If you pay money for a fast hand movement, the hand moves faster. That is how reward works. But with age, this gas pedal gets pressed less forcefully. Scientists tested this in 56 people: half young (around 20 years old), half older (around 59 years old). All of them moved a robot handle toward a target on a screen. Sometimes they got 50 pence for a good result, sometimes not.
Young people sped up more in response to reward: their hand gained 22.3 centimeters per second more speed, while in older adults it was only 12.9. Movement time decreased by 94.6 milliseconds in the young and by 44.4 in the older group. But stopping accuracy did not get worse, and older adults even stopped more precisely. So reward presses less on the gas, but the steering stays responsive.
This matters for rehabilitation after a stroke: monetary incentives for speed may be less effective for older adults. Instead, it may be better to reward accuracy or simply completing the task. So a banknote at the finish line is a good motivator for young people, but older adults may need something different.
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.