:11,760 Speaker 1: Why do they bother. It's because any image that remains 291 00:19:12,160 --> 00:19:16,840 Speaker 1: perfectly fixed on one position on the retina will become invisible. 292 00:19:17,720 --> 00:19:20,120 Speaker 1: Here's how to prove this to yourself. If you wear 293 00:19:20,480 --> 00:19:24,159 Speaker 1: contact lenses, take a marker and draw a small shape 294 00:19:24,200 --> 00:19:25,879 Speaker 1: on the front of your contact right in the middle. 295 00:19:26,200 --> 00:19:29,040 Speaker 1: When you put the contact back in place on your eye, 296 00:19:29,280 --> 00:19:32,439 Speaker 1: you'll see something there, but it won't last long. It 297 00:19:32,640 --> 00:19:39,360 Speaker 1: rapidly fades to invisibility. Now, this phenomenon underscores the fundamental 298 00:19:39,400 --> 00:19:42,959 Speaker 1: fact that brains care about change. Just like with the 299 00:19:43,200 --> 00:19:49,040 Speaker 1: Troxler effect, features that don't change yield little information about 300 00:19:49,040 --> 00:19:54,960 Speaker 1: the world. All the important information comes from things in flux. Now, 301 00:19:55,000 --> 00:19:58,040 Speaker 1: if you don't have contact lenses, don't worry, because you're 302 00:19:58,160 --> 00:20:03,119 Speaker 1: already performing a similar experiment without knowing it. So you 303 00:20:03,200 --> 00:20:06,720 Speaker 1: have blood vessels that sit on top of your retina 304 00:20:06,720 --> 00:20:09,480 Speaker 1: at the back of your eye, and these blood vessels 305 00:20:10,000 --> 00:20:13,800 Speaker 1: should be seen superimposed on top of everything you look 306 00:20:13,840 --> 00:20:18,320 Speaker 1: at because they're smack in front of your photoreceptors. But 307 00:20:18,359 --> 00:20:23,040 Speaker 1: these blood vessels are totally invisible to your perception. Just 308 00:20:23,080 --> 00:20:26,240 Speaker 1: like the drawing on your contact lens. These blood vessels 309 00:20:26,359 --> 00:20:30,879 Speaker 1: are fixed in position with respect to your retina, So 310 00:20:30,920 --> 00:20:35,359 Speaker 1: no matter how much your eyes move, they can't refresh 311 00:20:35,520 --> 00:20:39,280 Speaker 1: the image of these blood vessels. Even though the vessels 312 00:20:39,280 --> 00:20:44,800 Speaker 1: interpose themselves between you and the world, they perceptually disappear. 313 00:20:44,880 --> 00:20:47,880 Speaker 1: It's like a magic trick. Now you might have noticed 314 00:20:47,920 --> 00:20:52,320 Speaker 1: a flash of these vessels when the eye doctor shines 315 00:20:52,359 --> 00:20:55,520 Speaker 1: the pen light in your eyes. Boom, there they are. 316 00:20:56,119 --> 00:20:59,639 Speaker 1: In this situation, the beam of light can cause the 317 00:20:59,720 --> 00:21:04,399 Speaker 1: vessel to cast a shadow at an unusual angle, and 318 00:21:04,440 --> 00:21:08,080 Speaker 1: your visual system suddenly takes notice something unexpected has just 319 00:21:08,160 --> 00:21:10,760 Speaker 1: occurred at the retina, and that's the only time you 320 00:21:10,880 --> 00:21:15,639 Speaker 1: witness this massive network that obstructs your view. If you 321 00:21:15,680 --> 00:21:18,919 Speaker 1: haven't seen this before, pause this podcast. Go into a 322 00:21:19,000 --> 00:21:21,680 Speaker 1: dark room and shine a beam of light in your eye. 323 00:21:21,920 --> 00:21:25,080 Speaker 1: From an angle, you'll see the blood vessels appear in 324 00:21:25,119 --> 00:21:27,920 Speaker 1: front of you. Just note that your visual system will 325 00:21:27,920 --> 00:21:30,919 Speaker 1: adapt fairly quickly, so the trick is to keep moving 326 00:21:30,960 --> 00:21:35,320 Speaker 1: the light to different angles to maintain the image. So 327 00:21:36,160 --> 00:21:41,679 Speaker 1: this strategy of ignoring the unchanging keeps your brain poised 328 00:21:41,920 --> 00:21:46,040 Speaker 1: to detect anything that moves or shifts or transforms at 329 00:21:46,040 --> 00:21:50,199 Speaker 1: the extreme. This is how reptile visual systems work. A 330 00:21:50,320 --> 00:21:53,800 Speaker 1: reptile can't see you if you stand still because they 331 00:21:54,000 --> 00:21:58,440 Speaker 1: only register change. They don't bother with position, and such 332 00:21:58,520 --> 00:22:02,760 Speaker 1: a system is perfectly sufficient. Reptiles have been surviving and 333 00:22:02,880 --> 00:22:06,199 Speaker 1: thriving for tens of millions of years. You probably remember 334 00:22:06,240 --> 00:22:09,040 Speaker 1: the scene in Jurassic Park where they say don't move. 335 00:22:09,080 --> 00:22:11,800 Speaker 1: The dinosaurs can't see you if you don't move. Well, 336 00:22:12,200 --> 00:22:16,840 Speaker 1: this is why reptiles ignore anything that does not change. 