意识的本质是什么？

神经科学在破译我们的大脑如何思考和感知周围环境方面取得了进展，但认知的一个核心特征仍然非常神秘：即我们的许多感知和思想都伴随着拥有它们的主观体验。意识，我们给那种体验起的名字，目前还无法解释——但科学至少开始理解它了。在这一集中，意识研究员Anil Seth和主持人 Steven Strogatz 讨论了为什么我们的感知可以被描述为“受控幻觉”，意识如何影响被称为“裙子”的互联网轰动，以及人们在家里如何帮助研究人员编目我们体验世界的各种方式。

在Apple Podcasts 、 Spotify 、 Google Podcasts 、 Stitcher 、 TuneIn或您最喜欢的播客应用程序上收听，或者您可以从Quanta 流式传输。

阿尼尔赛斯

Anil Seth (01:42)：谢谢邀请我。很高兴和你在一起。

Strogatz (01:44)：好吧，我不得不说，这是我最喜欢也是最令人费解的事情之一。我真的不知道从哪里开始。我的意思是，意识是如此神秘。我有时会有这种不可思议的感觉，大概一年一次或两次。我会看着浴室的镜子，刮胡子。然后我有种毛骨悚然的感觉：这团在镜子里看着我的东西是什么？比如，里面有谁？

赛斯(02:11)：是的，欢迎来到我的世界。这听起来像是对我每一天的描述。现在，从某种意义上说，当你去吃晚饭并离开你的正常生活时，你就把神秘抛在脑后了。但它确实有这种习惯，它会随你去任何地方。大多数时候，我都会有这样的时刻。我也会尝试和训练自己，不断地反思和冥想我们头骨中有这种带电肉酱的日常奇迹。不知何故，结合身体及其与世界的互动，不仅仅是复杂的生物机器在运转：还有主观体验。感觉就像是我，感觉就像是你——使用来自哲学家托马斯·内格尔的定义。

(02:58) 这仍然非常令人震惊。成为一张桌子或一把椅子并没有什么感觉。但这是意识的根本奥秘。这既是一个深刻的科学和哲学之谜，也是一个非常个人化的谜。因为部分“感觉”是成为一个特定的人的感觉。做你自己。成为你或成为我。

Strogatz (03:22)：你刚刚介绍了“自我”这个词。你可以意识到各种各样的事情；你也可以意识到有一个自我。我们是否应该开始尝试梳理与意识相关的不同概念？什么是意识？它与自我意识有何不同？

赛斯(03:39)：我认为这是个好主意。当涉及到一个知之甚少的现象时，定义总是存在这个问题。回顾科学史，我想我们都知道定义并不是一成不变的，你确定了一个，然后你就试着弄清楚基础科学是什么。定义总是随着我们的理解而演变。

(04:00) 对于意识，我从哲学家Thomas Nagel的这个定义开始，他只是说，对于一个有意识的有机体，它就像是那个有机体。感觉就像是什么。是的，这是相当循环的。但我喜欢它，因为它击中了靶心，它只是在谈论经验，而且它对它遗漏的东西很有用。将意识隐含地与其他事物联系起来通常很诱人——这在之前的许多其他例子中也发生过——无论是智力，还是拥有语言或以特定方式行事。或者以一种明确的、反思的自我意识知道我是谁。

(04:40) 所有这些都可能是人类意识的各个方面。但一般而言，意识与这些其他事物都不一样。这只是那种体验的原始事实。但是在那里面，你确实可以做进一步的划分。而且我认为这在划分问题方面很有启发性，因此我们可以从一种分而治之的策略中获得意识。

(05:03) 我喜欢用三种方式来做这件事。完全有意识的水平。当您处于全身麻醉或无梦睡眠时，您会失去它。然后你会意识到你周围的世界。然后在其中，有做你自己的经历，做你现在的那个人。

Strogatz (05:20)：我认为这是你的书的一个了不起的方面，就对我作为读者的帮助而言，能够考虑以各种方式解决问题。你提到了四个层次：意识的层次，就是你所说的意识的内容或内容的问题；我们所意识到的或我们所感知的；自我意识；然后第四个，你说，这真的是你的奥秘吗？

赛斯(05:47)：嗯，实际上我认为第三个和第四个是一样的。

Strogatz ：好的，好的。

赛斯(05:49)：但是体验做你自己的方式有很多种。所以我们可以在不知道我们正在拥有这些体验的情况下拥有自我体验。我可以体验与这个物体相关联，也就是我的身体，我可以有情绪和情绪。原则上，所有这些都可以在不附加名称和一组记忆的情况下展开。

(06:13) 因此，在内容、水平和自我的每一个领域内，我们当然可以做出更细粒度的区分。我们可以问这些更细粒度的区别是否在实验室或诊所有任何牵引力——它们是否在自然界中挑选出连接？或者他们没有？它们是我们编造的东西吗？我认为这是意识研究游戏的一部分。我们可以弄清楚我们的哪些区别在现实世界中具有吸引力。

