Reward expectation yields distinct effects on sensory processing and decision making in the human brain

TL;DR

The study shows how reward expectations separately influence attention and decision-making in the human brain.

Contribution

The study identifies distinct neural mechanisms for reward expectation effects on sensory processing and decision-making.

Findings

Space-specific reward expectation modulates sensory sensitivity, not decision criteria.

Choice-specific reward expectation affects decision-making, not sensory sensitivity.

Neural markers of attention correlate with space-specific reward effects, not choice-specific ones.

Abstract

Reward expectation robustly guides both attention and decisions. Yet, whether common or distinct mechanisms mediate each of these processes remains unknown. Previous studies have often conflated the effect of reward expectation on sensory processing and decision-making because locations selected for sensory prioritization (sensitivity effects) were also prioritized for decisions (criterion effects). Here, we identify distinct forms of reward expectation that separably control spatial attention and decisional biases in human cortex. Sensitivity and criterion were independently modulated when expected rewards varied across locations (“space-specific”) or choices (“choice-specific”), respectively. Only sensitivity, not criterion, modulations reflected a limited, conserved attentional resource. Established neural and physiological signatures of attention, including gain modulation of event-related potentials, alpha-band power lateralization, and eye-movement biases, were elicited only by space-specific reward modulation. By contrast, neural correlates of decisional biases, including pre-stimulus alpha power suppression, selectively accompanied choice-specific reward modulation. Attention-related neural markers predicted sensitivity modulation by space-specific reward expectation but not criterion modulation by choice-specific reward expectation, indicating their distinct underlying mechanisms. Our findings uncover fundamentally dissociable behavioral and neural underpinnings of reward expectation effects on sensory and decisional selection, with critical implications for understanding how reward, attention, and choice are linked in the human brain.

Expecting a reward can shape behavior in diverse ways. For example, monkeys may focus their attention on tree branches containing the most plentiful fruit to identify ripe ones based on visual features, such as color or texture. However, they must also choose to act quickly and pick this fruit to thwart their conspecifics. In other words, reward expectation can influence not only how attention is engaged but also how choices are made. Yet, these two effects have been frequently conflated in laboratory tasks. Here, with a task that decouples reward expectation’s effects on attention from those on decision-making, we uncover their distinct neural correlates. Our results show how reward shapes attention and biases choices independently in the human brain.

Reward expectation modulates attention and decision-making, but it is not clear whether common or distinct mechanisms mediate each of these processes. This study shows that spatial manipulation of reward expectation selectively modulates sensitivity, while choice-based manipulation of reward expectation selectively affects decision-making.

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