337 00:22:17,640 --> 00:22:22,119 Speaker 1: So let's return to the waterfall illusion. Why doesn't your 338 00:22:22,200 --> 00:22:26,560 Speaker 1: visual system shift so much that the waterfall is perceived 339 00:22:26,720 --> 00:22:30,040 Speaker 1: as standing still. Well, first, there might be limits to 340 00:22:30,080 --> 00:22:35,000 Speaker 1: the recalibration. It simply can't recalibrate enough to subtract off 341 00:22:35,000 --> 00:22:37,800 Speaker 1: the massive motion of the falls. But I think there's 342 00:22:37,840 --> 00:22:41,400 Speaker 1: another possibility, which is that you haven't watched the waterfall 343 00:22:41,800 --> 00:22:45,280 Speaker 1: for long enough, and if you did, it would eventually 344 00:22:45,320 --> 00:22:48,600 Speaker 1: recalibrate all the way. How long might that take? Two 345 00:22:48,640 --> 00:22:52,440 Speaker 1: months of steering at the waterfall two years. In theory, 346 00:22:52,520 --> 00:22:54,959 Speaker 1: if you were to watch for a long enough time, 347 00:22:55,480 --> 00:22:59,200 Speaker 1: then the short term changes in your visual system would 348 00:22:59,200 --> 00:23:04,119 Speaker 1: eventually to longer lasting changes, leading eventually to changes at 349 00:23:04,160 --> 00:23:09,359 Speaker 1: the deepest levels of the system. So ever present background 350 00:23:09,400 --> 00:23:13,439 Speaker 1: motion would become invisible to us. And this leads to 351 00:23:13,480 --> 00:23:16,400 Speaker 1: a crazy speculation that I made in my book Live Wire. 352 00:23:16,560 --> 00:23:21,600 Speaker 1: It's crazy, but logically sound. Are parts of the world 353 00:23:21,760 --> 00:23:26,080 Speaker 1: invisible to us that should be obvious. Imagine there was 354 00:23:26,080 --> 00:23:31,560 Speaker 1: something like a cosmic rainfall that had existed your entire life. 355 00:23:31,640 --> 00:23:35,280 Speaker 1: It would be completely invisible to you because you've never 356 00:23:35,320 --> 00:23:39,080 Speaker 1: seen otherwise. So your visual system would have set the 357 00:23:39,200 --> 00:23:44,120 Speaker 1: downward motion as it's zero point. If the cosmic rain 358 00:23:44,359 --> 00:23:47,399 Speaker 1: suddenly stopped, it would seem as though the whole world 359 00:23:47,400 --> 00:23:51,160 Speaker 1: were suddenly moving upward. We would believe that something had 360 00:23:51,280 --> 00:23:55,800 Speaker 1: just appeared ascending rain, even though the real rain had 361 00:23:55,880 --> 00:24:00,359 Speaker 1: just ended. And this situation could happen in any sensory channel. 362 00:24:00,440 --> 00:24:04,960 Speaker 1: Imagine the beat beep of a cosmic alarm clock with 363 00:24:05,000 --> 00:24:07,879 Speaker 1: no snooze button all the time, all throughout the cosmos 364 00:24:07,960 --> 00:24:12,080 Speaker 1: bee beep beep. If it were totally regular, you wouldn't 365 00:24:12,119 --> 00:24:15,440 Speaker 1: hear it because your brain would have adapted to it. 366 00:24:15,880 --> 00:24:20,520 Speaker 1: If the cosmic alarm suddenly ceased, everyone would hear a 367 00:24:20,680 --> 00:24:23,560 Speaker 1: great beat, beat, beat, but we would have no idea 368 00:24:23,600 --> 00:24:28,119 Speaker 1: that we were experiencing the after effect with the external 369 00:24:28,200 --> 00:24:36,600 Speaker 1: sound totally inside our heads. Successful adaptation makes regularities invisible. 370 00:24:53,480 --> 00:24:57,560 Speaker 1: So we've been talking about these illusions as the results 371 00:24:57,600 --> 00:25:00,720 Speaker 1: of adaptation, but there's actually the other way to look 372 00:25:00,760 --> 00:25:06,280 Speaker 1: at this. These illusions result from prediction. So if you 373 00:25:06,320 --> 00:25:09,560 Speaker 1: subtract away the downward motion of the waterfall or the 374 00:25:09,720 --> 00:25:13,159 Speaker 1: rocking of the boat, or the drawing on your contact lens, 375 00:25:13,560 --> 00:25:19,439 Speaker 1: that is equivalent to predicting its continued existence. In other words, 376 00:25:19,480 --> 00:25:24,159 Speaker 1: when brain circuitry adjusts, it's making a guess about what 377 00:25:24,320 --> 00:25:27,080 Speaker 1: the world is likely to be in the next moment. 378 00:25:27,680 --> 00:25:31,959 Speaker 1: It stops talking about news that is expected to continue. 379 00:25:32,160 --> 00:25:35,720 Speaker 1: So think again about your retinal blood vessels. They are 380 00:25:35,800 --> 00:25:41,439 Speaker 1: perceptually invisible because your visual system predicts them away. It 381 00:25:41,600 --> 00:25:44,960 Speaker 1: knows they are going to be there, so it ignores them. 382 00:25:45,240 --> 00:25:49,760 Speaker 1: It's only if those expectations are violated, like when a 383 00:25:49,840 --> 00:25:52,760 Speaker 1: light shines in from a strange angle that your brain 384 00:25:53,160 --> 00:25:58,440 Speaker 1: spends any energy on representing that data. Your brain doesn't 385 00:25:58,480 --> 00:26:02,240 Speaker 1: want to pay the energy car of spiking neurons, so 386 00:26:02,320 --> 00:26:06,520 Speaker 1: the goal is to reconfigure the network to waste as 387 00:26:06,640 --> 00:26:11,200 Speaker 1: little power as possible. If a pattern