Strogatz (06:20)：太好了，我很感激，因为在这个播客中，我们试图谈论科学，尤其是科学中的大谜团。但我想强调科学这个词。有些事情我们可以思考，但这些事情超出了科学领域，原则上什至无法检验或反驳。我认为你真的专注于意识的科学方面——我相信你的哲学方面也喜欢思考无法回答的问题。

赛斯(06:41)：好吧，我不认为哲学只是在思考无法回答的问题。我认为科学和哲学确实在理解一些尚不清楚令人满意的理解是什么样子的事情上共同努力。现在，如果我们处于人类基因组计划的阶段，我们不一定需要哲学，在这个阶段我们确切地知道我们在做什么，而这只是我们如何做的一种工程问题。但是当谈到意识时，仍然是一个谜，不仅关于它是如何发生的，而且关于成功的答案甚至看起来会是什么样子。

Strogatz (07:08)：我很欣赏你在这里使用“解释”这个词，因为我想进入你有时称之为意识“真正问题”的问题，而不是“简单问题”。那么真正的问题是什么？

赛斯(07:39)：所以科学和哲学真的仍然需要彼此。要知道，有了一个，没有哲学的科学有点盲目，没有科学的哲学有点跛脚。所以我从来没有正式学习过哲学，但它一直存在于我的环境中。与哲学家交谈和合作，甚至亲自尝试一些哲学思想，让我受益匪浅。我想我们需要它。它使科学保持诚实，并有助于引导它提出正确的问题。

(08:16) 但我认为仍有一些我觉得不太吸引人的意识方法，这些方法原则上是不可检验的，可能是纯粹的哲学立场。最近有一种观点非常流行，叫做泛心论，这种观点认为意识不是大脑产生的东西，或者与特定种类的大脑过程或生物过程相同，但它是基本的和无处不在的。它不知何故无处不在，存在于电荷或质能等一切事物中。从表面上看，这可能是一个吸引人的想法，因为如果你只是说意识从一开始就存在，那么你就不必解释它是如何在某些地方而不是其他地方产生的。

(08:16) 但它并没有真正解释任何事情。这不仅是因为它不可测试；它不会导致任何可以测试的东西。这就是我觉得令人反感的地方。我认为哲学观点，它们本身很少是可检验的。就像唯物主义——我有点认同的观点，认为意识是一种自然现象，并且在某种程度上是大脑和身体等物质事物的属性。这本身可能是不可测试的。但它所做的是它导致了可测试的事情，并且随着时间的推移让我们能够解释我们本来无法解释的关于意识的事情。

(09:47) 真正的问题是如何根据意识在大脑和身体中的潜在机制来解释、预测甚至控制意识的特性。这听起来像是我们应该尝试做的一件显而易见的事情，对吧？但实际上并没有那么多，因为我正在谈论的这些意识属性我们应该尝试解释，它们主要是经验性的，或者我们称之为现象学属性。这是一个非常长的词，但它真正的意思是意识体验作为体验出现的方式——而不是它们允许我们做这么多，或者它们在大脑的认知结构方面可能具有什么功能。

(10:30) 比如，为什么视觉体验与情感体验不同？视觉体验，它们具有空间特征，它们具有对象，并且事物会移动。情感体验没有这些东西，对吧？它有价：事情是好是坏。所以真正的问题是将大脑中的机制与现象学的这些性质联系起来。

(10:54) 我之所以称其为“真正的问题”，是因为有点反感——对大卫·查默斯(David Chalmers)的这种“难/易问题”的区别进行了友好、友好的反击，它确实主导了很多当代科学和意识哲学。之所以不同，是因为意识的难题是一个巨大而可怕的谜团。这是我们在本次对话开始时提到的问题。意识究竟是如何发生的？以特定方式排列的物质是什么让体验发生的？我的意思是，Chalmers 自己是这样说的，他说：人们普遍认为经验是从物理基础上产生的，但我们没有很好的解释它为什么以及如何产生。为什么物理处理会产生丰富的内心生活？它应该这样做在客观上似乎是不合理的，但它确实如此。这是一个难题。这不仅仅是困难。在没有人真正知道好的答案是什么样子的概念意义上，这很难。

(11:59) 然后 Chalmers 将其与简单问题区分开来。简单的问题，基本上，这些都是关于大脑如何工作的问题，你根本不需要将意识带入画面。你知道，大脑如何将感觉信号转化为行动和做出决定等等。

(12:17) 我对这种方法的担心是要么你专注于这个极具挑战性的难题，要么你根本没有真正关注意识。我认为有一个中间立场，它非常有成效，事实上很多人已经在做，那就是：是的，你接受意识的存在，它与大脑和身体密切相关，你只是尝试解释它的属性。希望当你这样做的时候，这个难题的表面神秘感会一点一点地开始减少。你不一定会以这种方式解决难题，但你可能会解决它。以至于它最终消失在一股形而上学的烟雾中。我们意识到，尽管我们还没有开始解决这个大问题，但我们实际上已经有了一个非常好的自然主义解释，它从意识的潜在机制方面告诉我们很多关于意识的事情。这就是科学解释最终应该做的一切。

