If, like me, you're not a traditionally "good" singer, someone who's witnessed you singing may have called you tone deaf and begged you to stop. Not only is this rude and potentially traumatizing, it's also likely untrue. Only about four percent of humans are medically tone deaf (also known as amusia) meaning their brains don't process music the way the majority of ours do. For most of us, there are other reasons we may not sing in key (we'll get to that later), but the brains of those who are actually tone deaf have structural differences—either from birth or injury—that prevent them from communicating variations in pitch. Individuals with amusia typically don't enjoy music and have trouble humming a simple melody after hearing it.

Sing Wise explains this phenomenon: "While normal brains process sounds in a series, with the front and parietal cortices receiving signals that have been processed previously in the auditory cortex, the tone-deaf brain has a disrupted path for this information, routing the two regions in parallel and independent pathways. Thus, information about the wrong note never makes it to the auditory cortex, while the information that does arrive at the front parietal cortex is never consciously recognized…Although the brain itself might be able to acknowledge the difference between changing notes, the individual will not generally be aware that he or she is singing the wrong notes. Some tone-deaf people believe that they are actually singing the correct melody of a song, until someone else tells them differently. (Even then, they are usually not convinced that their singing is as off key as they've been told it is.)"

One of the first empirical studies of tone deafness was led by cognitive neuropsychologist Isabelle Peretz in 2002, and defined "congenital [a.k.a. you're born with it] amusia as a new class of learning disabilities that affect musical abilities." This study gave the oft informally diagnosed phenomenon a medical name and, with its 11 tone deaf participants, explored why it happened.

Interestingly, people with amusia can recall lyrics and typically have normal speech and language processing functionality. The 2002 study found that its amusic participants could generally identify spoken lyrics when heard separate from the melody. It is not a hearing issue—the brain technically hears the notes correctly, but doesn't communicate them properly to the part of the brain that consciously perceives the notes. Thus, key elements that make up a song—including the pitch variations that make up the melody—cannot be understood by amusic folks, so it doesn't really make sense to them.

As The Atlantic wrote in 2013, Peretz did a follow up study in amusic children in 2012 to see if listening to popular music daily, combined with the plasticity of their young brains, could help remedy their condition. Unfortunately, it did not. It was a 2013 study conducted in Lyon, France that identified the areas of the brain impacted by tone deafness using magnetoencephalography (MEG) scanners. Not only did their frontal and auditory cortices display impaired functioning during the early part of encoding melodic information, those areas of the brain also had physical abnormalities, including more gray matter–where processing happens–and less white matter–which communicates between the gray matter and other parts of the body–in the frontal cortex than is "normal."

While there is no known remedy for reducing tone deafness, as The Atlantic stated, it is possible that training programs—beyond simply listening to music—could help support "pitch perception and memory—those two basic skills essential to the ability to recognize music."

"Melody is perhaps the most identifiable element of a musical composition," writes MasterClass. It defines melody as "a collection of musical tones that are grouped together as a single entity. Most compositions consist of multiple melodies working in conjunction with one another. In a rock band, the vocalist, guitarist, keyboardist, and bassist are all playing melodies on their respective instruments. Even the drummer is playing one." It continues to explain that the melody is made of two main parts: the pitch, or "the actual audio vibration produced by an instrument" (including one's voice) and the duration, or how long the pitch will sound (which is measured by whole notes, half notes, etcetera).

Since amusic brains have trouble communicating changes in tone, they won't be able to identify the melody as distinct. As Hello Music Theory explains, "A melody should be relatively simple to memorize and reiterate…A melody must be separate enough from the notes around it (the harmony) in order to be recognized as a melody." Without a melody, a song may not be very memorable or distinguishable from another with the same chord progression, and it will definitely be hard to hum along to. Since tone deaf listeners can't consciously hear the melody, music probably sounds something like a mushy sound soup to them.

So what about all the people who probably aren't medically tone deaf, but struggle to sing in the right key? As Sing Wise reminds us, "A common mistake is confusing or associating all persistent pitch problems with tone deafness…If the individual is able to hear the sound and knows what sound he or she wants to produce but can't seem to imitate that sound or reproduce that specific pitch at will, he or she may not be tone deaf, and may be aided by vocal training. If the individual recognizes when he or she has hit a sour note, then tone deafness is likely not the problem."

The article’s author points to some causes of pitch errors, which may stem from limited early exposure to music, not using one's singing voice, or the psychological wounds caused from past criticism around their voice. While these issues may intermingle, addressing the latter, they write: "To avoid hurtful defeat and to prevent further humiliation, the singer becomes the first to run himself or herself down and declare that he or she can't sing. It can be very difficult for a person to confront all the painful defeats that he or she has experienced in being labeled tone deaf or in being called a terrible singer or someone with no musical talent. Oftentimes, in these cases, the individuals are too loosely diagnosed as being tone deaf, but not before the label has already emotionally affected them. It then takes a lot of courage and motivation to work on the problem."

So, whether it's your friend, child, student or random enthusiastic karaoke participant, please don't mock their voice or tell them they're tone deaf! If you're not a neuroscientist or trained doctor that can test their tone deafness, it's not your place. The good news is, in the case of the non-tone-deaf singer, it is possible to improve their voice and use of their vocal instrument with a voice coach and/or vocal training exercises. And if you're someone who's been labeled tone deaf and wants vindication by proving you're not, Harvard University has an online tone-deafness test you can take. But if you actively listen to and enjoy music, you're likely in the clear, and you can point your rude friends (hi friends!) in the direction of this article.