streams in that's 388 00:26:11,320 --> 00:26:16,520 Speaker 1: predictable or even partially guessable, the system saves energy by 389 00:26:16,600 --> 00:26:20,119 Speaker 1: structuring itself around that input, so it is not to 390 00:26:20,160 --> 00:26:24,040 Speaker 1: be surprised by it. If your brain is quieter, that 391 00:26:24,119 --> 00:26:28,439 Speaker 1: means there are fewer violations of expectations. Things in the 392 00:26:28,480 --> 00:26:34,040 Speaker 1: outside world are going approximately as forecast. In other words, 393 00:26:34,080 --> 00:26:38,840 Speaker 1: an energy conscious brain wants to predict away everything possible 394 00:26:39,200 --> 00:26:44,560 Speaker 1: so it can save its energy for just representing the unexpected. 395 00:26:45,400 --> 00:26:51,199 Speaker 1: Silence is golden. So although many neuroscientists think of activity 396 00:26:51,200 --> 00:26:54,880 Speaker 1: in neurons as the representation of things in the world, 397 00:26:55,280 --> 00:26:59,800 Speaker 1: it may turn out that spikes are the unpredicted, energy 398 00:27:00,000 --> 00:27:06,399 Speaker 1: expensive part. The representation of something totally expected would be 399 00:27:06,480 --> 00:27:10,960 Speaker 1: nothing but a hush falling over the neuronal forest. The 400 00:27:11,000 --> 00:27:16,080 Speaker 1: system makes adjustments only when it gets surprised. If your 401 00:27:16,080 --> 00:27:18,600 Speaker 1: brain thinks that all bricks weigh the same amount, and 402 00:27:18,640 --> 00:27:21,760 Speaker 1: then you attempt to pick up a brick made of lead. 403 00:27:22,320 --> 00:27:27,800 Speaker 1: The violation of your expectation causes cascades of changes to 404 00:27:27,880 --> 00:27:31,520 Speaker 1: deal with this new turn of events. But in contrast, 405 00:27:31,560 --> 00:27:36,240 Speaker 1: if everything is successfully predicted, there's no need to change anything. 406 00:27:37,280 --> 00:27:40,399 Speaker 1: For these reasons. When you first look at the Troxler picture, 407 00:27:40,720 --> 00:27:43,439 Speaker 1: you notice the blobs, and when you first put in 408 00:27:43,480 --> 00:27:47,600 Speaker 1: the contact lens you detect the drawn on shape. But 409 00:27:47,720 --> 00:27:51,720 Speaker 1: after a short time, your brain adjusts itself. It's no 410 00:27:51,800 --> 00:27:55,960 Speaker 1: longer surprised. Let me give you another example of the 411 00:27:56,000 --> 00:28:00,359 Speaker 1: brain predicting things away. So I talked in a previous 412 00:28:00,400 --> 00:28:05,360 Speaker 1: episode about the neosensory wristband, which converts sounds into patterns 413 00:28:05,400 --> 00:28:09,160 Speaker 1: of vibration on the skin, and deaf people wear the wristband, 414 00:28:09,480 --> 00:28:11,920 Speaker 1: and with time they can start to hear the world 415 00:28:12,280 --> 00:28:14,920 Speaker 1: through the signals that get to their brain via the skin. 416 00:28:15,400 --> 00:28:17,480 Speaker 1: If you're interested in learning more, that was episode twelve. 417 00:28:17,840 --> 00:28:19,679 Speaker 1: But the point I want to make here is what 418 00:28:19,880 --> 00:28:24,159 Speaker 1: happens when a hearing person first puts on the wristband. 419 00:28:24,480 --> 00:28:28,480 Speaker 1: They always react with surprise when they're feeling all the 420 00:28:28,520 --> 00:28:30,880 Speaker 1: sounds of the world, and they say WHOA, this thing 421 00:28:30,960 --> 00:28:33,840 Speaker 1: is picking up on my own voice. They're always startled 422 00:28:33,840 --> 00:28:37,080 Speaker 1: by that because it seems like they shouldn't be registering 423 00:28:37,119 --> 00:28:40,400 Speaker 1: their own speech. But of course, your ears pick up 424 00:28:40,400 --> 00:28:44,000 Speaker 1: on your voice all the time. It's typically the loudest 425 00:28:44,160 --> 00:28:47,760 Speaker 1: voice in your conversations because your own mouth is the 426 00:28:47,840 --> 00:28:52,800 Speaker 1: closest one to your ears. But because you can perfectly 427 00:28:52,920 --> 00:28:58,200 Speaker 1: predict your own vocalizations, you hardly hear your own voice. 428 00:28:58,240 --> 00:29:02,960 Speaker 1: You don't notice it your brain is predicting it away. 429 00:29:03,800 --> 00:29:06,720 Speaker 1: Or take this example, when people wear the wristband, they're 430 00:29:06,800 --> 00:29:11,120 Speaker 1: struck by the volume of other predictable sounds that they 431 00:29:11,160 --> 00:29:13,960 Speaker 1: normally pay no attention to because they're the ones who 432 00:29:14,000 --> 00:29:17,400 Speaker 1: create the sounds, like flushing the toilet or closing the 433 00:29:17,440 --> 00:29:20,600 Speaker 1: door behind them, or their own footsteps. It's not that 434 00:29:20,760 --> 00:29:25,400 Speaker 1: your auditory system doesn't register these sounds, but instead it's 435 00:29:25,400 --> 00:29:29,680 Speaker 1: that you actively predict them away. So you flush the 436 00:29:29,720 --> 00:29:32,480 Speaker 1: toilet or close the door or walk and these things 437 00:29:32,560 --> 00:29:35,920 Speaker 1: don't sound particularly loud to you, but it becomes obvious 438 00:29:35,960 --> 00:29:38,840 Speaker 1: when you're wearing the wristband. You can't believe how loud 439 00:29:38,880 --> 00:29:42,800 Speaker 1: these events are because your brain has not yet learned 440 00:29:42,960 --> 00:29:45,960 Speaker 1: to predict the signals coming up your arm, so your 441 00:29:46,040 --> 00:29:52,080 Speaker 1: brain actively recalibrates because that allows it to burn less energy. 