LiveScience.com is reporting that researchers from the University of Washington have discovered neurons in the brainstems of rats whose sole function is to identify new sounds while ignoring ongoing and predictable background noises. The scientists believe these specialized neurons are present in all vertebrates, including humans in whom they probably play a significant role in speech processing.
The neurons, referred to by the researchers as “novelty detector neurons,” remember patterns of sound. If a pattern is repeated, they will stop firing. If the sound changes, or a new sound is detected, they will begin firing again. The neurons are able to detect changes in all aspects of sound including pitch, timbre, cadence, and volume.
The novelty detector neurons behave as a filter of sorts, stopping what they deem as unimportant sounds from rising through the neural pathways to the higher level processing areas of the cortex. This explains why you are able to tune out background noises in your environment, but your attention is immediately piqued when you hear something out of place.
The results of the research are published in the December 2005 European Journal of Neuroscience.