Alzheimer’s disease often creeps up slowly on our loved ones, scattering subtle hints that their mental processes aren’t quite as sharp as they once were. It can be difficult to determine if someone with the earliest stage of Alzheimer’s should continue living alone, or driving, or cooking unsupervised.

But University of Iowa scientists may have hit upon a solution: Their research suggests that tests of visual perception and memory may go a long way toward determining if people with early-stage Alzheimer’s should stay on the road or hand over their keys.

The researchers tested the cognitive, motor and visual skills of forty older drivers with early-stage Alzheimer’s disease and more than one-hundred older drivers with no signs of dementia. They found that drivers with Alzheimer’s scored lower on all of the tests.

The researchers then fitted a car with special sensors and hidden cameras, and took each driver on a road test. The drivers with early-stage Alzheimer’s were more likely than the healthy drivers to straddle lanes, respond slowly to traffic lights and commit other driving errors.

The researchers then compared each driver’s cognitive abilities with their actual driving skills and found that the tests were surprisingly accurate at predicting road readiness. The most telling tests were those where the person was shown a series of shapes and figures, and was later asked to recall those images.

The tests aren’t widely available yet, but scientists hope they will be soon, so families can better decide which direction to go in.