442 00:29:53,200 --> 00:29:58,000 Speaker 1: But there's an even deeper principle at work here in 443 00:29:58,040 --> 00:30:01,400 Speaker 1: the darkness of your skull. You your brain is striving 444 00:30:01,520 --> 00:30:06,080 Speaker 1: to build an internal model of the outside world. When 445 00:30:06,080 --> 00:30:09,479 Speaker 1: you walk around your house, you don't pay any attention 446 00:30:09,600 --> 00:30:13,080 Speaker 1: to the environment because you already have a good model 447 00:30:13,120 --> 00:30:16,200 Speaker 1: of it. In contrast, when you're driving in a foreign 448 00:30:16,360 --> 00:30:18,920 Speaker 1: city you're trying to find a way to a particular hotel, 449 00:30:19,320 --> 00:30:22,920 Speaker 1: you're forced to look around at everything, the street signs, 450 00:30:22,960 --> 00:30:26,080 Speaker 1: the store naims, the building numbers because you don't already 451 00:30:26,080 --> 00:30:30,000 Speaker 1: have a good model of what to expect. So how 452 00:30:30,000 --> 00:30:33,880 Speaker 1: do you build up a good internal model? What is 453 00:30:33,960 --> 00:30:37,600 Speaker 1: the neural technology that allows you to zoom in on 454 00:30:37,640 --> 00:30:41,320 Speaker 1: those data points that don't match your expectation while ignoring 455 00:30:41,400 --> 00:30:45,840 Speaker 1: everything else that's already counted for. We call this attention. 456 00:30:46,880 --> 00:30:52,320 Speaker 1: You pay attention to the unexpected bang, or the unforeseen 457 00:30:52,400 --> 00:30:56,640 Speaker 1: brush on your skin, or the surprising movement in your periphery. 458 00:30:57,520 --> 00:31:01,920 Speaker 1: Attending allows you to put your high resolution sensors on 459 00:31:02,080 --> 00:31:05,440 Speaker 1: the problem and figure out how to incorporate it into 460 00:31:05,480 --> 00:31:09,280 Speaker 1: your model. Ah that's just the lawnmower. Ah, that's the kitten. Ah, 461 00:31:09,320 --> 00:31:14,200 Speaker 1: that's the housefly. Your model is now updated. In contrast, 462 00:31:14,600 --> 00:31:17,160 Speaker 1: you don't pay any attention to the feeling of the 463 00:31:17,240 --> 00:31:20,520 Speaker 1: shoe on your left foot, because you already have an 464 00:31:20,520 --> 00:31:24,680 Speaker 1: internal model of it, and that model is consistently predicting 465 00:31:24,760 --> 00:31:28,040 Speaker 1: what you're receiving, at least until you get a pebble 466 00:31:28,080 --> 00:31:31,960 Speaker 1: in your shoe that draws your attention because suddenly the 467 00:31:32,120 --> 00:31:38,240 Speaker 1: model calls for an update. The difference between predictions and 468 00:31:38,400 --> 00:31:43,800 Speaker 1: outcomes is the key to understanding a strange property of learning, 469 00:31:44,160 --> 00:31:47,840 Speaker 1: which is that if you're predicting something perfectly, your brain 470 00:31:48,000 --> 00:31:50,920 Speaker 1: doesn't need a change. Further so, say you learn that 471 00:31:51,000 --> 00:31:53,760 Speaker 1: the ding of your phone predicts that you just got 472 00:31:53,760 --> 00:31:57,680 Speaker 1: a text message. Your brain will quickly learn the relationship 473 00:31:57,680 --> 00:32:00,680 Speaker 1: between those two, in large part because of the relevance 474 00:32:00,720 --> 00:32:03,640 Speaker 1: of text messages to your social life. Then let's say 475 00:32:03,680 --> 00:32:07,400 Speaker 1: your phone gets a software update, and as a consequence, 476 00:32:07,440 --> 00:32:10,960 Speaker 1: the arrival of the text message is now signaled by 477 00:32:11,040 --> 00:32:14,920 Speaker 1: a ding plus a vibration. It turns out that your 478 00:32:14,960 --> 00:32:18,920 Speaker 1: brain won't train up on the vibration. This is an 479 00:32:18,920 --> 00:32:23,600 Speaker 1: effect known as blocking. Your brain already knows that the 480 00:32:23,720 --> 00:32:26,440 Speaker 1: ding predicts the text, so it has no need to 481 00:32:26,560 --> 00:32:31,360 Speaker 1: learn about something new. If your phone merely vibrates without 482 00:32:31,400 --> 00:32:35,520 Speaker 1: the ding, your brain won't know the meaning of that queue. 