Summary: Researchers resolved a long-standing debate regarding “adaptive efficiency”, how the human brain allocates finite neural energy when processing predictable versus unexpected events. The study reveals that the brain utilizes a dual-strategy framework to balance speed and accuracy in milliseconds.
When faced with a predictable situation, the brain triggers a pre-emptive response to save energy and time, though it skips encoding the finer details. Conversely, when confronted with a surprise, the brain treats the event like a vital software update, instantly directing energy to gather rich sensory data from the environment. This explains why unexpected occurrences are encoded into our internal memory with far greater spatial precision and vivid detail.
Key Facts
- The Dual-Strategy Framework: The study proves the brain does not prioritize expected information over unexpected information or vice versa. Instead, it manages both simultaneously to optimize its interaction with the environment.
- The Software Update Mechanic: During surprising events, the brain immediately redirects energy resources to harvest dense sensory details, updating its internal model of the world to improve future readiness.
- Predictive Millisecond Gains: When an event is familiar, the brain primes a physical response before the event even occurs, buying precious milliseconds at the cost of deep memory encoding.
- Two-Stage Familiarity Response: EEG data revealed that the brain handles expected events in two distinct phases: first by anticipating and priming the body to act, and second by actively suppressing deep environmental processing once the prediction is confirmed.
- Cortical Timeline Clarity: Both expected and unexpected events register in the cortex within 100 milliseconds, but unexpected flashes produce significantly stronger, clearer neural representations in brain wave data.
Source: University of Sydney
Australian researchers have uncovered what happens behind the scenes in our brain when we’re faced with a predictable situation versus a surprise, giving vital clues in a long-standing mystery in neuroscience.
The researchers found that during surprising events, our brain is wired to direct energy to take in more sensory information from our environment.
This is why we remember unexpected events more vividly and accurately. Our brain then updates its own internal memory.
In comparison, when something is familiar or expected, the brain begins to respond to it before it even happens, which is what saves precious milliseconds. When something predictable appears, the brain makes us respond faster but doesn’t bother encoding it in full detail.
“Our study is a fascinating insight into how the brain uses predictions to help us better perceive and interact with the world,” says senior author Dr Reuben Rideaux from the School of Psychology at the University of Sydney.
“Our brain is constantly under pressure to make decisions, receiving a huge amount of sensory information from our environment. So, it needs to save energy where it can.
“When the brain is faced with a predictable situation, it goes ‘I already know what this is, I don’t need to spend energy processing it carefully.’
“But during unexpected events it’s like a software update or patch. Our brain wants to update our internal memory of the world to make sure we’re prepared for the future, so the energy is dedicated to collect as much information as possible from our environment,” says Dr Rideaux.
The findings, published in The Journal of Neuroscience, resolves a long-standing debate in neuroscience about ‘adaptive efficiency’, how our brain allocates neural energy to meet the pressures of environmental demands.
“The debate had been focused on whether the brain prioritised expected or unexpected information,” said lead author PhD candidate Ziyue Hu, from the School of Psychology.
“We’ve found the answer is both. The brain has its cake and eats it too.”
“It’s incredible because this process all happens in milliseconds. This advances our understanding of how the brain balances speed and accuracy and how prediction and attention shape how we perceive the world.”
Managing surprises
The best real-world example that demonstrates this is professional sport. For high performance athletes, their experience enables them to predict and respond more quickly.
“Imagine a professional tennis player who knows where her opponent’s next serve is going to land. Their experience makes them move towards that spot before the ball is even struck and to get her racket in position to hit it back cleanly. Her brain had already prepared a motor response for the likely location and didn’t bother encoding the precise location of the ball that confirmed what it already predicted,” says Dr Rideaux.
“That prediction buys her precious milliseconds, but if you ask her to recall frame by frame, exactly where the ball bounced inside the service box, her memory will be fuzzy.
“But it’s the rare surprise serve down the middle, which she’ll remember with vivid spatial precision.”
