Crows can evaluate visual info twice as fast as mammals

本文为原文前 6,000 字符的节选翻译，完整内容请查看原文。

Much of what we know about how a brain makes decisions comes from studying monkeys watching dots. In a task known as a random-dot-motion task, a cloud of flickering specks drifts weakly in one direction while the subject tries to determine whether—and in which direction— it’s moving. The task has shown that in the primate neocortex, neurons gather visual evidence over time, with their firing rates climbing until they cross a threshold, when the animal commits to a decision. But avian brains don’t have a neocortex, so it wasn’t obvious how they made similar decisions.

我们对大脑如何做出决策的了解，很大程度上源于对猴子观察点的研究。在一项被称为“随机点运动任务”的实验中，一团闪烁的斑点会微弱地向一个方向漂移，而受试者需要判断它是否在移动以及向哪个方向移动。该任务表明，在灵长类动物的新皮层中，神经元会随着时间的推移收集视觉证据，其放电率不断攀升，直到跨越某个阈值，动物便会做出决定。但鸟类大脑没有新皮层，因此它们如何做出类似的决策并不显而易见。

“This was the big question,” said Andreas Nieder, a neurobiologist at the University of Tübingen. “How [would] a differently organized avian brain encode decisions?” To find out, Nieder and his colleague Philipp Schmidbauer put two carrion crows through the same task the monkeys faced, recording their brain activity along the way. The crows solved the task the same way primates do, using the same mathematical logic despite having a very different brain structure. And they did it two times faster.

图宾根大学的神经生物学家安德烈亚斯·尼德（Andreas Nieder）说：“这是一个大问题。组织结构不同的鸟类大脑将如何编码决策？”为了找出答案，尼德和他的同事菲利普·施密德鲍尔（Philipp Schmidbauer）让两只小嘴乌鸦完成了猴子所面临的相同任务，并在此过程中记录了它们的大脑活动。尽管大脑结构截然不同，但乌鸦使用与灵长类动物相同的数学逻辑解决了这一任务。而且，它们的速度快了两倍。

A brain built different: Nieder and Schmidbauer put two hand-raised crows in front of a touch-sensitive monitor showing a cloud of white dots on black, with some fraction of them drifting coherently left or right or up or down. The birds’ job was to report the overall direction by pecking one of the targets that flanked the display. Correct answers earned them a mealworm. “We intentionally wanted to have exactly the same random-dot motion task,” Nieder said. “The only difference was that the crows had to peck to indicate their decision, whereas monkeys were indicating by making an eye movement.”

大脑结构不同：尼德和施密德鲍尔将两只人工饲养的乌鸦放在一个触摸屏显示器前，屏幕上显示着黑色背景下的一团白点，其中一部分白点会一致地向左、向右、向上或向下漂移。鸟类的任务是通过啄击显示屏两侧的目标来报告整体方向。回答正确可以获得面包虫作为奖励。尼德说：“我们特意想要进行完全相同的随机点运动任务。唯一的区别是，乌鸦必须通过啄击来表明它们的决定，而猴子则是通过眼球运动来表示。”

The researchers varied how many dots moved together, ranging from 81 percent of the dots coherently moving together, which is trivially easy to determine, down to 3 percent, which is barely distinguishable from noise. They also included a zero percent condition, in which there was no correct answer. Both birds scored better than chance, even when only three percent of the dots were moving. While the crows worked at the task, the team recorded from 248 neurons in the NCL (nidopallium caudolaterale)—a region at the top of the avian processing hierarchy that is widely regarded as the functional counterpart of the primate prefrontal cortex, despite being built differently.

研究人员改变了共同移动的点的数量，从81%的点一致移动（这很容易判断）到3%（几乎无法与噪声区分）。他们还包括了一个零百分比的条件，即没有正确答案。即使只有3%的点在移动，两只鸟的得分也高于随机水平。当乌鸦执行任务时，研究小组记录了NCL（尾侧新纹状体）中的248个神经元——这是鸟类处理层级顶端的一个区域，尽管结构不同，但被广泛认为是灵长类动物前额叶皮层的功能对应物。

Birds and mammals parted evolutionary ways more than 360 million years ago, and bird brains evolved a different architecture. The mammalian cortex is arranged as stacked sheets of cells, while the equivalent tissue in a bird is organized into dense clusters, with no layering at all. This alternative architecture, Nieder’s study found, proved faster. Measured from the moment that the dots appeared to the moment the bird’s head started turning to peck at the button, the crows averaged 235 milliseconds. In closely matched versions of the task, monkeys took roughly 410, 490, and 600 milliseconds in three studies. The obvious question was whether the birds simply sacrificed accuracy for speed, but it turned out they did not.