Strogatz (13:19)：如果我们能给出这些区别的具体示例，我认为它可能会有所帮助。所以你之前提到了我们拥有的视觉体验。例如，如果我看到红色的东西，你可能会天真地说，“好吧，我知道这与闻到闻起来像花的东西是不同的。”因为 – 好吧，超级天真但有一点生物学背景，在视觉的情况下，我的视觉皮层正在点亮。你知道，我大脑特定部分的神经元是活跃的，而在气味的情况下，它是我大脑嗅觉部分的东西。那么，这种解释方式是简单的，而不是困难的吗？

赛斯(13:59)：恐怕又是另一回事了。更多的是语用学，这是一个很好的起点。但是，这一领域的许多实证研究都是通过寻找相关性来进行的。所以你可能会发现，每当你有视觉体验时，你视觉皮层中的某些神经元确实会以特定方式亮起。当您闻到玫瑰花香时，您的嗅觉皮层中的神经元会以特定方式亮起。当然，然后你可以在你的经历中发生的事情和你大脑中发生的事情之间建立关联。

(14:32) 但是相关性，事物之间仅存在相关性，并不能真正告诉你这些相关性是如何以及为什么获得的。正如我们从统计学和物理学中都知道的那样，相关性并不是解释。我的意思是，这里有所有这些奇怪相关性的精彩例子，比如巴黎的离婚率与威斯康星州的奶酪价格相关等等。没错，不管是什么。有些事物只是任意关联的，有时甚至是统计产物。

(15:04) 挑战在于超越相关性，展示为什么这些神经元以这种特定方式表现？为什么这给了我们表征视觉体验的特殊属性——它在空间中延伸，有颜色，有物体，与情感体验不同？

(15:23) 这就是我的意思。这是不容易的一点。我的意思是，这真的是一个挑战。这不是难题。但这无疑是一个极具挑战性的问题。但我认为这是神经科学的东西，在计算模型和一些数学和物理学的推动下，这是一种我们可以掌握并取得进步的方法。

(15:42) 好吧，我给你举个例子。例如，在视觉中——我面前有一杯茶——如果我把它举在我面前，我对这个杯子的体验是它是一个三维物体，它有一个背面，即使我的眼睛无法直接看到背部。你知道，它有一些反对的东西。这是一个有趣的现象学性质；它并不适用于一切。如果你凝视着毫无特色的蓝天，它看起来不像是一个物体。如果你盯着太阳看然后移开视线，就会有残像，感觉不像是物体。情绪不像物体。所以这是视觉体验的一个有趣属性。我们如何解释这是如何发生的？

(16:25) 嗯，这就是乐趣的开始。然后你可以开始构建关于大脑机制如何产生知觉的理论，以及这些大脑机制如何以特定方式排列，解释我们视觉体验的这种客体特性。在这种情况下，我很久以前写的想法是，即使我们没有直接看到它，我们也会感知到杯子的背面，因为大脑正在预测如果我们是的话它会得到的感官信息旋转杯子。它有点知道哲学家阿尔瓦·诺埃 (Alva Noë)和凯文·奥雷根 (Kevin O’Regan)所说的感觉运动意外事件。大脑知道如果我以特定方式旋转杯子会发生什么。我们的想法是，正是这种内在的知识——我们没有意识到我们的大脑拥有关于感官信号如何对动作做出反应的知识——可以解释某些视觉体验的“客观性”。就是这个主意。然后，当然，你必须尝试和测试它，这真的很难。

Strogatz (17:37)：好吧，这部分思考起来非常有趣，而且感觉非常深刻、科学，并且有点令人震惊。所以我想到了很多来自魔法、视错觉、心理学实验的例子。你在书中使用的短语“受控幻觉”，感觉这就是你现在正在侵占的领域。

赛斯(17:58)：完全正确。是的。这很有趣——这不是我想出的短语。我从我的一位高级导师那里听说过它，真的， Chris Frith ，他从其他地方听说过，等等。但它有一点坚持的力量。没有比喻是完美的，但这可以帮助我们把握住。

(18:16) 因此，受控幻觉概念背后的想法是，我们对世界和自我的体验，它们并不是对实际存在的内容的直接读出，尽管在我们的体验中它可能看起来是这样。清晨睁开眼睛，眼前是一个世界。似乎世界正通过你眼睛和其他感官的透明窗户将自己倾注到你的脑海中。但这不是正在发生的事情。当然，从柏拉图，然后是康德，然后是科学，当然，这在哲学中已经得到认可。我们所经历的那种感知是对传入的感官信息的积极解释。而这种感官信息，它没有标签，比如：“我来自猫或咖啡杯，”或“我是红色的或绿色的”，或者“我来自杯子的背面”，甚至“我来自心脏或胃部”。从大脑的角度来看，它是电脉冲。这只是活动。

(19:15) 所以这个想法是大脑总是试图找出它获得的感官信息的最可能原因。它不能直接知道世界是什么样的。我的意思是，谁知道这个世界到底是什么样的？这真是一个物理学家的问题。这当然不会直接反映在我们的经验中。然后大脑总是试图对它获得的感觉信号的原因做出最好的猜测。

