The Speed of Human Thought: 10 Bits per Second
A team of researchers at Caltech has tackled the challenge of measuring the speed of human thought, estimating it to be around 10 bits of information per second—a figure that may seem puzzlingly slow. For comparison, one estimate of the slowest average internet download speed in the U.S. in 2024 was 93 megabits per second (Mbps), though this figure represents data transfer, not the meaningful information conveyed.
What Are “Bits” in This Context?
The term “bit” is familiar in computing, where it represents one of two possible states: 0 or 1. However, in information theory, the concept of a “bit” extends beyond this binary definition to represent the amount of information conveyed. This is often measured in “Shannons,” a unit named after Claude Shannon, the father of information theory.
Vincent Gripon, an associate professor at Télécom Bretagne, offers a helpful analogy: “To understand the concept of information, it is essential to differentiate it from that of data. Let’s take an example. I have a friend who has just given birth. I send her a text message to ask her the sex of the newborn. In my vision of things, there is an equal chance that it will be a boy or a girl. Her response will therefore send me exactly one Shannon. To answer me, she will probably send me a sentence made up of several characters, each represented by several bits. I will therefore receive several dozen bits of data for a single Shannon”
Sensory Overload vs. Conscious Processing
Our brains are inundated with sensory data at staggering rates. It’s estimated that the visual cortex transmits 100 million bits per second of data to the deeper areas of the neocortex. Yet, most of this data is irrelevant to our conscious experience, which processes information far more selectively.
Scientists have long been intrigued by this disparity, examining how much information various systems convey. While our sensory organs take in up to 109 bits per second, our conscious thoughts operate at a fraction of that speed.
Measuring the Speed of Thought
Quantifying human thought is no small feat. In a recent study, researchers analyzed tasks like typing a handwritten manuscript. They noted that an expert typist can produce 120 words per minute, equating to about 10 keystrokes per second.
However, the entropy—or unpredictability—of English means that only about 1 bit of meaningful information is conveyed per character. When tasked with typing random sequences of characters, typists’ speeds dropped dramatically, underscoring how much we rely on language’s inherent redundancy.
From this, the researchers estimated the speed of thought during such tasks to be roughly 10 bits per second. They found similar results across a range of activities, including playing Tetris, solving Rubik’s Cubes, and listening to spoken English.
A Cognitive Paradox
“This is an extremely low number,” co-author Markus Meister remarked. “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?”
The findings have implications for fields like brain-computer interface development. While enhancing brain power with technology sounds promising, it may be constrained by the natural limits of human cognition—akin to connecting fiber-optic internet to outdated hardware.
Survival by Simplicity
Why is human thought so slow? The researchers propose that this speed suffices for survival. “Our ancestors have chosen an ecological niche where the world is slow enough to make survival possible. In fact, the 10 bits/s are needed only in worst-case situations, and most of the time our environment changes at a much more leisurely pace.”
Unanswered Questions
Despite their intriguing findings, the researchers acknowledge that their estimate raises more questions than answers. Notably, it highlights a stark contrast: while our peripheral nervous system absorbs environmental information at gigabit-per-second rates, our conscious thought processes operate at a snail’s pace by comparison.
“In particular, our peripheral nervous system is capable of absorbing information from the environment at much higher rates, on the order of gigabits/s,” the team concludes. “This defines a paradox: The vast gulf between the tiny information throughput of human behavior, and the huge information inputs on which the behavior is based. This enormous ratio – about 100,000,000 – remains largely unexplained.”
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