The Brain That Predicts Before It Perceives
The Brain That Predicts Before It Perceives
A new theoretical framework describes a brain that does not wait for sensory information to arrive before deciding what the world contains. Instead, it anticipates. Instead, it anticipates. It generates predictions about what is about to happen — the shuffle of footsteps, the flutter of wings — and only then checks those predictions against the incoming sensory stream. This view departs from the traditional model of perception, which held that the brain passively receives sensory details, decodes their features, and matches them to stored templates in memory. That model now has a serious challenger.
Two of the world’s leading neuroscientists have brought an updated understanding of brain function and structure to this question. Lisa Feldman Barrett, who studies the psychology and neuroscience of emotion at Northeastern University, and Earl Miller, who studies how the brain carries out goal-directed behavior at the Massachusetts Institute of Technology, collaborated on a new view of categorization. [1] Their framework, published in the pages of Nature Reviews Neuroscience, describes how the brain constantly reconstructs its categories moment to moment based not only on senses and memory, but on the body’s immediate physiological needs. [3]
At the heart of their framework is a counterintuitive insight. While people may have the impression that their categories reflect an objective reality, Barrett and Miller argue that the brain projects categories onto the world in response to the body’s survival needs. Before a person is even aware of sensory impressions, the brain is already preparing the body to behave in ways that maintain the energetic resources that power physiological systems. In this way, the brain’s predictions — rather than the cumulative effects of sensory information — ultimately shape and limit how we categorize objects and features of the world.
Every moment, the body is awash in sensory signals. Photons hit the retinas. Waves of compressed air collide with the eardrums. Volatile molecules bind to receptors in the nostrils, and chemicals slather the taste buds. Pressure and heat activate nerve endings in the skin. The brain navigates this torrent by doing an enormous amount of data compression. Through a process known as categorization, the brain turns the messy, noisy, information-rich world into objects, people, concepts, and emotions that can be understood and acted on at the level of experience.
The traditional approach to categorization struggles to account for the extraordinary flexibility in the way we assign labels to features of the world. On a clear day on an open street, a sudden rhythmic patter is a pigeon taking flight. Yet in a dimly lit alley at night, the same sound is the shuffle of a stranger’s footsteps. How can the brain categorize similar sets of sensory signals in radically different ways for different situations? The answer, according to Barrett and Miller, lies in prediction rather than passive reception.
The duo’s framework is “a fresh perspective on categorization,” said Luiz Pessoa, a neuroscientist from the University of Maryland. [4] Their idea of “the maintenance of the energetic constraints of life as fundamental to how we structure our categories,” he said, is “really important to pursue.” Also new in Barrett and Miller’s framework is the hypothesis that categorization does not happen in a particular area of the brain, but across the entire organ and beyond. To understand how organisms form categories, they argued, neuroscientists have to look all over the nervous system, from head to toe.
How Two Heavyweights Found Common Ground
For many years, these two influential neuroscientists were in the same orbit, but had never collaborated directly. Miller measures high-level electrical patterns in the brain to better understand the mechanisms driving a model of neural computation known as predictive coding. Predictive coding regards our perceptions as products of the brain’s predictions, rather than a scene built from sensory signals it passively receives. Typically, during a normal sensory scene without novel information — relaxing at home, for instance — the brain generates predictive signals about the environment that dominate incoming sensory signals.
These predictive signals are known as feedback signals, and they stand in contrast to the sensory “feedforward” signals that arrive from the outside world. But when something unexpected happens — an event that deviates from the predictive model — the sensory feedforward signals, such as those arriving in the visual cortex, run up against the predictive feedback signals. This difference creates prediction errors. When sensory signals violate the predictive model, they might enter conscious experience as a feeling of surprise.
“Your brain has to constantly make predictions about what’s going to happen in the next few seconds because it’s got to filter out most of the incoming sensory information,” Miller said. “It can’t process it all, so it’s mainly looking for things that mismatch predictions because it’s more informative.” This filtering mechanism is not a minor detail of neural computation. It is the fundamental strategy that allows a finite brain to cope with an infinite stream of sensory data. Without prediction, the brain would drown in information.