(19:44) 它是怎么做到的？好吧，这是现代的解释。这是一种称为预测处理或预测编码的理论，或者是最近另一种形式的主动推理。这个想法很简单。这是大脑总是在预测世界的方式或身体的方式。它使用感官信号来更新、校准这些预测，使它们与世界保持联系，其方式不一定通过准确性来滴定，而是通过它们对生物体的效用来滴定。所以我们看世界不是它本来的样子，而是我们自己的样子。

(20:25) 但这里有一个真正具有挑衅性的转变，那就是要意识到——或者至少这是假设——我们所感知的不仅仅是大脑的预期所调节的，而是根据它们构建的。因此，我们所体验的世界确实是由内而外，而不是由外而内。而感官信号，它们只是报告我们所说的预测错误，即大脑的预期与实际情况之间的差异每个级别的处理。

(20:56) 所以当我体验到我面前拿着的这个杯子时，感知内容，那个杯子的“杯子”，那不是进入眼睛的光波的读数。这是大脑对正在发生的事情的最佳猜测，由进入视网膜的光波等进行校准。

(21:16) 所以这就是我使用“受控幻觉”这个词的原因，因为它与幻觉的共同理解相同，即它是一种来自内部的体验。但控制同样重要。我当然不是说我们的经验是任意的，或者现实世界不存在或类似的东西。不，世界存在。但我们对它的体验始终是一种建构，始终是一种解释行为。它由来自世界的感官信号控制。进化已经非常确定，我们的感知体验会为我们的行为服务。

(21:56) 当然，他们也可能出错。那就是当我们得到有趣的幻觉，为什么魔术会起作用以及所有这些奇妙的东西的时候。但是我们所看到的——对我来说，这只是一件值得反思的美好事情。它可以追溯到非常基本的东西，比如颜色。我的意思是，颜色不是世界的一种独立于思维的属性。尽管看起来可能是这样。我们的大脑从无色电磁辐射的混合物中产生颜色。就颜色而言，我认为这确实是一个有力的例子。因为从某种意义上说，我们所经历的比那里的要少。因为我们只检测到电磁波谱中的一小部分能量，现实中的一小部分——对我们大多数人来说，或多或少的三个波长。但是在这三种波长中，我们生成了几乎无限丰富的调色板。因此，我们对颜色的体验既少于又多于实际存在的东西。

(22:52) 我认为同样奇怪的映射也适用于我们体验的所有其他方面。它不仅仅是过滤那里的东西。它是一种使用感官信号来构建这种体验的结构，这种对世界的主观体验具有各种有助于我们行为的属性。但是这些属性，它们是存在的。它们存在于何处？它们处在大脑、身体和世界之间的持续互动中。它们不仅存在于世界之外，也不仅仅存在于大脑中。

Strogatz (23:19)：在这一点上，我觉得我们必须举几个例子，我相信我们的许多听众都知道，甚至在我们进行这次对话时可能会想到这些例子。第一个是，正如你在解释光波撞击我们的视网膜时所做的构造中提到的颜色，我想到的是“裙子”。看起来是蓝色或金色的裙子的形象，取决于你是谁。你能不能提醒我们几年前病毒式传播的模因是什么，它与这次谈话有什么关系？

这件衣服是什么颜色的？人们对他们的看法不同。

赛斯（23:48）：其实我记得很清楚，因为当时我正在教一门课。我最近还与人合着了一本关于儿童视觉错觉的书，名为Eye Benders 。我在教书——我在上午中午左右回到办公室，关于这张我从未听说过的名为“裙子”的图片，只有大量的语音邮件和电子邮件，因为在那之前没有人听说过它早晨。这是一张在社交媒体上疯传的连衣裙照片，因为世界一半的人认为这条裙子是蓝色和黑色的，而另一半的人则认为它是白色和金色的。令人着迷的不是这里有一种奇怪的颜色幻觉，而是人们坚持自己的特定感知的信念——完全无法，至少一开始，无法理解另一种方式看到它是可能的。对我来说也是如此，我看着它，我想，“等一下。这听起来像是一个骗局，或者是假的或者什么的。”我想，嗯，那绝对是一条蓝黑相间的裙子。我在实验室问的前五个人，他们也说是蓝色和黑色，我想，“好吧，这里没什么可看的。”然后下一个人说：“你在说什么，这显然是白色和金色。”那时我想“好吧，这很有趣。”

(25:05) 这是一个引人入胜的例子，不仅说明了大脑如何构建诸如颜色之类的东西——它们不只是将它们读出来——还说明了这个过程对于我们每个人来说是如何以我们通常不会注意到的方式不同的.这需要一些奇怪的社区实验……顺便说一下，这件衣服从来没有被设计成心理学实验。这是发现心理学的一个很好的例子。有人刚刚发布了这张图片，它变得疯狂了。它基本上是颜色恒常性。基本现象是色觉起作用的原因。如果你从外面拿一张白纸，在室内，它看起来仍然是正常的白色阴影。这有点令人惊讶，因为进入你眼睛的光的波长平衡会完全改变。但是大脑所做的是，它对此进行了补偿。它在确定事物应该是什么颜色时考虑了环境照明。而且室内的灯光一般比较偏黄，室外的灯光比较偏蓝，即使是阴天也是如此。所以它总是主动补偿周围的光。对于这件裙子的照片，碰巧它对于环境照明可能是什么完全模棱两可。上下文很少。如果你回头看，这条裙子几乎占据了整个画面。所以一些人的大脑认为它是在室内拍摄的，而另一些人则认为它是在室外拍摄的。那是一种理论。还有其他理论。但这对我来说就像一个简单的故事。

