Tone-Deafness and the Brain

January 19, 2021

Written by: Lindsay Ejoh

Do you consider yourself to be a good singer? Can you “carry a tune” by yourself, or do people tend to cringe when you sing along to your favorite songs? If your response is the latter, then you may, like 10-15% of the human population, be tone-deaf. Tone-deafness, also known as amusia, is the inability to sing in tune or perceive when a pitch is off-tune. This condition can be categorized as an agnosia, or a disorder marked by the inability to process and categorize a sensory stimulus1. Other examples of agnosias include prosopagnosia, the inability to recognize familiar faces, or tactile agnosia, the inability to recognize objects by touch. Tone-deafness is a type of auditory agnosia, and can be present from birth or begin later in life as a result of damage to the brain from a head injury, for example. So how do we produce song, and why are some people unable to sing in tune?

How singing works: 

The process of vocal production is complex and must be planned and constantly corrected in order to produce an accurate pitch. As we breathe in, muscles in our throat called vocal cords open up and then come together again when we exhale. Air passing through closed vocal cords causes them to vibrate and create sound, which is amplified as it moves up the rest of the throat. How does the brain plan and perceive this activity? First, the motor planning areas of the brain decide to initiate a certain sound, and communicate with the brain’s motor production areas, which cause your vocal cords to close up and produce that sound. Then, special neurons in the auditory cortex of the brain, which are only sensitive to sounds that you make, and not to sounds that you hear, are activated by the sound coming from your vocal cords. These neurons are thought to give feedback on the quality of your sung pitches. That feedback is sent to an error correction center in the brain via a structure called the arcuate fasciculus2 (see Figure 1). So in short, your brain plans a note, sings it out, and checks to see if that note was accurate via auditory feedback, correcting the pitch if need be.

Figure 1: Feedback loop that underlies singing and pitch correction. Premotor cortex plans vocal chord movement, then the motor cortex initiates the movement and the vocal chords close. Then, air passes through the vocal chords vibrates, producing a sound. The auditory cortex assesses this sound, and sends projections through the arcuate fasciculus to an error correction center. If an error is detected, the premotor cortex will plan a slightly different movement, and the cycle restarts.

What goes wrong in tone-deaf individuals?

Several studies have been conducted on tone-deaf humans to investigate which aspect of the vocal production process is faulty. A research group at Northeastern University sought to answer this by playing off-pitch musical notes to individuals with normal hearing and those who are tone-deaf. They measured summed electrical activity in their brains (brain waves, essentially) with an electroencephalography (EEG) device3. The researchers found that the subjects without amusia were able to report when a pitch was inaccurate, and their brain waves showed two responses to off-pitch notes, one occurring immediately after the bad note, and another response a few milliseconds later. Tone-deaf people produced the first early response as well, but their brain waves did not show the late response at all. The scientists proposed that the early response is the brain recognizing the off-pitch note, and the late response is the conscious awareness of that event. Therefore, it’s possible that the brains of tone-deaf people do, in fact, recognize off-pitch notes, but only on a subconscious level. It is the conscious processing of off-pitch notes that is missing.

Other experiments have used MRI (Magnetic Resonance Imaging) to show that tone-deaf people have a decreased volume of brain matter in the arcuate fasciculus, the brain region responsible for providing auditory feedback after a sung tone2. Perhaps these individuals have trouble correcting the pitches they sing due to an inability of the brain to give feedback. Another way to study the brain is to use non-invasive brain stimulation to temporarily disable specific areas, essentially simulating temporary brain damage. Some scientists used this technique in non-tone-deaf people to determine the roles of brain regions known to be important for auditory perception and production4. After temporarily shutting off these regions, they saw that people who were able to sing on pitch prior to the experiments lost that ability. Later, after recovering from the stimulation, these individuals were able to sing normally again. Therefore, scientists concluded that these brain regions are necessary for on-pitch singing.

Tone-deafness, a blessing in disguise?

From these studies and others, we can conclude that tone-deaf people are unable to consciously process inaccurate pitches that they hear and therefore cannot correct the pitches they sing. Interestingly, people with amusia are still able to enjoy music, whether it is on pitch or not. Think of a time you heard a singer go off-pitch. I bet you were unable to truly enjoy that performance. Maybe tone-deafness is a blessing in disguise, in a round-about way? 

Now that you’ve read this article, do you consider yourself to be tone-deaf? Don’t be too hasty to say you are— people tend to underestimate their ability to sing on pitch. Studies show that 60% of people report that they cannot accurately imitate melodies, but only 10-15% of the population actually have amusia. Perhaps try singing your favorite song to a loved one. If they love it, you may be in the clear! Or maybe…they’re tone-deaf too. 

References

  1. Mitchell, K. (2011, January 18). The Neuroscience of Tone Deafness. Retrieved November 17, 2020, from https://www.scientificamerican.com/article/the-neuroscience-of-tone/
  2. Loui, P., Alsop, D., & Schlaug, G. (2009). Tone Deafness: A New Disconnection Syndrome? Journal of Neuroscience,29(33), 10215-10220.
  3. Isabelle Peretz, Elvira Brattico, Miika Järvenpää, Mari Tervaniemi, The amusic brain: in tune, out of key, and unaware, Brain, Volume 132, Issue 5, May 2009, Pages 1277–1286.
  4. Hohmann, A., Loui, P., Li, C. H., & Schlaug, G. (2018). Reverse Engineering Tone-Deafness: Disrupting Pitch-Matching by Creating Temporary Dysfunctions in the Auditory-Motor Network. Frontiers in Human Neuroscience, 12.

Cover Image from Unsplash user Vidar Nordli-Mathisen

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