In her work, Barrett has applied these ideas of prediction and anticipation to our theoretical understanding of emotions. Central to her work is the concept of allostasis: how an organism predictively regulates its energy use. In her view, emotion categories — fear, happiness, anger — resemble predictive “action plans” that the nervous system generates to activate behaviors that have served the organism well before. For example, a worked-up bodily state, with elevated heart rate, fast breathing, and tense muscles, in the context of being chased by a dog, would indicate the emotion category “fear” to activate certain behaviors and use energy resources to fight or run away.
Traditionally, emotions were thought to be hardwired in specific circuits present from birth. Barrett has helped show that we construct emotional categories in relation to signals both from within the body and from the external context. This represents a fundamental shift in how scientists understand the relationship between bodily states and emotional experience. The body is not just a passive vehicle for the brain; it is an active participant in the construction of meaning.
In 2025, Barrett reached out to Miller to see if he would be interested in putting their ideas together to create a new framework for categorization — one that would move beyond the filing-cabinet model to include their ideas about prediction and allostasis. “Even really brilliant scientists can sometimes be guided by traditional thinking, which can be hard to get beyond,” she said. “He understood what I was saying immediately.” So she asked if he wanted to write a paper together. Miller said yes.
“In our discussions it became clear we were cut from the same cloth,” Miller said. “What I love about Lisa is that she is always thinking in big-picture terms. … Both of us, we are not afraid to say things that run counter to the standard way of looking at things.” The collaboration brought together two complementary approaches: Miller’s focus on the electrical patterns that reveal how the brain computes, and Barrett’s focus on how the body’s energetic needs shape the categories we form. Together, they began to sketch a unified framework.
Categories as Survival Tools, Not Filing Cabinets
As animals, organisms are tasked with surviving through change — in the environments they are embedded in, and in their own bodies as well. Because they have limited energy, time, and computational resources, understanding every detail of every situation is impossible. That means they have to take shortcuts to stay alive. That is where categories come in. “A category is an event in which different things are treated as similar or equivalent in a particular situation,” Barrett said. Categories might be as basic as “food,” “threat,” or “mate.” Humans have a remarkable ability to form much more detailed categories, including highly abstract ones.
Philosophy departments discuss categories such as “justice,” “truth,” and “beauty.” These abstract categories are not tied to specific sensory features in the way that a category like “apple” might be. Yet they still serve the same fundamental function: they allow organisms to treat different things as equivalent so that they can act quickly and efficiently. The function of categorization, Barrett said, is to use past experiences that resemble a new situation to implement behaviors that keep our bodily systems functioning.
The category “apple” might be defined through physical features — smooth, round, red, palm-size — but it also includes a set of behavioral policies for how to interact with it: “good for eating” or “throw out when rotten.” This means that a category is never just a list of features. It is always tied to action. It tells the organism not only what something is, but what to do about it. This action-oriented view of categorization represents a significant departure from the traditional filing-cabinet model.
“The point that is important about categorization is that you do all that for a purpose,” said Timothy Buschman, a neuroscientist from Princeton University. [5] “The reason for categorization is to support the current task. Whatever it is that you want or whatever situation you are in, you are categorizing something according to what meaning it has for you.” This perspective explains why the same sound can be categorized as a pigeon in one context and a stranger in another. The category is not determined by the sound alone, but by the meaning the sound has for the organism in that particular moment.
The framework proposed by Barrett and Miller suggests that categorization is not a late-stage process that happens after sensory processing is complete. Instead, it is woven into the very fabric of perception, shaping what is seen, heard, and felt from the very beginning. The brain is not a passive receiver of the world; it is an active constructor of it. And the categories it constructs are not reflections of objective reality, but tools for survival.
This view has profound implications for understanding perception, emotion, and even consciousness itself. If the brain projects categories onto the world in response to the body’s needs, then what is perceived is never a direct window onto reality. It is always a construction — a useful fiction that keeps the organism alive. Future research building on Barrett and Miller’s work will likely examine how the brain’s predictive mechanisms and allostatic regulation work together across the entire nervous system.
Sources
2. Massachusetts Institute of Technology