Both light and sound travel as waves, with characteristics that allow people with typical vision and hearing to perceive and categorize them when they reach their eyes and ears: “That’s a black dog barking,” someone might say.

But while people can easily name colors—specific frequencies and wavelengths of light—few can do the same for musical notes, that is, for specific frequencies and wavelengths of sound. Hearing a musical note and naming it is beyond the expertise of most people.

In fact, this ability is rare enough that society celebrates people who can label musical notes heard in isolation: They are said to have “perfect pitch,” or, as scientists who study auditory perception call the ability, “absolute pitch.” More common is “relative pitch,” the ability to name musical notes in relation to one another on a scale (“do, re, mi”) but not without a reference note. Both require musical training, but it’s not clear what separates people with perfect pitch from people with relative pitch.

For psychologists and neuroscientists at the University of Chicago who study absolute pitch, the rarity of the ability raises an interesting question about the relationship between sensory processing and cognition: What makes some musicians so good at identifying musical sounds? Is it the way their brains process sounds or their musical training?

New research from a UChicago team, including psychology doctoral student Katherine Reis, AB’19, AM’21, and Howard Nusbaum, LAB’72, the Stella M. Rowley Professor of Psychology, suggests it’s both. They identified a specific cognitive response to musical notes that correlates with having perfect pitch more strongly than any other known factor—a likely indication that these rare individuals have a neurological advantage in identifying sounds. However, the paper’s findings also show that experience and training play a role in pitch recognition.

For the paper, published in July in Nature: Scientific Reports, Reis and Nusbaum worked with other UChicago researchers to design a study comparing people with and without perfect pitch on a series of tasks.

Thirty-one trained musicians participated in the study: 16 with perfect pitch and 15 without it. They completed a task that required naming piano notes and naming “pure” sine tones generated by a computer (these represent exact frequencies without an instrument’s timbre).

In each trial, the scientists used noninvasive electrodes to monitor how participants’ brains and nervous systems reacted to sounds. In particular, they looked at a measure called the “frequency following response” (FFR)—essentially, how quickly and faithfully the brain internally recreates externally produced sound waves. The researchers then recorded how accurately the participants identified the pitches, along with details about their prior training in music.

The researchers found that in both groups, the people who most accurately recreated a pitch’s sound wave in their brains were the best at correctly identifying those pitches. The FFR predicted people’s performance on pitch identification better than any metric previously used in studies of perfect pitch, including musical training.

“As a result of our study, we now know that features of the FFR predict absolute pitch ability even better than the developmental factors that people usually associate with absolute pitch, like the age you first learned an instrument,” Reis says—a signal that absolute pitch possessors may have a built-in advantage when it comes to naming notes.

Participants also tended to be better at naming notes played on a piano as compared to the computer-generated sine tones. Those with perfect pitch averaged 98 percent accuracy on piano and 77 percent for sine tones, while those without averaged 29 percent accuracy on piano and 25 percent for sine tones.

According to UChicago doctoral student John Veillette, SB’19, AM’21, a coauthor on the paper, these results suggest that timbres—which are conferred by upper harmonics in sound frequencies and give instruments their unique, familiar rings—play an important role in pitch recognition. This, Reis says, implies that experience is probably involved in pitch recognition, since even people with self-reported perfect pitch weren’t “perfect” when the notes were produced in an unfamiliar way.

While the study shows that frequency following response is a very strong predictor of perfect pitch, that doesn’t mean it’s immutable. Despite the differences between the brains of individuals with and without perfect pitch, previous work indicates FFR itself is not a “fixed” trait. In other words, people without perfect pitch may be able to improve their FFR and their ability to name notes over time, according to the scientists.

For Nusbaum, this variability was not surprising. He has spent years studying perfect pitch alongside other scientists, including study coauthors Shannon Heald, AB’02, AM’05, PhD’12, an assistant instructional professor in the Department of Psychology, and Stephen Van Hedger, AB’09, AM’12, PhD’15, now an assistant professor of psychology at Huron University College in Ontario.

They have argued consistently that perfect pitch is not a dichotomous ability that people either have or do not have: instead, it may be better thought of as a continuous spectrum.

“Perfect pitch was long thought to be a rare ability that only some children could acquire if they had the right musical training in early childhood,” Nusbaum says. “However, this study provides further evidence that while the differences in people’s ability to categorize notes are real—and related to cognitive processing—our brains develop in tandem with the skills we practice over our entire lives. So, when it comes to pitch learning, practice, in a sense, really does make ‘perfect.’”