Strogatz (26:39)：不过，对我来说，还有另一个例子。我是说，谢谢。这是一个很好的解释，即使你说它是一个理论。但我发现其中最令人惊叹的是一位名叫丹·西蒙斯的心理学家的作品。所以我亲身经历过，我就尽量简单的讲一个小故事。我正在听某人的演讲——实际上，一位科学家，也是一位优秀的科普作家，名叫马里奥·利维奥 ( Mario Livio) 。还有他，所以他在一个座无虚席的大礼堂里做了这个演讲。他说，“我要给大家看一段视频。球员们会以一种非常混乱的方式在他们之间来回传递篮球。他们以复杂的方式四处走动。而且他们有的身穿黑色制服，有的身穿白色制服。我希望你专心……”现在，我在努力回忆，他是说只专心于那些穿着黑色球衣的球员吗？

Seth (27:28)：没错，实际上有两个篮球在转。所以黑衣人有一个球，他们传给对方。白衣人又拿了一个篮球，互相传来传去。正如你所说，它们都以复杂的模式四处游荡。你被要求只关注穿白衣服的人并计算他们之间传球的次数，而不要担心穿黑衣服的人。

Strogatz (27:50)：所以——为了进一步说明我那天的经历，演讲者说，“你在做计数任务时可能会听到一些人在笑。不要因此而分心。这是一项复杂的任务。集中注意力，一定要仔细计算穿白色球衣的球员的传球次数。”所以我就那样做了，我按照别人告诉我的去做，其他人也一样。我会让你从那里拿走它。

赛斯（28:17）：所以人们这样做。当视频停止时，你通常——你四处走动，然后说，“好吧，那有多少传球？”人们想出了数字。有时他们做对了，有时他们做错了。这很有挑战性。然后，你知道的，我不知道是否要泄露妙语，因为如果人们没有这样做，他们真的应该自己做。所以我建议不要说出实际发生的事情。但基本的想法是，我们有这样一种印象，即我们真的只是看到了外面的东西，尤其是当我们直视它的时候。这个演示的作用——它被称为无意失明的演示——它表明那是不正确的。我们所经历的与实际存在的截然不同，这对人们来说可能非常有趣，尤其是当他们知道发生了什么的时候。我很想把它留给人们去尝试。

Strogatz ：好，让我们开始吧。

赛斯(29:18)：还有另一个例子，我不鼓励人们尝试，原因会变得很清楚。这是一种相关的现象，称为变化失明。在变化失明中，发生的事情是，如果某些东西在——我们的视觉体验再次是最简单的环境，但它也适用于其他领域。如果某事变化非常缓慢，而我们正专注于其他事情，我们通常不会注意到变化。因此，就像房间的整个背景可能会改变颜色一样，我们可能不会注意到，等等。

(29:48) 它表明的一件事是我们感知的变化与变化的感知不同。现在变化可以是一种很像颜色、很像形状的特征。仅仅因为某些事情正在发生变化并不一定意味着我们经历了变化。我认为这非常有趣，因为我们倾向于认为变化只是客观现实中发生的事情的一种特性。如果我们对现实的看法发生变化，那么我们就会经历变化。但不，我们对变化的体验本身就是一种感知，是大脑对正在发生的事情的最佳猜测。这是心理学中研究得非常透彻的现象。

(30:25) 当我在 2000 年代中期回到圣地亚哥做博士后时，我经常去这个叫 Del Mar 的地方冲浪。那里有一条小街——我会在第九大道拐弯，就在 101 号公路旁，这是一个左转弯。我这样做了很多次。然后有一天我做到了，我被拖过来并给了一张罚单。我说：“怎么回事？”我不明白。那个星期，那里竖起了一个“禁止左转”的标志，这是我不知道的。似乎没有什么充分的理由，因为这是一条通向大海的死胡同。我想，“等一下，我没看到标志。”当然，我也是基于零钱盲视的现象，决定挑战这张票的。 Because to get out of a ticket like that, you can say, you can argue that the sign was not visible. And if the sign isn’t visible, then you’re not responsible for not adhering to it. So my argument was that, well, yes indeed, the sign was within my eyeline. But because of change blindness, I was not expecting the sign to be there. It changed when I wasn’t there, nobody put it up while I was looking, you know, I literally did not perceive it. So if I didn’t experience it, then I can’t be held responsible for making that No Left Turn.

Strogatz (31:45): And what did the judge say?

Seth (31:47): And … I’ll leave you in suspense. It did drag on because I wrote a written deposition. And then that was rejected. And then in California, eventually you can go to traffic court. And I thought, I’m going to traffic court. And so I have my day in court, and I prepared this little PowerPoint presentation about change blindness and had photos. I mean, this sounds insane now, looking back. I mean, I must have had more useful things to do. And of course, it turns out, all that mattered was whether the cop who had given you the ticket showed up or not. If the cop didn’t show up, then basically you got let off. And if the cop did show up, then your ticket was upheld. Whatever clever defense that you had was really not that relevant. So it was, it was a bit sobering. But you know, I still think it was a valid defense. I still think that’s what happened.