The research
To study this phenomenon, 40 participants viewed simple visual flashes appearing around a circle while researchers measured their brain activity using EEG (recording brain waves) and tracked their pupil responses.
The research team recorded the participant’s reaction times and accuracy. But crucially, at times the researchers would manipulate and deliberately change the pattern of the flashes.
Participants responded more quickly and accurately to expected events, but when asked to recall the exact location, their memory was worse than after the unexpected flashes.
One surprising finding was our brain reacts to familiar events in two stages.
The first is when the brain first predicts what is about to happen and so prepares and primes our body to react quickly.
The second is when the brain recognises that the event is what it expected, and it saves energy by not processing this information from the environment as deeply.
Both expected and unexpected events were represented in the cortex within 100 milliseconds of participants seeing the flash, but the unexpected events were represented more clearly in the brain waves than the expected ones.
For the next stage of the research, Dr Rideaux’s team is interested in understanding how these mechanisms develop over time, and what ecological factors influence those pathways.
The team is also interested in exploring how these mechanisms can be applied in artificial brains (neural networks and artificial intelligence) to improve their efficiency or performance.
Key Questions Answered:
A: High-performance athletes rely heavily on experiential predictions to bypass standard processing delays. For example, a tennis player’s brain reads an opponent’s body language to anticipate where a serve will land, priming her motor cortex and moving her racket into position before the ball is even struck. This buys her crucial milliseconds, though her memory of exactly where the ball bounced will be fuzzy because her brain skipped processing the redundant details.
A: In the first stage, the brain projects an internal prediction onto the immediate future, priming the nervous system and body to react instantly to the expected input. In the second stage, once the sensory input arrives and matches the prediction, the brain recognizes the redundancy and shuts down deeper, energy-expensive processing, effectively telling itself that the information is already known.
A: Researchers tracked 40 participants using high-density EEG to monitor brain waves and advanced eye-tracking to record pupil responses while they viewed simple visual flashes arranged in a circle. By establishing predictable pattern sequences and then suddenly manipulating or breaking those patterns with surprise flashes, the team was able to directly contrast reaction speeds, memory recall accuracy, and the clarity of cortical signals.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neuroscience research news
Author: Ivy Shih
Source: University of Sydney
Contact: Ivy Shih – University of Sydney
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Faster but less precise: expectation enhances response speed while reducing sensory fidelity” by Ziyue Hu, Dominic M. D. Tran and Reuben Rideaux. Journal of Neuroscience
DOI:10.1523/JNEUROSCI.0154-26.2026
Abstract
Faster but less precise: expectation enhances response speed while reducing sensory fidelity
The brain’s remarkable ability to process continuous sensory inputs with adaptive efficiency – balancing flexibility while minimizing metabolic cost – is thought to rely on predictive mechanisms that generate and update internal models that leverage statistical regularities in the environment. However, it remains unclear whether this efficiency arises from prioritizing reliable, expected events or informative, unexpected ones, as they offer complementary adaptive advantages.
To isolate genuine expectation effects, we combined electroencephalography (EEG), pupillometry, and behavioural measures in a paradigm that independently manipulated task relevance (selective attention) and stimulus predictability, while minimizing stimulus repetition at identical spatial locations to control for low-level adaptation.
Human participants (both sexes) responded faster and more accurately to expected events, which was enhanced when attention was engaged; however, these events were reproduced with lower precision, independent of attention. Feature-specific neural decoding revealed pre-stimulus effects of attention and post-stimulus effects of expectation, with no interaction between the two. Attention increased decoding accuracy, while expectation reduced accuracy.
The reduced representational fidelity for expected events appeared rapidly (∼100–200 ms after stimulus onset) and correlated with individual differences in perceptual precision. Collectively, our findings indicate two complementary processes that define how the brain leverages redundancy in the environment: an early (pre-stimulus) mechanism, which supports rapid motor responses to expected events and is mediated by attention, and a later (post-stimulus) process, which dampens sensory responses to expected events and is unaffected by attention.
