When an Ear Witness Decides the Case
Spoken clearly, the sounds “dah” and “bah” are easy to distinguish. Yet if you play a film clip in which the soundtrack says “dah” while the image on the screen shows a mouth saying “bah,” people will swear they heard “bah.”
If you ask people to count the number of times that a light flashes, and you flash the light seven times together with a sequence of eight beeping tones, people will say the light flashed eight times.
When confronted with conflicting pieces of information, the brain decides which sense to trust. In the first scenario, those clearly percussing lips could never be articulating a “d,” and so vision claimed the upper hand. But on matters that demand a temporal analysis, and making sense of similar sounds in a sequence, the brain reflexively counts on hearing.
Click click click. You can listen to a series of clicks at 20 beats per second and know they are separate clicks rather than a single continuous tone. Run a series of images together at 20 frames per second and — welcome to the movies.
“The temporal resolution of our vision,” said Barbara Shinn-Cunningham of Boston University, “is an order of magnitude slower than what our auditory system can cope with.”
It’s easy to take hearing for granted, that sprawling stereophonic Babylonia where the gates never close and there are soapboxes for all. You can shut your eyes against a bright sun or avert your gaze from a grim scene. But when one neighbor’s leaf blower sets off another neighbor’s car alarm, hey, where are my earlids? We’ve been called the visual primate, and the size of our visual cortex dwarfs the neural platform assigned to audition. Most people, when asked, claim they would rather lose their hearing than their sight.
Yet in ways that researchers are just beginning to appreciate, we humans are beholden to our ears. Mechanically, electrically, behaviorally and cosmetically, our paired sounding boards are a genuine earmark of our species. And if the words aural and oral are often confused, they should be, for our ears and our mouths jointly gave us our voice.
Scientists now suspect that the origin of human language owes as much to improvements in the early hominid ear as to more familiar spurs like a changing vocal tract or even a generally expanding brain. In one recent molecular analysis, John Hawks of the University of Wisconsin reported that eight genes involved in shaping the human ear appear to have undergone significant changes over the past 40,000 years, some as recently as the dawn of the Roman Empire. Only with highly refined auditory infrastructure, researchers said, could our ancestors have tuned in to the sort of tiny fluctuations in pressure waves that characterize all human speech, let alone properly conjugated Latin.Moreover, the avidity with which our auditory sense seeks to organize ambient noise into a meaningful acoustical pattern — a likely consequence of our dependence on language — could help explain our distinctly human musicality.