A banknote taped to the finish line makes your hand fly faster. In the lab, that banknote was replaced with a 50-pence coin, and the finish line with a target on a screen. The researchers recruited 28 young people and 28 older adults, seated them at a robot handle, and asked them to steer a cursor toward the target. Sometimes they were paid for speed and accuracy, sometimes not. The question was simple: does reward press the gas pedal equally hard at different ages?
Young people accelerated more in response to reward: their peak speed jumped by 22.3 centimeters per second, while in older adults it rose by only 12.9. Travel time dropped by 94.6 milliseconds in the young and by 44.4 in the older group. The difference is nearly twofold. But stopping accuracy suffered in no one, and on average older adults stopped even more precisely than young ones. In older adults the gas pedal is pressed less hard, but they hold the steering wheel more firmly.
When a distracting signal appeared along the way, reward spurred both groups equally: reaction time shrank by the same amount. But the price for speed was shared: participants more often grabbed at the false target, sacrificing choice accuracy. This shift toward speed at the expense of accuracy did not depend on age. So aging does not blunt the response to reward as a whole; it acts selectively.
Previously it was unclear whether age weakens sensitivity to reward equally for action selection and for action execution. Now it is clear: in older adults, execution is less responsive to money, while selection is not. This pattern fits the idea that different brain regions responsible for decision-making and for movement age unevenly. Direct neurobiological confirmation is still lacking, but the behavioral picture is clear.
Let's return to the banknote at the finish line. A young person runs after it at full speed; an older person runs too, but not as fast. Yet both see equally well where to run. Reward remains a gas pedal, it's just that with age this pedal becomes stiff. And the steering wheel, fortunately, does not rust.
Older participants on average stopped more accurately than young ones, even when they moved more slowly. This confirms a everyday observation: with age, people more often prefer reliability over speed.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.