483 00:32:35,560 --> 00:32:39,480 Speaker 1: It has learned nothing about that. This phenomenon of blocking 484 00:32:39,680 --> 00:32:43,800 Speaker 1: makes sense when we understand that changes in the brain 485 00:32:43,920 --> 00:32:48,120 Speaker 1: happen only when there's a difference between what was expected 486 00:32:48,400 --> 00:32:53,479 Speaker 1: and what actually happened. So having an internal model of 487 00:32:53,520 --> 00:32:57,160 Speaker 1: the world allows us to make predictions and quickly detect 488 00:32:57,480 --> 00:33:01,120 Speaker 1: when we're wrong, which tells us where to attend and 489 00:33:01,240 --> 00:33:03,760 Speaker 1: how to update things. And this sort of system, by 490 00:33:03,800 --> 00:33:07,400 Speaker 1: the way, is becoming interesting to engineers thinking about the 491 00:33:07,440 --> 00:33:11,280 Speaker 1: future of machinery. Several companies are starting to work on 492 00:33:11,360 --> 00:33:16,160 Speaker 1: devices that operate this way, from tractors to airplanes. An 493 00:33:16,280 --> 00:33:20,000 Speaker 1: internal model of the world allows a machine to make 494 00:33:20,040 --> 00:33:24,480 Speaker 1: its best guesses about the events that are expected to unfold, 495 00:33:24,800 --> 00:33:28,120 Speaker 1: and when events are consistent with the predictions of the 496 00:33:28,160 --> 00:33:31,760 Speaker 1: machine's algorithm, nothing has to change, and it's only when 497 00:33:31,800 --> 00:33:35,520 Speaker 1: the inputs go off script that the software needs to 498 00:33:35,560 --> 00:33:40,560 Speaker 1: pay attention to update the machines model. Okay, so now 499 00:33:40,560 --> 00:33:44,120 Speaker 1: that we've talked about all the ways that your system adapts, 500 00:33:44,680 --> 00:33:48,360 Speaker 1: it will now be easy to understand how drugs modify 501 00:33:48,480 --> 00:33:53,880 Speaker 1: nervous systems. When you consume a drug, that changes the 502 00:33:54,000 --> 00:33:57,360 Speaker 1: number of receptors for that drug in the brain to 503 00:33:57,400 --> 00:33:59,960 Speaker 1: such an extent that you can look at a brain 504 00:34:00,240 --> 00:34:04,720 Speaker 1: after a person has died and determine his addictions by 505 00:34:04,880 --> 00:34:10,480 Speaker 1: gauging his molecular changes. This is why people become desensitized 506 00:34:10,600 --> 00:34:15,279 Speaker 1: or tolerant to a drug. The brain comes to predict 507 00:34:15,440 --> 00:34:19,640 Speaker 1: the presence of the drug. It adapts its receptor expression 508 00:34:20,080 --> 00:34:24,120 Speaker 1: so it can maintain a stable equilibrium when it receives 509 00:34:24,160 --> 00:34:28,360 Speaker 1: the next hit. In a physical literal way, the brain 510 00:34:28,480 --> 00:34:33,080 Speaker 1: comes to expect the drug to be there. The biological 511 00:34:33,120 --> 00:34:38,200 Speaker 1: details have calibrated themselves accordingly, and because the system now 512 00:34:38,320 --> 00:34:42,040 Speaker 1: predicts a certain amount to be present, more of the 513 00:34:42,160 --> 00:34:47,640 Speaker 1: drug is needed to achieve the original high. This recalibration 514 00:34:47,840 --> 00:34:52,320 Speaker 1: that's the basis of the ugly symptoms of drug withdrawal. 515 00:34:52,800 --> 00:34:56,080 Speaker 1: The more the brain is adapted to the drug, the 516 00:34:56,200 --> 00:34:58,640 Speaker 1: harder the fall is when the drug is taken away 517 00:34:59,400 --> 00:35:03,200 Speaker 1: with draw All symptoms vary by a drug, from sweating 518 00:35:03,239 --> 00:35:05,839 Speaker 1: to shakes to depression, but what they all have in 519 00:35:05,880 --> 00:35:11,960 Speaker 1: common is a powerful absence of something that was anticipated. 520 00:35:12,920 --> 00:35:16,319 Speaker 1: I suggested in my book Live Wire that this understanding 521 00:35:16,360 --> 00:35:21,560 Speaker 1: of neural predictions also gives us an understanding of heartbreak. 522 00:35:21,960 --> 00:35:26,040 Speaker 1: And this is because the people that you love become 523 00:35:26,200 --> 00:35:30,600 Speaker 1: part of you, not just metaphorically but physically. You absorb 524 00:35:30,840 --> 00:35:35,080 Speaker 1: people into your internal model of the world. Your brain 525 00:35:35,719 --> 00:35:42,040 Speaker 1: refashions itself around the expectation of their presence. So after 526 00:35:42,080 --> 00:35:45,520 Speaker 1: the breakup with a lover, or the death of a friend, 527 00:35:45,719 --> 00:35:50,919 Speaker 1: or the loss of a parent, the sudden absence represents 528 00:35:51,280 --> 00:35:56,759 Speaker 1: a major departure from homeostasis. As Khalil Jabraun put it 529 00:35:56,840 --> 00:36:01,000 Speaker 1: in the prophet quote and ever has a bin that 530 00:36:01,120 --> 00:36:05,400 Speaker 1: love knows not its own depth until the hour of separation. 