A duo of researchers at Caltech have attempted to quantify the speed of human thought, putting it at a somewhat perplexing 10 bits of information per second. To put that into perspective, one estimate of the slowest average download speed in the USA in 2024 clocked in at 93 megabits per second (Mbps), though the amount of information conveyed is lower.
First up, what are we talking about here? Your thoughts may (surprisingly slowly, it turns out) assume that we are talking about the “bits” we see in everyday computing. In computing terms, a bit can have one of two values, often represented by a binary digit, either one or zero. But that doesn’t correspond to the amount of information conveyed, sometimes referred to as a “Shannon” after Claude Shannon, often referred to as the “father of information theory”.
“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,” Vincent Gripon, Associate Professor at Télécom Bretagne, explains in a translated piece for The Conversation.
“Our brain is accustomed to this fact. It is estimated that one hundred million bits per second of data are transmitted from the visual cortex to the deep areas of our neocortex. Most of this data is completely useless to us, and moreover carries very little information.”
Scientists studying information theory have attempted to quantify the information of various systems, including how much information is conveyed in each syllable of language and how much information there is in the entire visible universe. In doing so, they have hit upon a bit of a puzzle: Our brains are constantly bombarded with sensory data at an incredible rate, estimated to be 109 bits per second, and yet our conscious thoughts process information at a far slower rate.
Human thought, as you might expect, is a difficult thing to quantify. Attempting to do so, the authors of a new study looked at tasks performed by humans and the amount of information processed during it. For example, they looked at the task of manually typing out a hand-written manuscript.
“An advanced typist produces 120 words per minute. If each word is taken as 5 characters, this typing speed corresponds to 10 keystrokes a second. How many bits of information does that represent? One is tempted to count the keys on the keyboard and take the logarithm to get the entropy per character, but that is a huge overestimate. Imagine that after reading the start of this paragraph you are asked what will be the next let…” the team writes in their paper.
“English contains orderly internal structures that make the character stream highly predictable. In fact, the entropy of English is only ∼ 1 bit per character. Expert typists rely on all this redundancy: If forced to type a random character sequence, their speed drops precipitously.”
From this, they were able to estimate that the speed of thought the typist operates at when typing a random character sequence is around… 10 bits per second. Looking at other tasks, from playing Tetris to solving Rubix Cubes in controlled conditions, and listening to English, the team estimated that most of these tasks take place at a similar, surprisingly slow, rate.
“This is an extremely low number,” Markus Meister, co-author of the paper, said in a statement. “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?”
While our brains deal with an avalanche of sensory data, our conscious thoughts appear to operate at a far slower rate. The team notes that this could have implications, for example, in the field of creating brain-computer interfaces. While we (and by we, we mean tech bros) may dream of creating brain-computer interfaces to speed up human brainpower, it could turn out that we are limited by the speed of our own cognition, like trying to connect to fiber optic internet through a Game Boy – your hardware will limit what you can get out of it.
More generally, it raises a number of questions about human cognition, such as why our nervous system can process thousands of items in parallel, while our conscious thought chugs along at such a slow pace.
“How can humans get away with just 10 bits/s? The tautological answer here is that cognition at such a low rate is sufficient for survival,” the team writes. “More precisely, 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.”
While an interesting estimate of the information speed in human thought, the team stresses that it raises more questions than it answers, offering an avenue for further exploration in the future.
“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 writes. “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.”
The study is published in the journal Neuron.
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