MONTREAL- 「Listen to this,」 Daniel Levitin said. 「What is it?」 He hit a button on his computer keyboard and out came a half-second clip of music. It was just two notes blasted on a raspy electric guitar, but I could immediately identify it: the opening lice to the Rolling Stones' 「Brown Sugar.」

Then he played another, even shorter snippet: a single chord struck once on piano. Again I could instantly figure out what it was: the first note in Elton John's live version of 「Benny and the Jets.」

Dr. Levitin smiled. 「You hear only one note. And you already who it is,」 he said. 「So what I want to know is: How we do this? Why are we so good at recognizing music?」

This is not merely some epiphany that a music fan might have while listening to a radio contest. Dr. Levitin has devoted his career to exploring this question. He is a cognitive psychologist who runs the Laboratory for Music Perception, Cognition and Expertise at McGill University in Montreal, perhaps the world's leading lab in probing why music has such an intense effect on us.

「By the age of 5 we are all musical experts, so this stuff is clearly weird really deeply into us,」 said Dr. Levitin, 49.

This summer he published 「This Is Your Brain on Music」 (Dutton), a guide ti the emerging neuroscience of music. Dr. Levitin is an unusually deft interpreter, full of striking scientific trivia. For example we learn that babies begin life with synesthesia, the trippy confusion that makes people experience sounds as smells or tastes as colors. Or that the cerebellum, a part of the brain that helps govern movements, is also wired to the ears and produces some of our emotional responses to music.

Dr. Levitin is singular among music scientists for actually having come out of the music industry. Before getting his PH.D. he spent 15 years as a record producer, working with artists including Blue Oyster Cult and Chris Isaak. While still in graduate school he helped Stevie Wonder assemble a best-of collection. He has earned nine gold and platinum albums.

Martin Grant, the dean of science at McGill, compares Dr. Levitin's split professional personality to that of Brian Greene, the pioneering string-theory scientist who also writes mass-market books. 「Some people are good popularizers and some are good scientists, but not usually both at once,」 Dr. Grant said, 「Dan's actually cutting edge in his field.」

Scientifically, Dr. Levitin's colleagues credit him for focusing attention on how music affects our emotions, a subject that was often covered by previous generations of psychoacousticians, who studied narrower questions about how the brain perceives musical sounds. 「The questions he asks are very, very musical, very concerned with the fact that is an art that we interact with, not just a bunch of noises,」 said Rita Aiello, an adjunct professor in the department of psychology at New York University.

Ultimately, scientists say, his work offers a new way to unlock the mysteries of the brain: how memory works, how people with autism think, why our ancestors first picked up instruments and began to play, tens of thousands of years ago. Not all of Dr. Levitin's ideas have been easily accepted. He argues, for example, that music is an evolutionary adaptation: something that men developed as a way to demonstrate reproductive fitness. (Before you laugh, consider the sex lives of male rock stars.) Music also helped social groups cohere. 「Music has got to be useful for survival, or we would have gotten rid of it years ago,」 he said.

But Steven Pinker, a cognitive scientist at Harvard known for his defense of evolutionary psychology, has publicly disparaged this idea. Dr. Pinker has called music 「auditory cheesecake,」 something pleasant but no evolutionarily nutritious. If it is a sexual signal for reproduction, then why, Dr. Pinker asked does 「a 60-year-old woman enjoy listening to classical music when she's alone at home?」

Nonetheless Dr, Levitin continues his work. He also continues to perform music, doing several gigs a year with Diminished Faculties, a band composed entirely of professors and students at McGill. On a recent December afternoon members assembled in a campus ballroom to do a sound check for their performance that evening at a holiday party. Playing a blue Stratocaster, Dr. Levitin crooned the Chris Isaak song 「Wicked Game.」 「I'm not a great guitarist, and I'm not a great singer,」 he said.

But he is not bad, either, and still has those producer's ears. When 「Wicked Game」 ended, the bass player began noodling idly, playing the first few notes of a song that seemed instantly familiar to all the younger students gathered. 「That's Nirvana, right?」 Dr. Levitin said, cocking his head and squinting.」 『Come As You Are.' I love that song.」