531 00:36:06,960 --> 00:36:11,000 Speaker 1: In this way, your brain becomes like a negative image 532 00:36:11,080 --> 00:36:14,640 Speaker 1: of everyone you've ever come in contact with. Your lovers, 533 00:36:14,680 --> 00:36:19,360 Speaker 1: your friends, your parents. They fill in their expected shapes, 534 00:36:20,000 --> 00:36:22,799 Speaker 1: and just like feeling the waves after you've departed the 535 00:36:22,840 --> 00:36:27,239 Speaker 1: boat or craving the drug when it's not there, so 536 00:36:27,480 --> 00:36:30,799 Speaker 1: your brain calls for the people in your life to 537 00:36:30,960 --> 00:36:35,520 Speaker 1: be there. And when someone moves away or rejects you, 538 00:36:36,040 --> 00:36:43,280 Speaker 1: or dies, your brain struggles with its thwarted expectations. Slowly 539 00:36:43,480 --> 00:36:47,520 Speaker 1: through time, it has to readjust to a world without 540 00:36:47,600 --> 00:36:51,279 Speaker 1: that person. Now I want to cover one more thing 541 00:36:51,320 --> 00:36:54,840 Speaker 1: in today's episode, which is how your brain knows how 542 00:36:54,880 --> 00:36:57,719 Speaker 1: to adjust. And I suggest it in Live Wire that 543 00:36:57,760 --> 00:37:02,120 Speaker 1: there's a very simple but surprise strategy underlying all this. 544 00:37:02,680 --> 00:37:07,680 Speaker 1: And to understand this, consider something like phototropism in plants. 545 00:37:07,719 --> 00:37:13,280 Speaker 1: This is where plants capture maximum light by constantly adjusting 546 00:37:13,320 --> 00:37:16,640 Speaker 1: their position. So if you watch a plant growing in 547 00:37:16,760 --> 00:37:20,400 Speaker 1: fast motion, you'll see that it doesn't grow straight towards 548 00:37:20,440 --> 00:37:24,200 Speaker 1: the light source. Instead, it overshoots its trajectory by a 549 00:37:24,239 --> 00:37:26,719 Speaker 1: little bit, then it undershoots by a bit, and back 550 00:37:26,760 --> 00:37:30,840 Speaker 1: and forth. It's not a pre planned mission. It's a 551 00:37:30,960 --> 00:37:35,520 Speaker 1: spastic dance with constant correction. And by the way, you 552 00:37:35,560 --> 00:37:40,040 Speaker 1: find something similar in the strategy that bacteria use to 553 00:37:40,120 --> 00:37:43,520 Speaker 1: find food. When they're searching for the center of a 554 00:37:43,640 --> 00:37:46,480 Speaker 1: food source, like a bit of sugar that's fallen on 555 00:37:46,520 --> 00:37:49,680 Speaker 1: the kitchen counter, they make their way to the sugar 556 00:37:49,760 --> 00:37:56,400 Speaker 1: by employing three elegantly simple rules. One randomly selected direction 557 00:37:56,640 --> 00:38:00,280 Speaker 1: and move in a straight line. Two if things are 558 00:38:00,320 --> 00:38:04,560 Speaker 1: getting better, keep going. Three if things are getting worse, 559 00:38:05,239 --> 00:38:10,080 Speaker 1: randomly change directions by tumbling. In other words, the strategy 560 00:38:10,280 --> 00:38:13,800 Speaker 1: is to lock down the approach when conditions are improving 561 00:38:14,160 --> 00:38:18,360 Speaker 1: and dump it when it's not working. By this simple policy, 562 00:38:18,520 --> 00:38:21,840 Speaker 1: a bacterium can quickly and efficiently work its way to 563 00:38:21,920 --> 00:38:26,920 Speaker 1: the densest point of the food source. So I've proposed 564 00:38:26,920 --> 00:38:30,080 Speaker 1: that there's a similar principle at work in the brain. 565 00:38:30,200 --> 00:38:33,840 Speaker 1: Instead of working its way towards maximizing sunlight or food, 566 00:38:34,640 --> 00:38:41,399 Speaker 1: it works towards maximizing information. And I call this strategy infotropism. 567 00:38:42,239 --> 00:38:49,320 Speaker 1: The hypothesis suggests that neural circuitry constantly shifts to maximize 568 00:38:49,360 --> 00:38:52,560 Speaker 1: the amount of information it can extract from the world. 569 00:38:53,280 --> 00:38:55,840 Speaker 1: So consider what we've heard in some of the previous episodes. 570 00:38:55,880 --> 00:38:58,759 Speaker 1: We saw the way the brain comes to figure out 571 00:38:58,800 --> 00:39:01,960 Speaker 1: its sensory organs, its eyes and ears and nose and fingertips. 572 00:39:02,280 --> 00:39:04,480 Speaker 1: When you're a baby, you don't know what those data 573 00:39:04,480 --> 00:39:07,799 Speaker 1: streams mean, and your brain figures it out with experience. 574 00:39:08,400 --> 00:39:10,560 Speaker 1: And we saw the way a brain comes to learn 575 00:39:10,560 --> 00:39:12,920 Speaker 1: how to control a body, no matter if that body 576 00:39:13,200 --> 00:39:17,240 Speaker 1: possesses fins or legs or robotic arms, whatever the case. 577 00:39:17,680 --> 00:39:22,880 Speaker 1: The brain fine tunes its circuitry to maximize data it 578 00:39:23,000 --> 00:39:26,359 Speaker 1: streams from the world. So this fine tuning is helped 579 00:39:26,360 --> 00:39:30,680 Speaker 1: along by rewards, which cause broadcasts throughout the circuitry to 580 00:39:30,719 --> 00:39:35,040 Speaker 1: announce that something worked. In this way, with a minimum 581 00:39:35,080 --> 00:39:41,080 Speaker 1: of preprogramming, the system works out how to optimize its 582 00:39:41,200 --> 00:39:44,759 Speaker 1: interaction with the world. Or Another example is that your 583 00:39:44,800 --> 00:39:48,279 Speaker 1: brain will adjust to whatever language you're exposed to as 584 00:39:48,320 --> 00:39:51,440 Speaker 1: a baby, such that you can hear those sounds, but 585 00:39:51,520 --> 00:39:55,560 Speaker 1: you lose the ability to distinguish other sounds and other languages. 