鸟类和哺乳动物在超过3.6亿年前分道扬镳，鸟类大脑进化出了不同的结构。哺乳动物的大脑皮层排列成堆叠的细胞层，而鸟类中对应的组织则组织成致密的簇，完全没有分层。尼德的研究发现，这种替代性的结构被证明更快。从点出现到鸟头开始转向啄击按钮的那一刻测量，乌鸦平均耗时235毫秒。在匹配度极高的任务版本中，三项研究显示猴子分别耗时约410、490和600毫秒。显而易见的问题是，鸟类是否仅仅为了速度而牺牲了准确性，但事实证明它们并没有。

Hunting for shortcuts: “This would be a simple explanation, that they are very fast at the cost of precision. But that’s not what’s happening,” Nieder said. Crows were as good as monkeys or humans in the same task. “We’ve never forced the crows to be as quick as possible,” Nieder explained. “We just gave them a self-paced decision. And even in this situation, they were twice as fast compared to any monkey or human that I’m aware of.”

寻找捷径：“这会是一个简单的解释，即它们以牺牲精度为代价换取了速度。但事实并非如此，”尼德说。乌鸦在同一任务中表现得和猴子或人类一样好。尼德解释道：“我们从未强迫乌鸦尽可能快地完成任务。我们只是让它们自主决定节奏。即使在这种情况下，与我所知的任何猴子或人类相比，它们的速度也快了两倍。”

One possible reason for the crows’ speed was that their’ brains were working on a fixed deadline, and the data initially seemed to support that. In primates, difficulty has a large effect on how long a decision takes. In the crows, reaction times ran from 220 milliseconds at the easiest task to just 254 at the hardest, a difference of only 34 milliseconds. But Nieder doesn’t think this means an avian brain is just wired to produce answers on a timer. “If you zoom in, there is a statistical increase in the reaction time when the coherence is going down,” Nieder said. “They show the same effect as mammals. It’s just much less pronounced, because everything happens much faster.”

乌鸦速度快的一个可能原因是它们的大脑在固定的截止时间内工作，数据最初似乎支持这一点。在灵长类动物中，难度对决策所需的时间有很大影响。而在乌鸦中，反应时间从最简单任务的220毫秒到最难任务的254毫秒，仅相差34毫秒。但尼德并不认为这意味着鸟类大脑只是被设定为按计时器产生答案。尼德说：“如果你仔细观察，当一致性下降时，反应时间在统计学上确实有所增加。它们表现出与哺乳动物相同的效应。只是这种效应不那么明显，因为一切发生得快得多。”

There are no shortcuts, he explained, as the crows had to look at the direction of dots’ movement and process this information—they didn’t have any other cues. “That’s why I think they do accumulate evidence. They have to,” Nieder said. Catching the evidence: The recordings of neuronal activity show the evidence accumulation in action. Just under a quarter of the neurons sampled, 58 of 248, fired differently depending on which direction the bird would eventually choose, and these neurons started registering that decision incredibly early—about 70 milliseconds after the dots appeared and roughly 170 milliseconds before the bird’s head moved.

他解释说，没有捷径可走，因为乌鸦必须观察点的运动方向并处理这些信息——它们没有任何其他线索。尼德说：“这就是为什么我认为它们确实在积累证据。它们必须这样做。”捕捉证据：神经元活动的记录显示了证据积累的过程。在采样的神经元中，不到四分之一（248个中的58个）会根据鸟类最终选择的方向而产生不同的放电，这些神经元在极早的时候就开始记录该决定——大约在点出现后70毫秒，在鸟头移动前约170毫秒。

“The neurons were accumulating sensory evidence, which is very reminiscent of what monkey neurons would do in the neocortex,” Nieder said. This kind of signal in the brain is called a decision variable, a running tally of evidence that can climb toward a commitment. “It turns out that what we find in the crow brain looks basically the same,” Nieder said. “And that’s interesting considering their brains have evolved very distinctly, as if evolution has found the same physiological mechanism twice, independently.”

“神经元正在积累感官证据，这非常让人想起猴子神经元在新皮层中的工作方式，”尼德说。大脑中的这种信号被称为决策变量，是一种可以向承诺攀升的证据累计计数。尼德说：“事实证明，我们在乌鸦大脑中发现的情况基本相同。考虑到它们的大脑进化得非常独特，这很有趣，就好像进化两次独立地发现了相同的生理机制一样。”

So far, the team can’t attribute the crows’ speed to any one particularly fast process. Nieder’s leading explanation is that nearly every biological process runs faster in birds than in mammals. Life in the fast lane: “We cannot really point our finger to one specific process that is totally faster. It is probably a cascade of different processes that are faster,” Nieder explained. This cascade, he said, begins with vision, since avian visual systems are exquisitely movement-sensit

到目前为止，研究小组无法将乌鸦的速度归因于任何一个特别快的单一过程。尼德的主要解释是，鸟类几乎所有的生物过程都比哺乳动物快。快车道上的生活：“我们无法真正指出某一个完全更快的特定过程。这可能是一系列不同过程共同加速的结果，”尼德解释道。他说，这种级联反应始于视觉，因为鸟类的视觉系统对运动极其敏感。