Summary: Researchers at the University of Sydney have resolved a long-standing question about “adaptive efficiency” — how the brain divides limited neural resources when processing expected versus unexpected events. The study shows the brain uses a two-part strategy that balances speed and accuracy in a matter of milliseconds, prioritizing rapid action for predictable inputs and richer sensory encoding for surprises.
When an event is predictable, the brain prepares a fast, energy-saving response and reduces detailed encoding of sensory information. By contrast, surprising events trigger an immediate reallocation of resources to capture dense sensory detail and update internal models of the world. This explains why unexpected moments are often remembered with greater spatial precision and vividness.
Key facts
- Dual-strategy framework: The brain does not simply favor expected over unexpected information (or vice versa). Instead, it operates both strategies in parallel to optimize interaction with the environment.
- “Software update” mechanism: Surprising events prompt the brain to shift energy toward collecting detailed sensory data, effectively updating its internal model to improve future predictions.
- Predictive millisecond gains: For familiar events, the brain primes motor and perceptual systems before the event occurs, saving reaction time but sacrificing detailed memory encoding.
- Two-stage familiarity response: EEG evidence shows predictable events are handled in two phases: an early anticipatory priming phase and a later suppression phase that reduces deep sensory processing when predictions are confirmed.
- Cortical timeline: Both expected and unexpected events evoke cortical representations within roughly 100 milliseconds, but unexpected stimuli produce stronger, clearer neural signatures.
Source: University of Sydney
Australian neuroscientists have clarified what happens in the brain during predictable situations versus surprises, offering important insight into how we conserve neural energy while maintaining flexibility.
The team observed that surprising events prompt an immediate increase in sensory sampling: the brain diverts extra energy to collect and encode detailed information from the environment. This selective reallocation boosts the fidelity of memory traces for unexpected stimuli.
Conversely, when a stimulus is familiar or predicted, the brain prepares and primes the body to act before the event arrives. This predictive preparing saves milliseconds that can be crucial for rapid behavior, but it comes at the cost of processing sensory detail less deeply — which makes precise recall of those predicted details weaker.
“Our study offers a clear view of how prediction helps us perceive and act efficiently,” said senior author Dr Reuben Rideaux, School of Psychology, University of Sydney. “The brain constantly faces a flood of sensory input, so it must allocate energy strategically. For predictable events it economizes, and for surprises it gathers more information to update internal models.”
The findings, published in the Journal of Neuroscience, address a longstanding debate about whether the brain prioritizes expected or unexpected inputs. Lead author Ziyue Hu, a PhD candidate at the School of Psychology, explains the answer is that the brain does both — blending speed and precision depending on context.
Managing surprises in real life
A practical example comes from elite sport. Experienced athletes often anticipate opponents’ actions and move before an event occurs. For instance, a professional tennis player may position her racket based on opponent cues, preparing a motor response that improves reaction time. Because the brain has already committed to a predicted outcome, it may not encode the exact landing spot of a routine serve with high fidelity. In contrast, a truly surprising shot will trigger intensive sensory encoding and a vivid, precise memory.
The research approach
Forty participants viewed brief visual flashes presented around a circle while researchers recorded high-density EEG (brain waves) and tracked pupil responses. The experiment manipulated predictability: sequences were made predictable and then occasionally broken with surprising flashes. Behavioural measures recorded reaction time and accuracy, and participants later reported the precise spatial location of flashes.
Participants responded faster and more accurately to expected events, especially when attention was engaged, but their reproductions of expected locations were less precise than for unexpected events. EEG decoding showed distinct temporal dynamics: attention enhanced pre-stimulus representations and supported rapid responses, while expectation reduced post-stimulus representational fidelity. These changes emerged rapidly, around 100–200 ms after stimulus onset, and correlated with individual differences in perceptual precision.
Implications and next steps
Understanding these complementary mechanisms — an early, attention-linked anticipatory process and a later, expectation-driven suppression of sensory detail — clarifies how the brain leverages redundancy to balance speed and metabolic cost. The research team plans to explore how these mechanisms develop across the lifespan, which ecological factors influence them, and whether similar principles can improve efficiency in artificial neural systems.
Key questions answered
Q: How do elite athletes use the brain’s predictive mechanisms to outperform opponents?
A: Skilled athletes rely on learned predictions to bypass slower sensory processing. By anticipating likely outcomes based on experience, their nervous system primes motor actions in advance, gaining crucial milliseconds. Because the brain treats the predicted details as redundant, memory for those specifics is often less accurate than for unexpected events.
Q: What happens during the brain’s two-stage response to familiar events?
A: First, the brain generates a prediction that primes perception and motor systems to react quickly. Second, when the incoming stimulus matches the prediction, the brain suppresses deeper, energy-intensive sensory processing, conserving resources by treating the input as redundant.
Q: How was the phenomenon tested in the lab?
A: The study used high-density EEG, pupillometry and behavioural tests with 40 participants viewing predictable and unexpected visual flashes. By comparing reaction speed, recall precision and neural representations when patterns were preserved versus violated, researchers isolated the distinct effects of attention and expectation.
Editorial notes
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full by the editorial team.
- Additional context was provided by 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: Ziyue Hu, Dominic M. D. Tran and Reuben Rideaux. “Faster but less precise: expectation enhances response speed while reducing sensory fidelity.” Journal of Neuroscience. DOI: 10.1523/JNEUROSCI.0154-26.2026 (open access).
Abstract (summary)
The study examines how predictive mechanisms enable adaptive efficiency by balancing rapid responses with metabolic cost. Using EEG, pupillometry and behavioural measures while independently manipulating attention and predictability, the authors show that attention supports pre-stimulus readiness and faster responses, whereas expectation reduces post-stimulus sensory fidelity. These complementary processes explain how the brain leverages environmental redundancy to prioritize either speed or detailed encoding depending on whether inputs are expected or surprising.