586 00:39:56,200 --> 00:40:02,480 Speaker 1: This is all infotropism at work. Baby's brains adjust to 587 00:40:02,560 --> 00:40:07,360 Speaker 1: maximize the data that matters around them. On a longer 588 00:40:07,400 --> 00:40:11,080 Speaker 1: time scale, when a person goes blind, other senses take 589 00:40:11,120 --> 00:40:14,600 Speaker 1: over the visual cortex, and in an upcoming episode we'll 590 00:40:14,640 --> 00:40:17,239 Speaker 1: learn how neurons actually pull this off, but for now, 591 00:40:18,080 --> 00:40:22,040 Speaker 1: note that we can interpret this takeover as in photropism. 592 00:40:22,160 --> 00:40:26,279 Speaker 1: The brain is maximizing its resources so that it can 593 00:40:26,640 --> 00:40:30,360 Speaker 1: best interpret whatever data flows in. And just think about 594 00:40:30,400 --> 00:40:34,600 Speaker 1: the Mecullic effect with the horizontal and vertical colored lines. 595 00:40:35,160 --> 00:40:39,280 Speaker 1: Your visual system works to separate the dimensions of color 596 00:40:39,320 --> 00:40:44,120 Speaker 1: and orientation because it's trying to maximize information from the world, 597 00:40:44,640 --> 00:40:47,160 Speaker 1: and so accordingly, it doesn't want to mix together these 598 00:40:47,600 --> 00:40:51,960 Speaker 1: separable measures. So although the effect is typically viewed as 599 00:40:52,080 --> 00:40:56,120 Speaker 1: simply a fun visual illusion. The work happens under the 600 00:40:56,160 --> 00:41:00,839 Speaker 1: hood for a deeper reason. If something were causing a 601 00:41:00,920 --> 00:41:05,120 Speaker 1: tinge to appear on lines, like some strange overhead lighting 602 00:41:05,200 --> 00:41:09,360 Speaker 1: or something wrong with your optics, your brain would reorganize 603 00:41:09,360 --> 00:41:13,440 Speaker 1: itself to take care of this, canceling out this weird relationship, 604 00:41:13,920 --> 00:41:18,319 Speaker 1: and by doing so, it would maximize your capacity to 605 00:41:18,480 --> 00:41:23,960 Speaker 1: extract information about colors and orientations separately. By separating two 606 00:41:24,000 --> 00:41:28,480 Speaker 1: dimensions that statistically should be unyoked, your brain can best 607 00:41:28,680 --> 00:41:32,319 Speaker 1: gather information from the world. Here's a cool example of 608 00:41:32,360 --> 00:41:37,200 Speaker 1: infotropism at the level of neurons, the retina in your eye, 609 00:41:37,480 --> 00:41:41,400 Speaker 1: the set of photoreceptors the back of your eye captures 610 00:41:41,480 --> 00:41:43,719 Speaker 1: the light of the world and tells the brain what 611 00:41:43,800 --> 00:41:47,400 Speaker 1: it's seeing out there. But it reads the world differently 612 00:41:47,640 --> 00:41:50,680 Speaker 1: in the day and in the night. So in bright 613 00:41:50,840 --> 00:41:54,440 Speaker 1: daylight there are plenty of photons to capture, and so 614 00:41:54,600 --> 00:41:58,239 Speaker 1: each photoreceptor just takes care of its own tiny dot 615 00:41:58,360 --> 00:42:01,600 Speaker 1: of the scene, and this gives nice and high resolution. 616 00:42:02,320 --> 00:42:06,280 Speaker 1: But at night it's a different story. There are few 617 00:42:06,360 --> 00:42:09,919 Speaker 1: photons to be captured, and so now the important job 618 00:42:09,960 --> 00:42:12,920 Speaker 1: of the retina is to detect that something was there, 619 00:42:13,440 --> 00:42:17,319 Speaker 1: even if it can't tell that with high resolution. So 620 00:42:17,440 --> 00:42:21,440 Speaker 1: at night, the photoreceptors do their work very differently. Essentially, 621 00:42:21,480 --> 00:42:26,239 Speaker 1: they join forces with their neighbors. They change the details 622 00:42:26,239 --> 00:42:30,400 Speaker 1: of their internal molecular cascades so they can link arms 623 00:42:30,440 --> 00:42:34,600 Speaker 1: with one another. Now they're operating as a team, they 624 00:42:34,600 --> 00:42:38,200 Speaker 1: can detect much lower levels of light, they can detect 625 00:42:38,239 --> 00:42:41,279 Speaker 1: fewer photons out there. So what we have here is 626 00:42:41,280 --> 00:42:46,360 Speaker 1: this beautiful and sophisticated strategy that has the retina operate 627 00:42:46,560 --> 00:42:50,239 Speaker 1: differently as the light levels go up or down. When 628 00:42:50,280 --> 00:42:54,160 Speaker 1: it's bright out, the system achieves high spatial resolution, and 629 00:42:54,200 --> 00:42:59,200 Speaker 1: when it's dark, photoreceptors pool together to have a better 630 00:42:59,480 --> 00:43:03,360 Speaker 1: chance to catch photons, which results in vision that's more 631 00:43:03,400 --> 00:43:08,120 Speaker 1: sensitive to dim light but blurrier in resolution. You've surely 632 00:43:08,200 --> 00:43:10,560 Speaker 1: noticed this at nighttime when you can't quite make out 633 00:43:10,800 --> 00:43:13,520 Speaker 1: what something is out there, whereas it would be easy 634 00:43:13,520 --> 00:43:16,880 Speaker 1: in the daytime. So the point here is that your eyes, 635 00:43:16,960 --> 00:43:22,719 Speaker 1: your retinas, put enormous work into shifting themselves around to 636 00:43:23,080 --> 00:43:28,040 Speaker 1: maximize information that matters whether the photons are plentiful or 637 00:43:28,080 --> 00:43:33,120 Speaker 1: they're rare. The retina optimizes itself to get useful data. 638 00:43:33,160 --> 00:43:35,560 Speaker 1: In the day, it captures the most detail so that 639 00:43:35,600 --> 00:43:39,200 Speaker 1: it can spot the rabbit at the distance. In dim light, 640 00:43:39,360 --> 00:43:43,160 Speaker 1: it shifts to higher sensitivity to capture whatever's out there 641 00:43:43,320 --> 00:43:48,560 Speaker 1: with lower detail, capturing the shadowy essence of the jaguar 642 00:43:48,719 --> 00:43:52,279 Speaker 1: lurking in the gloom. Mother Nature figured out not only 643 00:43:52,320 --> 00:43:56,200 Speaker 1: how to build an eye, but also how to adjust 644 00:43:56,239 --> 00:43:59,560 Speaker 1: its circuitry on the fly, so it can operate well 645 00:43:59,880 --> 00:44:03,839 Speaker 1: in different contexts, all to make the best use of 646 00:44:03,880 --> 00:44:08,560 Speaker 1: what's available. It is infotropic. Just like the plant seeks light, 647 00:44:09,040 --> 00:44:13,680 Speaker 1: the retina seeks data, and more generally, as we've seen 648 00:44:13,719 --> 00:44:17,960 Speaker 1: in this episode, the brain is always seeking information. It 649 00:44:18,120 --> 00:44:22,880 Speaker 1: constantly adjusts its circuitry to maximize the data it can 650 00:44:22,960 --> 00:44:26,279 Speaker 1: draw from the world. So if you're staring at a waterfall, 651 00:44:26,680 --> 00:44:30,280 Speaker 1: it discounts the downward motion so it can be sensitive 652 00:44:30,320 --> 00:44:33,440 Speaker 1: to other things. If you put on yellow sunglasses, your 653 00:44:33,480 --> 00:44:37,239 Speaker 1: brain discounts that shift in color so that it can 654 00:44:37,280 --> 00:44:41,680 Speaker 1: be more sensitive to other information. And you can detect 655 00:44:41,800 --> 00:44:44,360 Speaker 1: this shift when you take off the sunglasses and you 656 00:44:44,400 --> 00:44:48,439 Speaker 1: have a big blue color after effect. So to wrap up, 657 00:44:48,840 --> 00:44:51,360 Speaker 1: this episode plugs into the big picture we've been talking 658 00:44:51,360 --> 00:44:53,600 Speaker 1: about in many episodes, and we'll see in many more, 659 00:44:54,000 --> 00:44:57,600 Speaker 1: which is that the brain is locked in silence and darkness, 660 00:44:57,680 --> 00:45:01,319 Speaker 1: and its job is to build an internal model of 661 00:45:01,360 --> 00:45:04,520 Speaker 1: the outside world. And what we're seeing a little more 662 00:45:04,560 --> 00:45:08,800 Speaker 1: clearly now is that its internal model is really there 663 00:45:08,880 --> 00:45:13,279 Speaker 1: to make predictions. If the world proceeds as expected, the 664 00:45:13,320 --> 00:45:17,520 Speaker 1: brain saves energy. So when the world changes, let's say, 665 00:45:17,520 --> 00:45:19,960 Speaker 1: becoming a place with lots of downward motion or yellow 666 00:45:20,040 --> 00:45:24,120 Speaker 1: light or something, the brain adjusts to match it so 667 00:45:24,160 --> 00:45:27,640 Speaker 1: that it can be maximumly positioned to gather new information 668 00:45:28,040 --> 00:45:33,480 Speaker 1: that's unexpected. So these after effect illusions seem funny and 669 00:45:33,560 --> 00:45:36,960 Speaker 1: may be trivial, but they're actually a powerful way for 670 00:45:37,040 --> 00:45:41,560 Speaker 1: us to reveal this constant adaptation that your brain is doing. 671 00:45:42,280 --> 00:45:44,200 Speaker 1: Over the course of many episodes coming up, we're going 672 00:45:44,239 --> 00:45:48,040 Speaker 1: to see how fundamentally the brain is a prediction machine, 673 00:45:48,200 --> 00:45:54,040 Speaker 1: and that is the driving engine behind its constant self reconfiguration. 674 00:45:54,680 --> 00:45:58,319 Speaker 1: By modeling the state of the world, the brain reshapes 675 00:45:58,360 --> 00:46:02,840 Speaker 1: itself to have good expectation and therefore to be maximally 676 00:46:03,000 --> 00:46:10,720 Speaker 1: sensitive to the unexpected. Go to Eagleman dot com slash 677 00:46:10,760 --> 00:46:14,839 Speaker 1: podcast for more information and to find further reading. Send 678 00:46:14,920 --> 00:46:17,799 Speaker 1: me an email at podcasts at eagleman dot com with 679 00:46:18,000 --> 00:46:21,080 Speaker 1: questions or discussions, and I'll be making an episode soon 680 00:46:21,120 --> 00:46:28,280 Speaker 1: in which I address those. Until next time, I'm David Eagleman, 681 00:46:28,480 --> 00:46:30,239 Speaker 1: and this is Inner Cosmos.