Strogatz (32:37): Well, alright, so as we move toward the end of our discussion here, I think we should start talking about the self. I’m reminded of expressions that you have been using earlier in this conversation where you say things like, “the brain’s best guess,” or “the brain is trying to make sense of…” It almost makes me picture what people used to call the homunculus. Like, there’s a little person inside your head who’s looking out through your eyes, trying to make sense of the world. It’s sort of: the self, what is it? I mean, who’s in there? Who is it that’s trying to make sense?

Seth (33:09): Yeah, I mean, so this is why when I say the brain believes this, or the brain predicts this, I tried to be careful to say the brain rather than you. Because I think the experience of being you, the experience of self, is another kind of controlled hallucination. It’s another kind of brain-based best guess, OK? And this is another challenge to this sort of naive how-things-seem view of perception.

(33:32) Now, just as it seems as though there’s a real world out there that just pours itself into our minds, it might also seem to us that the self is the thing that does the perceiving. This quiddity, this essence of you or me, maybe the soul that resides somewhere homunculus-like inside the skull, doing all the perceiving and then deciding what to do and then pulling various meat strings in the body to make actions happen.

(34:00) And I think this is fundamentally mistaken. And again, this is not a new thing to say. Here, the philosopher David Hume , Scottish philosopher, had what he called “the bundle theory of self,” which is the idea that the nature of self is just an ongoing collection of perceptions. It’s not the thing that does the perceiving. It’s another kind of perception, but this time based at least in part on the body. So just as the brain, in trying to make sense of what’s out there in the world, is making predictions about the causes of signals that come into the eyes and the ears and so on, it’s also trying to figure out what’s happening inside the body and trying to also control the body too. And this also happens, in my view anyway, through a process of the brain creating predictions and using them to update sensory signals, but in this case from the body. Or when making actions to use predictions to actually, you know, overwhelm sensory data so they become self-fulfilling predictions, so that if I move my arm to pick up the cup again, now that’s a kind of self-fulfilling prediction about where my arm will be.

(35:10) But the key point is that there’s a common principle here underlying experiences of the world, and experiences of the self. They’re both forms of perceptual prediction. Neither of them reflect things as they really are. And both can be subject to illusions — they can both go awry in various ways.

(35:32) So lots of the book is kind of taking this idea that we build up about how our perception of the world works, and then turning the lens inward to understand how the same core principle can explain experiences of selfhood. And these include not just the sort of high-level aspects of self that “I’m Anil Seth, and I live in Brighton” and so on and so on, and “I remember this funny story about getting a ticket in San Diego.” But much more basic elements of self too, like the fact that this object that I call my body is part of myself — emotions and moods are part of self, experiences of free will. Now, they are not the consequences of some almost supernatural causal power that sweeps in and changes the course of physical events in the world. No, that’s another kind of perception of what my body is doing.

(36:23) I’ve come to think this is a very satisfying view of self, that all these different elements of what it is to be me or to be you can be understood as forms of perception that play some role in guiding the behavior of the organism. And it can also help us understand what happens when these processes go wrong. There’s so many conditions in psychiatry and neurology, and that we can induce in the lab using virtual reality, where we can tease apart these elements of self so that some remain and some are altered. The more you do this, the less sense it makes to presume that there is such a thing as a unified, stable, unchanging essence of anyone.

Strogatz (37:07): It’s mind-boggling. Hard to think about. But I appreciate hearing which direction the research is going. And so I would like to talk to you about the sorts of studies you’re doing with your group, you in your lab right now, on perceptions — what you’re calling the Perception Census .

Seth (37:23): Yeah, thank you. We’re doing a few, I think, really fun things at the moment.

(37:28) Before I mention the Perception Census, I just wanted to mention one thing we’re working on, which I think is maybe interesting to you, too, because it’s all about emergence , which I know is a topic that you’ve written some great stuff about. Now, emergence is often imbued with slightly spooky properties, like there’s the whole that has something that the parts don’t have. And there’s this sort of idea that conscious experiences emerge from neural activity in some way. And that can either be in a spooky way, where you say there’s at some point this new thing comes into existence, which is consciousness, which wasn’t there. Or you can attack it in a more pragmatic way, much as we might try to explain how flocks of birds have flockiness. And there’s something about a flock of starlings — this happens in Brighton in the winter, actually, the starlings, they roost on the pier every evening. And the flock seems to have an existence, an autonomy of its own, that the individual starlings do not. And there’s nothing spooky or mysterious about that.

(38:28) But there’s a challenge in using mathematics to capture that relationship, to capture the flockiness of a flock. So this is one line of research that we’re pushing quite hard on now. How can we develop these kinds of measures and apply them to neural dynamics, to the activities of neurons, to say: Are conscious states associated with a sort of flockiness of neural activity, if you like, and what kind of flockiness?

