A groundbreaking study reveals that our brains use separate pathways to enhance our senses and influence our choices when a reward is on the line, with surprising implications for attention, decision-making, and even addiction.
Have you ever noticed how your focus sharpens when the stakes are high? Whether you’re a gamer trying to spot an enemy for a crucial win, a shopper scanning a crowded shelf for a sale item, or an animal in the wild seeking the ripest fruit, the promise of a reward fundamentally changes how you pay attention. For decades, neuroscientists have understood this basic principle: rewards guide behavior. But the inner workings of this process have remained surprisingly murky. When you focus on a rewarding goal, is your brain simply turning up the volume on your senses, or is it also subtly changing the rules of how you make decisions? And are these processes one and the same?
A new study from the Indian Institute of Science (IISc) has untangled this complex relationship, revealing that the brain treats these two functions—sensory enhancement and decision-making—as remarkably separate processes. The research, led by Sridharan Devarajan, an Associate Professor at the Centre for Neuroscience, and his PhD student Ankita Sengupta, demonstrates that the expectation of a reward splits our cognitive functions down two distinct neural pathways. One path sharpens our senses, and the other sways our choices, and they don’t appear to talk to each other nearly as much as we thought.
Designing an Experiment to Tease Apart the Brain
To understand how the brain handles rewards, the researchers needed to isolate two key components of attention: sensitivity and bias. Sensitivity is your ability to actually perceive or detect something—like visually identifying the subtle flicker of a changing pattern on a screen. Bias, on the other hand, is your tendency to lean toward a particular decision, regardless of the sensory information. For example, if you get a big reward for saying “yes,” you might be more inclined to say “yes” even when you’re unsure.
Previous studies often struggled to separate these two effects because they were tangled together. To overcome this, the IISc team designed a clever two-part experiment involving 24 participants. In both parts, participants watched a screen with two striped patterns on either side and had to report if they detected a brief change in the orientation of the stripes. While they performed the task, the researchers monitored their brain activity with EEG (electroencephalography) and tracked their eye movements.
In the first part of the experiment, designed to test sensitivity, the reward was tied to a specific location. Detecting a change on one side of the screen always yielded a fixed number of points, while the other side offered a variable reward that could be much higher. Naturally, participants learned to focus their attention on the side with the potential for a bigger prize. They became more sensitive to changes on that high-reward side.
In the second part, the researchers tested for bias. This time, the reward wasn’t tied to a location but to a specific choice. For instance, on some trials, participants would get more points for reporting “Yes, a change occurred” compared to “No, nothing changed,” regardless of whether a change actually happened. This setup was designed to make them more biased toward choosing the more rewarding option.
A Tale of Two Neural Systems
The results from the first task were exactly what you might expect from classic theories of attention. When a higher reward was associated with a location, participants’ brains went into high alert for that area. Their eyes were drawn to the high-reward side, and EEG recordings showed a ramp-up in brain signals typically associated with focused visual attention. In short, the promise of a reward made them better at seeing.
But the second task delivered a genuine surprise. When the reward was tied to a choice (the bias task), participants predictably became more likely to make the more profitable decision. If saying “yes” paid more, they said “yes” more often. The shock came when the researchers looked at their brain activity. None of the classic neural signatures of attention appeared. The brain’s attention centers remained quiet, and their eye movements showed no favoritism toward either side of the screen. The brain was influencing their decision without engaging the sensory-enhancement machinery of attention at all.
“Unexpectedly, changing bias did not result in any signatures specific to the attention centres in the brain,” explains Sengupta. This finding is a crucial piece of the puzzle. It shows, for the first time, that sensitivity and bias are not just different concepts but are governed by separate neural mechanisms. The brain appears to have two distinct tools it can use when rewards are on the line: one that physically directs our sensory spotlight (attention for sensitivity) and another that quietly adjusts the scales of our judgment (a cognitive nudge for bias).
From the Lab to Real Life: Implications for Addiction and Impulsivity
This discovery does more than just redraw a map of the brain; it has profound practical implications for understanding human behavior and mental health. It suggests that our actions are shaped by a delicate interplay between these two separate reward-driven systems. One system, linked to sensory attention, helps us forage for information. The other, linked to decision-making centers, helps us act on it.
This separation could be key to understanding conditions where reward processing goes haywire. Think about compulsive gambling, for example. This behavior involves a complex mix of heightened attention to potential wins and an overwhelming bias toward risky decisions, even in the face of negative consequences. The findings from this study suggest that these might be driven by two different brain circuits running in overdrive. An overactive sensitivity system might keep a person glued to the flashing lights of a slot machine, while a runaway bias system relentlessly pushes them to make the impulsive choice to play again.
As Sridharan notes, this research could help design better tools to understand risk-taking tendencies and could inform new treatments for addiction. By recognizing that sensory attention and decisional bias are distinct processes, therapists and clinicians might be able to develop more targeted interventions that address the specific neural imbalance driving a person’s behavior.
Ultimately, this study paints a more nuanced picture of how we navigate a world full of incentives. The promise of a reward doesn’t just turn up a single
