All participated in functional magnetic resonance imaging (fMRI) brain scans. The information captured there was mapped and analyzed with computer modeling.

A bit of anatomy may be helpful here. The brain processes sound in a small area called the auditory cortex. It is found along both sides of your head, just above your ears, in what is known as the temporal lobes.

The auditory cortex has regions of its own and scientists have plotted out “tonotopic” maps, meaning that the neurons are laid out in order of their best frequency response. These maps show where specific frequencies are processed within these regions.

The researchers found that all participants with perfect pitch had larger auditory cortical areas than the others. Other trained musicians and those in the control group had cortical areas that did not differ much in size from each other.

One surprise was that the larger auditory cortical areas were not used for sharper tuning, as researchers expected. Rather, those with perfect pitch used that extra territory for tuning a broader range of frequencies. Those kinds of measurements had never been captured before.

They also found evidence that argues against an often-discussed “critical period” theory that perfect pitch is possible only in people whose musical training begins before the age of 7. Several participants with perfect pitch had not started musical instruction until their late teens or even early 20’s, McKetton said. The vast majority of musicians do not have perfect pitch despite thousands of hours of training and practice.

It is not known if someone with zero musical training could have perfect pitch. Certainly, they couldn’t call out the notes if they have had no music theory. But it might be possible to test their ability to identify frequencies, Schneider said. That was not part of this research.

There is a range of capacity, too. People with perfect pitch can identify the note almost instantly and some of them can also identify the frequency. For example, they could say “A4” — the note “A” in the fourth octave — and they could also say “440 Hertz,” the precise modern-day frequency for that note.

There are other fascinating twists to all of this.

When Schneider’s 14-year-old son, Felix, heard about this research he told his dad he had perfect pitch. When Schneider tested him, though, he got every note wrong — until they adjusted the results for someone who plays the trumpet, as Felix does. Trumpets are tuned one whole step differently than pianos. So playing a “C” on the trumpet is the same as playing a “B-flat” on the piano. When Felix made that one-step correction in his answers, he was 100 percent accurate. He has perfect pitch.

In another study McKetton did, a 70-year-old man said he had perfect pitch but got every note wrong when he was tested. She then noticed that all of his responses were one tone off. The perceptual change in pitch may have been due to age-related changes in the stiffness of the basilar membrane within the cochlea of the inner ear, she said. When she asked him to adjust his answers by one tone, he was 100 percent accurate.