UCLA neurobiologists report that they may have discovered how the brain subconsciously measures the passing of milliseconds, intervals too small to consciously detect. An accurate brain “clock” is essential for understanding speech, such as detecting the ending and beginning of words, and other functions. Trouble calculating milliseconds may even be linked to dyslexia. Some scientists suggest that the rhythmic pulsing of brain cells act as the internal clock. However, Dean Buonomano and his UCLA colleagues don’t agree. In their experiment, described in the scientific journal Neuron, a subject heard two tones preceded by a “distracting” tone. While the time between the two tones was always the same, it *seemed* different depending on when the “distracting” tone played. From a New Scientist article, complete with sound files so you can try the experiment yourself:
According to Buonomano, the brain would not be so easily tripped up if it could compare the timing of the tones to a reference clock in the brain. He says the finding suggests that the brain relies on external cues rather than an internal clock to determine the length of split-second events.
Buonomano suggests that the brain instead times these short events by comparing how long it takes different nerve signals to travel from one part of the brain to another.
He likens this to tossing one pebble after another into a lake and measuring the time that has elapsed between them by calculating when the waves they generate reach a certain point. And he notes that if an additional pebble precedes them, this can alter the pattern of waves they generate.
A simple sound can create a “wave” of nerve signalling in the brain. So Buonomano believes the first tone heard in each sequence altered the perception of timing between the two subsequent tones by distorting the cascade of nerve signals they generated.