Newport Beach, California--Neuropsychologists may wind up owing a debt to the devil--an auditory illusion known as the "devil in music," that is. How the illusion is perceived depends on what language a listener grew up speaking, researchers reported here on 7 December at the Acoustical Society of America's 140th meeting. And those perceptions might ultimately help psychologists understand how the brain wires itself during childhood.

For more than a decade, psychologist Diana Deutsch of the University of California, San Diego, has been studying an auditory illusion based upon the tritone, two notes played a half-octave apart. With a computer, Deutsch created ambiguous notes by superimposing tones from many octaves. Although listeners can perceive one of these notes as a C, say, they can't tell whether it's a high C, middle C, or low C. Indeed, the tone doesn't really belong to any octave at all.

Things got interesting when Deutsch compared tritone pairs of ambiguous notes. Even though neither note is higher or lower than the other, people consistently perceive one tone as high and the other as low. But they don't agree which is which. Stranger still, how subjects perceive the illusion seems to depend on where they grew up.

To test whether a mother tongue determines how a person interprets an ambiguous tritone, Deutsch and colleagues studied two groups of subjects who had emigrated to California from Vietnam. The first group came to the United States as children, and though Vietnamese was their first language, most no longer spoke it fluently. The second group, on the other hand, arrived in the United States as adults and spoke little English. Both sets of people born in Vietnam perceived the tritones in the same way--but differently from their California-born neighbors, whom Deutsch had studied earlier. Perception of the tritone, she believes, depends on what language an infant heard.

The study "reinforces the idea that early linguistic background affects perception" in adults, says Magdalene Chalikia, a psychologist at Minnesota State University in Moorhead. As an infant learns its first language, that is, the brain may adjust its neural connections in a way that affects the perception of sounds. But for the moment, scientists have little idea how each language rewires the brain. "You can't make predictions," sighs Chalikia. "It's frustrating." The devil, it turns out, is in the details.

--CHARLES SEIFE

Related sites
Listen to the tritone paradox
An earlier lay language summary of related research
Listen to other musical illusions