The Surprising Speed of Thought: How Fast Does the Human Brain Really Process Information?
We all like to think of ourselves as quick-witted, but a study from Caltech calculates that our brains process information at the extremely slow speed of around 10 bits per second. This leisurely pace may have long evolutionary roots, despite our sensory systems gathering data about 100 million times faster. The human brain is often said to be the most powerful computer in the world, and its efficiency is undisputed. But how fast does it actually work, in computer terms? Biologists at Caltech have quantified the rate of human thought in terms of bits.
Digitally speaking, one bit is a single 1 or 0, and a string of them are used to code information. A bit is a basic unit of information in computing. A typical Wi-Fi connection, for example, can process 50 million bits per second. In the new study, researchers applied techniques from the field of information theory to a vast amount of scientific literature on human behaviors such as reading and writing, playing video games, and solving Rubik's Cubes, to calculate that humans think at a speed of 10 bits per second.
Layers of the Brain Cortex
Quantifying Human Thought
The researchers on the new study first set out to define one bit in human terms. Of course, it varies based on the specific mode of information processing - with reading and writing, for example, they quantify one bit as one character of text, and in listening to speech it’s essentially one sound.
- For writing, they started with the example of a professional typist. They can type at a speed of 120 words per minute, and with an average of five characters per word that comes out to 10 keystrokes, or bits, per second.
- With audio, the recommended rate to make sure your speech can be understood is up to 160 words per minute. Applying the same math, this comes out to 13 bits per second.
The team goes on to calculate similar bit rates for extreme examples of human information processing. That includes solving Rubik’s cubes at world record speeds, which comes out at 11.8 bits/sec, digit memorization challenges (4.9 bits/sec), professional Tetris (7 bits/sec), and speed card challenges (17.7 bits/sec), which involve studying a randomized deck of cards and recalling the order.
From this, the team concludes that around 10 bits per second is a good average for the rate of human thought. Compared to artificial data transmission systems, that’s extremely slow - Wi-Fi speeds, for example, are usually measured in hundreds of millions of bits.
It’s even slow compared to our own hardware - sensory organs and the nervous system. The team calculates that a single cone photoreceptor in the human eye can transmit information at around 270 bits/sec, which comes out to a staggering 1.6 billion bits/sec per eye. The optic nerve seems to then compress it down to about 100 million bits/sec. However, that still dwarfs our rate of thought, especially considering the huge amounts of input streaming in from our other senses at the same time.
"Every moment, we are extracting just 10 bits from the trillion that our senses are taking in and using those 10 to perceive the world around us and make decisions,” said Markus Meister, corresponding author of the study.
Individual neurons have the capacity for much faster data rates, but in practice they usually operate at around 10 bits/sec, the team says. This could be a holdover from our most ancient ancestors, who needed to focus on just moving towards food and away from predators. As such, we can really only have one “train of thought” in the forefront of our mind at a time.
“Our ancestors have chosen an ecological niche where the world is slow enough to make survival possible,” the researchers write in the paper. “In fact, the 10 bits per second are needed only in worst-case situations, and most of the time our environment changes at a much more leisurely pace.”
Implications and Paradoxes
“This is an extremely low number," Meister says. "Every moment, we are extracting just 10 bits from the trillion that our senses are taking in and using those 10 to perceive the world around us and make decisions. This raises a paradox: What is the brain doing to filter all of this information?"
There are over 85 billion neurons in the brain, with one third of these dedicated to high-level thinking and located in the cortex. Individual neurons are powerful information processors and can easily transmit more than 10 bits per second of information. But why don't they? And why do we have so many if we're thinking so slowly? Meister suggests that, given the discovery of this "speed limit" in the brain, neuroscience research ought to consider these paradoxes in future studies.
Another conundrum that the new study raises is: Why does the brain process one thought at a time rather than many in parallel the way our sensory systems do? For example, a chess player envisioning a set of future moves can only explore one possible sequence at a time rather than several at once. The study suggests that this is perhaps due to how our brains evolved.
Research suggests that the earliest creatures with a nervous system used their brains primarily for navigation, to move toward food and away from predators. If our brains evolved from these simple systems to follow paths, it would make sense that we can only follow one "path" of thought at a time. "Human thinking can be seen as a form of navigation through a space of abstract concepts," the researchers write. The team emphasizes the need for future research into how this constraint-one train of thought at a time-is encoded in the architecture of the brain.
The implications for future technology are a little worrying. The researchers say that computers, robots and AI can process information much faster than us, and will only get faster.
“The discussion of whether autonomous cars will achieve human-level performance in traffic already seems quaint: roads, bridges, and intersections are all designed for creatures that process at 10 bits/sec,” the team writes. “When the last human driver finally retires, we can update the infrastructure for machines with cognition at kilobits/sec. By that point, humans will be advised to stay out of those ecological niches, just as snails should avoid the highways.”
It’s also bad news for anybody hoping to augment their cognitive abilities with AI, through systems like Elon Musk’s Neuralink. No matter how fast the computer half gets, our squishy, antique hardware will still be the bottleneck.
“Based on the research reviewed here regarding the rate of human cognition, we predict that Musk’s brain will communicate with the computer at about 10 bits/sec,” the paper reads. “Instead of the bundle of Neuralink electrodes, Musk could just use a telephone, whose data rate has been designed to match human language, which in turn is matched to the speed of perception and cognition.”
The study does require a little bit of number-fudging though. Brain bits and computer bits aren’t perfectly comparable - for example, systems like ASCII take seven bits to encode each character, compared to the new claim of one character per bit in the brain.
Caltech researchers have quantified the speed of human thought: a rate of 10 bits per second. However, our bodies' sensory systems gather data about our environments at a rate of a billion bits per second, which is 100 million times faster than our thought processes. This new study raises major new avenues of exploration for neuroscientists, in particular: Why can we only think one thing at a time while our sensory systems process thousands of inputs at once?
The paper is titled "The Unbearable Slowness of Being: Why do we live at 10 bits/s?" Funding was provided by the Simons Collaboration on the Global Brain and the National Institutes of Health.
Comparison of Information Processing Speeds
| System | Processing Speed |
|---|---|
| Human Brain (Average) | 10 bits/second |
| Single Cone Photoreceptor (Human Eye) | 270 bits/second |
| Optic Nerve | 100 million bits/second |
| Typical Wi-Fi Connection | 50 million bits/second |