DURING the second world war, aircrews who had to calculate mission routes and bomb trajectories found that their instruments – mechanical computers packed with cogs and gears – performed better in the air than on the ground. Realising that the plane’s vibrations were helping to make the instruments’ sticky moving parts move more freely, engineers began building small vibrating motors into them to make them more accurate. This was one of the earliest applications of dither, or the deliberate addition of noise.
Noise is usually a nuisance, as anyone who lives under a flight path or has tried to listen to a distant AM radio station can testify. But to engineers it can be a godsend, and now its benefits are cropping up in biology, too. More than a decade of research suggests that under some circumstances, a small injection of noise can sharpen up the way in which an organism senses its environment. For example, crayfish are better at detecting the subtle fin movements of predatory fish when the water is turbulent rather than still. Humans are better able to recognise a faint image on a screen when a dash of noise is added to it.
In these cases the noise source is external to the organism, but they raise an intriguing possibility: could evolution have beaten the wartime engineers to it and incorporated dither into the brain itself? A group of neuroscientists is now claiming to have found just that, in the form of neural circuits that are “noisy by design”. If they’re right, it may be that dither is a common feature in nature.
A working definition of noise…