(38:54) And so this is something we’re doing, I think it’s really fun because it for me, it hits the one bullseye of philosophy taking a concept which has some tricky meanings, mathematics, using math to sharpen that and turn it into something you can apply, and then consciousness research — trying to explain something about a conscious experience, which as a whole, a unifying thing, can arise from the activity of many individual parts. So that’s one topic that I’m very excited to be working on at the moment.

(39:21) The other is very different. The other is this idea — it’s really following on from our conversation about perception, and especially “the dress.” So remember, the dress, of course, was this one example, where it suddenly became very clear that people can have very different experiences even for the same thing — in this case, this photo. The mistake to make is to assume that if it’s not some weird situation like the dress, then we all experience the world in the same way. And we don’t.

(39:53) I mean, there’s a very old concept called neurodiversity — well, “old,” I mean back to the ’90s. And it also makes the point that, just as we all differ on the outside in skin color and height and so on, we all have different brains, at least a little bit. So we’re likely to differ on the inside too. The term neurodiversity, though, has tended to become associated with particular conditions like autism, or ADHD. And I think that again, a bit like the dress, really, it can reinforce the wrong idea that if we don’t have a neurodivergent condition, then we see the world as it is and we all see it the same way.

(40:31) And what we’re trying to do in my lab now — and this is a collaboration with Fiona McPherson at University of Glasgow and others. This Perception Census is a large sort of citizen science project to try and understand the whole range of how we experience things differently. You know, some people might see colors differently. Other people might have more vivid mental imagery. We might experience the flow of time to be different from one person to another. Our expectations, our tendency to see faces in clouds, let’s say, that might differ from one person to another too. And very little is known about this hidden landscape of inner diversity.

(41:08) So the Perception Census is trying to put that right. It’s basically, in practice, it’s a set of online simple, quite fun (we hope), short, interactive little experiments and illusions and demonstrations that are well suited to map out how we all vary on the inside. All you need is your own computer, and anyone can take part anywhere in the world. We’ve had more than 20,000 people take part so far, from 100 countries or more. We’re trying to make this a real landmark study, so the more people that take part in it, really the better. And everybody does make a difference. And people taking part, they also learn about perception too, both in general and about their own ways of perceiving. So this is a bit of a call to action too, if anybody listening to this is keen to help advance the science and learn more about the area, then please give the Perception Census a go. I’d be very grateful.

Strogatz (42:03): Do you want to give us a website?

Seth (42:05): The website, indeed. It’s perceptioncensus.dreammachine.world , which is a bit odd. But if you just search for “Perception Census,” or even go to my website, which is anilseth.com , which is probably easier to remember, you’ll find the Perception Census straightaway.

Strogatz (42:21): That will be really fun to try. I’m going to try it myself.

(42:24) I can’t resist asking a little bit about animals and machines, though, too. I mentioned in the introduction, that that’s something any pet owner — as some of my listeners will know, I do have my beloved dog, Murray. I won’t say I have any beloved computers, it’s not the same thing. But still, that seems obvious to a pet owner that my dog is conscious. Is that right?

Seth (42:46): Yeah. And I think you’re right. I think you’re right. But you might be right for the wrong kinds of reasons. And you know, by the way, I wonder — we don’t have our beloved computers yet. But as we get, you know, from these chatbots like ChatGPT , maybe that might soon change. There’s that fantastic movie by Spike Jones called Her — you know, the guy falling in love with an operating system. So I think these things are up for grabs.

(43:09) But I mean, we humans, we have this tendency to anthropomorphize, to project conscious minds into things that are similar to us in a way that’s overly shaped by their similarity to us or how they interact with us. And this can lead us to assign consciousness of a particular kind to things that might not have it and deny it to other things that might. The key thing to remember when considering this question is that consciousness — this brings us back to the beginning — is not the same thing as intelligence or having reason or having language or anything like that. It’s any kind of experience whatsoever.

(43:44) So if we judge other animals by their possession of these kinds of human-like characteristics, then we’re going to go wrong. All mammals share the same basic neuronal hardware that seems critical for consciousness in humans. That’s my claim, anyway; not everyone is going to agree with that. But I think it’s a done deal to assume that all mammals, and this includes mice, rats, dolphins, as well as monkeys, orangutangs, and so on, are conscious. But in different ways — you know, we humans, we just inhabit one small region of a vast space of possible minds . Beyond mammals, it gets really hard. And we still can’t help being driven by intuitions. I spent a week with octopuses many years ago in Italy. And this made such an impression on me because these creatures, they don’t seem similar to us at all. But the sense that there’s a conscious presence there is so palpable. They have a curiosity about their world. And they have a lot of neurons too.

(44:44) But there’s a big challenge. I think it’s very likely that very many animals have consciousness because consciousness is a very functional thing. You know, it brings a lot of information together for an organism in a way that’s sort of unified and also informative with respect to what actions should be made. We experience the body in motion and the state of the world all kind of at once. So it’s solving a problem for organisms about how to take a lot of things into account in a relevant way for continued survival. So I think it’s likely, but it’s incredibly hard to come up with 100% confidence about this stuff, especially when we get beyond mammals to insects, to fish, to bacteria. Where do you draw the line? It’s very hard — or even to know whether there is a line to draw, or whether consciousness just kind of peters out into nothingness in a very, very graduated fashion.

