If someone plunks a random piano key, a tiny minority of people can identify the note based on its sound alone. These people boast perfect pitch, the ability to recognize individual sound frequencies without any external reference. But even these gifted few are not truly perfect. A new study shows that their errors, though subtle, provide a previously unseen glimpse into how biological and environmental factors together shape hearing.

Absolute pitch, commonly known as perfect pitch, results from the confluence of early musical training and a rare genetic endowment. Yet the neurology underlying absolute pitch (and its converse, congenital tune-deafness, or amusia) remains obscure. In the new study, researchers identified about 1,000 people who could instantly and effortlessly label each of a series of randomly presented acoustical tones. Results revealed that people with absolute pitch formed a distinct clump of scores, far outside the normal range of ability. “There are people who have this exquisitely perfect pitch-naming ability, and the rest of us are just guessing,” says the study’s lead author, geneticist Jane Gitschier of the University of California, San Francisco. That fact, combined with previous family heritability studies, suggests that, unlike most complex traits, perfect pitch may be governed by only one gene or at most very few.

The study also exposed an Achilles’ heel for people with absolute pitch: the notes surrounding A. Volunteers with perfect pitch were far more likely to mistake a G-sharp for an A than to make any other error. They also perceived A-sharp frequently as A. The researchers suggest that this pattern may reflect the use of the note A as a universal tuning frequency in bands and orchestras. As a result of this disproportionate exposure, the group hypothesizes, the note may act as a “perceptual magnet,” fooling the mind into lumping nearby tones into the A category.

In its ongoing research, Gitschier’s group is trying to isolate a gene that governs absolute pitch, with the goal of then probing its molecular machinery. Ultimately, Gitschier says, she hopes to use absolute pitch as a platform for better understanding how the brain changes as a result of experience—a phenomenon known as neuroplasticity. The new findings, according to Dennis Drayna, a geneticist at the National Institute on Deafness and Other Communication Disorders who studies pitch perception, “open the door to a powerful and precise measure of learning and neuroplasticity within the auditory system. You can look at this only in people who have absolute pitch because those are the only people for whom this learning effect is going to be stable and measurable.”