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Mind

World Science Festival: Listening to Illusions of Sound

DiscoblogBy Joseph CalamiaJune 7, 2010 6:30 PM

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Do you see a hovering white triangle in this picture? This optical illusion employs "illusory contours"--pieces of an image purposefully arranged to trick your brain into seeing the whole thing. Neuroscientist Jamshed Bharucha says that we play similar tricks with our ears: "The brain is basically a pattern-recognition machine. We are desperate to find patterns." Bharucha spoke on a seven-person panel last Thursday at "Good Vibrations: The Sound of Science," a World Science Festival event in New York. Bharucha asked a crowded auditorium at Hunter College to identify a sound. Shouts of "birds" rang out. One person yelled, "R2D2." Bharucha followed the clip with a similar sounding song, and then another. After playing a combination of the three, whispers rose from the audience. From disparate bird noises came recognizable speech: "Where were you a year ago?" Some applauded. To make this aural illusion, Bharucha first looked at a spectrogram of the spoken question. By picking out only three of the most energetic pieces--harmonics--of the speech, he could use a synthesizer to create the three bird-song cues. Like the dark portions of the optical illusion above, these sounds are incomplete pieces of the whole, but important triggers. Looking for a message in these songs--especially when nudged to look for speech--we can find it as the crowd did. "Suddenly, whoa, you hear it," Bharucha said. We learn to search for the patterns in our native language even in the womb, Bharucha says. He cites studies showing that eight-day-old infants have a preference for their mother's language, clearly before they have developed spoken-language skills, and even when that language is spoken by someone other than the child's mother. Other patterns emerged in the other panelists' works. Moderated by WNYC's John Schaefer, the discussion also included biophysicist Christopher Shera, astrophysicist Mark Whittle, and composer Jacob Kirkegaard. Shera described otoacoustic emissions--when the mechanical workings of our inner ears echo into something we can record and listen to. He records these emissions in humans and animals, including anesthetized tigers. "It's very useful," he joked, "that the ear is is not immediately adjacent to the teeth." Kirkegaard uses tones in his music to incite these emissions, so that our own hearing contributes to his melodies. Whittle ended the talk with the "sounds" of the Big Bang, a mapping of background radiation from the universe's creation onto frequencies we can hear. He described the early universe as a pipe organ with pipes 400,000 light years across, and said that if we had actually been there to listen, we wouldn't have heard anything, since the pitch was too low and the melody would have taken too long to sound. In fact, too long doesn't mean much, since he says we would have died instantly. Related content: Discoblog: “Seeing” Sounds and “Hearing” Food: The Science of Synesthesia 80beats: Forget the Hearing Aid: Why Not Regrow Inner Ear Cells? Not Exactly Rocket Science: How our skin helps us to listen DISCOVER: Dog Eared

Image: Wikimedia / Fibonacci

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