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If physicists are ever to entangle humans they'll need to understand the role that noise plays in the experiments. Now they've carried out the first tests to find out.

The eye is a remarkable detector. Neuroscientists have long known that a single rod taken from a retina can respond to single photons. That's comparable to the best artificial detectors.

But the performance of living and breathing humans is significantly worse. When researchers fire photons into the eyes of volunteers, it takes a hundred or so photons to reliably induce a response. Much of this difference is down to the fact that only about 10 per cent of the photons that enter the cornea actually reach the retina. 

But that still leaves an order of magnitude between the detection efficiency of individual rods and the behaviour of humans. Why the difference?

Today, Gibran Manasseh and pals at the University of Geneva provide an answer. 

These guys fired varying numbers of photons into the eyes of 12 healthy volunteers and who they asked to press a button when they perceived a flash. At the same time, the researchers measured each volunteer's brain activity using EEG recordings.

The results make for interesting reading. These guys say that half the subjects regularly reported false positives, saying they saw a flash when no photons had been sent. 

They say the retina itself introduces some noise but their new result is that the brain itself introduces even more noise. "The brain adds a large contribution to the decrease in sensitivity," they conclude.

Why is this important? This group at the University of Geneva led by Nic Gisin has an other interesting project on the go that we've looked at before.

To read more, click here.