科学与数学twitter.com
想了解我们的大脑有多离谱吗？
“You want to know something about how bullshit insane our brains are?” (2018)
2019 — 2022，它一次次回到首页
黑点是上首页（≥ 50 分）的那次投稿，空心点是没冲上去的投稿，点越大分数越高。
导读
这是 Foone 在 Twitter 上的一串科普长帖，讲人类视觉系统有多“离谱”：眼球不断扫视（saccade）时世界并不会抖动，因为大脑把画面在时间上“倒推”补齐；视网膜上有盲点，大脑直接填上背景；视网膜细胞会因激光、衰老或遗传疾病而损坏，大脑也会悄悄做错误修正，直到修不过来才暴露出来。结论是：我们看到的稳定世界，很大程度上是大脑编造出来的。
为什么经久不衰：它把每个人天天经历却从未察觉的感知机制拆开给你看，例子具体、语气好笑，读完之后你会对自己眼睛和大脑的“可信度”产生持久的怀疑——这种颠覆感不会过时。
HN 评论精选
大脑补全和“时间倒推”是进化给出的优雅解法，而不是缺陷；我们对意识与现实的错位本不该惊讶。
所以我的视觉系统是把图像回溯到我开始移动眼睛的那一刻，从而呈现出一个连贯的世界？换个说法：既然时间旅行不可能，那我感知到的必然是过去——我活在过去，只是视觉系统把空洞补上，让我以为自己在感知当下。我不明白这为什么被说成“离谱疯了”，在我看来这是个绝妙的解法，比那种“每次转眼就黑屏一下”的工程方案好太多。顺便说，这种怪事在人类意识里比比皆是，比如高个子的人感知世界更“滞后”，以便把脚上传来的神经冲动和视觉刺激对成同一时刻。我们早就知道这类现象，也知道自由意志的幻觉之类更深的结论，可每次发现“意识体验”和“实际发生的事”对不上，还是照样大惊小怪。所以我们就是一堆有缺陷的肉袋子，脑机制荒谬又反直觉——真希望生物学的方案有 VR 那么深思熟虑。幸好我的视觉系统是进化造的，不是 Valve 或索尼造的。
jonnypotty查看英文原文
So my visual system takes an image and projects it back through time to when I started moving my eyes to present a consistent image of the world? Or, alternatively, I have to be perceiving the past as time travel is impossible, I am living in the past and my visual system can fill in the holes and make it seem like I'm always perceiving the present. Why this is presented as bullshit insane I have no idea. It seems like an amazingly brilliant solution to me, much better than the 'engineering' solution suggested where your vision flashes black every time you move your eyes. Also worth mentioning this weirdness is repeated in human consciousness all the time. Like the theory (tested as far as we can) that tall people perceiving the world further in the past so they can reconsile nerve impulses from their feet as happening at the same time as visual stimulus. We've known about phenomenon like this for a long time as well as other deeper revelations like, what is sometimes called, the illusion of free will. And yet we constantly act surprised that our conscious experience of the world doesn't correlate to what we find out is 'actually' happening. So we are flawed meat bags with insane, non sensical brain mechanics, if only our biological solutions were as well thought out as VR eh? How glad am I that the incredible complexity and subtly of evolution created my visual system and not Valve or Sony.
童年“看见秒针倒走”的怪事，可以用大脑向后外推运动的机制解释。
我第一次了解到这个机制——尤其是“大脑知道眼睛在动，于是调整你看到的东西以保证看到‘正确’的画面”那部分——立刻解释了我小时候一个特别困惑的现象：我偶尔会“抓到”浴室里的挂钟（指针式，有秒针）倒退走了一秒。可无论我盯着看多久，它都不再发生，只有在我刚把注意力转过去时，它偶尔会倒走一下。用“大脑把运动向后外推”来解释就完全说得通：秒针每跳一格会轻微震动，如果我恰好在它跳动后那零点几秒的震动期看向它，它可能真的在极轻微地倒退，而大脑把这个外推成了一整秒的倒退。说到底，又是一个视错觉。
MauranKilom查看英文原文
When I first learned about this, especially the "Because your brain recognizes it's moving and adjusts what you see to make sure it sees the 'right' thing" part, it explained a phenomenon that really confused me as a child: I would sometimes "catch" our bathroom clock (analog, with second hand) going backwards for a second. But no matter how long I stared at it, it wouldn't happen again. Only when I turned my attention to it would it sometimes seem to go backwards for the first second. With the "your brain extrapolates the movement backwards" this makes perfect sense if the second hand will vibrate a bit on each tick. Apparently, if I focused on the clock while the second hand was vibrating for a fraction of a second after moving, it might be moving ever so slightly backwards at that moment, which is extrapolated to a full second of backward movement. In the end it's just another optical illusion.
