Hierarchical Predictive Processing: How Daydreaming Reality Saves Energy

Your brain's sensory systems take in roughly 11 million bits of information per second, but conscious awareness handles only about 50. What happens to the rest? It turns out your brain isn't passively recording reality—it's actively hallucinating it, using predictions to fill in what it expects to see, hear, and feel. The sensory data serves mostly as error correction.

This is the core insight of Hierarchical Predictive Processing (HPP), a framework emerging from the work of Andy Clark, Karl Friston, Anil Seth, and others that reconceptualizes the brain not as a passive perceiver but as a prediction machine continuously generating hypotheses about the world and updating only when those hypotheses fail.

The implications are striking: consciousness may be a "controlled hallucination" where your brain's best guess about reality becomes your subjective experience. But this isn't a flaw—it's an engineering solution to an impossible problem. No finite system can process practically infinite information. Prediction compresses the computational load, but it comes at a cost: the brain must choose what to predict, what to ignore, and when prediction errors matter enough to update the model.

While standalone, this meetup adds to our previous discussions on Kahneman's dual-process theory, and emergent complexity. Where Kahneman described what the brain does (fast intuition vs. slow analysis), predictive processing explains why and how—and reveals that the separation may be less clean than System 1/System 2 suggests. The (relatively) simple rules of coordination between neurons form the basis for emergent complexity and sparse computation which leads to consciousness with a mere 20 watts. This does have its drawbacks, as made explicit by the No Free Lunch theorems.

Join us to explore how the brain constructs reality, why perception sometimes fails spectacularly, and what happens when the prediction machinery operates under different conditions.

Necessary viewing to attend this meetup: Why Your Brain Blinds You For 2 Hours Every Day — Kurzgesagt (12 min)

Deeper videos / text (optional):

• Recommended TED Talk: Your Brain Hallucinates Your Conscious Reality — Anil Seth (17 min)
• How Your Brain Alters Your Reality (W/ Anil Seth) | TED
• It's Bayes All The Way Up — Scott Alexander (Slate Star Codex blog, 2016)
• The Experience Machine: How Our Minds Predict and Shape Reality by Andy Clark (2023 Pop Sci)

Technical references:

• Whatever next? Predictive brains, situated agents, and the future of cognitive science | Behavioral and Brain Sciences | Cambridge Core, Andy Clark (2013)
• Thermodynamics of Prediction | Phys. Rev. Lett. Still et. al (2012)
• No free lunch theorems for optimization | IEEE Journals & Magazine Wolpert & Macready (1997)
• Surfing Uncertainty by Andy Clark (2016 textbook)
• The Predictive Mind — Jakob Hohwy (2013 textbook)

Format: After an intro summary by the hosts, we will breakup into rotating groups and discuss with the aid of a handout (https://bit.ly/4shZmiE). We will regroup for the conclusions.