Special neurons in the brain stem of rats focus exclusively on novel sounds and help them ignore predictable and ongoing noises, a new study finds.
The same process likely occurs in humans and may affect our speech, and even help us laugh.
The "novelty detector neurons," as researchers call them, quickly stop firing if a sound or a pattern of sounds is repeated. They will briefly resume firing if some aspect of the sound changes. The neurons can detect changes in pitch, loudness or duration of a single sound and can also note shifts in the pattern of a complex series of sounds.
"It is probably a good thing to have this ability, because it allows us to tune out background noises like the humming of a car's motor while we are driving or the regular tick-tock of a clock," said study team member Ellen Covey, a psychology professor at the University of Washington.
Leave me in a room with a ticking clock and I start to go spare. The ticking — even the ticking of a very small, very quiet watch — drives me up the wall. It's like having someone chip away at my soul. I'm always aware of the noise of the engine when I'm driving, and tend not to notice when the engine noise changes slightly: as far as I'm concerned, it just always sounds like an irritatingly loud engine. I also have a major problem with making out one person's speech amongst the general hubbub of lots of other people speaking. I know I don't have dodgy hearing, because I can pick out tiny details of sound when I'm mixing or listening to music. So the existence of these neurons could explain a lot. I think mine are broken.