脑损伤造成的视野缺损不是黑洞，而是“不存在”，随后大脑会像帖子里说的那样用背景填充做错误修正。
当视觉系统的另一端（大脑）出问题时，同样很有意思。我姑妈视觉皮层有过一次很小的中风，不可思议的是，它只影响了右眼视野的右上象限，其他一切正常。她告诉我，受影响的那块视野并不是黑的（你以为会是黑的），她形容它是“空”——它根本不存在，没有合适的词能描述那种视觉感受。有意思的是，随着大脑有所恢复，那块“空”变小了，然后大脑开始做“错误修正”，对她来说“空”消失了，但那块区域并不提供任何视觉信息，就像推文里说的，被“背景”填满了。
refurb查看英文原文
It's also fascinating when the other end of the visual system (the brain) has issues. My aunt had a very small stroke in her visual cortex. Incredibly it only impacted the visual processing in the upper right quadrant of the right eye. Everything else was fine. She was telling me that the affected part of her field of vision wasn't black (as you'd expect). She described it as "empty". It just wasn't there. There were no good words to describe how that looked visually. Interestingly as her brain recovered somewhat, the "empty" area got a bit smaller, then her brain started to do "error correction" and to her, the "empty" part is gone, but it doesn't provide any visual information. Similar to the tweets, it's just filled with "background".
亲身经历印证了大脑长期掩盖视网膜损伤，一旦补偿失效症状会“突然”出现，并提醒新视觉异常要立即就医。
我有（所幸较轻的）遗传性视网膜疾病。你如果读到帖子里讲激光和眼睛损伤的部分，基本就是那种情况，只不过“激光”是缺陷基因而不是外部伤害。我可以证实：一开始我的大脑对损伤的纠错做得极其出色，但最近几年它终于“透出来”了。有一天我在徒步时视野里突然出现黑点；之后某天早上醒来，我注意到视野里有大片黑色光晕，几秒后就消失了；再过几周，视野边缘开始出现闪烁的视觉伪影。这很可怕，因为我不知道这是一个持续几十年的过程、只是我现在才察觉，还以为照这个速度几周内就会全盲。所幸并非如此：损伤一直以缓慢恒定的速度增加，只是纠错机制把它藏得非常好，直到藏不住，所以感觉上退化速度比实际严重得多。不过还是提醒：发现任何新的视觉异常请立刻去检查——我的情况是缓慢的遗传问题，但有时是视网膜脱落，早发现通常一个手术就能解决。
ryanschneider查看英文原文
I have a (thankfully mild) inherited retina disorder. If you read the part about lasers and eye damage it’s basically that, but the “lasers” are faulty genes rather than anything external causing the eye damage. And I can verify that at first my brain did an incredibly good job at error-correcting over it, but in the last couple years it’s finally been able to “peek through”. One day I was hiking and suddenly had black spots in my vision. Then after that I woke up one morning and noticed large black halos in my vision that went away after a couple seconds of being awake. A couple weeks later and I started getting flashing visual artifacts in the edge of my vision. Which is/was terrifying because I didn’t know this was a multi-decade process I was just becoming aware of and instead assumed that if I just noticed this much visual degradation in a couple weeks then surely I’ll be completely blind in a couple more? Thankfully that’s not how it works, the damage has been increasing at a slow steady constant, it’s just that the processes in place to correct for said damage do a _really_ good job at hiding it, until they don’t, so the rate of degradation seems much worse than it actually is. That said, please if you notice any new visual artifacts get them checked up on _immediately_, while my case is a slow genetic issue sometimes it’s a detached retina, which can happen for any number of reasons and can usually be reversed quite easily with surgery if caught early. I was “lucky” mine was genetic rather than physical trauma, since I didn’t go see someone until things got noticeably worse.
历次讨论
同类还值得读
如果月球只有 1 像素：一个极其精确的太阳系模型（2014）
If the moon were only 1 pixel: A tediously accurate solar system model (2014)
一个网页版太阳系模型，以“如果月亮只有 1 像素”的真实比例呈现：你必须一路横向滚动，才能体会行星之间空旷到何等程度。
科学与数学上首页 7 次 · 2014–2025joshworth.com编辑精选沉浸式线性代数（2016）
Immersive Linear Algebra (2016)
《Immersive Linear Algebra》是一本完全免费、开放在线的线性代数“超文本教科书”，其最大特色是大量可交互的图形：读者可以直接拖动、操作图中的向量、矩阵和变换…
科学与数学上首页 5 次 · 2015–2024immersivemath.com编辑精选如何将贝果切成两个相连的半环（2009）
How to Slice a Bagel into Two Linked Halves (2009)
数学家 George Hart 的经典教程，演示如何用一刀把贝果切成两个相互扣住的环，并附上切割步骤与数学原理。
科学与数学上首页 5 次 · 2009–2022georgehart.com“犹太问题”：一组用于歧视的数学题
Jewish problems
一篇 arXiv 论文，整理并讨论苏联时期犹太学生在申请大学数学系时被问到的特殊数学难题：这些题往往有简单解法却极难想到，被用作面试中拒绝犹太考生的手段。
科学与数学上首页 5 次 · 2011–2021arxiv.org你的身体并非为长久而造：人类死亡率数据的一课
Your body wasn’t built to last: a lesson from human mortality rates
文章从人类死亡率随年龄变化的统计规律出发，解释身体并非为长久使用而设计：年轻时死亡风险较低，之后随年龄近似指数上升，像复杂系统在不断累积损伤。
科学与数学上首页 5 次 · 2009–2018gravityandlevity.wordpress.com