(45:39) So the strategy that I think is best is we just need to generalize out very slowly. And the more we learn about the basis of human consciousness, the more we can understand about how conscious experiences might unfold in other animals. And the extent to which that’s true across all animals — the further we go, the harder it is. But we should try. And when in doubt, there’s this thing called the precautionary principle, which is to basically be quite conservative about this and say, OK, if there’s a chance that X is conscious, let’s assume that’s true, so that we don’t cause suffering unnecessarily.

Strogatz (46:18): That last comment makes me think about one of the most fascinating things — I mean, I really do love your book, I have to say — and one of the parts I had not known a thing about before had to do with human patients, who we used to describe as being in a vegetative state. What I was going for was a study where you talked about the use of having people imagine playing tennis, or moving around in their house, and what that has revealed about the conscious experiences of people that we might otherwise tend to deny having consciousness.

Seth (46:52): Right. So I think this example underlines that studying consciousness is not just some sort of luxurious indulgent pursuit to satisfy our existential itches. It’s something that has real practical importance. And in neurology, there are people who suffer very severe brain damage: They appear to be unconscious. You know, they don’t respond to any verbal commands or interactions. They don’t seem to display any voluntary behavior. But they still go through sleep and wake cycles. They’ll wake up, their eyes will open. But very informally, it seems like there’s nobody home.

(47:29) My friend and colleague Adrian Owen , and his colleagues Melanie Boly and others a while ago, now more than 10 years ago, they did this now very famous experiment where they had a patient who was apparently in this vegetative state. And they asked her to do two things at different times. One time, they asked her to imagine playing tennis for about 30 seconds while in the brain scanner, by the way, and at other times, they asked her to imagine walking around the rooms in her house. Of course, there’s no obvious response.

(48:03) But when you analyze what was going on in her brain, the areas of the brain that we know from other studies are heavily involved in planning smooth movements of the sort that you do when you’re playing tennis, those were highly active. And importantly, it’s not just the auditory cortex, it’s not just an automatic response to sound or language. These are the parts of the brain that light up when somebody understands the content and is actively engaging in imagination — stuff that’s very hard to conceive how it could be done without consciousness. And then when imagining walking around their house, same thing. There’s another set of brain regions, which are quite separate, which are again not just auditory or language areas, which reliably light up when people are imagining moving around in some sort of spatially organized way. And when she was given that instruction, we saw those areas light up.

(48:59) So to Adrian Owen and colleagues, this is really convincing evidence that this person was conscious, even though it was not clear from the outside. And then of course, you can use that technique, take it one step further and establish a channel of communication. And you can say, “OK, if you want to say yes, then imagine playing tennis. And if you want to say no, imagine walking around your house.” It’s a very laborious and slow method of communication. But for these people, it’s much better than nothing. And you can of course, you can ask, eventually, questions like, are you in pain? And things like this.

(49:36) And there are so many people in this state — I mean, I don’t know exactly how many, but tens of thousands across the world. So understanding whether they’re conscious or not, and then how to interact with them and how to generate prognostics about the likelihood of recovery, this is all stuff that’s happening. And it’s happening because of the interaction of consciousness research with, in this case, clinical neurology.

(50:00) And there are so many examples that are similar that underline the practical relevance. Animal welfare, where we started, that would be another one. Now we want to make our decisions on a rational basis, not on some just completely ascientific assumptions or indeed on the basis of our anthropomorphic tendencies. Ideally, we want to know what the capacity for suffering is likely to be in different kinds of organisms, and make our animal welfare decisions on that basis.

Strogatz (50:27): Well, this has been such a wide ranging, utterly fascinating conversation. I really wish I could keep you here all day. But I think I better let you go. Anil Seth, thank you so much for joining us today,

Seth (50:39): Steve, it’s been a pleasure. Thanks for having me again.

Announcer (50:41): Explore more science mysteries in the Quanta book Alice and Bob Meet the Wall of Fire , published by the MIT Press, available now at amazon.com , barnesandnoble.com or your local bookstore. Also, make sure to tell your friends about The Joy of Why podcast and give us a positive review or follow where you listen. It helps people find this podcast.

Strogatz (51:13): The Joy of Why is a podcast from Quanta Magazine , an editorially independent publication supported by the Simons Foundation. Funding decisions by the Simons Foundation have no influence on the selection of topics, guests or other editorial decisions in this podcast or in Quanta Magazine . The Joy of Why is produced by Susan Valot and Polly Stryker. Our editors are John Rennie and Thomas Lin, with support by Matt Carlstrom, Annie Melchor and Zack Savitsky. Our theme music was composed by Richie Johnson. Julian Lin came up with the podcast name. The episode art is by Peter Greenwood, and our logo is by Jaki King. Special thanks to Bert Odom-Reed at the Cornell Broadcast Studios and the staff at Pier Studios in Brighton, England. I’m your host Steve Strogatz. If you have any questions or comments for us, please email us at [email protected] Thanks for listening.