Given that our level of alertness varies throughout the day, it only makes sense that we should avoid performing attention-demanding tasks when we're at our drowsiest. An experimental new Android app is designed to determine when those times are, by examining users' eyes.

When we're in an alert state, our sympathetic nervous system causes our pupils to dilate so that we can take in information more easily. On the other hand, when we're tired, our parasympathetic nervous system causes our pupils to contract. With that in mind, a team at Cornell University developed the AlertnessScanner app, which utilizes a smartphone's front-facing camera to gauge the size of users' pupils.

In an initial study, test subjects were prompted to use the app to manually take photos of their pupils, once every three hours. Additionally, six times a day they completed a five-minute phone-based Psychomotor Vigilance Test (PVT), which is an established method of gauging reaction time. When the results of the two alertness-testing methods were compared, they were found to be very similar.

That said, it was determined that most people wouldn't like having to make a point of using the app so many times every day. Additionally, in order to properly image the test subjects' pupils, the infrared filters of the phones' cameras had to be removed.

The first problem was addressed by adapting the app so that it automatically took a one-second-long burst of 30 pupil photos whenever users unlocked their phones – something that most people already do multiple times daily. Improvements in the resolution of smartphone cameras solved the second problem. In a second study conducted a year after the first, it was found that a phone's 13-megapixel front-facing camera could adequately image the pupil, even with its infrared filter left in place.

"Since people use their phones very frequently during the day, we were thinking we could use phones as an instrument to understand and measure their alertness," says doctoral student Vincent W.S. Tseng, lead author of a paper on the research."If you want to get something very important done, then probably you should execute this task while you're at the peak of your alertness; when you're in a valley of your alertness, you can do something like rote work. You'll also know the best time to take a break in order to allow your alertness or energy to go back up again."