Summary: New research shows that reward expectation separates sensory sensitivity from decision bias in the human brain. Using eye-tracking and EEG during a controlled visual task, investigators found that attention-related brain systems ramp up when rewards increase perceptual sensitivity, but these same attention signatures do not accompany shifts in decision bias. This reveals distinct neural pathways by which rewards influence perception and choice.
Decision bias—our tendency to favor a “yes” or “no” response because it is more rewarding—appeared to be driven by different neural processes than those that enhance sensory sensitivity. These results clarify how reward, attention, and decision-making interact and point to separate mechanisms for improving perception versus changing choice preferences.
Key facts
- Separated processing: Reward expectations modulate perceptual sensitivity and decisional bias through distinct brain mechanisms.
- Attention signatures: Sensitivity increases recruit classic visual attention markers (eye movements, ERP gain, alpha-band lateralization); bias shifts do not.
- Clinical relevance: Understanding these pathways could inform approaches to impulsivity, gambling, and addiction where reward-driven choice and attention interact.
Context and motivation
Animals and humans routinely prioritize rewarding targets in their environment—think of selecting the ripest fruit on a tree. That behavior involves both directing attention to promising locations and deciding whether to act. While reward clearly affects both perception and choice, it has been unclear whether the same neural systems mediate improvements in sensory processing and changes in decision preferences.
Sridharan Devarajan, Associate Professor at the Centre for Neuroscience, Indian Institute of Science (IISc), together with PhD student Ankita Sengupta, set out to disentangle how reward expectation affects two core components of attention: sensitivity (the ability to detect subtle visual changes) and bias (the tendency to report a change because it is more rewarding).
Their study, published in PLOS Biology, used a carefully controlled experimental design to separate space-specific reward effects that target sensory prioritization from choice-specific reward effects that shift the decision criterion.
Experimental design
Twenty-four participants completed a two-part visual task while researchers recorded eye movements and EEG. In the sensitivity-focused task, participants viewed two Gabor patches—one on each side of a screen—that briefly flickered and sometimes changed orientation. Correctly reporting a detected change earned monetary points. Critically, rewards were arranged so that one side offered a fixed number of points while the other side offered a variable number that could be higher or lower than the fixed side. Over trials, participants learned which side yielded greater reward and directed their attention accordingly, becoming more sensitive to small orientation changes on the higher-value side.
In the bias-focused task, the manipulation changed: the reward for reporting “yes” versus “no” (change vs. no change) varied on one side relative to the other. That setup encouraged participants to favor the response that offered higher reward, creating a choice-specific bias without altering the spatial allocation of sensory attention.
Key findings
When reward manipulation was space-specific (favoring one location), participants’ gaze shifted toward the higher-value side and classic attention-related EEG signatures increased. Event-related potentials showed gain modulation, alpha-band power lateralized toward the rewarded location, and eye-movement patterns reflected focused spatial attention—together indicating enhanced sensory processing and sensitivity.
In contrast, when rewards were choice-specific and encouraged a decisional bias, participants were more likely to select the higher-reward response but did not show the attention-related eye or EEG patterns seen in the space-specific condition. Instead, choice-specific reward effects were accompanied by different neural correlates, such as pre-stimulus alpha suppression, that appear tied to decision processes rather than sensory gain.
These results demonstrate a clear dissociation: space-specific reward expectation drives attentional sensory enhancement, while choice-specific reward expectation alters decision criterion through separate neural mechanisms.
Implications
By separating how rewards influence perception versus choice, the study provides a framework for understanding complex behaviors where attention and reward interact. The findings may help design experiments and interventions targeting risk-taking, impulsivity, and maladaptive reward-seeking—relevant to conditions such as problem gambling and certain addictions—by distinguishing whether problems arise from altered sensory prioritization or from biased decision strategies.
About this research
Author: Sridharan Devarajan
Source: IISC
Contact: Sridharan Devarajan – IISC
Image: The image is credited to Neuroscience News
Original research: Open access. “Reward expectation yields distinct effects on sensory processing and decision making in the human brain” by Sridharan Devarajan et al., PLOS Biology.
Abstract (concise)
Reward expectation strongly influences both attention and decision-making, but previous work often conflated spatial prioritization with changes in decision criterion. This study identifies distinct forms of reward expectation that separately control spatial attention (sensitivity) and decisional biases (criterion) in the human cortex. Space-specific rewards selectively elicited established attention signatures—ERP gain modulation, alpha-band lateralization, and eye-movement biases—and predicted sensitivity improvements. By contrast, choice-specific rewards produced decisional bias accompanied by different neural signatures, such as pre-stimulus alpha suppression, without engaging classic attention markers. These dissociable behavioral and neural effects clarify how reward, attention, and choice are linked in the human brain.