Science: The Time Is All In Your Mind

Scuse me while I kiss this guy ," Jimi Hendrix did not sing in "Purple Haze," but a lot of people heard it that way anyway: somehow in his listeners' ears the break between "the" and "sky" got moved one phoneme to the right. One question is why that kind of mistake (a "mondegreen") doesn't happen more often in ordinary speech, and the answer, says Dean Buonomano of the UCLA Brain Research Institute, is that the brain has a surprisingly sensitive mechanism for measuring time intervals as short as 10 or 20 milliseconds--much less than the duration of an eye blink. In a paper last week in the journal Neuron, Buonomano proposed a theory of how the brain keeps track of time intervals smaller than a second--and, surprisingly, it isn't anything like a clock.

For a long time, the example of the clock led biologists to look for something analogous in the brain, an all-purpose central timekeeper that counted off milliseconds and added them up. But no such structure has ever been found. Instead, Buonomano believes, time is measured by tracking changes in neurons as they propagate through the brain following some kind of signal or event, such as hearing a sound that could be either the word the or the start of this. Imagine throwing a pebble into a pond, he says; you could calculate how much time has gone by at any moment by comparing how far the ripples have spread with a set of reference pictures for different intervals. The brain does something similar, he believes--and within a margin of error of just 10 percent.

Obviously, measuring small intervals of time is useful for decoding speech and for music. Less obviously, this ability could prove useful in other sensory modes, such as touch: the degree of roughness of a surface such as sandpaper is conveyed, Buonomano speculates, in part by sensing how much time goes by between bumps as one's finger moves along it. Auditory, visual and touch centers of the brain each appear to have this timing capacity. Someday Buonomano's insight may be useful in treating conditions, such as dyslexia, that involve impairments to language. For now, though, it's worth a smile the next time your kid puts his hand over his chest and intones, "I led the pigeons to the flag ... "

© 2007